A visual programming system for automated problem solving

Abstract

Although new AI planning algorithms and techniques are being developed and improved rapidly, there is a lack of efficient and easy to use systems able to incorporate and utilize them. Furthermore, while visual representation facilitates design, maintenance and comprehension of planning domains and problems, very few systems incorporate it. This paper presents VLEPPO, an integrated system aiming at visually modeling planning domains and problems through a convenient graphical interface, while maintaining compatibility with the Planning Domain Definition Language (PDDL), with import and export features. Solutions to planning problems can be obtained by invoking different planners employing the web services technology. The demonstration of the system is performed through a case study involving web service composition viewed as a planning problem.

Introduction

Planning has been an active research area since the early days of AI (Weld, 1999), and its applications have been extremely useful in cases when agents act in dynamic environments. Several formalisms for the representation of planning domains and problems have emerged over time, among which Planning Domain Definition Language (PDDL) (Ghallab et al., 1998) has dominated and become a standard. Over the same period of time, numerous algorithms, methods and techniques have been proposed (Hendler, Tate, & Drummond, 1990).

Most of the algorithms and techniques developed so far mainly focus on improving the efficiency of planning systems in terms of required time and resources. Although the results are in many cases impressive, there are not many successful examples of planning systems adapting to industrial use. This can be partly attributed to technical reasons such as the tendency of existing planning systems to be bound to a specific algorithm which might be overwhelmed by the amount of data they have to deal with, as it is becoming more and more immense. This brings on the requirement for systems that have the ability to incorporate multiple state-of-the-art algorithms before they are rendered outdated with respect to current problem demands. Therefore, there is a need not only for more efficient and scalable algorithms, but also for systems that, instead of being limited to a single algorithm, are flexile enough to adapt and employ new algorithms and techniques.

Furthermore, another important issue is the lack of systems that facilitate the development and deployment of planning domains and problems. Modelling and encoding them in some definition language such as PDDL, necessary as it is, can be tiresome and error-prone. It should not be assumed that the designer will always be a planning expert, and even in such cases, visual interfaces can save a lot of time and effort required, while reducing the number of errors and prevent inconsistencies. Visual interfaces in planning systems liberate the designers from the requirement to pay attention to syntax and facilitate focusing on the semantics and structure of the problem at hand.

This paper presents an attempt to approach the design and solving of planning problems while taking into account the aforementioned issues. The result of this research was the development of VLEPPO (Visual Language for Enhanced Planning Problem Orchestration), which is an integrated system for visually modeling and solving planning problems that aims at:

• offering a convenient and intuitive graphical interface which simplifies modeling, facilitates maintenance and promotes understanding of planning domains, even for non-expert users;

• conforming to the current standards for domain and problem representation, such as PDDL, thus facilitating communication with planning systems that comply with this standard;

• providing a high degree of flexibility in integration of different planning algorithms on top of the local one by employing the current web services technology.

The VLEPPO system provides interoperability with the PDDL language, as it can import domains and problems from PDDL files for visualization, validation and maintenance purposes and at the same time export the designed or modified domains and problems to PDDL. Furthermore, it offers separate but interoperable editors for planning domains and problems facilitating modular design and definition of new problems corresponding to existing planning domains. Moreover, as far as planners are concerned, the web services technology enables the proposed system to communicate with planners implemented or wrapped and deployed as web services; therefore, the user is not limited to a single planning algorithm, while the implementation language and platform of the planning algorithms is not a restriction.

The rest of the paper is organized as follows: Section 2 describes some formalisms and standards used for the representation of planning domains and problems, while Section 3 gives an overview of VLEPPO and its architecture. Sections 4 Visual design of planning problems with VLEPPO, 5 Import and export functions, 6 Obtaining solutions to planning problems elaborate on the features of the system, while a case study involving web service composition is described in Section 7. Related work in the area is presented in Section 8, and finally, Section 9 concludes the paper and poses future directions.