Associations

Overview

Associations define ontological relationships between defs. An association is a tag used on defs to cross-reference related defs via symbols. We use the term association to denote def-to-def relationships versus instance data relationships, which utilize ref tags.

Associations are def tags where the value is a list of symbols. Most foundational def relationships are associations including:

• is: defines supertypes used to build taxonomy tree
• tagOn: annotates a tag to be used with a given type

In the following example both is and tagOn are associations which create a relationship between defs:

def: ^yearBuilt
is: ^number
tagOn: ^site

As a convenience, association tags can use as a simple symbol value. But, they are always normalized to a list. Association tags are never used on instance data; they are strictly used only on defs.

Reciprocal Of

The reciprocalOf tag is applied to an association to define its inverse term. For example:

• tags is reciprocalOf of tagOn (and vice versa)
• quantities is reciprocalOf of quantityOf (and vice versa)

Reciprocals are used to coin terms that are intuitive for bi-directional relationship queries. However, to promote consistency, it is desirable to only declare associations in one direction. Typically, "child-to-parent" is the preferred direction for declaring associations. For example, it is more convenient to declare tagOn for value tags than to enumerate all the tags for a given entity type. This design also provides more flexibility for late binding of associations in separate libs. We use the computedFromReciprocal tag to capture this concept. For example, tags is annotated with the computedFromReciprocal marker. This means its tags must be not used directly as a def tag (it exists only to provide an inverse term for tagOn).