Detecting Feature Interactions and Feature Inconsistencies in CPL

Yiqun Xu

Thesis submitted to the
Faculty of Graduate and Postdoctoral Studies
in partial fulfillment of the requirements for the degree of
Master of Computer Science

Under the auspices of the
Ottawa-Carleton Institute for Computer Science
University of Ottawa

Ottawa, Ontario, Canada
September 2003

© Yiqun Xu, Ottawa, Canada, 2003

Abstract

Internet Telephony grants users the power of developing their own
telephony services, and the Call Processing Language (CPL) has been
designed to to fulfil this target. However, this objective confronts a
major obstacle known as the feature interaction problem, which describes
the situation that one feature or service is violated by another in
overall system behaviour.

This thesis addresses a Feature Interaction detection approach  for CPL.
Starting with a review of the  issue of Feature Interaction, we extend
the traditional Feature Interaction definition to Intention Interaction
and Policy Interaction in Internet Telephony. Existing related work is
discussed as well.

We  also give an overview of Internet Telephony, and analyse the
structure of CPL. A logic-based language, the Simple Formal Specification
Language (SFSL) is introduced to express  formally the  intention
of CPL scripts. Method of translating CPL into SFSL  is presented as
well. Based on the SFSL specifications, we propose detection rules to
identify feature interactions in CPL, locally and pair-wise.

An automatic detection tool applying the detection rules is implemented
in SWI-Prolog. Finally,  in order to validate the correctness of the
detection rules, we prove the  logical incoherencies behind these rules
using Predicate Logic.


Keywords:  Feature Interaction, Detection, Logic, Prolog, CPL, Internet
Telephony, Formal Method, Software Engineering