This part of ISO 10303 specifies the resource constructs that group elements of product data into collections in order to describe aspects of products. This part of ISO 10303 is applicable to the description of properties of products. The following are within the scope of this part of ISO 10303: — the specification of contexts for representation; — the specification of elements of representation; — the association of elements of representation with one or more contexts in which they are combined to represent a concept; — the association of elements of representation such that one defines another; — a structure for relating two representations such that one participates in the definition of the other; — a structure for relating two representations in which one does not participate in the definition of the other; — constraints to prevent the recursive definition of instances of an element of representation; — the specification of the transformation of one element of representation to another by specifying the input and output of the transformation; — the specification of the transformation of one element of representation to another by specifying the transforming function. The following are outside the scope of this part of ISO 10303: — the complete specification of types of representation, types of elements of representation, and types of representation context; — the specification of the uses of representation; — the association of representation with any of its possible uses; — constraints requiring a directed relationship between representations; NOTE A directed relationship exists between items A and B if the meaning of the relationship of A to B is different from the meaning of B to A. A and B are peers in a non-directed relationship. A directed relationship can be specified in an annotated EXPRESS schema that uses or specializes this schema. — constraints forbidding cyclic structures of related representations; — constraints requiring a directed relationship between the contexts in which related representations exist; — constraints forbidding cyclic structures of relationships between representation contexts.