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Review of semantic enablement techniques used in geospatial and semantic standards for legacy and opportunistic mashups Laurent Lefort, Australian Ontology Workshop 2009. Standards for Semantic Sensor Mashups. Outline of the talk. Which standards for which mashups?

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standards for semantic sensor mashups

Review of semantic enablement techniques used in geospatial and semantic standards for legacy and opportunistic mashupsLaurent Lefort, Australian Ontology Workshop 2009

Standards for Semantic Sensor Mashups

outline of the talk
Outline of the talk
  • Which standards for which mashups?
    • Server-side/legacy or client-side/opportunistic
  • Semantic-enabled?
    • Semantic enablement pathways
    • Links and annotations
    • Meshup “value pyramid”
  • Review of specific standards
    • XLink, RDFa, SAWSDL/hRESTs
  • Failure risk and validation issues
  • Conclusion

CSIRO. Standards for Semantic Sensor Mashups

web 2 0 3 0 sem web rocks xml and wsdl don t anymore
Web 2.0 & 3.0 (Sem Web) rocks XML and WSDL don’t (anymore)

WHICH STANDARDS FOR WHICH MASHUPS?

Matt Jones

http://www.flickr.com/photos/

blackbeltjones/3150215637/

CSIRO. Standards for Semantic Sensor Mashups

motivations w3c semantic sensor network incubator group
Motivations: W3C Semantic Sensor Network incubator group

Enable semantic service integration

Enable semantic mashups

Semantic annotations

Ontology-enabled

reference datasets

Ontology-enabled APIs

Sensors and

Observations

Linking Open Data

resources

Semanticaly-annotated

OGC services

(SOS, SPS, SAS, …)

OGC Services

(SOS, SPS, SAS, SES)

  • Semantic annotations
  • for OGC services?
  • for Mashups?

Registries &

Dictionaries

Sensor and obs.

To begin the formal process of producing ontologies that define the capabilities of sensors and sensor networks

To develop semantic annotations of a key language used by services based sensor networks

(especially the ones developed by the Open Geospatial Consortium)

CSIRO. Standards for Semantic Sensor Mashups

server side mashups web 1 0 2 0
Server-side mashups (Web 1.0 & 2.0)
  • Server-side mashups
    • Server-side software component accessing XML files, Databases, SOAPful or RESTful web services
    • The result is generally packaged as a web service
  • For legacy resources:
    • Complex APIs
    • Workflow engine and wrappers
    • Output in XML

CSIRO. Standards for Semantic Sensor Mashups

client side mashups web 1 0 2 0
Client-side mashups (Web 1.0 & 2.0)
  • Client-side mashup:
    • Client-side scripts accessing mashable resources (RESTful services mostly)
    • The result is packaged into an interactive web application
  • For opportunistic mashups:
    • Simpler APIs
    • Scripting languages
    • Output in HTML

CSIRO. Standards for Semantic Sensor Mashups

server side semantic mashups web 3 0
Server-side semantic mashups (Web 3.0)
  • Server side mashup:
    • Semantic enablement of XML files, Databases, SOAPful or RESTful web services (SAWSDL)
    • Integration with linking open data and ontologies services through triple stores (APIs or resources)

CSIRO. Standards for Semantic Sensor Mashups

example of semantic composition server side
Example of semantic composition (server side)
  • Composer’s Workbench
    • XML-RDF
    • Wrap complex services using semantic annotations mapping WSDL/XML schema to DL ontology (also SQL DBs)
    • New requirements: provenance XG

Cameron et al. (2009) Semantic Solutions for Integration of Federated Ocean Observations

CSIRO. Standards for Semantic Sensor Mashups

client side semantic mashups web 3 0
Client-side semantic mashups (Web 3.0)
  • Client side mashup:
    • Enrichment of HTML resources with RDFa markup allowing to “lift” the content into RDF
    • Reduction of number of APIs to handle by scripts (SPARQL or equivalent)

CSIRO. Standards for Semantic Sensor Mashups

example of semantic pipes client side
Example of semantic pipes (client side)
  • Sensor masher (browser-based)
    • RDF-HTML (RESTful services, Javascript)
    • Avoid the use of proprietary or product-specific APIs
    • Leverage URI-based data integration (Linked Open Data)
    • Lightweight pipes (user-defined) based on DERI Pipes

Danh Le Phuoc (2009): SensorMasher : publishing and building mashup of sensor data

CSIRO. Standards for Semantic Sensor Mashups

semantic enablement where
Semantic enablement: where?

CSIRO. Standards for Semantic Sensor Mashups

four semantic enablement pathways server side 1 2 3 or client side 3 4
Four semantic enablement pathways: Server-side (1,2, 3) or client-side (3,4)
  • 1. Include RDF (SKOS/OWL) resources in XML using XLink,
  • 2. Annotate SOAPful web services with SAWSDL
  • 3. Annotate RESTful web services with hRESTs (SA-REST/MicroWSMO),
  • 4. Include RDF (SKOS/OWL) resources in HTML using RDFa.

XML

HTML

1

1

3

3

2

1

4

1

CSIRO. Standards for Semantic Sensor Mashups

a possible use case with all types of mashups bundled together
A possible use case with all types of mashups bundled together

1

2

3

2

3

3

4

CSIRO. Standards for Semantic Sensor Mashups

meshup value pyramid
Meshup “value pyramid”
  • Semantic mashups over
    • RDFa content embedded in web pages
    • Linked Open Data resources
    • XML, database and web service resources
  • Meshup
    • A semantically mashable semantic mashup
    • a mashup consuming and serving SW content,
  • RDFa standard is disruptive
    • New generation of SW apps
    • New “value pyramid” top

HTML

RDF

XML

Extension of Kingsley Idehen’s pyramid:

“Getting The Linked Data Value Pyramid Layers Right (Updated)”

CSIRO. Standards for Semantic Sensor Mashups

meshup standard value pyramid vs tbl s cracks and mortar
Meshup standard “value pyramid” vs. TBL’s Cracks and Mortar

Tim Berners-Lee, Cracks and Mortar

W3C TPAC 2007

CSIRO. Standards for Semantic Sensor Mashups

meshup standard value pyramid vs new cracks and mortar
Meshup standard “value pyramid”vs. new “Cracks and Mortar”

CSIRO. Standards for Semantic Sensor Mashups

definitions links annotations lifting operations
Definitions: links, annotations, lifting operations
  • Links specifies the inclusion of remotely managed resources.
    • Mechanisms used to extend available content from any type of resources with information sourced from remotely managed content (type or instance).
    • Possible between two documents of the same type or between documents of different types.
  • Semanticannotations define how to map service capabilities to semantic definitions to enable the discovery or composition of web services.
  • The transition from XML-based services to RDF-based services is called a lifting operation (Farrell and Lausen 2007) and the inverse one, from RDF to XML is called a lowering operation.

CSIRO. Standards for Semantic Sensor Mashups

semantic enablement pathways using different linking and annotation standards
Semantic enablement pathways using differentlinking and annotation standards

Lifting operations

1

  • 1. Include RDF (SKOS/OWL) resources in XML using XLink,
  • 2. Annotate SOAPful web services with SAWSDL
  • 3. Annotate RESTful web services with hRESTs (SA-REST/MicroWSMO),
  • 4. Include RDF (SKOS/OWL) resources in HTML using RDFa.

RDFa

4

2

3

SAWSDL

hRESTs

2

3

4

XLink

1

CSIRO. Standards for Semantic Sensor Mashups

semantically enabled xml resources and xlink
Semantically-enabled XML resources and XLink

~1

CSIRO. Standards for Semantic Sensor Mashups

variants of xlink usage
Variants of XLink usage

CSIRO. Standards for Semantic Sensor Mashups

xlink and rdf
XLink and RDF

CSIRO. Standards for Semantic Sensor Mashups

usage of xlink in gml related to urns
Usage of XLink in GML – related to URNs
  • Conventions defined by the GML standard (Portele 2007)
          • Portele C. (2007): OpenGIS® Geography Markup Language (GML) Encoding Standard version 3.2.1 OGC 07-036 Open Geospatial Consortium 2007-08-27
    • Reference to an object element in the same GML document <myProperty xlink:href="#o1"/>
    • Reference to an object element in a remote XML document using the gml:id value of that object: <myProperty xlink:href="http://my.big.org/test.xml#o1"/>
    • Reference to an object element with a uniform resource name may be encoded as follows (a URN resolver is required): <myProperty xlink:href="urn:x-ogc:def:crs:EPSG:6.3:4326"/>
  • URN: Uniform Resource Name
    • May or may not correspond to Semantic Web resources
      • http://en.wikipedia.org/wiki/Uniform_Resource_Name
    • URN is a generic resource naming mechanism: the mapping of a URN to a class, property or individual is not normalised

CSIRO. Standards for Semantic Sensor Mashups

current xlink usage
Current XLink usage
  • Sheth Semantic Sensor Markup of Data and Services SSN-XG briefing
    • XLink @href pointing to individual
  • Luis Bermudez Enriching SOS services with Ontologies - OOSTethys/OceansIE and MMI SSN-XG briefing
    • XLink @href pointing to individual
  • Janowicz et al. (2009; forthcoming): Semantic Enablement for Spatial Data Infrastructures. Transactions in GIS. 
    • XLink @href pointing to individual with @role pointing to sawsdl:modelReference (should be arcrole)
    • Correct use of sawsdl:modelReference in XML schema but does not define the associated lifting script
  • Compton et al. (2009) A Survey of the Semantic Specification of Sensors, in Proc. International Workshop on Semantic Sensor Networks SSN’09 CEUR-WS Vol. 552
    • XLink @href pointing to undefined concepts (#AirTemperature)

CSIRO. Standards for Semantic Sensor Mashups

major issues with xlink and its usage in ogc
Major issues with XLink (and its usage in OGC)
  • ISSUE: URNs can point to an individual, a class or a property
    • No guidelines on these three types of URN
    • <swe:Quantity definition="urn:ogc:def:property:SBE:batteryCurrent">
  • Confusion between XLink @role vs. @arcrole
    • Ex of a property URN (here, @arcrole should be used): <swe:field name="Battery Current“ xlink:role="urn:ogc:def:property:powerSupply">
    • Same issue with the @definition attribute
  • Usage of @href (to an individual) generally correct
    • Because the majority of the community developing and using OGC standard plans to use SKOS to manage vocabulary elements

CSIRO. Standards for Semantic Sensor Mashups

semantically enabled web pages rdfa
Semantically-enabled web pages (RDFa)

4

CSIRO. Standards for Semantic Sensor Mashups

variants of rdfa usage comparable to xlink
Variants of RDFa usage comparable to XLink

CSIRO. Standards for Semantic Sensor Mashups

xlink rdfa comparison
XLink – RDFa comparison

CSIRO. Standards for Semantic Sensor Mashups

tentative use of rdfa instead of xlink
Tentative use of RDFa instead of XLink
  • Barnaghi et al. Sense and Sensíability: Semantic Data Modelling for Sensor Networks, in Proc. of the ICT Mobile Summit 2009, June 2009.
    • SWE’s @definition mapped to class
    • RDFa-inspired (to fix):
      • OWL-like attribute namespaces to clear
      • @about mapped to individual,
      • @datatype mapped to xsd type,
      • @resource used but without corresponding @property,
      • @ID used,
      • URI conventions?
  • It is important to note that RDFa obeys to a rigorous specification which allows the development and usage of generic lifting scripts

CSIRO. Standards for Semantic Sensor Mashups

variants of rdfa usage in relation to hrests
Variants of RDFa usage in relation to hRESTs
  • Two possibilities to do semantic markup of HTML files
    • Microformats
    • RDFa

CSIRO. Standards for Semantic Sensor Mashups

semantically enabled restful web services hrest microformat
Semantically-enabled RESTful web services (hREST-microformat)

~4

3

CSIRO. Standards for Semantic Sensor Mashups

semantically enabled restful web services hrest rdfa
Semantically-enabled RESTful web services (hREST-RDFa)

~4

3

CSIRO. Standards for Semantic Sensor Mashups

hrests microformat vs hrests rdfa
hRESTs-microformat vs. hRESTs-RDFa

CSIRO. Standards for Semantic Sensor Mashups

hrests rdfa preferred to hrests microformat
hRESTs-RDFa preferred to hRESTs-microformat
  • hRESTs-microformat forces the user to pick the service ontology and have access to the corresponding lifting script
    • SAREST ontology ~ what’s used in SAWSDL
      • http://knoesis.wright.edu/research/srl/standards/sa-rest/
    • MicroWSMO ontology: WSMO-Lite:
      • http://www.wsmo.org/ns/wsmo-lite/
  • hRESTs-RDFa allows to specify the service ontology the mapping definitions will be lifted to
    • e.g. one adapted to a specific platform
      • sensor networks, grid computing, …
  • It should be possible to have a similar freedom of choice with SAWSDL
    • It’s not the case right now (next slide)

CSIRO. Standards for Semantic Sensor Mashups

semantically enabled soapful web services
Semantically-enabled SOAPful web services

2

CSIRO. Standards for Semantic Sensor Mashups

failure risk analysis
Failure risk analysis
  • Opportunistic mashups depends on external resources which may disappear or evolve without notice,
    • especially mashable services and semantic resources,
  • The risks of failure are greater and more diverse than in other environments.
  • Question: where to start

CSIRO. Standards for Semantic Sensor Mashups

validator mashup framework unicorn universal conformance observation and report notation
Validator mashup framework: Unicorn (Universal Conformance Observation and Report Notation)
  • Unicorn (2006-2008)
    • Validator Mashup project at W3C
    • http://www.w3.org/QA/Tools/Unicorn/
  • HTML-only
    • Markup Validator,
    • CSS Validator,
    • Link Checker

CSIRO. Standards for Semantic Sensor Mashups

extend unicorn to build a complete top down validator mashup pyramid
Extend Unicorn to build a complete top-down validator mashup pyramid
  • Mashable validators
    • HTML validators
      • HTML + RDFa http://validator.w3.org/
      • HTML http://validator.nu/
    • SPARQL
      • SPARQL* http://www.sparql.org/validator.html
      • Linked Data (URIs)* http://vapour.sourceforge.net/
    • Linked Open Data
      • OWL http://owl.cs.manchester.ac.uk/validator/
      • RDF http://www.w3.org/RDF/Validator/
    • RDF-ization
      • SAWSDL, …: ?
      • GRDDL (service) http://www.w3.org/2007/08/grddl/
    • XML validators
      • WSDL http://www.validwsdl.com/ (via Wikipedia)
      • OGC valdiators
      • XLink SXLink?
  • Full list of W3C list validators: http://www.w3.org/QA/TheMatrix

CSIRO. Standards for Semantic Sensor Mashups

identification of area of future work
Identification of area of future work
  • Semantic annotation standards for both WSDL and REST services
    • Ontologies for different types of services
    • Lifting scripts for services
    • Guidelines on the part of HTML to be annotated for RESTful services
  • Controlled upgrade of legacy standards: need at least better guidelines (and validation tools)
    • XLink @role and @arcrole are easy to confuse
    • URNs mappings to individuals, class or properties should be specified unambiguously in OGC specifications (and elsewhere?)
    • Develop a RDFa style for XLink may help to separate the current usage of XLink (intra-XML) to new usages where XLink would be used in conjunction with semantic web resources
  • Validators and validator mashups
    • Higher risk of errors with mashups
    • Golden opportunity to re-engineer and mash existing validators
    • Some missing validators especially at the lower levels (e.g. XLink, URNs)

CSIRO. Standards for Semantic Sensor Mashups

conclusions
Conclusions
  • Semantic mashups complete existing semantic integration approaches but don’t replace them
    • Lightweight composition by end users with semantic pipes to explore opportunities
    • Transition to more stable infrastructure built on top of legacy services if the proof of concept phase is successful
  • Mashups require hybrid combination of XML, RDF and HTML standards
    • Some standards like XLink or RDFa are adaptable at different levels of the pyramid
    • Special care must be taken for the semantic upgrades of existing standards
  • Mashups requires new validation approaches
    • Which may also be based on mashups (Unicorn-like)

CSIRO. Standards for Semantic Sensor Mashups

thank you

Contact Us

Phone: 1300 363 400 or +61 3 9545 2176

Email: enquiries@csiro.au Web: www.csiro.au

Thank you

CSIRO ICT Centre

Laurent Lefort

Senior Software Engineer and W3C Office manager

Phone: +61 2 6216 7046

Email: laurent.lefort@csiro.au

Web: www.ict.csiro.au

slide42
Memo
  • GRDDL - A markup format for Gleaning Resource Descriptions from Dialects of Languages. It is a W3C Recommendation, and enables users to obtain RDF triples out of XML documents, including XHTML. It defines the syntax to include a reference to a lifting script in a source document - the lifting script can then be used to transform the document to RDF
  • Microdata - Allows nested groups of name-value pairs to be added to documents, in parallel with the existing content. A non-semantic alternatibe to RDFa
  • SAWSDL - A set of extension attributes for the Web Services Description Language and XML Schema definition language that allows description of additional semantics of WSDL components. Allows the user to record the mapping of WSDL elements to concepts defined in a reference ontology and to specify the lifting scripts which can be applied to the output of a service to transform it into a RDF file using the reference ontology concepts
  • hRESTs - A microformat to add additional meta-data to REST API descriptions in HTML and XHTML. Developers can directly embed meta-data from various models such an ontology, taxonomy or a tag cloud into their API descriptions. The embedded meta-data can be used to improve search (for example: perform faceted search for APIs), data mediation (in conjunction with XML annotation) as well as help in easier integration of services to create mashups.
  • SA-REST and Micro-WSMO: two similar methods to semantically annotate REST services using the same microformat (hRESTs) and a different target ontology. Similar basis than SAWSDL (including the possibility to include a reference to a lifting script) but applicable to an HTML-based description of a service).

CSIRO. Standards for Semantic Sensor Mashups