In computer science, an ABox is an "assertion component"—a fact associated with a conceptual model or ontologies within a knowledge base.
The terms "ABox" and "TBox" are used to describe two different types of statements in knowledge bases. TBox statements describe a domain of interest by defining classes and properties as a domain vocabulary. ABox are TBox-compliant statements that use the vocabulary.
TBox statements are sometimes associated with object-oriented classes and ABox statements associated with instances of those classes.
Together ABox and TBox statements make up a knowledge base or a Knowledge graph.
Examples of ABox and TBox statements
ABox statements typically have the form:
A is an instance of B
or
John is a Person
This should be contrasted with TBox statements (or definitions of domain resources) such as:
All Students are Persons
or
There are two types of Persons: Students and Teachers
TBox statements tend to be more permanent within a knowledge base and are used and stored as a schema or a data model. In contrast, ABox statements are much more dynamic in nature and tend to be stored as instance data within transactional systems within databases. With the newer, NoSQL databases and especially with RDF databases (see Triplestore) the storage distinction may no longer apply. Data and models can be stored using the same approach. However, models continue to be more permanent, have a different lifecycle and are typically stored as separate graphs within such database.