David Booth R D F & S O A

1 October 2003 Copyright © 2006 HP corporate presentation. All rights reserved.

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© 2008 Hewlett-Packard Development Company, L.P.

The information contained herein is subject to change without notice

RDF and SOADavid Booth, Ph.D. <[email protected]>

HP Software

SOA Symposium, Amsterdam, 8-Oct-2008

[Presented by Andrew Weaver, HP Software]

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


3 October 8, 2008 HP Software (c) 2008 - SOA Symposium

Outline

• PART 0: The problem

• PART 1: RDF: A lingua franca for informationexchange

• PART 2: Key Techniques for RDF in SOA


PART 0

The problem



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)


Problem 2: Integration complexity

• Multiple producers/consumers need to share data

• Tight coupling hampers independent versioning

ProvisioningDiscovery

ChangeManagement

Compliance ManagementIncident

Management

ReleaseManagement

Monitoring

Ticketing

Release Managers

Unix System

Administrators

Networking Engineers

Networking

Administrators

Compliance

Managers

Windows System

Administrators

Operation Centers

Storage

Administrators

Source Control



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


What to do?



PART 1

RDF: A lingua franca for information exchange

in SOA


What is RDF?

• Resource Description Framework

• Relational data model framework

• W3C standard >4 years

• Foundation of Semantic Web technology

• Language for making statements about things

• Used to express both:

−Ontologies (classes and relationships), and

− Instance data



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"


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



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.


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




• Blue App has model



• Red App has model

• Need to integrate Red & Blue models




• Step 1: Merge RDF

• Same nodes (URIs) join automatically



• Step 2: Add relationships and rules

• (Relationships are also RDF)




• Step 3: Define Green model

• (Making use of Red& Blue models)



• What the Blue app sees:

−No difference!




• What the Red app sees

• No difference!


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

RDF

Model

Transform

A1

A2

A3

B1

B2

C1

C2

X

Y

Z Ontologies

& RulesOntologies

& RulesOntologies

& Rules



Why?4. Looser coupling

• Without breaking consumers:

−Ontologies can be mixed and extended

− Information can be added

• Producer & consumer can be versioned more independently


Example of looser coupling

• RedCust and GreenCust ontologies added

• Blue app is not affected

(Blue app)

Consumer Producer



PART 2

Key Techniques for RDF in SOA


1. RDF message semantics

• Interface contract can specify RDF, regardless of serialization

• RDF pins the semantics

Consumer ProducerRDF



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?


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 . . .



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


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



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

Normalize

to RDF

Serialize as

XML/other/RDF

Service

Client

XML/other

Core App

Processing


3. REST-based SPARQL endpoints

Consumer Producer

SP

AR

QL

RDF

HTTP



REST-based SPARQL endpoints

• Why REST:

−HTTP is ubiquitous

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

−Looser process coupling



• What is SPARQL:

−Simple Protocol And RDF Query Language

−W3C standard

−Query language for RDF

−Modeled after SQL:

SELECT ...

WHERE ...




• 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


4. Aggregators• Gets data from multiple sources

• Provides data to consumers

• Does model transformation, caching, etc.

• Conceptual component -- not necessarily a separate service

Aggregator

A1

A2

A3

B1

B2

C1

C2

X

Y

Z Ontologies

& RulesOntologies

& RulesOntologies

& Rules

SP

AR

QL



Conclusions

• Value of RDF in data integration is well proven

• RDF can bring looser coupling to SOA

• Key techniques:

1. RDF message semantics

2. REST-based SPARQL endpoints

3. GRDDL to bridge from XML to RDF

4. Aggregators


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/

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











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





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

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





Outline

• PART 0: The problem

• PART 1: RDF: A lingua franca for information exchange

• PART 2: Key Techniques for RDF in SOA

© 2008 Hewlett-Packard Development Company, L.P.

The information contained herein is subject to change without notice

Questions?

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David Booth R D F & S O A