German version
OMG PLM Services - A Leap forward in Product Data Communication
Introduction
The long-term success of companies depends on the ability to produce innovative products in time, within cost, and of necessary quality. The ability to form value networks with selected and specialized innovation partners, to share development risks with a shrinking number of partners, and to reduce the number of development cycles with second- and third-tier suppliers at the same time becomes a crucial success factor. Thus a suitable collaboration backbone for seamless communication of product and project data across company borders becomes more and more necessary in order to realize integrated virtual processes and to connect distributed partners.
To meet these requirements, it is essential to build appropriate solutions on open and standardized state-of-the-art services. This enables each partner to realize flexible (online) access and, at the same time, ensures protection of investments.
The current standard OMG PLM Services 1.0 is a ProSTEP iViP working result and is standardized by the Object Management Group (OMG). It is the first standard comprising current XML and Web Services technologies with a STEP data model – thus providing both syntax and semantics. OMG PLM Services 1.0 is ready to use and has proven strong functional capabilities which support cross-company, cross-domain, cross-system and cross-technology collaboration. As a comprehensive framework based on the OMG Model Driven Architecture (MDA) OMG PLM Services provide a solid foundation for collaborative engineering scenarios like browsing in distributed product data structures, design in context, product data visualization, and others. Unique about OMG PLM Services 1.0 is that it supports industry-related use cases by defining both the informational and operational process-related aspects. The next version, OMG PLM Services 2.0, will include important upgrades – e.g. support of Engineering Change Management (ECM).
Download a brief presentation on the benefits of OMG PLM Services
To meet these requirements, it is essential to build appropriate solutions on open and standardized state-of-the-art services. This enables each partner to realize flexible (online) access and, at the same time, ensures protection of investments.
The current standard OMG PLM Services 1.0 is a ProSTEP iViP working result and is standardized by the Object Management Group (OMG). It is the first standard comprising current XML and Web Services technologies with a STEP data model – thus providing both syntax and semantics. OMG PLM Services 1.0 is ready to use and has proven strong functional capabilities which support cross-company, cross-domain, cross-system and cross-technology collaboration. As a comprehensive framework based on the OMG Model Driven Architecture (MDA) OMG PLM Services provide a solid foundation for collaborative engineering scenarios like browsing in distributed product data structures, design in context, product data visualization, and others. Unique about OMG PLM Services 1.0 is that it supports industry-related use cases by defining both the informational and operational process-related aspects. The next version, OMG PLM Services 2.0, will include important upgrades – e.g. support of Engineering Change Management (ECM).
Download a brief presentation on the benefits of OMG PLM Services
OMG PLM Services - The Collaboration Enabler
Cross-Company
The standard is suitable to implement cross-company scenarios with shared access to distributed PLM data sources. This is the major focus of the standard – to provide a common, easily available access mechanism to PLM information and to support collaborative engineering work in a heterogeneous system world. Standardized interfaces to the majority of the required PDM functionality allow short set-up times for establishing working partnerships. Organizational data are within the scope of the OMG PLM Services specification. So, all PLM information may be extended by creator and owner information as well as alias names suitable for cross-company referencing of parts, documents and others.
The scenario is realized by providing a definition for a common neutral data model and access methods based on common web technology, easily accessible for a large number of automotive companies. Using a web-based transport mechanism delegates aspects of authentication and authorization as well as encryption and other security requirements to already existing technologies and infrastructures. OMG PLM Services just adds a mechanism to access valid data by session-related identifiers. This allows efficient interactive scenarios.
Cross-Domain
The standard is suitable to implement cross-domain scenarios interconnecting PLM, CAD, ERP and other planning system data sources. The structural information provided by product or document information given in the PLM system provides a comprehensive access methodology to complete product definition data including support measurements for manufacturing, process data, logistics, change management and others.
Cross-System
The standard is suitable to implement aggregated simultaneous views on multiple PLM systems. Sharing a common data model as defined by the specification and merging such a common view is an obvious application. But OMG PLM Services provides not only a shared and system-independent view on PLM data but defines the semantics of access functions and the necessary answers of the PLM systems to form valid PLM data. The aggregated view on multiple PLM systems is a one system image on distributed data. Users are no longer forced to use multiple interfaces to assess data from different sources. OMG PLM Services furthermore allows easy exchange of viewers to meet different requirements of different user groups. The need for erroneous data replication is minimized.
Cross-Technology
The standard is suitable to implement integration scenarios with existing STEP file-based infrastructures. Due to the normative mappings between AP214 AIM – the data model exchanged in STEP files – and the XML representation – exchanged by the Web Services as defined in the OMG PLM Services specification – a complete round-trip and unambiguous data transfer scenario becomes feasible. All the necessary transformation steps are defined in the standard. Therefore, a seamless transformation between an XML message comprising a PLM data set of information and a corresponding complete STEP Part21 representation suitable for processing by an industry strength STEP processor is defined by the OMG PLM Services standard specification. Furthermore, the MDA nature of the specification would allow to extend the data exchange capabilities to other implementations or representations and support the interoperability and compliance of the different data representations.
An Example
The use case shown in figure 1 illustrates the application of the cross-company and cross-domain capabilities of the OMG PLM Services specification. An external design engineer is using his web-based front-end to select a design space and all associated construction elements within the structure at the OEM PLM exchange data set. With the help of effective PLM selection operations and lightweight viewing facility capable for web based geometry inspection the design engineer identifies the relevant changes in the structure and defines the geometry models which have to be exchanged. Then the engineer initiates an offline data exchange process to transfer the identified CAD models. The exchange process keeps track of all the interactions, converts CAD models according to the guidelines of the companies exchange processes and delivers the high volume data to the design engineer.
Figure 1: OMG PLM Services application
This example demonstrates the capability of the OMG PLM Services which allows the interaction of several tools on a neutral and open foundation – the PDM system providing the necessary structure information, the exchange infrastructure providing the data converting and messaging capabilities and the web browser technology providing easy access to cross-company and cross-domain functionality. Every single building block of this tool set is exchangeable with another one complying to the OMG PLM Services standard interface. The standard specification is effective enough to support all necessary functions.
Furthermore, the OMG PLM Services standard specification is usable for defining reliably processes at design engineers site to keep track of the changes to the design space, to update the meta data of the design task either in light-weight PDM tools or in the customers PDM system. After completing the design task updated and versioned data may be fed back to the OEM site and incorporated into the structure according to the guidelines. OMG PLM Services defines an effective framework for implementing such use cases.
The standard is suitable to implement cross-company scenarios with shared access to distributed PLM data sources. This is the major focus of the standard – to provide a common, easily available access mechanism to PLM information and to support collaborative engineering work in a heterogeneous system world. Standardized interfaces to the majority of the required PDM functionality allow short set-up times for establishing working partnerships. Organizational data are within the scope of the OMG PLM Services specification. So, all PLM information may be extended by creator and owner information as well as alias names suitable for cross-company referencing of parts, documents and others.
The scenario is realized by providing a definition for a common neutral data model and access methods based on common web technology, easily accessible for a large number of automotive companies. Using a web-based transport mechanism delegates aspects of authentication and authorization as well as encryption and other security requirements to already existing technologies and infrastructures. OMG PLM Services just adds a mechanism to access valid data by session-related identifiers. This allows efficient interactive scenarios.
Cross-Domain
The standard is suitable to implement cross-domain scenarios interconnecting PLM, CAD, ERP and other planning system data sources. The structural information provided by product or document information given in the PLM system provides a comprehensive access methodology to complete product definition data including support measurements for manufacturing, process data, logistics, change management and others.
Cross-System
The standard is suitable to implement aggregated simultaneous views on multiple PLM systems. Sharing a common data model as defined by the specification and merging such a common view is an obvious application. But OMG PLM Services provides not only a shared and system-independent view on PLM data but defines the semantics of access functions and the necessary answers of the PLM systems to form valid PLM data. The aggregated view on multiple PLM systems is a one system image on distributed data. Users are no longer forced to use multiple interfaces to assess data from different sources. OMG PLM Services furthermore allows easy exchange of viewers to meet different requirements of different user groups. The need for erroneous data replication is minimized.
Cross-Technology
The standard is suitable to implement integration scenarios with existing STEP file-based infrastructures. Due to the normative mappings between AP214 AIM – the data model exchanged in STEP files – and the XML representation – exchanged by the Web Services as defined in the OMG PLM Services specification – a complete round-trip and unambiguous data transfer scenario becomes feasible. All the necessary transformation steps are defined in the standard. Therefore, a seamless transformation between an XML message comprising a PLM data set of information and a corresponding complete STEP Part21 representation suitable for processing by an industry strength STEP processor is defined by the OMG PLM Services standard specification. Furthermore, the MDA nature of the specification would allow to extend the data exchange capabilities to other implementations or representations and support the interoperability and compliance of the different data representations.
An Example
The use case shown in figure 1 illustrates the application of the cross-company and cross-domain capabilities of the OMG PLM Services specification. An external design engineer is using his web-based front-end to select a design space and all associated construction elements within the structure at the OEM PLM exchange data set. With the help of effective PLM selection operations and lightweight viewing facility capable for web based geometry inspection the design engineer identifies the relevant changes in the structure and defines the geometry models which have to be exchanged. Then the engineer initiates an offline data exchange process to transfer the identified CAD models. The exchange process keeps track of all the interactions, converts CAD models according to the guidelines of the companies exchange processes and delivers the high volume data to the design engineer.
Figure 1: OMG PLM Services application
This example demonstrates the capability of the OMG PLM Services which allows the interaction of several tools on a neutral and open foundation – the PDM system providing the necessary structure information, the exchange infrastructure providing the data converting and messaging capabilities and the web browser technology providing easy access to cross-company and cross-domain functionality. Every single building block of this tool set is exchangeable with another one complying to the OMG PLM Services standard interface. The standard specification is effective enough to support all necessary functions.
Furthermore, the OMG PLM Services standard specification is usable for defining reliably processes at design engineers site to keep track of the changes to the design space, to update the meta data of the design task either in light-weight PDM tools or in the customers PDM system. After completing the design task updated and versioned data may be fed back to the OEM site and incorporated into the structure according to the guidelines. OMG PLM Services defines an effective framework for implementing such use cases.
OMG PLM Services Standardization
Background
STEP AP214 has proven its suitability as a PDM backbone data model and exchange infrastructure. It does not define a functional model, e.g. methods to access data, but STEP provides a language binding allowing for class instance and attribute access interfaces according to the standard data access interface (SDAI) technology.
The SDAI approach is applicable to distributed object model implementation techniques. But it does not allow efficient collaboration. A broadband connection is required, which is neither feasible due to network and firewall restrictions nor manageable in cross-company usage scenarios. Following the architecture of STEP, the SDAI is defined on instances of the Application Interpreted Model (AIM), but user data models are defined at the level of an Application Resource Model (ARM) which is very close to common vocabularies to describe real world scenarios. Comparing both model granularities shows an up to fivefold larger number of object instances on AIM level in comparison to an ARM-like model.
The same problem do other CORBA based specifications face – like the OMG PDM Enablers specification. Although, the OMG PDM Enablers specification supports higher level communication patterns its main disadvantages are the same as those of the SDAI-based approaches. Nevertheless, OMG PDM Enablers does address the problem of granularity of distributed objects by introducing a higher level data model.
The PDTnet approach gives a superior solution to this problem by addressing both requirements: introducing a coarse data model at AP214 ARM level and defining methods manipulating fractions of instances of this data model just by specifying a number of common functions chosen by careful prioritisation of use case scenarios. This technique maps naturally to XML-based infrastructures but imposes additional restrictions of suitable parser facility to non XML-based implementations like PDM systems.
OMG PLM Services 1.0: Specified Models and their Transformation
The main requirements of the OMG PLM Services standard are a single general STEP based standard for synchronous and asynchronous data exchange scenarios, standardization of the PDTnet approach, considering the technical contributions of both the existing OMG PDM Enablers as well as the prepared submission for OMG PDM Enablers version 2.0. As a result of this attempt in alignment with the evolving Model Driven Architecture (MDA) approach the STEP informational model provides a platform independent model, and the corresponding concrete mapping to a platform specific model is driven by the already existing PDTnet XML schema and web services definition. The only simple task was to define the necessary transformation steps between this models. The resulting transformation chain is shown in Figure 2 and described below.
Figure 2: OMG PLM Services Standard derivation
The complete transformation and model chain started with the already agreed upon PDM schema definition – a data model forming a common backbone of PDM-related STEP application protocols. The PDM schema is defined at AIM level. An EXPRESS-X mapping was defined to produce a suitable ARM representation – very well aligned with the STEP AP214 ARM model. The normative mapping between the AIM fragments and the ARM elements is already defined in AP214 by so-called mapping tables and becomes now tractable and executable by the mapping specification as given in the OMG PLM Services standard. The mapping guarantees a seamless integration between file-based data exchange techniques according to STEP Part21 and the new representations defined in OMG PLM Services, e.g. with the platform specific derivates as defined below.
Differences between the informational model defined in EXPRESS and the actual AP214 ARM model are minimal – undefined or ambiguous modelling entries have been defined by newly introduced elements simply derived from the AIM constructs or introduced additionally to reduce the complexity of the ARM model. Significant examples of this complexity reduction are the simple property concept or the simplified multi-language concept.
This EXPRESS model was called the PIM equivalence model because it was considered to be equivalent to the UML model of the Platform Independent Model (PIM) in the informational viewpoint. The necessary transformation of the EXPRESS model into the UML model was described by STEP Part25 which was defined at the same time as this specification was developed. In fact, OMG PLM Services was the first application of STEP Part25. This specification defines a mapping procedure to transform EXPRESS elements to XMI elements – the tool independent representation of UML models. The XMI definition of the OMG PLM Services is normative. The foundation for this definition is based on an interpretation of MOF-based meta-modelling techniques without defining a complete model for the EXPRESS language. Differences between both modelling techniques are bridged by domain knowledge and convenient assumptions.
The complete OMG PLM Services informational model specification provides a UML based notation of one of the most important data models of the STEP standard family. This UML model could be used together with the vast amount of revised data model element definition directly by established software development tools for cost-efficient company specific implementations. It is enriched by the textual definitions as given in AP214.
In a next step the definition of a suitable computational model was added. Influenced by the OMG PDM Enablers specifications and the framework required to realize the PDTnet functionality, a basic set on connection management and generic object factories was defined. With the help of a layered architecture approach very generic basic functions form with increasing level of detail and restrictions four compliance points – the generic, the XPath, the simple, and the PDTnet queries compliance point. The latter got its name because it reflects exactly the PDTnet use cases. The layered approach became feasible by replacing its XPath-like query definitions by a complete algebraic query language. XPath is defined as a special instance of this facility.
Both the informational and the computational models form the so-called Platform Independent Model (PIM). This PIM represents a comprehensive PLM reference model together with an effective functional mechanism. According to the MDA approach, this PIM is the starting point for the derivation of one ore more Platform Specific Model (PSM).
OMG PLM Services defines one PSM – a PSM with a normative XML schema representation of the informational model and a representation of the functional model suitable for a Web Services implementation.
The informational model in the XML Schema PSM is split into three parts – the model representing the informational model itself with all the artefacts corresponding to the AP214 ARM modelling elements, the model representing all the artefacts corresponding to the computational viewpoint in the generic, XPath and simple queries conformance points and a model representing the PDTnet queries conformance point. The latter two depend on the previously given definitions.
The resulting Web Services description is close to the originally defined PDTnet Web Services description but is now based on a solid and rigorous foundation so that it follows the requirements of a standard derivation from an UML model and it is given in normative web services description language (WSDL).
The specification is completed by some examples illustrating the usage scenarios defined in the requirements section.
Download a brief introduction to the OMG PLM Services 1.0
Reference Implementation
Experiences from other standardization efforts have shown significant impact of available example implementations to support third parties in understanding the specification and implementing compliant and interoperable applications. Both to support this intention and to evaluate the specification during its review phase in a distributed and cross-company scenario the ProSTEP iViP Association initiated a reference implementation.
The already existing PDM Implementor Forum of the ProSTEP iViP Association provided the necessary infrastructure. The server part of the reference implementation was deployed and the client part of the implementation is freely available for download, installation and usage. The reference implementation is available with all source code and comes with a comprehensive set of documentation. Project partners provided demonstration data.
STEP AP214 has proven its suitability as a PDM backbone data model and exchange infrastructure. It does not define a functional model, e.g. methods to access data, but STEP provides a language binding allowing for class instance and attribute access interfaces according to the standard data access interface (SDAI) technology.
The SDAI approach is applicable to distributed object model implementation techniques. But it does not allow efficient collaboration. A broadband connection is required, which is neither feasible due to network and firewall restrictions nor manageable in cross-company usage scenarios. Following the architecture of STEP, the SDAI is defined on instances of the Application Interpreted Model (AIM), but user data models are defined at the level of an Application Resource Model (ARM) which is very close to common vocabularies to describe real world scenarios. Comparing both model granularities shows an up to fivefold larger number of object instances on AIM level in comparison to an ARM-like model.
The same problem do other CORBA based specifications face – like the OMG PDM Enablers specification. Although, the OMG PDM Enablers specification supports higher level communication patterns its main disadvantages are the same as those of the SDAI-based approaches. Nevertheless, OMG PDM Enablers does address the problem of granularity of distributed objects by introducing a higher level data model.
The PDTnet approach gives a superior solution to this problem by addressing both requirements: introducing a coarse data model at AP214 ARM level and defining methods manipulating fractions of instances of this data model just by specifying a number of common functions chosen by careful prioritisation of use case scenarios. This technique maps naturally to XML-based infrastructures but imposes additional restrictions of suitable parser facility to non XML-based implementations like PDM systems.
OMG PLM Services 1.0: Specified Models and their Transformation
The main requirements of the OMG PLM Services standard are a single general STEP based standard for synchronous and asynchronous data exchange scenarios, standardization of the PDTnet approach, considering the technical contributions of both the existing OMG PDM Enablers as well as the prepared submission for OMG PDM Enablers version 2.0. As a result of this attempt in alignment with the evolving Model Driven Architecture (MDA) approach the STEP informational model provides a platform independent model, and the corresponding concrete mapping to a platform specific model is driven by the already existing PDTnet XML schema and web services definition. The only simple task was to define the necessary transformation steps between this models. The resulting transformation chain is shown in Figure 2 and described below.
Figure 2: OMG PLM Services Standard derivation
The complete transformation and model chain started with the already agreed upon PDM schema definition – a data model forming a common backbone of PDM-related STEP application protocols. The PDM schema is defined at AIM level. An EXPRESS-X mapping was defined to produce a suitable ARM representation – very well aligned with the STEP AP214 ARM model. The normative mapping between the AIM fragments and the ARM elements is already defined in AP214 by so-called mapping tables and becomes now tractable and executable by the mapping specification as given in the OMG PLM Services standard. The mapping guarantees a seamless integration between file-based data exchange techniques according to STEP Part21 and the new representations defined in OMG PLM Services, e.g. with the platform specific derivates as defined below.
Differences between the informational model defined in EXPRESS and the actual AP214 ARM model are minimal – undefined or ambiguous modelling entries have been defined by newly introduced elements simply derived from the AIM constructs or introduced additionally to reduce the complexity of the ARM model. Significant examples of this complexity reduction are the simple property concept or the simplified multi-language concept.
This EXPRESS model was called the PIM equivalence model because it was considered to be equivalent to the UML model of the Platform Independent Model (PIM) in the informational viewpoint. The necessary transformation of the EXPRESS model into the UML model was described by STEP Part25 which was defined at the same time as this specification was developed. In fact, OMG PLM Services was the first application of STEP Part25. This specification defines a mapping procedure to transform EXPRESS elements to XMI elements – the tool independent representation of UML models. The XMI definition of the OMG PLM Services is normative. The foundation for this definition is based on an interpretation of MOF-based meta-modelling techniques without defining a complete model for the EXPRESS language. Differences between both modelling techniques are bridged by domain knowledge and convenient assumptions.
The complete OMG PLM Services informational model specification provides a UML based notation of one of the most important data models of the STEP standard family. This UML model could be used together with the vast amount of revised data model element definition directly by established software development tools for cost-efficient company specific implementations. It is enriched by the textual definitions as given in AP214.
In a next step the definition of a suitable computational model was added. Influenced by the OMG PDM Enablers specifications and the framework required to realize the PDTnet functionality, a basic set on connection management and generic object factories was defined. With the help of a layered architecture approach very generic basic functions form with increasing level of detail and restrictions four compliance points – the generic, the XPath, the simple, and the PDTnet queries compliance point. The latter got its name because it reflects exactly the PDTnet use cases. The layered approach became feasible by replacing its XPath-like query definitions by a complete algebraic query language. XPath is defined as a special instance of this facility.
Both the informational and the computational models form the so-called Platform Independent Model (PIM). This PIM represents a comprehensive PLM reference model together with an effective functional mechanism. According to the MDA approach, this PIM is the starting point for the derivation of one ore more Platform Specific Model (PSM).
OMG PLM Services defines one PSM – a PSM with a normative XML schema representation of the informational model and a representation of the functional model suitable for a Web Services implementation.
The informational model in the XML Schema PSM is split into three parts – the model representing the informational model itself with all the artefacts corresponding to the AP214 ARM modelling elements, the model representing all the artefacts corresponding to the computational viewpoint in the generic, XPath and simple queries conformance points and a model representing the PDTnet queries conformance point. The latter two depend on the previously given definitions.
The resulting Web Services description is close to the originally defined PDTnet Web Services description but is now based on a solid and rigorous foundation so that it follows the requirements of a standard derivation from an UML model and it is given in normative web services description language (WSDL).
The specification is completed by some examples illustrating the usage scenarios defined in the requirements section.
Download a brief introduction to the OMG PLM Services 1.0
Reference Implementation
Experiences from other standardization efforts have shown significant impact of available example implementations to support third parties in understanding the specification and implementing compliant and interoperable applications. Both to support this intention and to evaluate the specification during its review phase in a distributed and cross-company scenario the ProSTEP iViP Association initiated a reference implementation.
The already existing PDM Implementor Forum of the ProSTEP iViP Association provided the necessary infrastructure. The server part of the reference implementation was deployed and the client part of the implementation is freely available for download, installation and usage. The reference implementation is available with all source code and comes with a comprehensive set of documentation. Project partners provided demonstration data.
Next Steps: OMG PLM Services 2.0
The next version, OMG PLM Services 2.0, will include important upgrades. It will support the collaboration standard Engineering Change Management (ECM, VDA4965), it will be fully harmonized with the latest edition of STEP AP214 (3rd Edition), and will provide improved performance and usability. The OMG PLM Services 2.0 will cover security right from the start.
The MDA nature of the OMG PLM Services standard allows additional implementation dependent models for other platforms. Attractive candidates are a J2EE compliant profile, a .NET compliant profile for a native language binding or even an IDL profile suitable for a CORBA-based implementation for specialized applications with low footprint and near real-time performance requirements.
Download a brief introduction of OMG PLM Services 2.0
The MDA nature of the OMG PLM Services standard allows additional implementation dependent models for other platforms. Attractive candidates are a J2EE compliant profile, a .NET compliant profile for a native language binding or even an IDL profile suitable for a CORBA-based implementation for specialized applications with low footprint and near real-time performance requirements.
Download a brief introduction of OMG PLM Services 2.0
