Introduction to RDF Data Model.

1. Introduction to the
RDF Data Model
Sources:
Ian Davis (Talis),
Prof. Praveen Rao (UMKC),
http://rdfabout.com/
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2. Introduction
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RDF stands for Resource Description Framework
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Companies developing RDF storage solutions
AllegroGraph, Virtuoso, BigOWLIM, Garlik 4store/5store, Mulgara, etc.
Companies managing data using RDF model
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W3C spec: http://www.w3.org/RDF/
1st spec in 1999, current standard from 2004
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Is a data model (like XML)
BBC, Google, Yahoo!, Best Buy, Newsweek, Pfizer, etc.
http://data.nytimes.com/home/about.html
To allow anyone to say anything about anything
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3. The Relational Model
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4. RDF Data Model
• RDF represents data as (s,p,o) triples
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s means subject, p means predicate or property, o means object
Can represent any assertion
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An assertion may or may not be a fact
Together, triples form a directed, labeled graph
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5. Example
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6. Example
• Relationship between entities/resources
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7. Global Naming
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URIs (!= URLs) provide the ability to identify things globally
and uniquely
RDF names things/resources with URIs
Can name infinite number of things using URIs
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Can use the fragment identifier ‘#’
Create different URIs for different things
If two users refer to the same URI, then they are talking
about the same thing
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8. RDF Graphs
• Can have named things, literals (text or numeric
values), named relations/properties, unnamed things…
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9. RDF Graphs
• Subjects can be URIs or unnamed
(a.k.a blank nodes)
• Predicates are URIs
• Objects can be URIs, literals, or unnamed
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10. Merging RDF Graphs
• Graphs from different sources can be merged
• Nodes with the same URI are considered identical
• Blank nodes can be kept separate
• Any RDF graph can be merged with any other RDF graph
• Any number of RDF graphs can be merged
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11. Example (1/2)
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12. Example (2/2)
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13. RDF vs. RDBMS
• Relational (RDBMS) model
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Separate databases with own schemas
Table row: assertion that relation is true for values in row
SELECT query: filter on assertions for given conditions
A relation is true (row exists) or false
• RDF model
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(Semantic) Web: a single giant graph database
s, p, o identified uniquely with URIs across the web
A relation is true (triple exists) or is unknown
• RDF more like OO model than RDBMS
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14. RDF vs. RDBMS example
foaf:name (predicate/property)
subject
object
_:personA
“John”
_:personB
“Jane”
_:personC
“Fred”
RDF triples expressed as binary relations in RDBMS
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15. RDF vs XML
• Not another XML format
• XML means
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Angle-brackets-slashes notation (think HTML)
Data model: tree (DAG) with different nodes
(elements, attributes)
• RDF means
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Notation: RDF/XML, Turtle, N-triples etc.
Data model: directed graph, uses URIs
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16. RDF Formats
• All are plain-text serialization formats
• RDF/XML: XML notation
• Notation3 (N3): superset of TTL, beyond RDF
• Turtle (TTL): subset of N3, used only for RDF
• N-Triples (NT), N-Quads (NQ): subset of TTL and N3
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Simpler/minimal
Easier to parse/generate
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17. Turtle
• Terse RDF Triple Language (TTL)
• Triples are terminated with a full stop
• URIs are enclosed in angle brackets (< and >)
• Literals are enclosed by double quotes
• <http://example.com/thing>
<http://example.com/relation> “Hello World" .
• Use @PREFIX to shorten URIs
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@PREFIX ex: <http://example.com/> .
ex:thing ex:relation “Hello World" .
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18. Turtle: Same Subject
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation "Some Text" .
ex:thing ex:otherrelation ex:otherthing .
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation "Some Text" ;
ex:otherrelation ex:otherthing .
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19. Turtle: Same Subject-Predicate
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation "Some Text" .
ex:thing ex:relation ex:otherthing .
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation "Some Text" ,
ex:otherthing .
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20. Turtle: Blank Node
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation _:a .
_:a ex:property "foo" .
_:a ex:property "bar” .
• Use _: followed by a label
• ‘a’ is the label – valid only within that particular RDF
document
• If _a: appears in a different document, it would refer
to a different node
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21. Turtle: Literals
• Literals can have a language
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation "Hello"@en .
ex:thing ex:relation "Bonjour"@fr .
• Literals can have a datatype
@PREFIX ex: <http://example.com/> .
ex:thing ex:relation "49"^^<http://www.w3.org/2001/XMLSchema#int> .
• But not both!
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22. Vendor 1:
Vendors example
vendor1:productX
dc:title "Cool-O-Matic" .
vendor1:productX
retail:price
vendor1:productX
vendor1:partno
vendor1:productY
dc:title "Fluffertron" .
vendor1:productY
retail:price
vendor1:productY
vendor1:partno
"$50.75" .
"TTK583" .
"$26.50" .
"AAL132" .
Vendor 2:
vendor2:product1
dc:title "Can Closer" .
vendor2:product2
dc:title "Dust Unbuster" .
Reviewer 1:
vendor1:productX
dc:description "This product is good buy!" .
Reviewer 2:
vendor2:product2 dc:description "Who needs something to unbust dust?
A dust buster would be a better idea,
and I wish they posted the price." .
vendor2:product2 review:rating review:Excellent .
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23. Links
• Government (US, UK), Wikipedia, World Bank, U.S.
Census, U.S. SEC, NYTimes, etc.
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http://www.w3.org/wiki/DataSetRDFDumps
http://data.nytimes.com/
http://data.gov.uk/
• http://librdf.org/parse
• http://www.rdfabout.com/demo/validator/
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