EDUTELLA

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EDUTELLA

• Presenter
• ??? GI125 ???

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Outline

• Why RDF
• Edutella
• Framework
• Services
• Edutella Query Service Goals
• Query Exchange Architecture
• An example query
• Smart learning space

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Why RDF

• Retrieving all songs by Eric Clapton does not
  need complex query languages
• In other scenarios, like exchanging educational
  resources, queries are more complex, which might
  even be complemented by domain specific
  extensions.

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Why RDF

• Learners and teachers want to retrieve
  educational resources
• by content
• by learning goals
• by level of difficulty (existing knowledge)
• by context restrictions (time,money,hardware/softw
  are, )

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Why RDF

• RDF / RDF Schema for Describing Distributed
  Resources
• RDF Resource Description Framework
• URIs to identify resources
• Combine resources and annotate resources with
  attributes, using ltSubject, Property, Valuegt
  Tuples
• 2. Using RDF / RDFS in the P2P context
• Distributed annotations for distributed resources
• Flexible schema definitions, which can be
  uniquely identified and combined, as well as
  extended by additional properties

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Edutella

• Each Edutella peer can make its metadata
  information available as a set of RDF statements
• Goal make the distributed nature of the
  individual RDF peers connected to the Edutella
  network completely transparent by specifying and
  implementing a set of Edutella services.

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Framework
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Framework
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Services

• The Query Service
• The Replication Service
• The Mapping Service
• The Mediation Service
• The Clustering Service

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Services

• Peers register the queries they may be asked
  through the query service
• Queries are sent through the Edutella network to
  the subset of peers who have registered with the
  service to be interested in this kind of query.
• The resulting RDF statements are sent back to the
  requesting peer.

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Services

• Replication
• Initial focus replication of metadata
• Mapping
• The Mapping service manages will manage
  mappings between different schemata and use these
  mappings to translate queries over one schema X
  to queries over another schema Y

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Services

• Mediation
• Mediation services actively mediate access
  between different services.
• Clustering
• Clustering services use semantic information
  semantic routing and semantic clusters.

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Edutella Query Service Goals

• An RDF repository
• Consists of RDF statements
• Describes metadata according to arbitrary RDFS
  schemas

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Edutella Query Service Goals

• Edutella Query Service serves both
• as query interface for individual RDF
  repositories located at single peers
• as query interface for distributed queries
  spanning multiple RDF repositories.

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Edutella Query Service Goals

• Abstract from different RDF storage layer query
  languages (e.g.SQL) and from user level query
  languages (e.g., RQL, TRIPLE)
• Uses the query exchange language family RDF-QEL-i
  as standardized query exchange language format
  transmitted in an RDF/XML format

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Query Exchange Architecture

• Edutella wrappers translate queries and results
  from the Edutella query and result exchange
  format to the local format of the peer and vice
  versa,
• And they connect the peer to the Edutella network
  by a JXTA-based P2P library.

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Query Exchange Architecture
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Query Exchange Architecture

• In order to handle different query capabilities ,
  several RDF-QEL-i exchange language levels
• Describe which kind of queries a peer can handle
• Conjunctive queries
• Relational algebra
• Transitive closure, etc.

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Query language levels

• Currently, RDF-QEL-1 to 5, differing in
  expressiveness
• RDF-QEL-1 can be expressed as a unreified RDF
  graph
• The complex ones are more expressive than RDF
  itself have to be expressed using reified RDF
  statements.

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RDF-QEL-1

• Query-by-example paradigm ? Queries represented
  using
• annotations to denote variables and constraints
  on them
• Any RDF graph query can be interpreted as a
  logical conjunctive formula
• Disjunction cannot be expressed.

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RDF-QEL-2

• extend RDF-QEL-1 by disjunction
• need to use reified RDF statements, joined
  together in an AND-OR tree

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RDF-QEL-3 and higher

• RDF-QEL-3 conjunction, disjunction
• RDF-QEL-4 recursion to express linear recursive
  query definitions - SQL3
• RDF-QEL-5 further levels allow arbitrary
  recursive definitions

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An example query
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An example query
ltlibBook about"http//www.xyz.com/sw.html"gt ltdc
titlegtSoftware Engineeringlt/dctitlegt lt/libBookgt
ltlibBook about"http//www.xyz.com/ai.html"gt ltd
ctitlegtArtificial Intelligencelt/dctitlegt lt/libB
ookgt ltlibAI-Book about"http//www.xyz.com/pl.htm
l"gt ltdctitlegtProloglt/dctitlegt lt/libAI-Bookgt
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An example query

• Return all resources that are a book having the
  title Artificial Intelligence or that are an AI
  book.

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Edutella query in Conzilla
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Smart learning space