Transcript On RDLs for PLCS

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On Reference Data Libraries for
Product Life Cycle Support
David Price
6th NASA-ESA Workshop on Product Data
Exchange, April 2004
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Topics
•
•
•
•
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AP239 Product Life Cycle Support
DEX architecture
Implementing a DEX
What is OWL?
Future and conclusions
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What is AP239?
• Product Life Cycle Support (PLCS) is a modular
STEP Application Protocol for complex assets (e.g.
ship)
– Configuration Management
• As-Designed, As-Realized, As-Maintained
– Support Engineering
• Support Required (activities, tasks, resources)
– Resource Management
• Spares, Who/what/when
– Maintenance and Feedback
• Failures, Replacements, …
• The above is a vast over-simplification
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PLCS Approach Fundamentals
• In ISO, standardize flexible data model that can
be tailored using Reference Data
• Data Exchange Sets (DEXs)
– Create “usage guides” for subsets of AP239
– Create “standard” Reference Data as a basis for
implementation
– Standardization in OASIS is planned
• Allow organization-specific extension to the
standard Reference Data for further tailoring
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The STEP Architecture
Application Activity Model
Application Reference Model
Application Interpreted Model
- What process do I want to
support?
- What are the information
requirements of the activity
in industry terminology?
- How do I model the
required information using
STEP and EXPRESS?
Design
Assembly
Components
definition
relationship
Build
Test
assm_rel
Components of a STEP Application Protocol
Implementation Method
- What implementation
technology do I need?
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The Modular STEP Architecture
Application Protocol
Normative Reference
to Application Module
Activity Model
MT = mapping table describes
ARM
MT
AIM
what AIM entity types are
used to exchange what
ARM concepts
Use entire module
Application
Modules
ARM
MT
AIM
Use individual entity types
ARM
MT
AIM
ARM
MT
AIM
Common Resource Schemas
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How do AP239/RDL relate?
PLCS Requirements
The red specializations do not
appear in the actual AP239
schema
Instead, they appear in
Reference Data Libraries
AP239 ISO Schema
Reference Data
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DEX Architecture
• STEPmod is the STEP Modules Repository
– AP239 PLCS ISO standard is specified here
• DEXlib is where DEXs are specified
– DEXs group and tailor “Capabilities”
– Capability defines subset of AP239 EXPRESS, reads
from STEPmod and allows usage guidance to be added
• Capabilities are reusable between different DEXs
– An XML Schema for data exchange is generated from
each DEX
– DEXlib is also where PLCS standard Reference Data is
defined
• STEPmod and DEXlib are XML-based
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STEPMod
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DEXLib
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Creating the DEX
DEX XML Schema
ISO Standard EXPRESS
to XML Schema mapping
Standard Reference
Data Library
allowed
classification
STEPmod
-express schemas
-text descriptions
adds usage
guidance to
DEXlib
-capability
-dex
-rdl selection
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Creating the DEX
The PLCS standard
EXPRESS information model
Extract:
• model defns.
• model subset
DEXlib
STEPmod
ISO 10303-239
Library of DEXs
A DEX:
• Subset of AP239
EXPRESS + XML Schema
• for contracting
• for software conformance
• usage guidance
Class hierarchy
PLCS
standard
RDL
Defines RDL
applicability
Extend through
sub classes
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Create using
Protégé
MOD
RDL
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When Implementing a DEX
•
Organizations will likely specify extensions to the
Standard Reference Data
– Extension is defined by declaring organization-specific
Classes as subclasses of the standard Classes
– So, there are likely two or more RD libraries used in a
DEX data exchange
1. The standard RD library
2. The organization extensions library
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System
A
translate
from
translate
to
System B
DEX-based XML
data exchange file
classification
classification
subClassOf
MoD Reference
Data Extensions
Standard Reference
Data Library
allowed
classification
OASIS DEXs
-Capability
-DEX
-RDL selection
-XML Schema
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What to do about Reference Data?
• We were contracted by UK MoD to do a survey of
candidates for Reference Data
• Goal
– Determine the best approach for Reference Data when
applied to PLCS DEX data exchange
• Scenario
– MoD has a specific business process to automate using
PLCS/DEX-based data exchange
• Technical Assumptions
– Exchange based on AP239 EXPRESS->P28 XML
– Enable inclusion and reference to RD
– Standard RD is extended in implementing organization
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Requirements arising…
• Create and manage standard RD
• Define what RD is used for what schema element
• Enable local extension of standard RD
– Local extensions come from elsewhere in industry or
within local organization
– Possible later integration of local into standard RD
• Support implementation of pre- and postprocessors
– RD may be embedded, exchanged or referenced
• Support implementation of business process/rules
– e.g. select, export, transfer, verify, import, report
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Initial Analysis
• Nothing to offer
– OASIS had nothing really supporting RD
– OMG had nothing really supporting RD
• although UML Profile for OWL is in-process
• Real candidates
–
–
–
–
–
15926-2
PLib
10303-54
W3C OWL
DEXLib DTD
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Our Conclusion
• While any of the candidates could be made to
work, for our set of requirements OWL made the
most sense
• In fact, we’ve also concluded that a specific set of
tools should be used
– Stanford University Protégé with OWL plug-in
– Open-source, platform independent (Java)
– Pre-load with template containing RDL, schemas, etc.
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What is OWL?
• The World Wide Web Consortium (W3C) created
the HTML and XML standards
• OWL is a next-generation language standardized
in the W3C.
– its purpose is to add “semantics” to the Web
• Therefore, it can be distributed and is Web-enabled and does
not assume a single source for everything
– In concept, it is very much like other data modelling
languages (it calls models or schemas “ontologies”)
• class, subclass, property, property type, instance/individual
– it supports added set theory and logic-based
statements about the classes and individuals
– it has more than one syntax, XML being one
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Classes and Property Restrictions
Class and subclasses
Properties of Class
Property
Restrictions
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OWL Instances/Individuals
Instance of Class “Person”
Property Values
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Why this approach?
• OWL satisfies RDL modeling requirements
– Class, multiple inheritance, properties, datatypes,
instances, reuse of models
– When UML Profile for OWL ready > Graphical RDL
• OWL satisfies RDL IT requirements
– XML syntax, Web enabled
– Easy map from 15926, 10303-54, etc.
• Other factors
– OWL will win in the market
• Industry and academic support
• Open-source tools available
– People outside of SC4 know OWL, not 15926 or PLib
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Details of RD Relationships
subClassOf
DEX-based XML
data exchange file
AP239 Schema
as OWL Classes
classification
classification
subClassOf
subClassOf
MoD Refdata Extensions
as OWL Classes
-added refdata classes
-added refdata/express usage
Standard Refdata
as OWLClasses
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Some Reference Data in OWL
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The EXPRESS/RD OWL Link
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More on “Why this approach?”
• For business process and rules, reasoners seem
like they have potential use
• While PLCS DEX exchange isn’t “Semantic Web”,
this lays the foundation for future PLCS Semantic
Web applications
• Makes “STEP” RDL usable by non-STEP
applications
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Use of RDL plus inference
RDL
Example of STEP, RDL
and Inference Engines
triggering processes
Class: FamilyCarType
Prop: Service interval = 10000 Km
Class: FastCarType
Prop: Service interval = 6000 Km
A FastCar
Onboard Engine
management
system
A FamilyCar
Onboard Engine
management
system
7000 Km
since last
service
9000 Km
since last
service
Maintenance Planning System
If Km since last service >
Service Interval then do service
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Use of RDL plus inference
• On board engine management system on a car
sends file to Maintenance Planning System
• File contains Type of Car and Kms since last
service (mileage)
• Maintenance Planning System looks up type of car
in RDL and gets Service Interval property
• Inference engine rule triggered on Service
Interval property and mileage and schedules a
service
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Why this toolset?
• Protégé meets OWL/RDL modeling requirements
– Can reuse existing ontologies (e.g. Dublin Core for
identification and versioning)
– Can create classes, properties and instances
– OWL plug-in supports import/export/database
• Open-source GUI, API, database backend,
reasoners
– Uses HP open-source Jena API
– Can add STEP-specific RDL plug-in if that becomes
necessary
• Widepsread use (14000+ downloads)
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The Obvious Concerns
• Semantic Web is still research
– Approach doesn’t depend on Semantic Web technology
– Using OWL as a modeling framework, the way 15926 is
a modeling framework
• OWL is not an ISO/SC4 standard
– Absolutely true! However, even a researchy W3C
standard like OWL is more widespread than EXPRESS
• Have I wasted all my investment in STEP?
– Absolutely not. Without the prior work, we would not
be in a position to quickly take advantage of OWL.
– Taking advantage of 15926 RDL
– We can translate OWL to EXPRESS or 15926 or …
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Conclusion
• The flexibility defined in the PLCS/DEX approach allows it
to be used across a wide domain
– However, that flexibility means PLCS/DEX implementation depends
on Reference Data
• The W3C OWL language provides very good capabilities
for defining, reusing, publishing and relating “models” and
“reference data”
– By being Web-enabled, RDLs can be linked and distributed
– OWL also enables the future use of logic engines as part of
PLCS/DEX implementations
• The use of XML for the exchange file and OWL for the RD
puts PLCS/DEX squarely into the mainstream, both now
and in the future
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