Reasoning about inconsistencies in natural language requirements

The use of logic in identifying and analyzing inconsistency in requirements from multiple stakeholders has been found to be effective in a number of studies. Nonmonotonic logic is a theoretically well-founded formalism that is especially suited for supporting the evolution of requirements. However, direct use of logic for expressing requirements and discussing them with stakeholders poses serious usability problems, since in most cases stakeholders cannot be expected to be fluent with formal logic. In this article, we explore the integration of natural language parsing techniques with default reasoning to overcome these difficulties. We also propose a method for automatically discovering inconsistencies in the requirements from multiple stakeholders, using both theoremproving and model-checking techniques, and show how to deal with them in a formal manner. These techniques were implemented and tested in a prototype tool called CARL. The effectiveness of the techniques and of the tool are illustrated by a classic example involving conflicting requirements from multiple stakeholders.