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DBOWL: A Scalable OWL-DL Reasoner
storage

DBOWL stores the OWL-DL ontologies in a relational database. We define a specific relational schema for our tool.

description

Tables are categorized into 4 types: ontology information tables, Tbox tables, Abox tables, and descriptions tables.
Ontology information tables include ontology_index and uri_index, which store the ID and the URL of all ontologies and the ID and the URI of all instances in the database respectively. Tbox tables store the subclass, subproperty, equivalent class and equivalent property relationships, the disjoint classes and the properties characteristics. This information is provided by the Description Logic reasoner. The hierarchy table stores all class/subclass pairs while the Hierarchyprops table stores all property/subproperty pairs. On the other hand, the equivalents table stores all class/equivalent class pairs while equivalentprops stores all pair property/equivalent property pairs. Finally, the disjoint table stores all pairs of disjoint classes and the propertytypes table stores if the property is transitive, symmetric or functional, if it is the inverse of another property and also its domain and range. Using these tables we can easily obtain the class and property hierarchies and the equivalent classes/properties of a specific class/property.
Furthermore, all the information needed for evaluating Abox inferences is also in the database. There is at least one table for each kind of possible class description in the ontology: enumeration (enumeration table), value restrictions (all, some, hasvalue tables), cardinality restriction max and min tables), intersection (intersec table), union (union table) and complement (complement table). These tables will be used to implement the Abox inference rules.
Finally, we create one Abox table for each class and each property in the ontology. The name of this table is the same as the class or property. These tables contain the IDs of instances explicitly defined as instances of the class or property. Tables representing classes contain only one column (ID) while tables representing properties contain two columns (SUBJECT, OBJECT). This relational schema allows all information about the ontology needed for implementing Tbox queries, and Abox inferences, to be contained in the database.

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