# Diagram types

There exist two kinds of Express diagrams, schema level diagrams and entity level diagrams.

- Schema level diagrams support the fact that one Express schema can interface other schemas. We distinguish between single and multiple schema level diagrams. A single level schema diagram represent only the tops level of the interfaced schemas. 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.

Express schemas can be handled in two different ways:

- Short form - this is the default one and covers the EXPRESS Schema as it is written with all the references to other schemas (USE FROM, REFERENCE FROM).
- Long from - here the schema is flattend - all the REFERENCE FROM and USE FROMS are removed and replaced by the interfaced types.

In layout mode a schema may be represented only partially or completely. For reference purpose a complete graphical layout with all details is typically needed. For explanatory purposes however it is desired to draw only the main objects and relations, but skip less important details.
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