rdf briefing
DESCRIPTION
A non-technical explanation of the main ideas and notions in RDF and RDF SchemaTRANSCRIPT
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RDF Briefing
Frank van HarmelenVrije Universiteit Amsterdam
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W3C StackXML:
• Surface syntax, no semanticsXML Schema:
• Describes structure of XML documentsRDF:
• Datamodel for “relations” between “things”RDF Schema:
• RDF Vocabulary Definition LanguageOWL:
• A more expressive Vocabulary Definition Language
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Meta-data
<name>
<symptoms>
<drug>
<drugadministration>
<disease>
<treatment>
IS-A
alleviates
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Meta-data in XML
syptos
drug
drugdstrto
dss
trtt
ts
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Meta-data in RDF
syptos
drug
drugdstrto
dss
<trtt>
IS-A
ts
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Bluffer’s guide to RDF (1)Object ->Attribute-> Value
triples
objects are web-resourcesValue is again an Object:
• triples can be linked• data-model = graph
pers05 ISBN...Author-of
pers05 ISBN...Author-of
MIT
ISBN...
Publ-by
Author-of Publ-
by
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Bluffer’s guide to RDF (2) Every identifier is a URL
= world-wide unique naming
Has XML syntax
Any statement can be an object• graphs can be nested
pers05 ISBN...Author-of
NYT claims
<rdf:Description rdf:about=“#pers05”> <authorOf>ISBN...</authorOf></rdf:Description>
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What does RDF Schema add?
• Defines vocabulary for RDF• Organizes this vocabulary in a
typed hierarchy• Class, subClassOf, type• Property, subPropertyOf• domain, range
Person
Author Reader
subClassOfsubClassOf
Lynda
type
communicatesTodomain range
Frank
type
communicatesTo
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RDF(S) have a (very small) formal semanticsDefines what other statements are
implied by a given set of RDF(S) statements
Ensures mutual agreement on minimal contentbetween parties without further contact
In the form of “entailment rules”Very simple to compute
(and not explosive in practice)
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RDF(S) semantics: examplesAspirin isOfType Painkiller
Painkiller subClassOf Drug Aspirin isOfType Drug
aspirin alleviates headachealleviates range symptom headache isOfType symptom
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RDF(S) semantics: examplesspr isOfType rr subClassOf rug spr isOfType rug
sprtsdtrts range sypto d isOfType sypto
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RDF(S) semanticsX R Y + R domain T X IsOfType TX R Y + R range T Y IsOfType TT1 SubClassOf T2 +
T2 SubClassOf T3 T1 SubClassOf T3
X IsOfType T1 +T1 SubClassOf T2 X IsOfType T1
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RDF(S) syntax: graphicsTurtle<http://sem-web-primer>
"Semantic Web Primer"
"Frank van Harmelen"
http://www.cs.vu.nl/~frankh
dc:title
fullname
homepage
dc:author
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RDF(S) syntax: XML
<rdf:RDF> <rdf:Description rdf:about="http://sem-web-primer" dc:title="Semantic Web Primer"> <dc:author> <rdf:Description fullname="Frank van Harmelen"> <homePage rdf:resource="http://www.cs.vu.nl/~frankh"/> </rdf:Description> </dc:author> </rdf:Description></rdf:RDF>
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RDF(S) syntax: Turtle
<http://sem-web-primer> dc:title "Semantic Web Primer" ; dc:author [ fullname "Frank van Harmelen"; homePage <http://www.cs.vu.nl/~frankh> ] .
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RDF(S)/XML relationshipXML is a just a syntax for RDF(S)
• (one of many)RDF(S) assigns meaning to some
terms• (XML doesn't)
This allows greater interoperability:• tools/tools• thesaurus/thesaurus• tools/thesaurus
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RDF(S)/XML relationshipAll identifiers are URL's
• Allows total decoupling of • document• thesaurus• meta-data
[<x> IsOfType <T>]
differentowners & locations
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Work by Heiner Stuckenschmidt@VUand Maria Taboada@Santiago
1. Converted EMTREE to RDF(S)2. Load into existing RDF(S) editor
(Protégé)3. Use existing RDF(S) wrapper for UMLS4. Deploy existing linguistic term mapper
RDF(S) interoperability:example: EMTREE UMLS
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RDF(S) interoperability:example: EMTREE UMLS
24305 EMTREE pref.names unique UMLS concept
2051 EMTREE pref.names multiple UMLS concepts
20071 EMTREE pref. name no UMLS concepts
34332 EMTREE pref. names + synonyms some UMLS concept(s): 74%
Effort = days
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RDF(S)/XML conversionstep-wise process description existshardest part is:
• mentally re-engineering the thesaurus model
make this model as sharable as possible
RDF does, XML doesn't
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Summary in quotes"RDF developers focus on its non-anglebracketty abstract information model rather than its representation in markup"
"RDF developers focus on its non-anglebracketty abstract information model rather than its representation in markup"
"the RDF information model is couched in terms of "resources" (aka things, objects, entities...) and their "properties" (aka relationships)"
"the RDF information model is couched in terms of "resources" (aka things, objects, entities...) and their "properties" (aka relationships)"
"RDF offers XML tools a way of being explicit about the content of (some subset of) XML documents"
"RDF offers XML tools a way of being explicit about the content of (some subset of) XML documents"
"RDF can be used to represent the claims implicit in XML Linking elements […] we can think about the resulting RDF data as a characterisation of what the XML was telling us"
"RDF can be used to represent the claims implicit in XML Linking elements […] we can think about the resulting RDF data as a characterisation of what the XML was telling us"
"RDF cares about the messages encoded in XML, not about the specific form of their encoding in elements and attributes"
"RDF cares about the messages encoded in XML, not about the specific form of their encoding in elements and attributes"
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Summary in quotes
"There is no algorithm for merging two XML Infosets, to enable us to pool knowledge acquired from diverse sources. The RDF information model, by constrast, was designed with data aggregation (rather than structured documents) in mind. Merging RDF data is trivial: add the triples extracted from two RDF/XML documents, and store them in a new one."
"There is no algorithm for merging two XML Infosets, to enable us to pool knowledge acquired from diverse sources. The RDF information model, by constrast, was designed with data aggregation (rather than structured documents) in mind. Merging RDF data is trivial: add the triples extracted from two RDF/XML documents, and store them in a new one."
syntactically…
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Things RDF(S) can’t doequalityenumerationnumber restrictions
• Single-valued/multi-valued• Optional/required values
inverse, symmetric, transitiveboolean algebra
• Union, complement…
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OWL: more expressivity
Full
DL
Lite
OWL Full Allow meta-classes etc
OWL DLNegationDisjunctionFull CardinalityEnumerated types
OWL Light(sub)classes, individuals(sub)properties, domain, rangeconjunction(in)equalitycardinality 0/1datatypesinverse, transitive, symmetrichasValuesomeValuesFromallValuesFrom
RDF Schema
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OWL also has a formal semantics
Defines what other statements are implied by a given set of statements
Ensures mutual agreement on content(both minimal and maximal)between parties without further contact
Can be used for integrity/consistency checking
Hard to compute (and rarely/sometime/always explosive in practice)
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OWL semantics: minimalvanGogh isOfType Impressionist
Impressionist subClassOf Painter vanGogh isOfType Painter
vanGogh painter-of sunflowerspainter-of domain painter vanGogh isOfType painter
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OWL semantics: maximalvanGogh isOfType Impressionist
Impressionist disjointFrom Cubist NOT: vanGogh isOfType Cubist
painted-by has-cardinality 1sun-flowers painted-by vanGoghPicasso different-individual-from vanGogh NOT: sun-flowers painted-by Picasso