TUWIEN MOR

From ONTORULE Show Case

MOR is a prototype reasoner for stratified evaluation of description logic programs.

Motivation

dl-programs are a loosely-coupled combination of logic programs and ontologies. Grounding in dl-programs is still considered a performance bottleneck, caused by having exponentially many rules to process. The goal of this work is to show that dl-programs can be efficiently evaluated by using RDBMSs.

Algorithm

The main idea behind the reasoner is to rewrite stratified dl-programs to Relational Algebra coupled with fixpoint evaluation. Given a stratified dl-program over DL-Lite ontologies, MOR returns the supported minimal model of the dl-program.

It performs the following steps:

1. Rewrites the ABox to a a set of facts (an extensional database).

2. For each dl-atom:

(a) rewrites the relevant TBox axioms and the conjunctive query corresponding to the dl-atom to a fresh set of rules (applying the Presto algorithm).

(b) adds rules for update to the DL KB of dl-atom.

(c) replaces dl-atoms with fresh atoms.

(d) evaluates the program by coupling fixpoint evaluation and RA expressions

The algorithm is related to the work on Datalog rewritability described in Ontorule Deliverable Deliverable D3.3. More details can be found at: http://www.kr.tuwien.ac.at/staff/patrik/docs/Thesis_PatrikSchneider_Original.pdf

Architecture

The implementation is based on Java, Owlgres, and PostgreSQL using recursive SQL queries. The recursive queries are based on the SQL:1999 standard and support just linear recursion.

The Architecture of MOR