Knowledge Representation Part VI Some more details when it comes to RDF etc Merging Graphs 3 When is a node in one graph the same node as a node in another graph In RDF this is solved ID: 556880
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1
Jan Pettersen Nytun, UiA
Knowledge RepresentationPart VI
Some more details when it
comes to RDF, etc.Slide2
Merging Graphs
[3]: When is a node in one graph the same node as a node in another graph
? In RDF, this is solved through the use of Uniform Resource Identifiers (URIs). Jan Pettersen Nytun, UIA, page 2Slide3
URIs Identify Web Resources
Web
addresses are the most common URIs, i.e., uniform Resource Locators (URLs).RDF resources are usually named
by
URI references (
URIrefs
).
URIref
= URI + optional fragment identifier at the end. E.g., http://www.example.org/people#tom were http://www.example.org/people = URL tom = fragment identifier http://www.example.org/people# = namespace
Jan Pettersen Nytun, UIA, page
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Jan Pettersen Nytun, UIA, page
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Graph MergingThe application is quite simple: A node from one graph is merged with a node from another graph—exactly, if they have the same URI.[ref. emanueledellavalle.org]:Slide5
Standard Namespace For RDF Predefined Terms
rdf:
Indicates identifiers used in RDF. The set of RDF identifiers is small. The global URI for the rdf namespace is: http://www.w3.org/1999/02/22-rdf-syntax-ns#If you open
http://
www.w3.org/1999/02/22-rdf-syntax-ns
(e.g., in Internet Explorer) you may see the list of RDF identifiers.
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RDF Identifier rdf:type
Jan Pettersen Nytun, UIA, page 6
[Ref. http://www.w3.org/TR/2014/REC-rdf-schema-20140225/]:Slide7
rdf:type
in http://www.w3.org/1999/02/22-rdf-syntax-ns
Jan Pettersen Nytun, UIA, page 7rdf:type is mostly being described by RDFS contructs,e.g., rdfs:domain.Slide8
Reification
In general: Taking
an abstract concept and making it concrete by having a proxy representing the abstract concept. Reification (computer science) from Wikipedia: …process …abstract idea about a computer program is turned into an explicit data model or other object created in a programming language. …By means of reification, something that was previously implicit, unexpressed,… is explicitly formulated and made available to conceptual (logical or computational) manipulation. Jan Pettersen Nytun, UIA, page 8Slide9
Reification Example 1
Many languages (e.g., Lisp) provide an
eval that effectively reifies the language interpreter.Jan Pettersen Nytun, UIA, page 9Slide10
Reification Example 2
Reification is widely used in conceptual modeling.
Reifying a relationship means viewing it as an entity. The purpose of reifying a relationship is to make it explicit, when additional information needs to be added to it.[ref Wikipedia]:Slide11
Reification In RDF - 1
Making an assertion (statement) about an assertion.
Example [4]: «Wikipedia says Shakespeare wrote Hamlet»Which express information about the statement: “Shakespeare wrote Hamlet”.The following triple does not cover this: :Shakespeare :wrote :Hamlet
.
How to do this?
Higher-order relationships may be used to solve this.
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HIGHER-ORDER RELATIONSHIPS
rdf:statement:
a triple with properties: rdf:subject, rdf:predicate, rdf:object rdf:subject, rdf:predicate, rdf:object : relate elements of statement tuple to a resource of type statement.Jan Pettersen Nytun, UIA, page 12Slide13
Reification In RDF - 2
“Wikipedia says Shakespeare wrote Hamlet
.”Using the RDF standard, we can refer to a triple as follows: q:n1 rdf:subject lit:Shakespeare; rdf:predicate lit:wrote; rdf:object lit:Hamlet. web:Wikipedia m:says q:n1.
Jan Pettersen Nytun, UIA, page
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Reification In RDF - 3
[4]: This
kind of metadata about statements often takes the form of provenance (information about the source of a statement, as in this example), likelihood (expressed in some quantitative form like probability, such as It is 90 percent probable that Shakespeare wrote Hamlet), context, or time frame… In such cases, it is useful to explicitly make a statement about a statement.
This
process is called
explicit
reification.
Jan Pettersen Nytun, UIA, page
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Another Example
Jan Pettersen Nytun, UIA, page 15
Explicit reification uses three properties,rdf:subject, rdf:predicate, and rdf:object, to define the three elements of a triple, and then assigns a URI to the triple. For example,
news:12345
rdf:subject
bb:WhiteyFord
;
rdf:predicat ebb:playsPosition; rdf:object bb:Pitcher.news:NewYorkTimes news:reports news:12345.Reification is an important concept, since assertions often need to be made as to the source, date, confidence, etc. of assertions in the domain of
discourse.
[ref. http://
franz.com/agraph/cresources/white_papers/SemWeb-Language-Primer.pdf]:Slide16
Ordered information in RDF
[4]: RDF provides a facility for ordering elements in a list format.
E.g., In Turtle:lit:Shakespeare b:hasChild (b:Susanna b:Judith b:Hamnet).This translates into the following triples, where
_:a
,
_:b
, and
_:c
are bnodes: lit:Shakespeare b:hasChild _:a. _:a rdf:first b:Susanna. _:a rdf:rest _:b. _:b rdf:first b:Judith. _:b rdf:rest _:c. _:
c rdf:rest rdf:nil.
_:
c rdf:first b:Hamnet
.
Jan Pettersen Nytun, UIA, page
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References
[1] David Poole and Alan
Mackworth, Artificial Intelligence: Foundations of Computational Agents, Cambridge University Press, 2010, http://artint.info/[2] http://www.w3.org/TR/swbp-n-aryRelations/[3] RDF 1.1 Primer, W3C Working Group Note, 24 June 2014[4] Semantic Web for the Working Ontologist, Second Edition: Effective Modeling in RDFS and OWL, May 20, 2011, by Dean
Allemang
,
James
Hendler
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