Section 3.1 illustrated how users can view the APIB contents at a very high level as collections of document types, choose a particular document type (IR), then view a specific document (Part 101), and then view individual portions of that document. Using a tree metaphor for the APIB, one can think of this as starting at the root node and traversing the APIB's search space by visiting successively higher leaves. Just as important is the ability to navigate backwards, that is from a more specific view of the APIB contents to a less specific, higher level one. For example, a user viewing a schema object might want to go back to the schema web page and choose another object from that schema, or a user might want to look at an IR's scope after viewing a schema from the IR. In order to facilitate traversal from a narrower, more detailed view to a broader, less detailed view, all of the web pages generated by the APIB Gateway's CGI scripts contain buttons near the bottom of the page for backtracking. These buttons provide hyperlinks from the current web page to all nodes in the APIB leading up to the root node. When a user clicks on a backtracking button, an APIB query is issued to generate the appropriate web page.
Figure 9: Backtracking buttons for entity dimension_curve_directed_callout.
As an example, consider the web page for the entity dimension_curve_directed_callout. Figure 6 showed the beginning of this web page. Figure 9 shows the backtracking buttons for this web page. The first button provides a link to the schema containing this entity. The second button links to the entity's IR Part. The third button links to the web page for choosing from among the IRs.
Another important capability is the ability to extract raw SGML text from the APIB. Since STEP AP developers re-use IR constructs as building blocks, they need to have a way to include portions of IR documents in their AP. For example, suppose an AP developer building an AP's EXPRESS schema wants to use the entity dimension_curve_directed_callout. Rather than rewrite an entity definition, the AP developer can obtain the SGML source for dimension_curve_directed_callout's web page by clicking on a View SGML Source button on the web page. A CGI script is then invoked which produces a web page containing the raw SGML for the entity definition. Figure 10 shows a portion of this web page. The AP developer can then extract the SGML from the APIB by using the web browser's ``Save'' command.
Figure 10: Portion of raw SGML data for entity dimension_curve_directed_callout.