Fresnel, Briefly

• Two-part vocabulary regarding graph display:
  • Selection: which part of the graph should be displayed
  • Styling: how should it be displayed
• Lenses do selection, Formats do styling
• Emphasis on simplicity and portability
  • Try to be general enough to detach from specific user-agent visualization paradigms
  • But without becoming entirely impractical
• Modular and extensible

• Today: a brief tour with examples; implementations; questions

Motivation: Portability

• Lots of homebrew solutions in RDF browsers to do the same thing
  • So stop reinventing the wheel
• Several ways to visualize an RDF graph
  • Easily share with others what's worked for you
  • Maybe provide representations that clue new users into a different visualization of the same resource
• Not everybody has time to make everything visually appealing

The Vocabulary

• Core portion must be fully implemented to be considered a Fresnel engine
  • Core: http://www.w3.org/2004/09/fresnel
• Extended portion can be taken in pieces
  • Extended: http://www.w3.org/2004/09/fresnel-extended
• Also in N3: core, extended

Lenses and Selection

• A lens specifies which resources it applies to and lists which properties of the resource to display
• Simple selectors choose resources of an RDF graph based on their rdf:type or the specific instance URI
• Example:

  :personLens a fresnel:Lens ;
     fresnel:classLensDomain foaf:Person ;
     fresnel:showProperties (
       foaf:name
       foaf:mbox
       foaf:nick
       foaf:homepage
     ) .
  

• Example matches any resource of rdf:type foaf:Person
• showProperties specifies properties and order
• Use fresnel:allProperties in the list to display all other properties that have not yet been explicitly named

Sublenses

• Reuse an existing lens to display details about an object of the current subject
• Example:

  :personLens rdf:type fresnel:Lens ;
    fresnel:classLensDomain foaf:Person ;
    fresnel:showProperties (
      foaf:name 
      foaf:mbox 
      foaf:nick
      foaf:homepage
      [ rdf:type fresnel:PropertyDescription ;
        fresnel:property foaf:knows ;
        fresnel:sublens :personLens ;
        fresnel:depth "5"^^xsd:nonNegativeInteger ] ) .
  

• Can specify multiple fresnel:sublens, with type determining which sublens is used
• Can specify depth for an upper limit for sublens calls; works for lens recursion as well

Selection Notes, Advanced Selectors

• Also in core:
  • Conflict resolution when more than one lens might apply
  • Displaying containers and lists
• Advanced selectors not part of core
• Use an XSD datatype to indicate the language of an advanced selector literal
• Fresnel Selector Language (FSL): Manual
• Also SPARQL (but nobody's touched integrating SPARQL into a Fresnel engine as of yet)

Formats and Styling

• Triggers off of properties or resources (emphasis on properties)
• Small set of interpretations of values (i.e., image, hyperlink)
• String labels of properties, string separators for values
• CSS hooks for an external CSS-like language to manage the aesthetics
• Usually grouped in a fresnel:Group so there can be consistency in the final rendering using several formats together

Format Example

• Example:

  :linkFormat a fresnel:Format ;
    fresnel:propertyFormatDomain foaf:homepage ;
    fresnel:propertyFormatDomain foaf:workInfoHomepage ;
    fresnel:propertyStyle "foaf-link" ;
    fresnel:value fresnel:externalLink ;
    fresnel:label "Related link: " .
  

• Sets the class of elements resulting from selection of foaf:homepage and foaf:workInfoHomepage to foaf-link
• Sets the elements of the values of properties to be hyperlinks
• Replaces the FOAF ontology labels for properties to "Related link:" in the final rendering

Abstract Display Model

• Description of how elements of display are represented in 'boxes'
• Resource box holds the resource and all its properties
• Property box holds a property - its label and all its values
• Label box holds the property label
• Value box holds one value which may contain a Resource
• Each box can be styled separately from its ancestors or constituents

Container box is part of the extension vocabulary, not in core

Other Formatting and Styling Features

• Explicitly link a lens to a format (must be in same group)
• Format conflict resolution when more than one format might apply
• Additional string content can be inserted at different places in the abstract display model: either before, after, before the first, or after the last in a set, if applicable

Output

• Not formalized; the Fresnel engine should output a tree with styling hooks
• SIMILE implementation spits out XML, transformed via XSLT to XHTML
• Any CSS generated is tied in part to the way the engine translates trees to XHTML

Known Implementations

• SIMILE's Fresnel Engine; Java, available in a Maven repository
  • used in Longwell
• Emmanuel's IsaViz (partial; fully implements FSL); Java, likely will utilize SIMILE engine
• Freie Universität Berlin's Horus; PHP
• DERI's Arago (dead); PHP
• Olin College (unknown)

Example: In Longwell

• Before (default presentation):
  
• After (FOAF lens):
  

Q&A

Questions