ISO 10303 specifies a language by which aspects of product data can be defined. The language is called EXPRESS. ISO 10303-11:2004 also specifies a graphical representation for a subset of the constructs in the EXPRESS language. This graphical representation is called EXPRESS-G. EXPRESS is a data specification language as defined in ISO 10303-1. It consists of language elements that allow an unambiguous data definition and specification of constraints on the data defined.

The following are within the scope of ISO 10303-11:2004:

• data types;
• constraints on instances of the data types.

The following are outside the scope of this part of ISO 10303:

• definition of database formats;
• definition of file formats;
• definition of transfer formats;
• process control;
• information processing;
• exception handling.

EXPRESS is not a programming language.