[referring to Description Logic] Not having CWA, or rather having the Open World Assumption (OWA) means that lack of knowledge of a fact does not immediately imply knowledge of the negation of a fact.

There are two features of Description Logic that are not shared by most other data description formalisms: DL does not make the Unique Name Assumption (UNA) or the Closed World Assumption (CWA). Not having UNA means that two concepts with different names may be allowed by some inference to be shown to be equivalent.

A Description Logic (DL) models concepts, roles and individuals, and their relationships.The fundamental modeling concept of a DL is the axiom - a logical statement relating roles and/or concepts. This is a key difference from the frames paradigm where a frame specification declares and completely defines a class.

The description logic community uses different terminology than the first-order predicate logic community for operationally-equivalent notions; some examples are given here:

FOL vs DL class - concept property or predicate - role object - individual

The Web Ontology Language [OWL] mostly uses FOL terminology, in spite of being an implementation of a description logic.