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Date created: 5/10/2003
Last updated: 1/15/2007
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PSL Ontology -- Current Theories and Extensions (version 2.8)

The axioms of PSL are organized into PSL-Core and a set of extensions. PSL-Core is the set of axioms written in CLIF (the Common Logic Interchange Format) and using only the nonlogical lexicon of PSL-Core. The extensions form a lattice of extensions to PSL-Core.

The purpose of PSL-Core is to axiomatise a set of intuitive semantic primitives that is adequate for describing the fundamental concepts of manufacturing processes. Consequently, this characterization of basic processes makes few assumptions about their nature beyond what is needed for describing those processes, and the Core is therefore rather weak in terms of logical expressiveness. In particular, PSL-Core is not strong enough to provide definitions of the many auxiliary notions that become necessary to describe all intuitions about manufacturing processes.

To supplement the concepts of PSL-Core, the ontology includes a set of extensions that introduce new terminology. An PSL extension provides the logical expressiveness to express information involving concepts that are not explicitly specified in PSL-Core. For each symbol in the nonlogical lexicon of an extension of PSL, there exist one or more axioms, written in CLIF, that constrain its interpretation. A distinction is drawn between definitional and nondefinitional extensions of PSL-Core. A definitional extension is an extension whose nonlogical lexicon can be completely defined in terms of PSL-Core. Definitional extensions add no new expressive power to PSL-Core. Nondefinitional extensions (also called core theories) are extensions of PSL-Core that involve at least one new primitive not contained in PSL-Core. All extensions within PSL must be consistent extensions of PSL-Core, and may be consistent extensions of other PSL extensions. However, not all extensions within PSL need be mutually consistent.

The organization of the extensions below reflects the Parts within standard ISO 18629. All files are updates to the standard, except for those marked by “x”, which are in progress. Other status indicators are: “c” (consistency proof completed) and “ca” (consistency verified by the automated theorem prover Vampire). The syntax of all files has been checked by automated theorem provers, see download page.

Core Theories


Outer Core

Duration and Ordering Theories

Resource Theories

Actor and Agent Theories

Definitional Extensions of PSL

Activity Extensions

Branch Structure


Embedded Activity Trees

Atomic Activities

Temporal and State Extensions





Embedded Activity Trees

Atomic Activities

Activity Ordering and Duration Extensions


Subactivity Occurrence Orderings

Resource Roles

Resource Sets

Processor Activity Extensions