Description logic (DL) is a formal knowledge representation language family. It exhibits more efficient decision problems than first-order predicate logic, and is amply relevant to semantic web efforts. DL uses formal reasoning on the concepts of terminological knowledge. Expressive DL answers complex queries beyond retrieval, based on constraints in the knowledgebase.

The expressive DL ZIQ is used to consider the task of 2-way regular path queries in this paper. The main result of this extensive research is that the authors “have shown that query entailment for a very rich class of queries beyond ... conjunctive queries ... is decidable ... in the DL ZIQ,” and the results are applicable to the World Wide Web Consortium (W3C) Web ontology language (OWL) 2 ontology standard. A positive theoretical movement is exhibited here, with a potential to advance the movement toward Web 3.0.

Details of the problem, with multiple theorems, ample proofs (many of which define algorithms), and examples to support these statements, are presented. It is a paper well worth reading by any computer scientist, as it is indeed a standalone textbook-chapter-like elaboration on the characterization and use of one powerful DL.