About PLCS Reference data

In order that the PLCS information model can be used in many different business contexts, it is deliberately generic. In other words EXPRESS entities are provided for representing constructs such as parts and properties. More precise semantic definition of constructs such as a safety critical part, or the number of gun firings property are not represented directly in the ISO 10303-239 standard. Instead provision is made to enable the same precision by classifying the basic constructs so refining or augmenting the meaning of the entity.

For example, there are many different types of properties associated with components that are relevant to product life cycle support. The information model allows the properties that can be associated with parts to be classified. Such classification is then used to specify the specific type of property. Any set of specific property types, such as mean time to failure that could have been provided by explicit modelling in the standard is likely to be incomplete. Furthermore, as business practices change, different properties are likely to be required over time and these can be introduced by means of a new class.

This approach relies on the use of a common set of classes between partners in a data exchange, together with a shared understanding of what each class means. This is referred to as "Reference Data". Reference data is defined to be life-cycle data that represents information about classes or individuals which are common to many facilities, or of interest to many users.

The Reference data classes are held in a shared class library referred to as a "Reference Data Library". A Reference Data Library (RDL) is a managed collection of reference data. Reference data is a key success factor for consistent sharing and integration of data, i.e. to ensure consistent meaning of data. The reference data add semantics to the AP239 model.

The standardized PLCS Reference Data is created and published using the W3C Web Ontology Language called OWL. OWL became a W3C Recommendation in February 2004. The OASIS PLCS TC Reference Data development process is described in the Developers information section.

Reference Data Architecture Overview

The standardized PLCS Reference Data is made up of several related datasets:

• a representation of a subset of the PLCS EXPRESS schema as an OWL ontology;
• the use of a subset of the Dublin Core meta-data elements and terms, with a few OASIS-specific extensions, for internal management of the Reference Data (e.g. creator and date modified);
• the Reference Data itself, which may include Classes, a Class hierarchy, Properties of the Classes and Instances or Individuals based on the Classes and relationships that specify which Reference Data elements are applicable for which PLCS EXPRESS schema elements and which combines the other datasets resulting in the complete library.

Figure 1 shows the architecture of the datasets.

Types of Reference Data

There are two types of Reference Data applicable to PLCS DEX usage scenarios:

1. PLCS standard Reference Data published through the OASIS PLCS Technical Committee. This is the Reference Data that all PLCS implementations must be able to support and that is the basis for the second type of Reference Data.
2. Extensions to the standard Reference Data. These may be shared, and perhaps standardized, across an industry sector, or may be project-, contract- or company-specific.

Each organization or project may extend the standardized Reference Data. Extensions are defined by importing the complete Reference Data Library and adding organization- or project-specific Subclasses of the standardized Reference Data Classes. Extensions are intended to be managed in separate datasets and only merged back into the standardized PLCS Reference Data as part of a harmonization, integration and revision process.

Information Technology for Publishing the Reference Data

The standardized PLCS Reference Data is created and published using the W3C Web Ontology Language called OWL. OWL became a W3C Recommendation in February 2004. Each dataset making up the standardized Reference Data is an OWL ontology itself. Each OWL ontology imports other ontologies as required. The Reference Data Library OWL ontology simply imports all the other ontologies, grouping them together in order to make extension simple. It is intended that organization- or project-specific extensions to the standardized Reference Data are created in their own OWL ontologies.

While OWL may have any of several formats, the OWL RDF/XML (unabbreviated) syntax is used for the PLCS Reference Data. This allows the use of XML-related languages and tools for the creation and management of the Reference Data.

OWL is by-design a Web-enabled techology and so publication of the standardized PLCS Reference Data is simply making the OWL files available on the Web. OASIS has specified that HTTP URIs (i.e. URLs) are to be used for their standards and so references to the Reference Data are made using those URIs at: http://docs.oasis-open.org where a 'plcs' folder holds the OWL files.

The development process is described in the Developers information section.

A Reference Data Development Tool

The PLCS DEX Reference Data OWL ontologies are developed using an open-source software application called Protégé and its related OWL plug-in. Read more about Protégé in the Software section.