Pegase+ Program Supervision Engine


PEGASE+ is an engine dedicated to program supervision knowledge-based systems, which can automate the choice and execution of programs from a library to accomplish a processing objective. The programs and their use are now considered as a part of the companies
patrimony that should not be lost and that should be easy to re-use and maintain. For this purpose, companies need to ``capitalise''
in a formal and readable form the necessary skills for the optimal use of programs, for documentation purposes and knowledge management in the companies.Techniques of program supervision have a twofold objective: both to favour the capitalisation of knowledge about the use of complex programs and to operationalise this utilisation for users not specialised in the domain.

Instead of developing each system from scratch, we design engines, independent rom specific applications, but yet dedicated to the particular task of program supervision.  A program supervision environment, provided by a software platform (named Lama) is used by a specialist of a library of programs to build a knowledge base. The result (obtained by the integration of the engine plus the knowledge base plus the library of programs) is a knowledge-based system for program supervision which can be utilised by an end-user to run an application.

The Pegase+ engine provides a HTN (hierarchical-task network) planner, an execution module, some evaluation facilities and a repair mechanism using repair and adjustment criteria. It works as a trial and error mechanism until the results are correct.
Pegase+ [IEE00, RFIA00] has been developped using the Lama software platform. It is written in C++ with a corresponding (optional) graphic interface written in Java.
Pegase+  is currently our most developed and tested engine in program supervision. Since 1994, several knowledge bases have been developed with Pegase+ in different application domains [ICVS99]. For example, in image processing for automatic target recognition [IVC99], in medical imaging [SPIE97], or for satellites images [IJRS96].

Knowledge Base

A knowledge base for Pegase+ mainly contains operators which are representations of programs (with descriptions of their data and parameters) and of typical combinations of programs, as well as criteria to guide the reasoning process.  The criteria are implemented in Pegase+ by specialised rule bases which are local to operators.
Experts can  express their knowledge at the expertise level, guided by a supervision-oriented description language named Yakl.This language is used both as a common storage format for knowledge bases and as a human readable format for writing and consulting knowledge bases. It allows experts to express all the different types of knowledge involved in program supervision.

Program Supervision Engine

Pegase+ engine uses a hierarchical planning technique for its construction phase.  A program supervision hierarchical planner works on a hierarchy representing abstraction levels between operators (abstract/composite and real/primitive ones).  A hierarchical planner first constructs an abstract plan, then refines it for a particular situation.  Hierarchical planning is preferred in program supervision, mainly because the expert often thinks in terms of abstract plan schemes.
The relations between the abstraction levels denote mainly alternative (choices) or sequential decompositions. A plan step corresponds to the
execution (or decomposition) of an operator in the hierarchy with a particular parameter instantiation.

Given a user's request and a knowledge base, the engine develops an execution plan\index{plan}, which correspond to the successive expansions of composite operators and execution of primitive ones. In fact it develops several tentative plans, some of them may be aborted, due to problems detected during reasoning. The solution plan, if it exists, is produced as a result of program supervision, as well as the output data.
 

Access and Documentation

The software can be down loaded by ftp, after agreement on the license. A full documentation of Pegase+, Yakl and the GUI is available.

Contact  Sabine.Moisan@sophia.inria.fr
Projet Orion
INRIA
2004 route des Lucioles - BP 93
06902 Sophia Antipolis cedex
France