© 2006 Hewlett-Packard Development Company, L.P.The information contained herein is subject to change without notice

RDF and SOADavid Booth, Ph.D. <dbooth@hp.com>

HP SoftwareSOA Symposium, Amsterdam, 8-Oct-2008

[Presented by Andrew Weaver, HP Software]

Latest version of these slides:http://dbooth.org/2008/soas/slides.ppt

2 April 10, 2023

Outline• PART 0: The problem• PART 1: RDF: A lingua franca for information

exchange• PART 2: Key Techniques for RDF in SOA

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PART 0

The problem

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Problem 1: Babelization• Proliferation of data models (XML schemas,

etc.)• Parsing issues influence data models• No consistent semantics• Data chaos

Tower of Babel, Abel Grimmer (1570-1619)

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Problem 2: Integration complexity• Multiple producers/consumers need to

share data• Tight coupling hampers independent

versioningProvisioningDiscovery

ChangeManagement

Compliance Management IncidentManagement

ReleaseManagement

Monitoring

Ticketing

Release Managers

Unix SystemAdministrators

Networking Engineers

NetworkingAdministrators

ComplianceManagers

Windows SystemAdministrators

Operation Centers

StorageAdministrators

Source Control

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Client/service versioning• Need to version clients and services

independently• Data models exchanged must evolve• No such thing as the model:

−There are several, slightly different but related models

Client v3

Client v2

Client v1

Service v3

Service v2

Service v1

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What to do?

8 April 10, 2023

PART 1

RDF: A lingua franca for information

exchangein SOA

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What is RDF?• "Resource Description Framework"• Relational data model framework• W3C standard >6 years• Foundation of Semantic Web technology• Language for making statements about

things• Used to express both:

−Ontologies (classes and relationships), and

−Instance data

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Key features of RDF• Syntax independent (specifies model)

−Some existing serializations: RDF/XML, N3, Turtle

−Focus on semantics

• Consistent semantics−Based on URIs

• Great for data integration problems−Data "mashups"

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Why RDF for SOA?1. Emphasis on semantics

−RDF is syntax independent

2. RDF is good at data integration

3. RDF helps bridge other formats/models

4. Looser coupling

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Why?1. Emphasis on semantics • RDF is syntax independent• RDF specifies information model -- not

serialization• Various serializations can be used

−RDF/XML, N3, Turtle, etc.

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Why?2. Easier data integration • New data models can be easily added• Old and new data models co-exist in

merged model• Relationships between the old and new

models are expressed explicitly• Both old and new can be used

simultaneously

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Why?2. Easier data integration• Blue App has model

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Why?2. Easier data integration• Red App has model

• Need to integrate Red & Blue models

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Why?2. Easier data integration• Step 1: Merge RDF• Same nodes (URIs) join automatically

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Why?2. Easier data integration• Step 2: Add relationships and rules• (Relationships are also RDF)

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Why?2. Easier data integration

• Step 3: Define Green model• (Making use of Red

& Blue models)

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Why?2. Easier data integration• What the Blue app sees:

−No difference!

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Why?2. Easier data integration• What the Red app sees• No difference!

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Why?3. RDF helps bridge other formats/models• Producers and consumers may use different

formats/models• Rules can specify transformations• Inference engine finds path to desired result model

RDFModelTransform

A1

A2

A3

B1

B2

C1

C2

X

Y

Z Ontologies& RulesOntologies& RulesOntologies& Rules

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Why?4. Looser coupling• Without breaking consumers:

−Ontologies can be mixed and extended

−Information can be added

• Producer & consumer can be versioned more independently

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Example of looser coupling• RedCust and GreenCust ontologies added• Blue app is not affected

(Blue app)

Consumer Producer

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PART 2

Key Techniques for RDF in SOA

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1. RDF message semantics• Interface contract can specify RDF,

regardless of serialization• RDF pins the semantics

Client ServiceRDF

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But Web services already use XML!• XML is well known and used• Legacy apps may require specific XML or

other formats that cannot be changed

• How can we gain the benefits of RDF message semantics while still accommodating XML?

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Custom XML serializations of RDF

Recall: RDF is syntax independent• Specifies info model -- not syntax!• Can be serialized in any agreed-upon way

Therefore:• Can view existing XML formats as custom

serialization of RDF!

How? GRDDL . . .

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What is GRDDL?• "Gleaning Resource Descriptions from Dialects of Languages"

• W3C standard• Permits RDF to be "gleaned" from XML• XML document or schema specifies GRDDL

transformation for that document (or type)−Each XML document/type can use a different

GRDDL transformation• GRDDL transformation produces RDF from

XML document−Typically written in XSLT

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2. GRDDL transformations from XML to RDF

Therefore:• Same XML document can be consumed by:

−Legacy XML app

−RDF app

• App interface contract can specify RDF−Serializations can vary

−Semantics are pinned by RDF

• Helps bridge XML and RDF worlds

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Bridging XML and RDF

• Input: Accept whatever formats are required−Use GRDDL to transform XML to RDF

• Output: Serialize to whatever formats are required −Generate XML/other directly (or even RDF!), or−SPARQL query can generate specific view first

Normalizeto RDF

Serialize asXML/other/RDF

Service

Core AppProcessingClient

XML/other

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3. REST-based SPARQL endpoints

Consumer Producer

SPA

RQ

LRDFHTTP

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REST-based SPARQL endpoints• Why REST:

−HTTP is ubiquitous

−Simpler than SOAP-based Web services (WS*)

−Looser process coupling

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REST-based SPARQL endpoints • What is SPARQL:

−W3C standard

−Query language for RDF

−Modeled after SQL:

SELECT ...

WHERE ...

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REST-based SPARQL endpoints • Why SPARQL:

−RDF gives looser data coupling

−Insulates consumers from internal model changes• Inferencing can transforms data to consumer's desired

model

−One endpoint supports multiple consumer needs• Each consumer gets what it wants

−Simpler interface for consumers• Uniform SPARQL interface instead of a different set of

parameters for each REST endpoint

• Takes the REST notion of "uniform interface" one step farther

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4. Aggregation and Transformation• Gets data from multiple sources• Provides data to consumers• Does model transformation, caching, etc.• Conceptual component -- not necessarily a separate

service

Aggregation &Transformation

A1

A2

A3

B1

B2

C1

C2

X

Y

Z Ontologies& RulesOntologies& RulesOntologies& Rules

SPA

RQ

L

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Conclusions• Value of RDF in data integration is well

proven• RDF can bring looser coupling to SOA• Key techniques:

−1. RDF message semantics

−2. GRDDL to bridge from XML to RDF

−3. REST-based SPARQL endpoints

−4. Aggregation and transformation

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More information• RDF and SOA:

http://dbooth.org/2007/rdf-and-soa/rdf-and-soa-paper.htm

• RDF:http://www.w3.org/TR/REC-rdf-syntax/

• SPARQL:http://jena.sourceforge.net/ARQ/Tutorial/

• GRDDL:http://www.w3.org/TR/grddl-primer/

38 April 10, 2023

Outline• PART 0: The problem• PART 1: RDF: A lingua franca for information

exchange• PART 2: Key Techniques for RDF in SOA

© 2006 Hewlett-Packard Development Company, L.P.The information contained herein is subject to change without notice

Questions?