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Facet: Building Web Pages with SPARQL

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Introduces the high-level design of an web templating API for providing read-only access to RDF data using SPARQL.

Introduces the high-level design of an web templating API for providing read-only access to RDF data using SPARQL.

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  • Transcript

    • 1. Facet Building Web Pages With SPARQL SWIG-UK Event, HP Labs November 23 rd 2007 Leigh Dodds Chief Technology Officer, Ingenta
    • 2. Problem Statement
    • 3. Where’s my RDF-native Web Framework?! There is no good system for integrating RDF repositories with existing an web framework (in Java)
    • 4. Design Constraints
    • 5.  
    • 6.  
    • 7.  
    • 8.  
    • 9.  
    • 10.  
    • 11.  
    • 12.  
    • 13. Design Constraints
      • A web page presents data that is a sub-graph (i.e. a view) over a larger RDF store, (the data model)
      • The extent of the sub-graph may vary for different presentations of the data, and may contain arbitrary properties
      • The description of the sub-graph (a lens) should be declarative
      • That sub-graph is “rooted” on a single primary resource (e.g. a Journal)
      • The identifier of the primary resource can be derived from the request URL, e.g. by rewriting the URI. And vice versa
        • Therefore, we don’t support blank nodes as primary resources
        • Or fragment identifiers in URIs!
      • The sub-graph should be serializable into an object graph for presentation to the templating system
    • 14. Facet Request Handling
      • To return a response we need to answer three questions…
      • What lens are we going to apply?
      • What data model are we going to apply it to?
      • What’s the identifier of the primary resource ?
    • 15. Lenses Describing views of RDF data
    • 16. A Simple Lens
      • PREFIX dc: <http://purl.org/dc/elements/1.1/>
      • CONSTRUCT {
      • ?item dc:title ?title .
      • ?item dc:language ?language .
      • }
      • WHERE {
      • ?item dc:title ?title .
      • OPTIONAL { ?item dc:language ?language . }
      • }
    • 17. Configuring Lenses
      • <rdf:RDF
      • xmlns:rdf=&quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;
      • xmlns:ja=&quot;http://jena.hpl.hp.com/2005/11/Assembler#&quot;
      • xmlns:view=&quot;http://metastore.ingenta.com/facet/lens/&quot;>
      • <rdf:Description
      • rdf:about=&quot;http://metastore.ingenta.com/facet/lens/Sparql&quot;> <ja:assembler>com.ingenta.facet….</ja:assembler>
      • </rdf:Description>
      • <view:Sparql
      • rdf:about=&quot; http://oecd.metastore.ingenta.com/views/just-the-title &quot;>
      • <view:query> sparql/just-the-title.rq </view:query>
      • </view:Sparql>
      • </rdf:RDF>
    • 18. Data Model Configuring RDF graphs
    • 19. Data Model Configuration
      • Jena Assembler API
      • Add notion of application level default data model
        • Uses well-known URI
      • Lenses may be configured to apply to a specific data model
        • Allows “sharding” of data models
      • <view:Sparql
      • rdf:about=&quot; http://oecd.metastore.ingenta.com/views/just-the-title &quot;>
      • <view:appliesTo rdf:resource=“…”/>
      • </view:Sparql>
    • 20. Resource Identifiers
    • 21. Mapping Resource Identifiers
      • In a RESTful application, each resource should have a single primary location
      • Allows resource identifiers to be derived using URL rewriting
      • http://test.sourceoecd.org/oecd/content/journal/18168116
      • http://oecd.metastore.ingenta.com/content/journal/18168116
    • 22. Serialization Mapping an RDF sub-graph to a Java object model
    • 23. Serialization
      • Primary resource is a ContentItem
        • Has an identifier and Map of properties
      • Walk through graph, beginning at “root” resource, mapping RDF statements to Map entries
      • Mapping of property names is configurable.
        • Default based on namespace prefix, E.g. dc_title
      • Mapping of objects of each statement to a suitable Java object
        • ContentItem, Map, List, Integer , etc
    • 24. Serialization (special cases)
      • Multilingual properties
        • Special casing (i.e. a hack!) to modify naming, e.g. dc_title_fr
      • Repeated properties, e.g. dc:subject
        • Use schema annotation to indicate these, and then Serialize to a List
      • XML Literals & Multi-lingual data
        • E.g. multi-lingual abstracts ( dc:description ) that contain XHTML markup
        • Use schema annotation, parse and create separate Map entries
    • 25. Additional Features
      • “ MultiLens”, applying multiple queries in series to build results
      • Automatic availability of URL parameters as SPARQL query parameters
      • Integral API support
        • RDF output for free; JSON output trivial
      • Simple content lifecycle, mapping to HTTP resource statuses
        • E.g. Content Not Found, Moved, Gone
        • Add type ( life:Deleted ) and properties ( life:newLocation ) to data
      • Support for URL Aliasing based on property values
        • /content/issn/1234-5678 -> /content/journal/abcdef
        • <prism:issn>
    • 26. Summary
      • Pros
      • By embracing a few limitations on RDF modelling, e.g. identifiers provides a very flexible means of building web pages from an RDF repository
      • Reliance on SPARQL and Jena API features provides great deal of configuration options
      • Good integration with existing web templating environments
      • Quick to learn
      • Cons
      • Model limitations mean its not suited to all RDF “in the wild”