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Last modified: July 06, 2000
Process Specification Language (PSL) and XML

In January 1999, NIST (National Institute of Standards and Technology, U.S. Department of Commerce) published some preliminary findings which "describe how the PSL semantic concepts may be mapped to the Extensible Markup Language (XML)." NIST's Process Specification Language (PSL) Project is organized under its Manufacturing Systems Integration Division (MSID). "For many years MSID has been involved in the definition of a neutral representation of product data, most recently realized through the STEP standard. With that effort well underway, another candidate area for a division focus is the representation of manufacturing process. Like product data, process data is also used throughout the life cycle of a product, from early indications of manufacturing process flagged during design, through process planning, validation, production scheduling and control. In addition, the notion of process also underlies the entire manufacturing cycle, coordinating the workflow within engineering and shop floor manufacturing."

An online example "Representing PSL as XML" has been created to llustrate "how data described by PSL semantics can be represented using XML (the Extensible Markup Language). The XML representation employs RDF (the Resource Description Framework). Although RDF is designed for specifying metadata about resources on the Web, a basic type system defined for RDF enables RDF to be used for specifying schemas. The example makes use of this RDF schema language." The PSL-XML project thus "undertakes to define a neutral representation (a language) for process which could be used for the sharing of process data among all of the functions identified above. Through research and input, this work will be continuously refined and expanded over the next few months."


  • "Representing PSL as XML." NIST. January 20, 1999 (or later). [local archive copy, text only]

  • "The Process Specification Language (PSL): Overview and Version 1.0 Specification" This document has been published as NIST Internal Report (NISTIR) 6459. "This document describes Version 1.0 of the Process Specification Language (PSL). PSL is an interchange format designed to help exchange process information automatically among a wide variety of manufacturing applications such as process modeling, process planning, scheduling, simulation, workflow, project management, and business process re-engineering tools. These tools would interoperate by translating between their native format and PSL. Then, any system would be able to automatically exchange process information with any other system via PSL. This document focuses specifically on PSL's rationale, semantic architecture, informal documentation, and the vision of how one would translate in and out of PSL." Includes Appendix B: "Mapping PSL Concepts to the EXPRESS Representation" and Appendix C: "Mapping PSL Concepts to the eXtensible Markup Language (XML) Representation." [cache]

  • From NISTIR 6459. "Appendix C: Mapping PSL Concepts to the eXtensible Markup Language (XML) Representation". XML's Strengths and Weaknesses as a Presentation Language for PSL: Vendors of mainstream software applications such as Internet browsers, database environments, and business productivity tools are either already supporting or intend to support XML in their products. Mapping PSL instances to XML will enable process specifications to be interpreted by these generic applications, lowering the barriers to data sharing. Another advantage of XML for representing process characterizations is its "tag-centric" syntax. XML is a natural fit for representing ordered sequences and hierarchies. Thus it is well-suited for describing PSL's ordering and subactivity relationships. The Resource Description Framework (RDF), a standard for specifying metadata, adds to XML's benefits. RDF has an XML serialization syntax, making it easy to embed resource descriptions in an XML document. Therefore, resources in an XML representation of a PSL instance can be referred to using RDF. Further, RDF Schema, a type system defined for RDF, is useful for describing PSL objects. Although XML has many strengths as presentation format for PSL, it has a major weakness. XML is not as rich a representation as KIF, or EXPRESS for that matter. In particular, there is no straightforward way in XML to describe arbitrary constraints between data elements in an information model. Such constraints could be represented using defrelation in KIF or by means of WHERE rules in EXPRESS. Because XML is deficient when it comes to specifying constraints, its presentational abilities for PSL are limited. Exactly what those limitations are is a topic for future research, but intuitively it seems that the aspects of the PSL ontology specified in KIF with defrelation must either be implicitly represented (as can be done with ordering and subactivity relationships) or omitted in an XML presentation. Also, since portions of the ontology are hard to specify in XML, XML is not suitable as an authoring environment for PSL. Guidelines for Mapping PSL to XML: To leverage XML's strengths while minimizing its weaknesses, we suggest some guidelines for mapping PSL to XML. (1) Use RDF Schema to represent the objects used in a process. (2) Represent timepoints as sequentially ordered groups of elements, with each timepoint element having a unique identifier. If the XML application uses a Document Type Definition (DTD), the unique identifier should be represented using an ID attribute so that references to the timepoint can be made using IDREF. Each timepoint element may optionally contain character data documenting the meaning of the timepoint. (3) For each activity, specify a unique identifier (with an ID attribute if using a DTD) and an activity name. If the activity contains subactivities, specify these within a container element. If the activity has no subactivities, specify the resources used with references to the appropriate class defined in the RDF Schema. (4) Specify occurrences of activities in sequential order with sub-activities enclosed inside parent activities. Each activity occurrence should have a beginning and ending time point and, if it cannot be decomposed into sub-activities, a list of RDF-defined resource instances it uses. References to timepoints and activities should correspond to their respective unique identifiers (and should be IDREFs if using a DTD). (5) Primitive lexicons from PSL extensions should be explicitly mapped to XML. Foundational theories and defined lexicons from PSL extensions should probably be omitted from the mapping, unless they describe containing or ordering relationships that can be easily represented implicitly."

  • An initial mapping of the PSL semantic concepts to the EXPRESS schema representation. Or get the entire EXPRESS source, [cache]

  • Version 1.0 of the database query mechanism which provides a more user-friendly view of the concepts in the PSL Ontology.

  • Informal documentation for the PSL Version 1.0 Specification

  • PSL FAQ Document

  • PSL Ontology

  • SiRPAC - Simple RDF Parser & Compiler

  • The Process Specification Language Project - NIST, PSL Home Page

  • [October 04, 1999] Conference presentation at Markup Technologies '99. December 9, 1999. 9:45 am - 10:30 am (Green Track) "Process representation using architectural forms: Accentuating the positive." By Joshua Lubell, Craig Schlenoff, National Institute of Standards and Technology. "The PSL (Process Specification Language) is a standard language for process specification that is intended to serve as an interlingua among 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. The PSL ontology is organized in modules, with a small set of core concepts and multiple extensions which add to the core. We are developing a mapping from the PSL semantic concepts to XML (Extensible Markup Language), using architectural forms to specify the relationship between the concepts in a process specification and the PSL core and extensions. An example demonstrates the usefulness of architectural forms for managing modular specifications, mapping non-PSL syntax to PSL terminology, and generating extension-specific data views." Also Postscript. [cache]

  • Camile Motor Works - manufacturing process interoperability scenario [local archive copy]

  • "A robust process ontology for manufacturing systems integration." - Technology spotlight document from

  • PSL Publications

  • Contact: Josh Lubell

  • Compare: Process Interchange Format (PIF)

  • KBS/Ontology Projects and Groups

  • "Ontology-Based Semantics." By Mihai Ciocoiu and Dana S. Nau. To appear in the Proceedings of the Seventh International Conference on Principles of Knowledge Representation and Reasoning (KR'2000) [Breckenbridge, Colorado, April 12-17, 2000]. "We consider the problem of providing semantics for declarative languages, in a way that would be useful for enabling automated knowledge exchange. If we only have one (first order) language, we can formalize what we mean for a set of sentences to be a translation of another, by requiring that the two sets share the same models. However, in order to formalize translation for the case where the two sets of sentences are of different languages, we need a different notion of semantics, capable of overcoming the language barrier. We introduce Ontology-Based Semantics with this purpose in mind. We show how ontologies can be used to make implicit assumptions explicit, and how they are integrated in our semantics in order to restrict the set of models a set of sentences has. We show how Ontology-Based Models can be used to formally define knowledge translation for the different language case in a similar way ordinary models can be used to define translation for the one language situation. We also provide a syntactical characterization of knowledge translation, that can be used as an effective procedure to check translatability, and we prove it to be sound and complete with respect to our semantic definition of translation."

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