Object properties

Relating knowledge subjects

Object properties (OP) connect a knowledge subject to an external object; they are also called relationship types or semantic relations. The bare word “relation” is avoided because it clashes with mathematical relations. OPs are the counterpart to data properties, which are “internal” to a subject.

Naming conventions on taoke.de group synonyms (e.g. ◊sameAs, ◊EQ, ◊Synonym). The triple {◊Subject, ◊Relation, ◊Object} is used for composite knowledge subjects. Instantiation follows object property definitions that relate two classes. In labeled property graphs, instances can carry extra data properties and further links, like class instances.

Typical OP families include social roles, family-style relations, and translations; chains of OPs yield derived paths (see OP composition). [ArSm2015] (p. 99) notes that a role is optional—the bearer need not occupy it in every situation. [AlHe2020]; role axioms in [BaMc2003].

An OP ◊OP connects classes ^C and ^D. The short definition (^C, ◊OP, ^D) corresponds to long-form domain and range axioms. A practical naming pattern uses the target class name with the ^ prefix replaced by ◊, plus inverse names such as ◊isEmployeeOf for ◊Employee.

Default cardinality inherits from ◊ObjectProperty unless overridden. Entailment links short and long forms: (c, ◊op, d) ⇔ (◊op, »Domain, c) ∧ (◊op, »Range, d) (canonical notation).

The example knowledge graph includes assertions such as (>NPS-Pablo_Picasso, ◊iof, ^natPerson), exhibition and artwork links, and inverse assertions obtained by swapping subject/object and using the inverse OP. Inverse pairs are declared with an »Inverse link between OP names.

Where OPs follow the naming guideline, inverse triples can be entailed: (ΣS, ◊op, ΣO) ↔ (ΣO, ◊op⁻¹, ΣS) when (◊op, »Inverse, ◊op⁻¹) holds in the graph.

Object-level relations appear as triples whose predicate links two subjects (or a subject to a literal where appropriate); the graph view helps validate structure and inverses.