Facet: Building Web Pages with SPARQL
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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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Facet: Building Web Pages with SPARQL Facet: Building Web Pages with SPARQL Presentation Transcript

  • Facet Building Web Pages With SPARQL SWIG-UK Event, HP Labs November 23 rd 2007 Leigh Dodds Chief Technology Officer, Ingenta
  • Problem Statement
  • Where’s my RDF-native Web Framework?! There is no good system for integrating RDF repositories with existing an web framework (in Java)
  • Design Constraints
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  • 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
  • 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 ?
  • Lenses Describing views of RDF data
  • 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 . }
    • }
  • 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>
  • Data Model Configuring RDF graphs
  • 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>
  • Resource Identifiers
  • 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
  • Serialization Mapping an RDF sub-graph to a Java object model
  • 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
  • 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
  • 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>
  • 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”