One of the most important characteristics of today's enterprises is that they are facing a rapidly changing environment and can no longer make predictable long term provisions. To adapt to this change enterprises themselves need to evolve and be reactive so that change and adaptation should be a natural dynamic state rather then something occasionally forced onto the enterprise. This necessitates the integration of the enterprise operation and the development of a discipline that organises all knowledge that is needed to identify the need for change in enterprises and to carry out that change expediently and professionally. This discipline is called Enterprise Engineering.

Previous research, carried out by the AMICE Consortium on CIMOSA, by the GRAI Laboratory on GRAI and GIM, and by the Purdue Consortium on PERA, (as well as similar methodologies by others) has produced reference architectures which were meant to be organising all enterprise integration knowledge and serve as a guide in enterprise engineering programs. The IFIP/IFAC Task Force analysed these architectures and concluded that even if there were some overlaps, none of the existing reference architectures subsumed the others; each of them had something unique to offer. The recognition of the need to define a generalised architecture is the outcome of the work of the Task Force.

Starting from the evaluation of existing enterprise integration architectures (CIMOSA, GRAI/GIM and PERA), the IFAC/IFIP Task Force on Architectures for Enterprise Integration has developed an overall definition of a generalised architecture. The proposed framework was entitled 'GERAM' (Generalised Enterprise Reference Architecture and Methodology). GERAM is about those methods, models and tools which are needed to build and maintain the integrated enterprise, be it a part of an enterprise, a single enterprise or a network of enterprises (virtual enterprise or extended enterprise).

GERAM, as presented below, defines a tool-kit of concepts for designing and maintaining enterprises for their entire life-history. GERAM is not yet-another-proposal for an enterprise reference architecture, but is meant to organise existing enterprise engineering knowledge. The framework has the potential for application to all types of enterprise. Previously published reference architectures can keep their own identity, while identifying through GERAM their overlaps and complementing benefits compared to others.

The scope of GERAM encompasses all knowledge needed for enterprise engineering / integration. Thus GERAM is defined through a pragmatic approach providing a generalised framework for describing the components needed in all types of enterprise engineering/enterprise integration processes, such as:

• Major enterprise engineering/enterprise integration efforts (green field installation, complete re-engineering, merger, reorganisation, formation of virtual enterprise or consortium, value chain or supply chain integration, etc.);
• Incremental changes of various sorts for continuous improvement and adaptation.

GERAM is intended to facilitate the unification of methods of several disciplines used in the change process, such as methods of industrial engineering, management science, control engineering, communication and information technology, i.e. to allow their combined use, as opposed to segregated application.

One aspect of the GERAM framework is that it unifies the two distinct approaches of enterprise engineering, those based on product models and those based on business process design. It also offers new insights into the project management of enterprise engineering and the relationship of integration with other strategic activities in an enterprise.

An important aspect of enterprise engineering is the recognition and identification of feedback loops on various levels of enterprise performance as they relate to its products, mission and meaning. To achieve such feedback with respect to both the internal and the external environment, performance indicators and evaluation criteria of the corresponding impact of change on process and organisation are required. The continuous use of these feedback loops will be the prerequisite for the continuous improvement process of the enterprise operation and its adaptation to the changes in the relevant market, technology and society.

GERAM provides a description of all the elements recommended in enterprise engineering and integration and thereby sets the standard for the collection of tools and methods from which any enterprise would benefit to more successfully tackle initial integration design, and the change processes which may occur during the enterprise operational lifetime. It does not impose any particular set of tools or methods, but defines the criteria to be satisfied by any set of selected tools and methods. GERAM views enterprise models as an essential component of enterprise engineering and integration; this includes various formal (and less formal) forms of design descriptions utilised in the course of design - as described in enterprise engineering methodologies - such as computer models, and text and graphics based design representations.

The set of components identified in GERAM is shown in Figure A.1 and is briefly described in this clause. Each component is then defined in more detail in A.3.

The GERAM framework identifies in its most important component GERA (Generalised Enterprise Reference Architecture) the basic concepts to be used in enterprise engineering and integration (for example, enterprise entities, life cycles and life histories of enterprise entities). GERAM distinguishes between the methodologies for enterprise engineering (EEMs) and the modelling languages (EMLs) which are used by the methodologies to describe and model, the structure, content and behaviour of the enterprise entities in question. These languages will enable the modelling of the human part in the enterprise operation as well as the parts of business processes and their supporting technologies. The modelling process produces enterprise models (EMs) which represent all or part of the enterprise operations, including its manufacturing or service tasks, its organisation and management, and its control and information systems. These models can be used to guide the implementation of the operational system of the enterprise (EOSs) as well as to improve the ability of the enterprise to evaluate operational or organisational alternatives (for example, by simulation), and thereby enhance its current and future performance.

The methodology and the languages used for enterprise modelling are supported by enterprise engineering tools (EETs). The semantics of the modelling languages may be defined by ontologies, meta models and glossaries which are collectively called generic enterprise modelling concepts (GEMCs). The modelling process is enhanced by using partial models (PEMs) which are reusable models of human roles, processes and technologies.

The operational use of enterprise models is supported by specific modules (EMOs) which provide prefabricated products like human skill profiles for specific professions, common business procedures (e.g. banking and tax rules) or IT infrastructure services, or any other product which can be used as a component in the implementation of the operational system (EOSs).

Potentially, all proposed reference architectures and methodologies could be characterised in GERAM so that developers of particular architectures could gain from being able to commonly refer to the capabilities of their architectures, without having to rewrite their documents to comply with GERAM. Users of these architectures would benefit from GERAM because the GERAM definitions would allow them to identify what they could (and what they could not) expect from any chosen particular architecture in connection with an enterprise engineering methodology and its proposed supporting components.

GERA defines the enterprise related generic concepts recommended for use in enterprise engineering and integration projects. These concepts can be categorised as:

a) Human oriented concepts

b) Process oriented concepts for the description of the business processes of the enterprise;

c) Technology oriented concepts for the description of the business process supporting technology involved in both enterprise operation and enterprise engineering efforts (modelling and model use support).

EEMs describe the processes of enterprise engineering and integration. An enterprise engineering methodology may be expressed in the form of a process model or structured procedure with detailed instructions for each enterprise engineering and integration activity.

EMLs define the generic modelling constructs for enterprise modelling adapted to the needs of people creating and using enterprise models. In particular enterprise modelling languages will provide construct to describe and model human roles, operational processes and their functional contents as well as the supporting information, office and production technologies.

GEMCs define and formalise the most generic concepts of enterprise modelling. Generic Enterprise modelling concepts may be defined in various ways. In increasing order of formality generic enterprise modelling concepts may be defined as:

• Natural language explanation of the meaning of modelling concepts (glossaries);
• Some form of meta-model (e.g. entity relationship meta schema) describing the relationship among modelling concepts available in enterprise modelling languages;
• Ontological theories defining the meaning (semantics) of enterprise modelling languages, to improve the analytic capability of engineering tools and, through them, the usefulness of enterprise models (typically, these theories would be built inside the engineering tools).

PEMs (reusable-, paradigmatic-, typical models) capture characteristics common to many enterprises within or across one or more industrial sectors. Thereby these models capitalise on previous knowledge by allowing model libraries to be developed and reused in a 'plug-and-play' manner rather than developing the models from scratch. Partial models make the modelling process more efficient.

The scope of these models extends to all possible components of the enterprise such as models of humans roles (skills and competencies of humans in enterprise operation and management), operational processes (functionality and behaviour) and technology components (service or manufacturing oriented), infrastructure components (information technology, energy, services, etc.).

Partial models may cover the whole or a part of a typical enterprise. They may concern various enterprise entities such as products, projects, companies, and may represent these from various points of view such as data models, process models, organisation models, to name a few.

Partial enterprise models are also referred to in the literature as 'Reference Models', or 'Type 1 Reference Architectures'. These terms have the same meaning.

EETs support the processes of enterprise engineering and integration by implementing an enterprise engineering methodology and supporting modelling languages. Engineering tools should provide for analysis, design and use of enterprise models.

EMs represent the particular enterprise. Enterprise models can be expressed using enterprise modelling languages. EMs include various designs, models prepared for analysis, executable models to support the operation of the enterprise, etc. They may consist of several models describing various aspects (or views) of the enterprise.

EMOs are products which can be utilised in the implementation of the enterprise. Examples of enterprise modules are human resources with given skill profiles (specific professions), types of manufacturing resources, common business equipment or IT infrastructure (software and hardware) intended to support the operational use of enterprise models.

GERA defines the generic concepts recommended for use in enterprise engineering and integration projects. These concepts can be classified as follows.

a) Human oriented concepts, covering human aspects such as capabilities, skills, know-how and competencies as well as roles of humans in the enterprise organisation and operation. The organisation related aspects have to do with decision level, responsibilities and authorities, the operational ones relate to the capabilities and qualities of humans as enterprise resource elements. In addition, the communication aspects of humans have to be recognised to cover interoperation with other humans and with technology elements when realising enterprise operations. Modelling constructs will be required to facilitate the description of human roles as an integral part of the organisation and operation of an enterprise. The constructs should facilitate the capture of enterprise models which describe

An appropriate methodology will also be required which promotes the retention and reuse of models that encapsulate knowledge (i.e. know-how possessed by humans expressed as an enterprise asset) during the various life phases of enterprise engineering projects.

b) Process oriented concepts, dealing with enterprise operations (functionality and behaviour) and covering enterprise entity life cycle and activities in various life-cycle phases, life history, enterprise entity types, enterprise modelling with integrated model representation and model views.

c) Technology oriented concepts, dealing with various infrastructures used to support processes and include for instance resource models (information technology, manufacturing technology, office automation and others), facility layout models, information system models, communication system models and logistics models.

Examples of enterprise reference architectures are provided by ARIS, CIMOSA, GRAI/GIM, IEM, PERA. ENV 40003 defines a general framework for enterprise modelling. ISO 14258 defines rules and concepts for enterprise models.

The role of humans in the enterprise remains fundamental. However sophisticated and integrated an enterprise can be, humans will always make the final decision. With the emergence of decentralised organisations, flat hierarchies, and responsibility and authority delegation, the knowledge about the roles of individuals and who is responsible for what becomes an invaluable asset for any enterprise especially those operating according to new management paradigms. Therefore, capturing this knowledge in enterprise models will prove to be very useful and enable flexible reaction to environmental changes. In addition the different factors describing the capabilities of humans have to be captured as well. Human factors are concerned with professional skills, experience, etc.

Typically humans may assume different roles during enterprise engineering and operation. Examples are: chief executive, chairperson, marketing, sales, technical (R&D), finance, engineering and manufacturing directors, product design, production planning, information systems, quality, product support, logistics, capital equipment, shop floor and site managers; assistant managers, accountants, cashiers, product, process and information system designers, production engineers, electrical and mechanical technicians, maintenance personnel, quality inspectors, supervisors and foremen, machine operators, storeroom and inventory persons, progress chasers, secretaries, drivers, cleaners, management and systems consultants, systems integrators, system builders, and IT suppliers and vendors. Also alternative organisational structures may be deployed, for example elements of an organisation may be linked hierarchically or heterarchically and demonstrate properties of holons, webs, nets, temples or clusters. Further organisational structuring may occur on a functional, process or geographic basis.

Often humans and groupings of humans will be assigned a number of roles and responsibilities which need to be carried out concurrently and cohesively, where each may involve different reporting lines and control procedures. Furthermore their roles can be expected to change over time as process requirements change and individual and group capabilities advance or decline. The ability to manage and deploy human resources effectively and collectively under complex and changing circumstances is key to the competitive position of an enterprise.

Although it is not practical to model all aspects of human roles within an enterprise, concepts are required to formally represent those human factors connected with enterprise integration. This should be achieved in a way that harmonises human roles with that of other human and technology elements, as an integral part of the organisation and operation of an enterprise. Hence the need for constructs which promote the capture of knowledge (possessed by humans) in the form of reusable enterprise models about

• The role of individuals and groups of individuals,
• The way in which organisational structures and constraints are applied to co-ordinate those roles, such as via the delegation of responsibilities and control and reporting procedures, and
• The capabilities and qualities of humans, treated as resource elements.

It is important to understand when, by whom and how decisions are made in the enterprise as well as who can fulfil certain tasks in the replacement of others.

Knowledge about the roles of humans and ways in which those roles can be harmonised can be capitalised and reused as an enterprise asset. The degree to which such knowledge can be formalised within computer processable models will directly influence the degree to which it can be capitalised. Computer processable models naturally facilitate analysis, transformation, storage and integration (based on common understandings). Whereas mental models retained and processed by humans will be less tractable for such purposes. However the retention and reuse of informal models (such as in the form of cause and effect relationships and shared mental models or images) can also be of significant benefit in realising improved cohesion in an enterprise. Hence even where formal modelling of human issues proves impractical the retention and reuse of knowledge should be encouraged by deploying suitable social processes, human organisational structures and methodologies and tools which promote explicit model capture and visualisation.

The ability to retain and reuse human factors knowledge can be of vital importance to the competitive position of an enterprise. Its reuse can enable an enterprise to

• Respond rapidly to new market opportunities or changes in environmental conditions,
• Reengineer its business (and manufacturing) processes,
• Improve its management and utilisation of resources as new products and services are launched, and
• Improve its resilience to the loss of core competencies in the form of knowledgeable human assets.

A taxonomy of human factors and their relation to the activity model would allow to relate human aspects to enterprise models. Needed are human role models on decision making, capabilities, socio-technical models (motivation, incentives, etc.), skill models, and organisational models, with others to be determined.

Human role models will support the definition of human responsibilities and authorisation in both the enterprise operation and its organisation. Such models will support the collection of relevant information and its recognition in the design of the operational system. GERA caters for human factors in its view concept (see A.3.1.5.3). This concept provides in its process oriented model views and technology oriented implementation view for the recognition of humans and the capturing of relevant information. Also the role of humans as an operational resource is recognised in these views. In this role the human skills and capabilities will be described. The human aspect of enterprise integration must also be thoroughly dealt with in the change methodology both in the human's role of change agent and in the role of potential and actual resource (see A.3.2).

A.3.1.3.1 General

Business process-oriented modelling aims at describing the processes in the enterprise capturing both their functionality (that is what has to be done and by what role) and their behaviour (that is when things are done and in which sequence). In order to achieve a complete description of the processes a number of concepts have to be recognised in the guiding methodology. The process-oriented concepts defined in GERA are:

• Enterprise entity life cycle and life-cycle phases;
• Life history,
• Enterprise entity types, and
• Enterprise modelling with integrated model representation and model views.

These concepts will be described in more detail below.

Figure A.2 shows the GERA life cycle for any enterprise or any of its entities. The different life-cycle phases define types of activities that are pertinent during the life of the entity. Life-cycle activities encompass all activities from identification to decommissioning (or end of life) of the enterprise or entity. A total of seven life-cycle activity types have been defined, which my be subdivided further as demonstrated for the design type activities which have been broken down into two lower level types of activities (based on the customary subdivision in many industries of design into preliminary- and detailed design activities). The life-cycle diagram used in the description of the life cycle of an entity is itself a model of the enterprise engineering methodology.

This is the set of activities which identify the contents of the particular entity under consideration in terms of its boundaries and its relation to its internal and external environments. These activities include the identification of the existence and nature of a need (or need for change) for the particular entity. In other words these are the activities which define what is the entity of which the life cycle is being considered.

The set of activities that are needed to develop the concepts of the underlying entity. These concepts include the definition of the entity's mission, vision, values, strategies, objectives, operational concepts, policies, business plans and so forth.

The activities needed to develop descriptions of operational requirements of the enterprise entity, its relevant processes and the collection of all their functional, behavioural, informational and capability needs. This description includes both service and manufacturing requirements and management and control requirements of the entity - no matter whether these will be satisfied by humans (individuals or organisational entities), or machinery (including manufacturing-, information-, control-, communication-, or any other technology).

The activities which support the specification of the entity with all of its components that satisfy the entity requirements. The scope of design activities includes the design of all human tasks (tasks of individuals and of organisational entities), and all machine tasks concerned with the entity's customer services and products and the related management and control functions. The design of the operational processes includes the identification of the necessary information and resources (including manufacturing-, information-, communication-, control- or any other technology).

Any life-cycle stage may be subdivided into sub-stages to provide additional structuring of life cycle activities. For example, see figure A.2 in which the design activity is divided into functional design and specification and detailed design to permit the separation and classification of:

a) Overall enterprise specifications (sufficient to obtain approximate costs and management approval of the ongoing project);

b) Major design work necessary for the complete system design suitable for fabrication of the final physical system.

The activities which define all those tasks which must be carried out to build or re-build (i.e. manifest) the entity. This comprises implementation in the broadest sense, covering:

a) Commissioning, purchasing, (re)configuring or developing all service, manufacturing and control software as well as hardware resources;

b) Hiring and training personnel, and developing or changing the human organisation;

c) Component testing and validation, system integration, validation and testing, and releasing into operation.

Note that the implementation description (documentation) may deviate from the design specification of the entity due to preferences or unavailability of specified components.

The activities of the entity which are needed during its operation for producing the customers product or service which is its special mission along with all those tasks needed for monitoring, controlling, and evaluating the operation. Thus the resources of the entity are managed and controlled so as to carry out the processes necessary for the entity to fulfil its mission. Deviations from goals and objectives or any feedback from the environment may lead to requests for change, which includes enterprise re-engineering or continuous improvement of its human and technology resources, its business processes, and its organisation.

These activities are needed for re-missioning, retraining, redesign, recycling, preservation, transfer, disbanding, disassembly, or disposal of all or part of the entity at the end of its useful life in operation.

The life history of a business entity is the representation in time of life-cycle tasks carried out on the particular entity during its entire life span. Relating to the concept described above, the concept of life history allows to identify the tasks pertaining to these different phases as activity types. This demonstrates the iterative nature of the life-cycle concept compared with the time sequence of life history. These iterations identify different change processes required on the operational processes and, or the product or customer services.

Typically, multiple change processes are in effect at any one time, and all of these may run parallel with the operation of the entity. Moreover, change processes may interact with one another. Within one process, such as a continuous improvement project, multiple life-cycle activities would be active at any one time. For example, concurrent engineering design and implementation processes may be executed within one enterprise engineering process with considerable time overlap, and typically in parallel with the enterprise operation.

Life histories of entities are all unique, but all histories are made up of processes which in turn rely on the same type of life-cycle activities as defined in the GERA life cycles (A.3.1.3.2). For this reason life-cycle activities are a useful abstraction in understanding the life history of any entity.

Figure A.3 illustrates the relations between life cycle and life history representing a simple case with a total of seven processes: three engineering processes, three operational processes, and one decommissioning process.

Figure A.4 shows how the life-cycle activities of two entities may be related to each other. The operation of entity A supports the life-cycle activities for design and implementation of entity B. For example, entity A may be an engineering entity producing part of entity B, such as a factory.

Conversely the life-cycle activities of entity A need to be supported with information about the life-cycle details of entity B. That is, to identify a plant, to define its concepts and requirements, and to design it, one must use information about which life-cycle activities of the plant's products need to be covered in the operation of this plant.

Examples of other relations between the life-cycle activities of enterprise entities may be defined. However, it is always the case that only the operational activities of entities influence the life-cycle activities of other activities. GERA introduces the concept of entity types and the relations between the different types. Many categories of enterprise entities can be defined. In the following two different ways of categorising enterprise types will be discussed: an operation oriented set and a generic and recursive set of enterprise entity types. The two sets have close relations to each other and both identify the product entity as the result of the operation of other entities.

These enterprise entity types, described below, are all concerned with different types of operations.

This type defines an enterprise (often with a short life history) which is created for the one-off production of another entity. Examples of project enterprise are: enterprise engineering project, one of a kind manufacturing projects, building projects, etc.

The project enterprise is characterised by its close linkage with the life cycle of the single product or service that it is producing. The management system of project enterprises is typically set up quickly, while the rest is created and operated in lock-step with the life-cycle activities of the product of the project.

Project enterprises are normally associated with, or created by repetitive service and manufacturing enterprises. A typical example would be an engineering project created by an engineering enterprise.

The products of project enterprises may be diverse, such as large equipment, buildings etc., or an enterprise (e.g. a plant, or an infrastructure enterprise).

This type defines enterprises supporting a type- or a family of products, produced in a repetitive or sustained mode. During their life history these business enterprises undergo multiple change processes. Examples of repetitive business enterprise are service enterprises, manufacturing plants, engineering firms, infrastructure enterprises, etc.

The products of the repetitive service and manufacturing enterprise may be diverse, such as non-enterprise product entities (see below); or products which are enterprises themselves, e.g. project enterprises are regularly created by engineering and building companies.

This type defines a very large class of entities including any artificial product, such as customer goods, services, hardware equipment, computer software, etc. These entities are not enterprises themselves, but their life cycles are described by GERAM.

A generic and recursive set of four enterprise entity types which have been defined as follows.

• Strategic Enterprise Management Entity (Entity Type 1), which defines the necessity and the starting of any enterprise engineering/integration effort.
• Enterprise Engineering/Integration Entity (Entity Type 2), which provides the means to carry out the enterprise engineering efforts defined by enterprise Entity Type 1. It employs a methodology (Entity Type 5) to define, design, implement and build the operation of the enterprise entity (Entity Type 3).
• Enterprise Entity (Entity Type 3), which is the result of the operation of Entity Type 2. It uses a methodology (Entity Type 5) and the operational system provided by Entity Type 2 to define, design, implement and build the products and customer services of the enterprise (Entity Type 4).
• Product Entity (Entity Type 4), which is the result of the operation of Entity Type 3. It represents all products and customer services of the enterprise.

This set may be complemented by a fifth entity type that represents the methodology needed for guiding the enterprise engineering and enterprise integration activities.

• Methodology Entity (Entity Type 5), which represents the methodology to be employed by any enterprise entity type in the course of its operation, which operation in general leads to the creation of another entity type.

The recursiveness of the first four entity types can be demonstrated by identifying the role of the different entities, their 'products' and the relations between them. Figure A.5 represents the chain of enterprise entity developments. The Entity Type 1 will always start creation of any lower level entity by identifying goal, scope and objectives for the particular entity. Development and implementation of a new enterprise entity (or new business unit) will then be done by a Entity Type 2 whereas a Entity Type 3 will be responsible for developing and manufacturing a new product (Entity Type 4). With the possible exception of the Entity Type 1 all enterprise entities will have an associated entity life cycle. However, it is always the operational part of the entity life cycle in which the lower entity is defined, created, developed and built. The operation itself is supported by an associated methodology for enterprise engineering, enterprise operation, product development and production support.

Figure A.5 shows both the life cycle of the methodology (Entity Type 5) and the process model of the methodology. There must be a clear distinction between the life cycle of the methodology (which is essentially the description of how a methodology is developed) and its process model which is the individual manifestation of the methodology entity itself used to support the operational phase of particular enterprise entities.

The operational relations of the different entity types are also shown in Figure A.6 which demonstrates as an example the contributions of the different entities to the life cycle of a manufacturing entity (Entity Type 3). The manufacturing entity itself produces the enterprise product (Entity Type 4) in the course of its operation phase.

The defined set of entity types is seen to be sufficient to allow representation of other types as well. For example, the distinction between on-of-a-kind or project related enterprise entities and continuous operation type enterprises would only require different parts of the life-cycle activities to be used in the life history of such entities. This is already indicated in Figure A.3 in which the engineering processes could relate to an Entity Type 2 and the operational processes to an Entity Type 3 which produces the product or customer services (Entity Type 4). The involvement of Entity Type 1 depends on the degree of change to be carried out in the change process.

Process modelling is the activity that results in various models of the management and control as well as the service and production processes, and their relationships to the resources, organisation, products etc. of the enterprise. Process modelling allows the user to represent the operation of enterprise entities and entity types in all their aspects: functional, behaviour, information, resources and organisation. This provides for operational use of the models for decision support by evaluating operational alternatives and for model driven operation control and monitoring.

Both the enterprise engineering process and the operational environment employ a significant amount of technology. Technology is either production oriented and therefore involved in producing the enterprise products and customer services, or management and control oriented providing the necessary means for communication and information processing and information sharing. Technology-oriented concepts have to provide descriptions of the technology involved in both the enterprise operation and the enterprise-engineering efforts.

For the operation oriented technology such concepts have to relate to models such as resource models and resource organisation models (e.g. shop floor models, system architectures, information models, infrastructure models), communication models (e.g. network models), etc.

All of these descriptions are applicable in the enterprise engineering environment as well. In addition, there are specific needs for information technology for the support of enterprise engineering (e.g. engineering tools, model development services and model enactment services for animation, simulation, and model based operation control and monitoring).

IT support for enterprise engineering as well as enterprise operation should provide two main functions:

GERA provides an analysis and modelling framework that is based on the life-cycle concept and identifies these three dimensions for defining the scope and content of enterprise modelling:

• Life-Cycle Dimension, providing for the controlled modelling process of enterprise entities according to the life-cycle activities;
• Genericity Dimension, providing for the controlled particularisation (instantiation) process from generic and partial to particular;
• View Dimension, providing for the controlled visualisation of specific views of the enterprise entity.

Enterprise modelling is the activity that results in partial or particular enterprise models (e.g. various models of the management and control as well as service and production processes, resources, organisation, products etc. of the enterprise). The life-cycle activities of an entity may define various models of that entity to be created. That is, the results of enterprise modelling are all the various designs, models prepared for analysis, executable models to support enterprise operation, and so on (see reference [13] of A.4.1).

The emphasis in enterprise modelling is currently on process and product models for representing enterprise operations. Process oriented modelling allows representing the operation of enterprise entities and entity types in all their aspects: functional, behaviour, information, resources and organisation. This provides for operational use of the models for decision support by evaluating operational alternatives and for model driven operation control and monitoring.

Enterprise models in general represent a very complex reality. In order to reduce this complexity enterprise models have to allow the representation of certain aspects (views) of the model. Aspects which represent part of the model which is relevant to the concerns of the user. This allows the manipulation of the model according to the user's concerns, without being disturbed by the overall complexity of an overall total model.

Enterprise modelling is not limited to process modelling of the enterprise. All other customary design and analysis activities that create descriptions, or models, of the enterprise in any phase of the life cycle (such as engineering drawings, charts etc.) also belong to this category. The reason for the emphasis on process modelling is only because this is a relatively new activity in enterprise design not earlier practised. This modelling activity is, however, over and above the already practised ones, not to replace them.

To decrease the apparent complexity of the resulting enterprise models GERA provides the view concept which allows the operational processes to be described as an integrated model, but to be presented to the user in different sub-sets (model views) of an integrated model (see Figure A.9). Views contain a subset of facts present in the integrated model allowing the user to concentrate on relevant questions that the respective stakeholders may wish to consider using enterprise modelling. Different views may be made available highlighting certain aspects of the model and hiding all others. The concept of view is applicable for models of all entity types across their entire life cycle. Modelling views are generated from the underlying integrated model. Any model manipulation (any change of the contents of a particular view), will be reflected in all relevant views and aspects of the model.

GERA defines a "finest mesh of subdivision" of the kinds of models deemed desirable, allowing for the fact that an even finer subdivision may be prescribed by a GERAM-compliant candidate architecture. The following subdivisions of models or model views have been identified in GERA:

• Entity Model Content Views: function, information, resource, organisation;
• Entity Purpose Views: customer service and product, management and control;
• Entity Implementation View: human implemented tasks, automated tasks (management and control technology and mission-support technology);
• Entity Physical Manifestation Views: software, hardware.

Additional views may be defined according to specific user needs.

GERAM does not require every view to be present in every life-cycle phase. However, it requires that the scope of the defined views is covered by any other different view subdivision. Thereby it is guaranteed that all relevant facts are captured. For example, it is not as important to have a separate software view and a separate hardware view as it is to model both software and hardware. The Enterprise Engineering Methodology decides which model to produce and which modelling language or formalism to use to describe that model. In other words the enterprise engineering process needs models for some pragmatic purpose. For example, models can be used to express concepts such as:

a) A design choice;

b) To simulate a process to find some process characteristics, such as cost or duration;

c) To analyse an existing process for finding inconsistencies or other problems in the information or material flow;

d) To analyse decision functions and find missing decisional roles.

The view concept is the generalisation of the view concepts of many architectures including CIMOSA, GRAI (and others). The GERA modelling framework allows for languages of different expressive power for each model view. This means that there is a choice of language in any particular view depending on what analysis capability (and therefore expressive power) is required, according to the enterprise engineering methodology's needs.

Four different model content views have been defined for the user-oriented, process representation of the enterprise entity descriptions: Function, Information, Organisation, and Resource.

The Function View represents the functionalities (activities) and the behaviour (flow of control) of the business processes of the enterprise. Decisional activities of the management related operations are represented, as well as transformational and support activities. The functional view of the management- and control system of an enterprise or entity is indeed the functional model of its decision system. (Note that the management- and control system of the enterprise is often called the decision system.) The function view includes functional models, process models, decision models, which differ in their expressive power (and competency, e.g. in terms of what analysis questions these models can answer) but all talk about some aspect of the enterprise function. As a result, the "function view" is a holding place for a host of possible models. Examples include CIMOSA (see references [8] and [14] of A.4.1) function view models, GRAI Grid (see reference [15] of A.4.1) and GRAI Net representations of decision centres, Petri nets, Event Driven Process Chains, Generalised Process Networks, QGERT, and GPSS models. All of the above types of models belong to the "function" view. Similar arguments can be developed for the information, for the organisation, and for the resource view.

The Information View collects the knowledge about objects of the enterprise (material and information) as they are used and produced in the course of the enterprise operations. The information is identified from the relevant activities and is structured into an enterprise information model in the information view for information management and the control of the material and information flow.

The Resource View represents the resources (humans and technical agents as well as technological components) of the enterprise as they are used in the course of the enterprise operations. Resources will be assigned to activities according to their capabilities and will be structured into resource models, e.g. for asset management.

The Organisation View represents the responsibilities and authorities on all entities identified in the other views (processes, information, and resources). It caters for the structure of the enterprise organisation by organising the identified organisational units into larger units such as departments, divisions, sections, etc.

Other modelling views may be defined if needed (such as ecological, economic) and supported by the engineering tools.

The entity model content views in particular covers a great deal. This is because there are many different languages which fit any given model view in this category.

Two different views, described below, allow to represent the model contents according to the purpose of the enterprise entity.

• The Customer Service and Product View represents the contents relevant to the enterprise entity's operation and to the operation results. This represents the mission of the enterprise entity being studied.
• The Management and Control View represents the contents relevant to management and control functions necessary to control that part of the enterprise entity which produces products or delivers services for the customer.

This view subdivision is defined to delineate the scope of the description of the enterprise, maintaining that the scope should extend to both the mission fulfilment part and the management part of the enterprise. An enterprise engineering methodology may propose that separate models or descriptions be prepared for these two parts.

The implementation of the enterprise entity may be presented in two different views, described below, based on the division between human and automated tasks.

• The Human Activities Views represents all information related to the tasks to be done by humans. The view distinguishes between the tasks that may be done by humans (extent of humanizability) and those that must be done by humans (extent of automation).
• The Automated Activities View presents all the tasks to be done by machines. This includes information related to those tasks to be carried out by mission support technology and those carried out by management and control technology (i.e. 'technology tasks'). The implementation view distinguishes between the tasks that may be done by machines (extent of automatability) and those that must be done by machines (extent of automation).

Two different views, described below, allow the user to represent the physical manifestation of the enterprise entity.

• The Software View represents all information resources capable of controlling the execution of the operational tasks in the enterprise. Examples are any computer program which can be stored in a computer or in any other control device enabling the execution of an operation task, or any set of instructions for humans with defined skills such that the instructions are for the humans to perform a task which they otherwise would not have been able to carry out. Software is also a controllable state, e.g. a configuration description of manufacturing hardware, such that the hardware in that configuration can perform a task provided the configuration is maintained for the duration of that task.
• The Hardware View represents all physical resources which have the capability to perform some sets of tasks in the enterprise. Examples are a computer system with given performance characteristics, an employee with given skills, or a machine with given functionality.

Figure A.10 shows an overlay of the different views identified above. The view categories are in general independent of each other, but certain combinations may be useful to represent specific aspects of the enterprise at particular life cycle phases. The availability of any view is subject of its implementation in the supporting engineering tool.

Enterprise engineering methodologies describe the processes of enterprise engineering. Their scope is defined in the GERA life-cycle concept. A generalised methodology like generalised architectures is applicable to any enterprise regardless of the industry involved.

An enterprise engineering methodology will help the user in the process of the enterprise engineering of integration projects whether the overall integration of a new or revitalised enterprise or in management of on-going change. It provides methods of progression for every type of life-cycle activity. The upper two sets of these activities (identification and concept) are partly management and partly engineering analysis and description (modelling) tasks. The requirements and design activity sets are mostly oriented towards engineering tasks throughout the process, including the production of enterprise models and designs throughout the process.

Enterprise engineering methodologies describe the process of enterprise engineering and will guide the user in the engineering tasks of enterprise modelling. Different methodologies may exist which will cover different aspects of the enterprise change processes. These may be complete integration processes, or incremental changes as experienced in a continuous improvement process.

The enterprise engineering process itself is usually directed to a repetitive service- or manufacturing enterprise or a project enterprise. The methodology may be specifically oriented to the type of enterprise or entity under consideration.

Note Four essential view types and their contents are shown. Other modelling views may be defined if needed and supported by the engineering tools.

Enterprise engineering may itself be carried out as a specific project. But the integration task may start at any one of the enterprise's life-cycles activities, not necessarily in the top 'identification' ones. For example: a given engineering project of a new plant may not have to start with the identification and concept definition of the plant, because the customer (who commissioned the design and building of the plant) may have already carried out these activities. In this case the engineering project enterprise should only specify the requirements and carry out the design/detailed design, and implementation (building) of the plant. Such engineering project will then use the requirements, design, and implementation parts of a complete enterprise engineering methodology.

Therefore, in an enterprise engineering methodology the processes relating to the different tasks of enterprise engineering should be defined independent of each other in order to allow for their combination in the context of the particular engineering task.

Enterprise engineering methodologies may be described in terms of process models or descriptions with detailed instructions for each type of activity of the integration process. This allows not only a better understanding of the methodology, but provides for identification of information to be used and produced, resources needed and relevant responsibilities to be assigned for the enterprise engineering process, in the course of project-management of integration projects. A process representation of a methodology could employ the relevant enterprise modelling languages. Enterprise engineering methodologies may also use modelling methodologies as components. A modelling methodology is a methodology with the aim of giving help to model developers who use a modelling language or set of languages, and describes how a model can be developed and validated (starting from scratch or using pre-defined partial models).

The major part of a methodology is a structured approach which defines not only all the steps/phases to be followed in an engineering and/or integration project, but also the way of involving as much as possible people working in the company (users) in the analysis and design of the manufacturing and service system.

The involving of company users is an important success factor for an integration project. It is considered that techniques used to build new manufacturing and service systems are currently difficult to understand for business users of the future system particularly in the domain of the Information Technology. Besides, according to the amount of investment necessary to build a new manufacturing and service system, one needs to be sure that the design solution of the new system meets the objectives defined in the initial user requirements. The design of the new system must be validated by users before any development or implementation.

The involving of people of the company will facilitate the final acceptance of the designed system and thus shorten the transition phase between the old and new systems. The methodology should make clear distinction between the two major phases of the design: user oriented design and technology oriented design. The experiences show that business people must be associated as much as possible in the user oriented design phase and as little as possible in detailed technology oriented design because it is an expert task (unless the technology considerations have a direct business effect).

The other aspect of human involvement in the enterprise is the place of humans in the designed entity, such as a plant.

To show the true place of the human in the implementation of the enterprise functions, there is a need to assign the appropriate ones of these tasks and functions developed in the Requirements Life-cycle Phase to the human element of the system. This can be done by considering the functional tasks as grouped in three boxes in the Preliminary Design Phase (see Figure A.11).

This action will separate the tasks of Mission Fulfilment and Management and Control as defined in the Requirements Analysis phase into three, thus assign the tasks or functions involved to the appropriate boxes which in turn define the automated information tasks which become the Information Systems Architecture functions and the automated manufacturing tasks which become the Manufacturing Equipment Architecture functions. The remainder (non-automated) become the functions carried out by humans as the Human and Organisational Architecture.

The split of functions for implementation between humans and machines forms the first definition of the implementation of the resulting manufacturing system. Because of the inclusion of humans, there must be three separate elements in the implementation scheme: the Information System Architecture, the Human and Organisational Architecture, and the Manufacturing Equipment Architecture.

Two lines, the Automatability Line and the Humanizability Line, can be defined giving the limits of automation and the limits of human involvement.

The Automatability Line shows the absolute extent of pure technologies in their capability to actually automate the tasks and functions. It is limited by the fact that many tasks and functions require human innovation, and so forth, and cannot be automated with presently available technology.

The Humanizability Line shows the maximum extent to which humans can be used to actually implement the tasks and functions. It is limited by human abilities in speed of response, breadth of comprehension, range of vision, physical strength, and so forth.

Still a third line, the Extent-of-Automation Line, can be drawn which shows the actual degree of automation carried out or planned in the subject enterprise entity. Therefore, it is the one which actually defines the boundary between the Human and Organisational Architecture and the Information Systems Architecture on the one side, and the boundary between the Human and Organisation Architecture and the Manufacturing (mission fulfilment) Equipment Architecture on the other side. Provided requirements such as timing and co-ordination are fulfilled, it makes no difference what functions are carried out by personnel versus machines, or what organisational structure or human-relations requirements are used. Therefore, the actual extent of automation is determined by political and human relations-based considerations as well as by technical ones. The location of the Extent of Automation Line is influenced by economic, political, social (customs, laws and directives, union rules), as well as technological factors.

In order to perform in an efficient way the analysis, the design and the implementation within an engineering and/or integration project, the methodology must associate with the available project management techniques in terms of project planning, project budgeting and control, project follow-up and so forth.

A logical separation can be made between a project life cycle and enterprise system life cycle (see A.3.1.3.4). Within the project life cycle

a) the control of the project is covered by the 'management and control' part of the project life cycle, and

b) the execution (operation) of the project is covered by the 'service to the customer' part,

as guided by the various phases defined in the life cycle of the system that is designed/built by the project. In this sense one of the main activities within the project management's operation is the planning of time and resources and the control of the steps to be executed and defined in the system life cycle.

Looking at the life history of a project it contains at least these three phases in time:

• Project start-up, aimed at defining the project organisation (various teams and managers), project preparation (definition of the what, who, when and how), project planning and the organisation of the project start-up meeting;
• Project control, aimed at acceptance of deliverables (hard and/or software, machines, various installations, etc.), monitoring of progress and continuous planning, managing problems and change, and executing reviews and auditing;
• Project termination, aimed at the general acceptance and the final evaluation of the project.

Examples of project management approaches associated with a methodology can be found in GIM, SADT etc.

A methodology must take the economic aspect into consideration. In fact, the choice of various investments depends on objectives that are often contradictory. To help designer to choose the best solution, both technical and economic views should be studied at the different steps of an integration project.

The methodology should allow the decomposition of the strategic objectives of the company into sub-objectives of each function; and the specification of the technical solution must be followed by a technical-economic evaluation. The economic evaluation can be split up in these 3 steps:

• Calculation of the cost of the solution;
• Performance measures of the solution;
• Comparison of the solution costs with the budget.

The aim of this approach is on the one hand, to compare the project cost against the investment budget, and on the other hand, to compare the solution performances against the technical objectives derived from the company strategy. This comparison will allow to economically validate or not the proposed solution.

Examples of technical-economic evaluation approach can be found in ECOGRAI, GEM (GRAI Evolution Methodology) or Activity Based Costing.

The engineering of an enterprise is a highly sophisticated, multidisciplinary management, design and implementation exercise during which various forms of descriptions and models of the target enterprise will be created.

To develop enterprise models potentially more than one modelling language is needed. The situation is similar to software engineering where there are no known languages that span the needs of all models in all phases of the life cycle. The set of languages must be competent to express the models of all areas defined in the modelling framework of the Generalised Enterprise Reference Architecture, GERA.

Enterprise models must represent the enterprise operations from various modelling viewpoints (see A.3.1.5.3). For each area of the GERA modelling framework, there may be a modelling language selected according to the enterprise engineering methodology, which is suitable for the expression of the respective models. In practice, the set of languages will be smaller then the set of areas to be modelled, with one language suitable for more then one area.

These two requirements must be satisfied in the definition of a complete set of enterprise modelling languages:

• Every area represented in the modelling framework (see Figures A.8 and A.10) must be covered for every enterprise entity type;
• A model developed in one subject area must be able to be integrated with models of other subject areas, if the information content of the model so requires.

Any subject area of modelling may be covered with more than one language, the languages being of different 'expressive power', meaning that some languages may only be useful for the description of the subject area but not suitable for certain analysis tasks. For example, the languages that belong to the function view may differ in their capability of expressing certain characteristics of functions. For example, the dynamics of the function, the behaviour of the function, the subdivision of the function into function types such as product management, resource management, and co-ordination and planning. The necessary expressive power, and thus the selection of languages, is related to the methodology followed.

An enterprise engineering methodology may prescribe some analysis tasks that require a given modelling language. However, there should not be any prejudice built into the modelling languages as to what the methodology will be. It is necessary for any enterprise engineering methodology to have access to a consistent set of modelling languages for typical enterprise engineering tasks. Therefore, such consistent and complete sets must be selected or developed, e.g. CIMOSA set of languages, the choice of the set of languages by the GRAI methodology, etc.

Enterprise modelling languages may be defined as modelling constructs. Modelling constructs represent the different elements of the modelled enterprise entity and improve both modelling efficiency and model understanding. The form (representation) of modelling constructs has to be adapted to the needs of people creating and using enterprise models. Therefore, separate languages may exist to accommodate the aspects of different users (e.g. business users, system designers, IT-modelling specialists, and others). In addition, modelling languages may allow the formation of higher level constructs out of more basic constructs (macro constructs) to enhance modelling productivity.

Model based decision support and model driven operation control and monitoring require modelling constructs which are supporting the end users. They have to represent the operational processes according to the users' perceptions.

The semantics of the modelling languages may be described in terms of ontological theories (see A.3.4). This is especially important if enterprise models are to support the enterprise operation itself, because the models in that case must be executable. However, the definition of the formal semantics should be supported by natural language explanations of the concepts as well.

Examples of modelling languages can be found in ARIS (see reference [18] of A.4.1), CIMOSA (see references [8] and [14] of A.4.1), GRAI/GIM (see reference [15] of A.4.1), IEM (see reference [17] of A.4.1) or the IDEF family of languages (see references [8] and [16] of A.4.1). Relevant standards are: ENV 12 204, which defines a reference set of twelve Constructs for Enterprise Modelling (Business Process, Capability Set, Enterprise Activity, Enterprise Object, Event, Object View, Object State, Order, Organisational Unit, Product, Resource, Relation), and; ISO 14258, which defines rules and concepts for enterprise models.

Generic enterprise modelling concepts are the most generically used concepts and definitions of enterprise engineering and modelling. The three forms of concept definition are, in increasing order of formality:

• Glossaries;
• Meta-models;
• Ontological theories.

Some requirements that must be met are as follows:

• Concepts defined in more then one form of the above must be defined in a mutually consistent way;
• Those concepts which are used in an enterprise modelling language must also have at least a definition in the meta-model form, but preferably the definition should appear in an ontological theory .

The terminology used in enterprise engineering can be defined in natural language as a glossary of terms. Such a glossary is a mandatory requirement for a complete generalised enterprise integration architecture and methodology. As a minimal requirement the glossary must define all concepts which are defined in the semi-formal meta-models and/or formal ontologies.

In the GERAM context, meta-models are conceptual models of the terminology component of modelling languages. They describe the concepts used, their properties and relationships, as well as some basic constraints, such as cardinality constraints.

Meta-models are situated between informal and formal expressions. Normally, they are represented as an entity relationship schema or in a language similar in expressive power. The terminology defined in the integrated meta-schema may also be considered as the schema (at any one time) of an enterprise engineering tool's database of enterprise models.

Ontological theories are formal models of the concepts that are used in enterprise representations. They capture rules and constraints of the domain of interest, allowing useful inferences to be drawn, to analyse, execute (e.g. for the purposes of simulation), cross check and validate models.

Ontological theories are a kind of generic enterprise model, describing the most generic aspects of enterprise-related concepts (function, structure, dynamics, cost, and so forth) and defining the semantics of the modelling languages used. They play a similar role to what 'data models' play in database design.

Enterprise modelling languages backed by ontological theories (and their supporting enterprise engineering tools) provide the user with enhanced analysis capabilities.

Since separate enterprise modelling languages may be used to describe various aspects/views of the enterprise it is important to stress that the ontological models must be integrated, i.e. the language definitions for views should be views of an integrated meta-schema (if such a meta schema is defined) and/or of its underlying ontological model (if the corresponding ontological theory is defined). This purely technical requirement allows enterprise engineering tools to be used to cross-check the mutual consistency of enterprise models produced in the enterprise engineering process.

Partial enterprise models (reusable reference models) are models which capture concepts common to many enterprises. PEMs will be used in enterprise modelling to increase modelling process efficiency. In the enterprise engineering process these partial models can be used as tested components for building particular enterprise models (EMs). However, in general such models still need to be adapted (completed) to the particular enterprise entity.

Partial models may be expressed as:

• Models which capture some common part of a class of enterprises;
• Paradigmatic (reference or prototypical) models which describe a typical enterprise of a class (prototype models can be subsequently modified to fit a particular case);
• Abstract models of a part or whole of a class of enterprises which capture the commonalities but leave out specific details (this type of type model is of the 'fill-in-the-blank').

Needed are partial models on human roles in decision making, on professional capabilities and skills, on socio-technical aspects (motivation, incentives, and so forth). Related partial models will be on enterprise organisation and the identification of human responsibilities and authorisation in those models.

The provision of reusable reference models of business processes can significantly improve the efficiency of enterprise modelling. These models represent a common view of the enterprise's operational processes and are concerned with various processes, such as purchasing processes, order processes, product development processes, administrative processes (representing workflow procedures or CSCW), relations with external organisations (e.g. banks).

Partial process models could be tailored to specific industries or industry types (like automotive, electronic components industry, or more specific industries, such as car suspension manufacturing, VLSI manufacturing, and so forth). Or the models may represent typical management and control systems, such as various forms of enterprise co-operation. For example, the modern paradigms of extended and virtual enterprises could be represented as partial models guiding interested parties in defining their specific forms of co-operation.

It is to be noted, that these models of business processes would typically use one or more forms of model view (see A.3.1.5.3), such as function and behaviour models, database schemata, and so forth. Typically partial process models would describe common functionality but leave the definition of the process behaviour to the decision of the particular enterprise.

Partial models may be presented on various levels of abstraction and using various model content views; e.g. ISO 9000 quality models are partial models, defining typical or required policies that must be adopted by quality accredited companies (some ISO 9000 standards go further and define in more detail certain aspects of the business process functions). Many companies create partial models in form of company-wide database schemata, which are then enforced in all company databases, or are used as a basis for such designs. (Such common database schemata can be used as standard interfaces between processes). Some partial models are provided as a system of model-fragments, which ensure that the resulting models define a high quality business process model as well as feasible system implementation.

Partial technology models will provide common descriptions of resources and their aggregations like shop floors, assembly lines, flexible manufacturing systems, office systems, IT systems, etc. All of these partial models will most probably be industry and/or country specific, providing common descriptions of components (linked to supplier catalogues), common operational rules, etc.

Partial models of IT systems can be all the components needed in communications and information processing, which will guide and enhance the design of information systems. This includes the enabling technology for enterprise engineering (EDI, STEP, HTML/WWW, etc.).

One important partial model commonly needed for enterprise engineering is the one of integrating services (see A.3.1.4.3) that provide portability across heterogeneous environments. These services have to include communication, processing/execution control, and presentation and information services. The definition of such services should itself refer to enabling standard definitions, such as: EDI; STEP; HTML/HTTP and all other communication protocols; CORBA-IDL; SQL3; Java services for execution, compilation, presentation etc.).

Such services can then be packaged in various ways as modular products or building blocks (see A.3.7).

Enterprise engineering tools will deploy enterprise-modelling languages in support of enterprise engineering methodologies, and specifically must support the creation, use, and management of enterprise models.

Enterprise engineering tools must support the analysis and evaluation of the models (or descriptions) of the enterprise, and its products, as well as allow the enactment of the models for simulation. These functions are needed for design decision making in the course of enterprise engineering.

Engineering tools should provide user guidance for the modelling process and provide useful analysis capabilities for the use of the models in the enterprise engineering process. That is, the tools help the user utilise the models for the advancement of the engineering process to the best possible extent, as well as releasing the models for operation to support decision making and model based operation monitoring and control.

An enterprise-engineering tool is required to support the simultaneous design/engineering activity of the enterprise entity in question. Therefore it needs to

• Support collaborative as well as individual design/engineering activity, and
• Provide a shared design repository, or database, which allows the management of all partial and particular models and descriptions that are used or produced in the enterprise engineering process, including formal models and any other informal design descriptions, document, etc.

Depending on the enterprise entity in question these engineering tools of the enterprise may display a great variety. If the object of design is a project (i.e. project enterprise) or an enterprise (such as a company) then the tools will be supporting the creation of the design of such enterprise, including its business processes, resources, organisation, etc. If the enterprise entity in question is a product, or product type, then the tools will be supporting the design of the product, such as functionality, geometry, control system, operator procedures, and so forth.

Through the potential integration of the enterprise engineering and model execution services there is scope for the engineering services to be interconnected with enterprise management services. (For example, the initial simulation of a project's execution may use similar tools to those which are utilised for continuous planning of the project during project execution.)

Engineering tools should enable the user to connect the models with the real business process, so as to keep the models up-to-date. Note that engineering tools may be either separate or integrated with the model execution environment (see A.3.7).

The ideal engineering environment should be modular so that alternative methodologies could be based on it. Therefore, engineering tools should provide an environment which is extensible rather than be based on a closed set of models, leaving space for alternative modelling methods (e.g. through enriching the modelling language constructs, or adding new views, as appropriate).

Some examples of engineering tools based on modelling languages (when the enterprise entity in question is the enterprise or a project enterprise itself) are: ARIS Toolset (ARIS, see reference [18] of A.4.1), FirstSTEP (CIMOSA), MOGO (IEM, see reference [19] of A.4.1), KBSI Tools (see reference [20] of A.4.1), METIS, etc. There are many examples for engineering tools of the enterprise for the case when the enterprise entity in question is a product; such tools include tools for product modelling and design, simulation, visualisation, control systems design, and so forth; e.g. STEP Tools.

Enterprise modules are implemented building blocks or systems (products, or families of products) that can be utilised as common resources in enterprise engineering and enterprise integration. As physical entities (systems, subsystems, software, hardware, and available human resources/professions) such modules are accessible in the enterprise, or can be made easily available from the market place. In general EMOs are implementations of partial models identified in the field as the basis of commonly required products for which there is a market. Enterprise modules may be offered as a set, such that if the design of the enterprise is following the partial models that form the basis of this set, then the resulting particular enterprise's business system can be implemented using some or all modules of this set of modules. One set of enterprise modules of distinguished importance is the Integrating Infrastructure that implements the required Integrating IT Services (see A.3.5.4.2).

The goal of enterprise modelling is to create and continuously maintain a model of a particular enterprise entity. A model should represent the reality of the enterprise operation according to the requirements of the user and his application. This means the granularity of the model has to be adapted to the particular needs, but still allows interoperability with models of other enterprises. Enterprise models include all those descriptions, designs, and formal models of the enterprise which are prepared in the course of the enterprise's life history.

Enterprise models are expressed in enterprise-modelling languages and are maintained (created, analysed, stored, distributed) using enterprise engineering tools. Both model creation and model use should be supported by real-time information services. The use of such services will ensure access to real time information in both enterprise environments, the engineering and the operational one.

Some important uses of enterprise models are

• Decision support for evaluating operational alternatives in the enterprise engineering process (enabling operation analysis and capturing the results of synthesis);
• Communication tool which enables the mutual understanding of issues between stakeholders of the enterprise, both internal and external ones;
• Model driven operation control and monitoring, for efficient business process execution, and
• Training of new personnel, where enterprise models serve as demonstration of the real business process for new employees.

Enterprise Operational Systems support the operation of a particular enterprise. They consist of all the hardware and software needed to fulfil the enterprise objective and goals. Their contents are derived from enterprise requirements and their implementation is guided by the design models which provide the system specifications and identify the enterprise modules used in the system implementation.

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Williams, T.J., "The Purdue Enterprise Reference Architecture," Computers in Industry, Vol. 24, No. 2-3, pp. 141-158., 1994.

Williams, T.J., Rathwell, G.A., and Li, Hong (Editors), A Handbook on Master Planning and Implementation for Enterprise Integration Programs, Report 160, Purdue Laboratory for Applied Industrial Control, Purdue University, W. Lafayette, IN, 1996.

Williams, T.J., The Purdue Enterprise Reference Architecture, Instrument Society of America, Research Triangle Park, NC, 1992. Purdue Reports are available from Purdue University (http://www.ecn.purdue.edu/IIES/PLAIC).

Bernus, Peter and Nemes, Laszlo, "A Framework to Define a Generic Enterprise Reference Architecture and Methodology," minutes, Eighth Workshop Meeting, IFAC/IFIP Task Force on Architectures for Enterprise Integration, Vienna, Austria, June 11-12, 1994.

Bernus, Peter and Nemes, Laszlo, "A Framework to Define a Generic Enterprise Reference Architecture and Methodology," minutes, Ninth Workshop Meeting, IFAC/IFIP Task Force on Architectures for Enterprise Integration, Ottawa, Canada, August 25-26, 1994; also in Proceedings of the International Conference on Automation, Robotics and Computer Vision (ICARCV'94), Singapore, November 10-12, 1994.

Bernus, Peter and Nemes, Laszlo, "Enterprise Integration, Engineering Tools for Designing the Business Process of Enterprise," paper presented at the Australian-Taiwan Joint Workshop on Materials, Wollongong East, NSW, Australia, June 26-27, 1995; minutes, Twelfth Workshop Meeting, IFAC/IFIP Task Force on Architectures for Enterprise Integration, Purdue University, West Lafayette, Indiana, USA, June 19-21, 1995.

Bernus, Peter and Nemes, Laszlo, A Framework to Define a Generic Enterprise Reference Architecture and Methodology, Divisional Report Number: MTM 366, CSIRO Division of Manufacturing Technology, Preston, Victoria, Australia 3072, undated. Also in minutes, Tenth Joint Meeting, IFAC/IFIP Task Force on Architectures for Enterprise Integration, Singapore, November 7-8, 1994, Grenoble, France, December 13, 1994.

Williams, T.J., "Contributions of the Purdue Enterprise Reference Architecture and Methodology (PERA) to the Development of a General Enterprise Reference Architecture and Methodology (GERAM)," in Proceedings of the Third International Conference on Automation, Robotics and Computer Vision (ICARCV'94), pp. 83-87, Singapore, November 9, 1994.

Williams, T.J. and Li, Hong, " Proposed Three-Dimensional Model of GERAM," minutes, Tenth Joint Workshop Meeting, IFAC/IFIP Task Force on Architectures for Enterprise Integration, Grenoble, France, December 13, 1995.

Williams, T.J., and Li, Hong, A Specification and Statement of Requirements for GERAM, Report 159, Purdue Laboratory for Applied Industrial Control, Purdue University, West Lafayette, IN, September 1995.

Bernus, P., and Nemes, L, Modelling and Methodologies for Enterprise Integration, Chapman and Hall, London, 1996. Contains papers on all the architectures discussed and related research by Task Force members and others.

Bernus, P., Nemes, L., and Williams, T.J. (Editors), Architectures for Enterprise Integration, Chapman and Hall, London, 1996. Revised book version of Williams (1993).

Williams, T.J. (Editor), Architectures for Integrating Manufacturing Activities and Enterprises, Technical Report, IFAC/IFIP Task Force, Purdue University, West Lafayette, IN, March 1993, revised May1993.

Williams, T.J., Bernus, P., Brosvic, J., Chen, D., Doumeingts, G., Nemes, L., Nevins, J.L., Vallespir, B., Vlietstra, J., and Zoetekouw, D., "Architectures for Integrating Manufacturing Activities and Enterprises," Proceedings, Twelfth IFAC Congress, Sydney, Australia, July 19-23, 1993; Chapman and Hall, London (1994); also presented at the IFIP WG5.3 Workshop on Toward World Class Manufacturing, Litchfield Park, Arizona, Sept. 13-16, 1993, and at the JSPE-IFIP WG5.3 Workshop on The Design of Information Infrastructure Systems for Manufacturing, Tokyo, Japan, Nov. 8-10, 1993. It was published in the Proceedings of both workshops as published by Elsevier-North Holland for IFIP.

Williams, T.J., Bernus, P., Brosvic, J., Chen, D., Doumeingts, G., Nemes, L., Nevins, J.L., Vallespir, B., Vlietstra, J., and Zoetekouw, D., "Architectures for Integrating Manufacturing Activities and Enterprises," Computers in Industry, Vol. 24, No.2-3, pp. 111-139, 1994; Control Engineering Practice, Vol. 2, No. 6, pp. 939-960, 1994.

Kosanke, K., and Nell, J.G. (Editors), Enterprise Engineering and Integration: Building International Consensus, Springer Verlag, 1997 (ISBN 3-540-63402-9).

Petrie, C.J., Jr. (Ed.), "Enterprise Integration Modelling," Proceedings of the First International Conference on Enterprise Integration Modelling Technology, MIT Press, 1992.

Scheer, A-W, Architecture for Integration Information System, Berlin, 1992.

Scheer, A-W, Enterprise-wide Data Modelling -- Information Systems in Industry, Springer Verlag, Berlin-Heidelberg, 1989.

Spur, G., Mertins, K., Jochem, R., Integrated Enterprise Modelling, Beuth-Verlag, Berlin, 1996.

Vernadat, F.B., Enterprise Modelling and Integration, Chapman and Hall, London, 1996. A general text of the field but presenting much on CIMOSA.