Property Characteristics — Where Reasoning Bites

Six characteristics, six different inferences

Characteristic	Means	Reasoner fires when
Functional	at most one value per subject	two values → merge / inconsistency
InverseFunctional	at most one subject per value	two subjects → merge them via owl:sameAs
Transitive	(a p b) ∧ (b p c) → (a p c)	builds the closure
Symmetric	(a p b) → (b p a)	doubles every triple
Asymmetric	(a p b) → ¬(b p a)	finds violations
Reflexive	every individual (a p a)	adds self-loops everywhere

The most underused: InverseFunctional

InverseFunctional is how you say "this is a primary key". If foaf:mbox is inverse-functional and two FOAF cards share the same email, the reasoner concludes the two individuals are owl:sameAs. That's deduplication via logic, for free.

Picture a family tree:

• hasParent is functional from one side in the legal sense (one biological mother).
• hasAncestor is transitive — your grandmother is an ancestor too.
• hasSibling is symmetric — if I'm your sibling, you're mine.
• parentOf and hasParent are inverses — one direction implies the other.
• isMarriedTo is symmetric but not transitive (good thing).

Picking the wrong characteristic produces nonsense. Picking the right one lets the reasoner draw your family tree from a fraction of the assertions.

Tools & resources

• OWL 2 Syntax — Object Property Axioms (transitive, symmetric, inverse, functional, IFP…): https://www.w3.org/TR/owl2-syntax/#Object_Property_Axioms
• FOAF spec — the textbook real-world use of owl:InverseFunctionalProperty on foaf:mbox: http://xmlns.com/foaf/spec/
• Property chain axioms worked example: https://www.w3.org/TR/owl2-primer/#Property_Chains
• OWL 2 RL property reasoning rules — if you're implementing forward-chaining: https://www.w3.org/TR/owl2-profiles/#Reasoning_in_OWL_2_RL_and_RDF_Graphs_using_Rules