|Help TOC > PLCS technical description > Data Exchange Specifications (DEXs)|
|Data Exchange Specifications (DEXs)||Date: 2010/03/17 11:20:10
The information model defined by ISO 10303-239 PLCS has a scope that is wider than most applications or any single data exchange. It is, therefore, unlikely that any software will be able to support or declare compliance to the entire range of information supported by ISO 10303-239 PLCS. Moreover, it would be impractical to contract for data compliant with ISO 10303-239 PLCS without a means of specifying the scope required. "Data EXchange specifications" ("DEXs") are defined in order to constrain the full information model to the scope required. The way that DEX Schemas constitute overlapping subsets of ISO 1030-239 PLCS data model is illustrated in Figure 1.
NOTE A DEX is similar in purpose to a STEP AP Conformance Class, but supported by additional usage guidance (mainly in the Capabilities) and Reference Data to ensure consistent implementation. These additional features of DEXs ensure consistent implementation of the underlying EXPRESS information model.
NOTE Not all the DEXs illustrated have been published, but drafts are available at the OASIS PLCS TC website (http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=plcs).Definition: Data Exchange Specification - a subset of the ISO 10303-239 PLCS information model, designed to support data exchange for specific activities, providing guidance and rules for how to use and combine the selected entities and external Reference Data in that exchange. Each DEX includes a complete EXPRESS schema. This is a subset of the ISO 10303-239 schema with a derived XML Schema. Both can be used to define and validate a data exchange file. A DEX defined and managed by the OASIS PLCS TC may be referred to as a "PLCS DEX", as opposed to a "Business DEX".
The actual data (i.e. a package of data that is exchanged or shared, or a data exchange file) that is in accordance with a DEX information model is referred to as a DEX data set.
The DEXs are defined to support specific business processes. A DEX may support a part of, one, or several information flows (arrows) from the PLCS Activity Model defined in AP239. The PLCS DEXs can be used to:
In addition to identifying a subset of the ISO 10303-239 PLCS information model, there is a requirement for guidance and rules for the consistent application and usage of different areas of that information model. This is achieved through the use of "Capabilities". Each Capability describes how a particular generic business concept (such as a "part" or an "approval") should be represented using a set of PLCS entities.
NOTE Capabilities are in development and will be included in a future release.
See Capabilities for further details.
Within each Capability, patterns for structuring and instantiating data are provided in the form of "Templates", which unambiguously define precisely which PLCS entities are required and how they should be populated. Each Capability defines one or more Templates and these form the building blocks of the data model that underlies each DEX. Each Template has just one parent Capability, but the Template may be used as a component of several DEXs, ensuring that the same concept is represented consistently.
Examples of Templates defined by the C001: assigning_identifiers Capability and used in all DEXs are the assigning_identification and assigning_identification_with_no_organization Templates.
See Templates for further details.
The information model defined by ISO 10303-239 (PLCS) is generic. It holds no business specific terms. These business semantics are represented by extending the PLCS information model through classification with so called Reference Data (RD). Reference Data allows for the semantic specialization (or grouping of elements) of the generic information model into Classes that make the context as specific as required for the data in question. This provides a mechanism for adapting the generic model to the requirements of more specialized domains. The use of the Reference Data is identified within the DEXs, Templates and Capabilities. The OASIS PLCS TC specifies a mechanism for the definition (and extension) of Reference Data Classes, and also defines a number of generic Reference Data Classes that may be specialized further by more specific Classes.
Examples of Reference Data Classes used by the C001: assigning_identifiers Template are the "Organization identification code" (urn:plcs:rdl:std:Organization identification code) and "Organization name" (urn:plcs:rdl:std:Organization name) Classes. These are used to indicate that an identifier used for an organization is, for example, a simple name or a formal identification code. If a formal identification code is indicated, more specialized Reference Data Classes may be used to specify that the code in question is, for example, a "CAGE" code or a "DUNS" code.
See Reference data for further details.
A DEX can also be used as a standard against which software can claim conformance. Conformant software is able to read and write data according to the DEX EXPRESS and XML schema a, using the rules defined in Templates, and to interpret the OASIS Reference Data Classes correctly.
A DEX can also (and similarly) be used as the basis of a contractual deliverable, although, in most cases, an additional Reference Data Library (RDL) would be required in order to provide specific semantics. If the generic PLCS DEX does not cover the scope of the contract completely, a Business DEX may be required. This is a further specialization of PLCS to operate within a more constrained Business Context. The context may be a project, an organization or enterprise. One or more Business DEXs may be defined within a context.
See Business DEXs for further details.
NOTE In order to distinguish between the similar terms used for the components developed by the OASIS PLCS TC and the business specific work, the terms may be prefixed "PLCS" or "OASIS" for the standardization work, and "Business" for the business specific work. A DEX that is standardized by the OASIS PLCS TC is then referred to as a "PLCS DEX" or as an "OASIS DEX", rather than a "Business DEX".
Different DEXs relate to different life cycle stages of a product. Some of the ways in which DEXs relate to each other and the kinds of data they share with each other is illustrated in Figure 2. The oval shapes represent business level data that is created or referenced by a DEX. Faults, Parts, Tasks etc. The Rectangles show the DEXs. The DEXs coloured grey indicate DEXs used to represent data in the design phase of the product life cycle, and the DEXs coloured yellow signify the DEXs used in the operational phase of the product life cycle.
The documentation of a DEX provides a description of its purpose, an account of the business process it supports, and usage guidance. It lists the Templates used, and which Reference Data Classes are used, and it provides an EXPRESS schema and an XML Schema that is derived from the EXPRESS that represents the ISO 10303-239 PLCS subset. Furthermore, it references the set of Capabilities that provide further usage guidance.
Each DEX is identified within the DEXlib repository by a number, an identifier and a name, e.g.
These are assigned to the DEX in the initial development process .
Each DEX comprises the following: