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Distributed Software Development
RDF Chris Brooks
Department of Computer Science University of San Francisco Department of Computer Science — University of San Francisco – p. 1/ ??
RDF
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RDF stands for Resource Description Framework
-^ Provides a way to describe properties that belong to objects. -^ Much like a relational database. -^ Can be serialized as XML, but it’s easiest not to get hung up onthe XML syntax initially.^ ◦ Built to be created and consumed by machines. Department of Computer Science — University of San Francisco – p. 2/ ??
Uses of RDF
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RDF is a very popular framework for describing resources onthe Web.^ ◦ RSS ◦ Mozilla ◦ Creative Commons ◦ FOAF ◦ Adobe’ XMP project ◦ Open Drectory Project
-^ All of these applications need a more powerful way ofrepresenting information than XML provides by itself. Department of Computer Science — University of San Fra 17-4:
RDF’s data model
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Recall that XML produces a tree-structured data model.
-^ This can make it hard to represent some sorts of knowledge. -^ How to denote that two elements share a sub-element? Department of Computer Science — University of San Francisco – p. 4/ ??
Representation in XML
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For example: DoorsBreak On Through Greatest Hits DoorsLight My Fire Greatest Hits DevoThrough Being Cool Greatest Hits Department of Computer Science — University of San Francisco – p. 5/ ??
RDF’s data model
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RDF represents data in terms of triples
-^ Subject, property, value - “http://www.cs.usfca.edu/ brooks/S05classes/cs682/slides/rdf.pdtitle, “RDF Lab” -^ Properties allow us to express relations between objects.^ ◦ In AI, we called these things predicates Department of Computer Science — University of San Fra
RDF’s data model
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From a set of RDF triples, we can construct an RDF graph.
-^ Subject and value are nodes^ ◦ Nodes can be^ • URIs - a generalized form of a URL • blank nodes - mostly useful as placeholders • literals - strings, values, etc. ◦ ◦^ Properties are edges. Department of Computer Science — University of San Francisco – p. 7/ ??
Resources
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An RDF document is a set of statements about resources ◦^ Documents, video clips, services
-^ A resource is something that has a location.^ ◦ Referred to with a URI -^ The subject of an RDF statement is a resource. Department of Computer Science — University of San Francisco – p. 8/ ??
Literals
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The object of an RDF statement can be a resource or a literal.
-^ Literals are typically strings. -^ For example: <rdf:Description rdf:about’http://www.cs.usfca.edu/˜ brooks’> <dc:creator> Brooks </dc:creator> </rdf:description> Department of Computer Science — University of San Fra 17-10:
Properties and statements
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A property is a relation between a subject and an object.
-^ A statement is a subject, a property, and an object. -^ This allows RDF statements to be placed in a graph model. -^ We called this a semantic network in AI. Department of Computer Science — University of San Francisco – p. 10/ ??
Reification
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It’s also possible in RDF to make statements about statements.
-^ This process is called reification <rdf:Description rdf:ID=’’item10245’’> <exterms:weight rdf:datatype=’’&xsd;decimal’’>2.4</exterms:weight> </rdf:Description><rdf:Statement rdf:about=’’#triple12345’’> <rdf:subject rdf:resource=’’http://www.example.com/2002/04/products#ite <rdf:predicate rdf:resource=’’http://www.example.com/terms/weight’’/> <rdf:object rdf:datatype=’’&xsd;decimal’’>2.4</rdf:object> <dc:creator rdf:resource=’’http://www.example.com/staffid/85740’’/> </rdf:Statement> -^ This lets you say things about who wrote a statement, when itwas added, the validity, and so on. Department of Computer Science — University of San Francisco – p. 11/ ??
FOAF
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We’ll be using a simple RDF language called FOAF(friend-of-a-friend)
-^ It’s a way to indicate other people that you know. -^ Consists of Person nodes, which have properties^ ◦ Name, title, etc. -^ One of the interesting properties is ’knows’. -^ the object of this is also a Person. Department of Computer Science — University of San Fran
