Section 3.1.6.2. Subcategory definitions

In the DDL1 formalism, particular relationships between data items may sometimes be stated within a text description or may be implied by the organization of the dictionary (where several data items are defined in the same data block and are understood to share the common attributes itemized in that data block).

Within DDL2, there are mechanisms for more formal and machine-parsable statements of relationships. The _sub_category.id attribute is a label shared by several data items within a category that are related in a specific way described by the associated _sub_category.description attribute. The relationships may be rather general, such as elements of a matrix; or they may be specific physical properties or attributes, such as the collection of axis lengths of a unit cell. The dictionary should list all such labels that occur within its included data definition blocks. Example 3.1.6.2 is an extract from the macromolecular dictionary.