dependence pattern

Secondary element.

A secondary data element is attached to a primary element.

Two data elements, one more prominent than the other.

Structure data by importance and connect elements by affiliation.

• The elements are ordered in a sequence.
• The primary element acts as flag to the secondary element.
• A descriptive separator connects the elements.

• Relations in entity-relationship models are secondary to entities.
• Attributes, properties, and annotations attached to data objects.
• Pointer types are secondary to the elements they point to (unless the pointer is a descriptive identifier).
• Directed connections, for instance subclass relationships.
• Attributes of attributes (dependent elements can be stacked).
• Members of a container.

• The choice between primary and secondary elements can be rather arbitrary (a connection could also be expressed as entity and some vice versa). For instance members of a container are secondary but collections only exist based on their member elements.
• Once fixed, it is difficult to switch primary and secondary.
• The primary element often modifies interpretation of the second (flag).
• It is not always clear whether a data element is an integral part of an element or an additional annotation. For instance language tags in RDF look secondary but they are an essential property of literals.

• If multiple secondary elements can exist without a primary element, they are rather structured in a container.
• A “connection” between two elements may be a dependence but it could also be a form of embedding or flag.
• Derivation looks similar to dependence and both may coincide but neither or both imply the other. Derived elements may also exist independent from the elements that they can be derived from.

Sets of dependencies with common elements can form graph structures.