OWL2 QL
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https://www.w3.org/TR/owl2-profiles/#OWL_2_QL The OWL 2 QL profile is designed so that sound and complete query answering is in LOGSPACE (more precisely, in AC0) with respect to the size of the data (assertions), while providing many of the main features necessary to express conceptual models such as UML class diagrams and ER diagrams. In particular, this profile contains the intersection of RDFS and OWL 2 DL. It is designed so that data (assertions) that is stored in a standard relational database system can be queried through an ontology via a simple rewriting mechanism, i.e., by rewriting the query into an SQL query that is then answered by the RDBMS system, without any changes to the data. OWL 2 QL is based on the DL-Lite family of description logics [DL-Lite]. Several variants of DL-Lite have been described in the literature, and DL-LiteR provides the logical underpinning for OWL 2 QL. DL-LiteR does not require the unique name assumption (UNA), since making this assumption would have no impact on the semantic consequences of a DL-LiteR ontology. More expressive variants of DL-Lite, such as DL-LiteA, extend DL-LiteR with functional properties, and these can also be extended with keys; however, for query answering to remain in LOGSPACE, these extensions require UNA and need to impose certain global restrictions on the interaction between properties used in different types of axiom. Basing OWL 2 QL on DL-LiteR avoids practical problems involved in the explicit axiomatization of UNA. Other variants of DL-Lite can also be supported on top of OWL 2 QL, but may require additional restrictions on the structure of ontologies.