# Overview

The JSDAI Express-G Editor is a tool to create graphical EXPRESS diagrams according to the specification of EXPRESS-G given in ISO 10303-11. In the following we abbreviate the name of this tool with JSDAI-EG.
In the current version JSDAI-EG works only in the layout mode. In this mode one or several EXPRESS schemas are given and compiled with the JSDAI ExpressCompiler in advance. The result of the compilation can then be used to layout EXPRESS diagrams according to the given EXPRESS schemas. For the future we plan to extend this tool also for the create mode; with this EXPRESS schemas can then be graphically created or modified.
JSDAI-EG operates on files with the extension .exg. These files contain the EXPRESS schema(s) and the graphical layout details. The .exg files are similar to .exd file which are generated by the JSDAI ExpressCompiler. A .exd file is needed to create a new .exg file or to update an existing one.
EXPRESS defines two kinds of diagrams, schema level diagrams and entity level diagrams:

- Schema level diagrams support the fact that one EXPRESS schema can interface other schemas. We distinguish further between single and multiple schema level diagrams.

- A single level schema diagram represent only one top schema and the directly interfaced schemas. Indirectly interfaced schemas are not visible.
- A multi level schema diagram is able to show the complete dependencies of many interacting schemas.

- In the Entity level diagrams all the data types such as entities, defined types with all their relations and attributes, are displayed

In layout mode a schema may be represented only partially or completely. For reference purpose a complete graphical layout with all details is typically required. For explanatory purposes however it is desired to draw only some main objects and relations, but skip less important details.
JSDAI-EG supports all features of EXPRESS-G given in the first and second edition of ISO 10303-11.
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