EXPRESS is a standard notation for describing data models. A data model is a description of the objects in a computer system along with with their properties and relationships. EXPRESS, like other data modeling notations, has two types of representation:
•a textual notation that precisely describes the details of the model referred to as EXPRESS.
•a graphical representation that is useful for human understanding of the model referred to as EXPRESS-G
EXPRESS is an ISO standard. It is part of the ISO Standard for the Exchange of Product model (STEP). As the name suggests, these standards arose from the manufacturing industry. Despite the source, EXPRESS is non-industry specific.
If you are familiar with entity-relationship diagrams, the EXPRESS-G notation is easy to understand. Rectangles represent entities. A line connects one entity to another if there is a relationship between the two. The basic textual EXPRESS is also easy to understand. The EXPRESS representation of an entity resembles the definition of a table in SQL.
However, EXPRESS offers a richer language for defining data models than the usual entity-relationship diagrams. These features are explained in this site.
Tool support for EXPRESS is limited. Earlier versions of Microsoft Visio contained a template for EXPRESS-G, but this template has been dropped from recent versions. There is an Eclipse plug in JDSAI which supports editing and validation of EXPRESS models and generates EXPRESS-G diagrams.