Standards for Semantic Mashups
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Standards for Semantic Mashups

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Description of the work done for the Semantic Markup activity of the Semantic Sensor Networks Incubator activity (at W3C). ...

Description of the work done for the Semantic Markup activity of the Semantic Sensor Networks Incubator activity (at W3C).

Presentation made at the Australian Ontology Workshop, Melbourne, December 2009. The full title of the paper is: "Review of semantic enablement techniques used in geospatial and semantic standards for legacy and opportunistic mashups" (and it is available via crpit.com)

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    Standards for Semantic Mashups Standards for Semantic Mashups Presentation Transcript

    • 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? • 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) 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 Enable semantic service integration Enable semantic mashups Semantic annotations Ontology-enabled Ontology-enabled APIs reference datasets Semanticaly-annotated Sensors and OGC services Observations (SOS, SPS, SAS, …) Linking Open Data resources OGC Services Semantic annotations Registries & (SOS, SPS, SAS, SES) - for OGC services? Dictionaries Sensor and obs. - for Mashups? 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 • 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 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 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) • 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 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) • 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? CSIRO. Standards for Semantic Sensor Mashups
    • 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 2 3 1 4 1 CSIRO. Standards for Semantic Sensor Mashups
    • A possible use case with all types of mashups bundled together Geospatial mashups Web pages mashups (HTML) Legacy Legacy OGC (XML/JSON+REST) OGC aggregator Geospatial mashups Geo Mashups services (e.g. ArcGIS) Web mashups Composed Model mashups Search Legacy (XML/JSON+REST) services services Model (XML+REST/ Model Mashups WSDL) Legacy mashups pipes (XML+REST/WSDL) 1 2 3 2 3 3 4 Semantic web page mashups (HTML+RDFa) RDF-ized RDF-ized OGC OGC Semantic mashups service Aggregator Geo Mashups Web mashups RDF-ized Search Composed Semantic Semantic mashups service pipes Model Mashups (RDF/JSON+SPARQL) CSIRO. Standards for Semantic Sensor Mashups
    • Meshup “value pyramid” • Semantic mashups over Mesh ups HTML • RDFa content embedded in web pages • Linked Open Data resources HTML/RDFa • XML, database and web service resources SPARQL protocol • Meshup RDF • A semantically mashable Linked Open Data resources semantic mashup • a mashup consuming and serving RDF-ization (Lifting layer) SW content, XML Legacy Resources • RDFa standard is disruptive (XML, Database, Web services) • New generation of SW apps • New “value pyramid” top 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 Mash ups HTML SPARQL protocol Linked Open Data resources RDF-ization (Lifting layer) Legacy Resources (XML, Database, Web services) Tim Berners-Lee, Cracks and Mortar W3C TPAC 2007 CSIRO. Standards for Semantic Sensor Mashups
    • Meshup standard “value pyramid” vs. new “Cracks and Mortar” Users HTTP + HTML (RDFa) + SVG + DOM + JS + Mashable APIs Mashup site Mashup Mesh site ups HTTP + HTML (RDFa) + SVG + DOM + JS + Mashable APIs Mashup SparQL site Ontology Mashup site of objects Virtual HTML/RDFa RDF data RDFa service HTML SPARQL protocol pages RDFa markup XML or JSON + HTTP + JS + Mashable APIs Linked Open Data resources SparQL SparQL Ontology Virtual Ontology Virtual of objects RDF of objects RDF data data RDF-ization (Lifting layer) Lifting service Lifting Lifting service script RDB-RDF XML Existing XSLT or Xquery Mapping Schema XML SQL Existing Legacy Resources GRDDL markup Schema SQL DB (XML, Database, Web services) CSIRO. Standards for Semantic Sensor Mashups
    • 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. • Semantic annotations 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 • 1 Include RDF 1. Mesh Lifting (SKOS/OWL) ups operations resources in XML RDFa 4 using XLink, HTML/RDFa • 2 Annotate SOAPful 2. web services with SPARQL protocol SAWSDL • 3 Annotate RESTful 3. web services with Linked Open Data resources hRESTs (SA- SAWSDL REST/MicroWSMO), hRESTs RDF-ization (Lifting layer) • 4 Include RDF 4. 2 3 (SKOS/OWL) XLink resources in HTML Legacy Resources 1 (XML, Database, Web services) using RDFa. CSIRO. Standards for Semantic Sensor Mashups
    • Semantically-enabled XML resources and XLink HTTP + HTML + SVG + DOM + JS + RDF + OWL + SPARQL SparQL Ontology Virtual of objects RDF data Lifting service Lifting ~1 script XML Existing XSLT or Xquery Schema XML GRDDL markup CSIRO. Standards for Semantic Sensor Mashups
    • Variants of XLink usage Inclusion of remote resources Model reference to ontological description Described in GML spec. xlink Xlink @role and @arcrole @href Existing Existing XML XML XLink XLink markup markup Xlink href Existing Xlink href Existing or URNs for XML or URNs for XML ontologies “data” (class or (instances) (types) (individuals) property) Inclusion of remote semantic resources Model reference to ontological description Xlink @href Xlink @role, @arcrole and SWE/GML@definition and SWE/GML @definition Existing Existing XML XML XLink XLink markup markup Existing Existing RDF OWL (instances) (types) CSIRO. Standards for Semantic Sensor Mashups
    • XLink and RDF Attribute Description Intended RDF xlink:href Identifier of the resource rdf:about of range which is the target of the resource association, given as a URI xlink:role Nature of the target rdf:about of class of resource, given as a URI range resource xlink:arcrole Role or purpose of the rdf:about of object target resource in property linking domain relation to the present element to range resource, given as a URI resource xlink:title Text describing the rdfs:comment association or the target resource CSIRO. Standards for Semantic Sensor Mashups
    • 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 • 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) • 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) HTTP + HTML (RDFa) + DOM + JS + RDF + OWL + SPARQL SparQL Ontology Virtual of objects RDF data RDFa service HTML pages RDFa markup 4 CSIRO. Standards for Semantic Sensor Mashups
    • Variants of RDFa usage comparable to XLink CSIRO. Standards for Semantic Sensor Mashups
    • XLink – RDFa comparison RDF mapping Xlink RDFa Domain instance about or src Domain class typeof Object property arc role rel Inverse object property rev Range instance href href or resource Range class role typeof Datatype property property Datatype property type role datatype Range value content or element content CSIRO. Standards for Semantic Sensor Mashups
    • 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 • Two possibilities to do semantic markup of HTML files • Microformats • RDFa CSIRO. Standards for Semantic Sensor Mashups
    • Semantically-enabled RESTful web services (hREST-microformat) HTTP + HTML + SVG + DOM + JS + RDF + OWL + SPARQL Semantically-enabled service Semantically- enabled output Lifting service ? for data RDF description of service Lifting Lifting Dynamic script operation XML and service Ontology ontology RESTful service of objects hard-coded Lifting HTML script hRESTs- description micro- Service formats ontology markup SA-REST or CSIRO. Standards for Semantic Sensor Mashups 3 ~4 MicroWSMO XSLT or Xquery
    • Semantically-enabled RESTful web services (hREST-RDFa) HTTP + HTML + SVG + DOM + JS + RDF + OWL + SPARQL Semantically-enabled service Semantically- enabled output Lifting service ? for data RDF description of service Lifting Dynamic script Lifting XML operation Ontology following RESTful service of objects RDFa spec. HTML hRESTs- description in-RDFa Service markup ontology 3 ~4 SA-REST or CSIRO. Standards for Semantic Sensor Mashups MicroWSMO XSLT or Xquery
    • hRESTs-microformat vs. hRESTs-RDFa RDF mapping hRESTs-microformat hRESTs-RDFa Domain instance id (URL-prefixed) about Domain class class (closed list) typeof Object property ref=”model” rel Inverse object property rev Range instance href or resource rdf:about of range class href typeof Datatype property property Datatype property type datatype Range value content or element content CSIRO. Standards for Semantic Sensor Mashups
    • 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 HTTP + HTML + SVG + DOM + JS + RDF + OWL + SPARQL Semantically-enabled service Semantically- enabled output Lifting service ? RDF for data XSLT or Xquery description of service Dynamic Lifting script Lifting service for description XML Lifting operation WSDL Web service Ontology and service of objects ontology hard-coded WSDL 2 SAWSDL Service Lifting XML markup ontology script Schema CSIRO. Standards for Semantic Sensor Mashups
    • 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 XML RDF HTML Web Triple Web pages services stores Ontologies SPARQL RDFa Semantic Linked Open Mashable Services Data web pages Legacy mashups Opportunistic mashups CSIRO. Standards for Semantic Sensor Mashups
    • 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 • Mashable validators • HTML validators • HTML + RDFa http://validator.w3.org/ • HTML http://validator.nu/ • SPARQL Mesh ups • SPARQL* http://www.sparql.org/validator.html • Linked Data (URIs)* http://vapour.sourceforge.net/ • Linked Open Data HTML/RDFa • OWL http://owl.cs.manchester.ac.uk/validator/ • RDF http://www.w3.org/RDF/Validator/ SPARQL protocol • RDF-ization • SAWSDL, …: ? Linked Open Data resources • GRDDL (service) http://www.w3.org/2007/08/grddl/ • XML validators RDF-ization (Lifting layer) • WSDL http://www.validwsdl.com/ (via Wikipedia) • OGC valdiators Legacy Resources • XLink SXLink? (XML, Database, Web services) • Full list of W3C list validators: http://www.w3.org/QA/TheMatrix CSIRO. Standards for Semantic Sensor Mashups
    • 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 • 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
    • 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 Thank you Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro.au Web: www.csiro.au
    • Backup slides
    • 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