# Unique name assumption

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The **unique name assumption** is a simplifying assumption made in some [ontology](/source/Ontology_(computer_science)) languages and [description logics](/source/Description_logic). In logics with the unique name assumption, different names always refer to different entities in the world.[1] It was included in [Ray Reiter](/source/Ray_Reiter)'s discussion of the [closed-world assumption](/source/Closed-world_assumption) often tacitly included in Database Management Systems (e.g. SQL) in his 1984 article "Towards a logical reconstruction of relational database theory" (in M. L. Brodie, J. Mylopoulos, J. W. Schmidt (editors), Data Modelling in Artificial Intelligence, Database and Programming Languages, Springer, 1984, pages 191–233).

The standard ontology language [OWL](/source/Web_Ontology_Language) does not make this assumption, but provides explicit constructs to express whether two names denote the same or distinct entities.[2][3]

- owl:[sameAs](/source/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.

## See also

- [Closed-world assumption](/source/Closed-world_assumption)

- [Coreference](/source/Coreference)

## References

1. **[^](#cite_ref-1)** [Russell, Stuart](/source/Stuart_J._Russell); [Norvig, Peter](/source/Peter_Norvig) (2003) [1995]. *[Artificial Intelligence: A Modern Approach](/source/Artificial_Intelligence%3A_A_Modern_Approach)* (2nd ed.). Prentice Hall. p. 333. [ISBN](/source/ISBN_(identifier)) [978-0137903955](https://en.wikipedia.org/wiki/Special:BookSources/978-0137903955).

1. **[^](#cite_ref-2)** Tao, Jiao; Sirin, Evren; Bao, Jie; McGuinness, Deborah L. (2010). [*Integrity constraints in OWL*](http://www.aaai.org/ocs/index.php/AAAI/AAAI10/paper/view/1931). Proc. AAAI.

1. **[^](#cite_ref-3)** [OWL Web Ontology Language Reference](http://www.w3.org/TR/owl-ref/)

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