Optimised Reasoning for SHIQ

The tableau algorithm implemented in the FaCT knowledge representation system decides satisfiability and subsumption in SHIQ, a very expressive description logic providing, e.g., inverse and transitive roles, number restrictions, and general axioms. Intuitively, the algorithm searches for a tree-shaped abstraction of a model. To ensure termination of this algorithm without comprimising correctness, it stops expanding paths in the search tree using a so-called 'double-blocking' condition