Process Specification Language (psl): Results of the First Pilot Implementation

In all types of communication, the ability to share information is often hindered because the meaning of information can be drastically affected by the context in which it is viewed and interpreted. This is especially true in manufacturing because of the growing complexity of manufacturing information and the increasing need to exchange this information among various software applications. Different manufacturing functions may use different terms to mean the exact same concept or use the exact same term to mean very different concepts. Often, the loosely defined natural language definitions associated with the terms contain so much ambiguity that they do not make the differences evident and/or do not provide enough information to resolve the differences. A solution to this problem is the development of a taxonomy, or ontology, of manufacturing concepts and terms along with their respective formal and unambiguous definitions. This paper focuses on the Process Specification Language (PSL) effort at the National Institute of Standards and Technology whose goal is to identify, formally define, and structure the semantic concepts intrinsic to the capture and exchange of process information related to discrete manufacturing. Specifically, it describes the results of the first pilot implementation, where PSL was successfully used as an interlingua to exchange manufacturing process information between the Knowledge Based System Inc.’s IDEF3-based ProCAP process modeling tool and the C++ based ILOG Scheduler. 1 No approval or endorsement of any commercial product in this paper by the National Institute of Standards and Technology is intended or implied. This paper was prepared by United States Government 1.0 INTRODUCTION As the use of information technology in manufacturing engineering and operations has matured, the capability of software applications to interoperate has become increasingly important. Initially, translation programs were written to enable communication from one specific application to another, although not necessarily both ways. As the number of applications has increased, and the information has become more complex, it has become much more difficult for software developers to provide translators between every pair of applications that need to exchange information. Standardsbased translation mechanisms have simplified integration for some manufacturing software developers by only requiring a single translator to be developed between their respective software product and the interchange standard. By only developing this single translator, the application can interoperate with a wide variety of other applications that have a similar translator between that standard and their application. The challenge of interoperability is especially apparent with respect to manufacturing process information. The term “manufacturing process information” refers to information describing the manufacturing operations needed to realize a product, including a high level description of the activity, resource requirements, ordering relations, temporal constraints, etc. Many manufacturing engineering, operations, and business software applications use process information, including production scheduling, manufacturing process planning, workflow, business process reengineering, simulation, process employees and guest researchers as part of their official duties and is, therefore, a work of the U.S. Government and not subject to copyright. realization, process modeling, and project management. Each of these applications utilizes process information in a different way, so it is not surprising that these applications’ representations of process information are different as well. The primary difficulty with developing a standard to exchange process information is that these applications sometimes associate different meanings to the terms representing the information that they are exchanging. For example, in the case of a workflow system, a resource is primarily thought of as the information that is used to make necessary decisions. In a process planning system, a resource is primarily thought of as a person or machine that will perform a given task. If one were to integrate a process model from a workflow and a process planning application, their first inclination would most likely be to map one resource concept to the other. This mapping would undoubtedly cause confusion. Therefore, both the semantics and the syntax of these applications need to be considered when translating to a neutral standard. In this case, the standard must be able to capture all of the potential meanings behind the information being exchanged. The Process Specification Language (PSL) project at the National Institute of Standards and Technology (NIST) is addressing this issue by creating a neutral, standard language for process specification to serve as an interlingua to integrate multiple process-related applications throughout the manufacturing life cycle. This interchange language is unique due to the formal semantic definitions (the ontology) that underlie the language. Because of these explicit and unambiguous definitions, information exchange can be achieved without relying on hidden assumptions or subjective mappings. 2.0 PROJECT APPROACH The plan for the PSL project has five phases: requirements gathering, existing process representation analysis, language creation, pilot implementation and validation, and submission as a candidate standard. The completion of the first phase resulted in a comprehensive set of requirements for specifying processes [SCH96]. In the second phase, twenty-six process representations were identified as candidates for analysis by the PSL team and analyzed with respect to the phase one requirements [KNU98]. Nearly all of the representations studied focused on the syntax of process specification rather than the meaning of terms, or semantics. While this is sufficient for exchanging information between applications of the same type, such as process planning, different types of applications associate different meanings with similar or identical terms. As a result of this, a large focus of the third phase involved the development of a formal semantic layer (an ontology) for PSL based on the Knowledge Interchange Format (KIF) specification [GEN92]. By using this ontology to explicitly and clearly define the concepts intrinsic to manufacturing process information, PSL was used to integrate two manufacturing process applications in the fourth phase of the project. This paper focuses on results of that pilot implementation. 3.0 OVERVIEW OF THE FIRST PILOT