The Unique Name Assumption (UNA) is a concept from ontology

Ontology (computer science)

In computer science and information science, an ontology formally represents knowledge as a set of concepts within a domain, and the relationships between those concepts. It can be used to reason about the entities within that domain and may be used to describe the domain.In theory, an ontology is...

 languages and description logic

Description logic

Description logic is a family of formal knowledge representation languages. It is more expressive than propositional logic but has more efficient decision problems than first-order predicate logic....

s. In logics with the unique name assumption, different names always refer to different entities in the world. The ontology language OWL

Web Ontology Language

The Web Ontology Language is a family of knowledge representation languages for authoring ontologies.The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web...

does not make this assumption, but provides explicit constructs to express whether two names denote the same or distinct entities.

• owl:sameAs is the OWL property that asserts that two given names or identifiers (e.g., URIs) refer to the same individual or entity.
• owl:differentFrom is the OWL property that asserts that two given names or identifiers (e.g., URIs) refer to different individuals or entities.