This part of ISO 13584 specifies:

• an EXPRESS schema for generic expressions;
• an EXPRESS schema for expressions, that models the subset of the allowed expressions in the EXPRESS language defined in ISO 10303-11 that corresponds to integer, real, Boolean and string data types. This schema uses the resources defined in the generic expression schema.

The following are within the scope of this part of ISO 13584:

• the exchange of expressions that involve both constants and variables;
• the function that checks whether or not a numeric expression should evaluate to an integer value;
• the constraints which ensure that an expression is semantically correct;
• the computation of the variables or functions used in an expression;
• the function that checks if an expression may be mapped on to the SQL query language.

The following are outside the scope of this part of ISO 13584:

• the assignment of values to variables within some context;
• the triggering mechanism that computes the value of an expression in a given context.