Named graph

Named graph
A Named Graph

Named graphs are a key concept of Semantic Web architecture in which a set of Resource Description Framework statements (a graph) are identified using a URI,[1] allowing descriptions to be made of that set of statements such as context, provenance information or other such metadata.

Named graphs are a simple extension of the RDF data model[2] through which graphs can be created but the model lacks an effective means of distinguishing between them once published on the Web at large.

Contents

Named graphs and HTTP

One conceptualization of the Web is as a graph of document nodes identified with URIs and connected by hyperlink arcs which are expressed within the HTML documents. By doing a HTTP GET on a URI (usually via a Web browser), a somehow-related document may be retrieved. This "follow your nose" approach also applies to RDF documents on the Web in the form of Linked Data, where typically an RDF syntax is used to express data as a series of statements, and URIs within the RDF point to other resources. This Web of data has been described by Tim Berners-Lee as the "Giant Global Graph".[3]

Describing a Named Graph

Named graphs are a formalization of the intuitive idea that the contents of an RDF document (a graph) on the Web can be considered to be named by the URI of the document. This considerably simplifies techniques for managing chains of provenance for pieces of data and enabling fine-grained access control to the source data. Additionally trust can be managed through the publisher applying a digital signature to the data in the named graph. (Support for these facilities was originally intended to come from RDF reification, however that approach proved problematic [4]).

Named graphs and RDF stores

While named graphs may appear on the Web as simple linked documents (i.e. Linked Data), they are also very useful for managing sets of RDF data within an RDF store. In particular, the scope of a SPARQL query may be limited to a specific set of named graphs.

Example

Assume the following (Turtle syntax RDF document has placed in a SPARQL-capable store with the name http://example.org/joe.

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
 
<http://example.org/joe#me> a foaf:Person .
<http://example.org/joe#me> foaf:homepage <http://example.org/joe/INDEX.html> .
<http://example.org/joe#me> foaf:mbox <mailto:joe@example.org> .
<http://example.org/joe#me> foaf:name "Joe Lambda" .

This data has been written in a more verbose form than necessary to show the triple structures

The homepage of the person with the email address mailto:joe@example.org can be obtained using the SPARQL query:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
 
SELECT ?homepage 
 
FROM NAMED <http://example.org/joe>
 
WHERE {
        ?person foaf:homepage ?homepage .
        ?person foaf:mbox <mailto:joe@example.org> .
}

The FROM NAMED here identifies the target graph for the query.

Named graphs and quads

Prior to the publication of the papers describing named graphs, there was considerable discussion about fulfilling their role within a store by using an arity above that of RDF triple statements. Where triples have the form <subject> <predicate> <object>, quads would have a form along the lines of <context> <subject> <predicate> <object>. Named graphs can be represented this way, as <graphname> <subject> <predicate> <object>, with the advantage that the <graphname> part will be a URI, giving the quad Web-global scope compared to arbitrary local statement names.

Formal definition

See.[5]

Specifications

There is currently no specification for named graphs in themselves beyond that described in[5] and[6] (which includes syntaxes for representing named graphs), however they do form part of the SPARQL Protocol and RDF Query Language specification.

See also

References

  1. ^ strictly speaking a URIRef
  2. ^ http://www.w3.org/TR/PR-rdf-syntax/ "Resource Description Framework (RDF) Model and Syntax Specification"
  3. ^ Giant Global Graph
  4. ^ Reification of RDF and N3)
  5. ^ a b Named Graphs, Provenance and Trust
  6. ^ TriX : RDF Triples in XML

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Graph theory — In mathematics and computer science, graph theory is the study of graphs : mathematical structures used to model pairwise relations between objects from a certain collection. A graph in this context refers to a collection of vertices or nodes and …   Wikipedia

  • Graph (mathematics) — This article is about sets of vertices connected by edges. For graphs of mathematical functions, see Graph of a function. For statistical graphs, see Chart. Further information: Graph theory A drawing of a labeled graph on 6 vertices and 7 edges …   Wikipedia

  • Named — BIND (Berkeley Internet Name Domain) Entwickler: ISC Aktuelle Version: 9.6.0 (7. Januar 2009) Betriebssystem: z. B. UNIX, NetBSD, FreeBSD, OpenBSD …   Deutsch Wikipedia

  • Graph continuous — In mathematics, and in particular the study of game theory, a function is graph continuous if it exhibits the following properties. The concept was originally defined by Partha Dasgupta and Eric Maskin in 1986 and is a version of continuity that… …   Wikipedia

  • Shrikhande graph — infobox graph name = Shrikhande graph image caption = The Shrikhande graph drawn symmetrically. namesake = S. S. Shrikhande vertices = 16 edges = 48 chromatic number = chromatic index = properties = Strongly regularThe Shrikhande graph is a named …   Wikipedia

  • Desargues graph — Named after Gérard Desargues Vertices 20 Edges 30 …   Wikipedia

  • Nauru graph — The Nauru graph is Hamiltonian. Vertices 24 Edges 36 Radius 4 …   Wikipedia

  • Turán graph — The Turán graph T(13,4) Named after Pál Turán v · …   Wikipedia

  • List of topics named after Leonhard Euler — In mathematics and physics, there are a large number of topics named in honour of Leonhard Euler (pronounced Oiler ). As well, many of these topics include their own unique function, equation, formula, identity, number (single or sequence), or… …   Wikipedia

  • Möbius–Kantor graph — Named after August Ferdinand Möbius and S. Kantor Vertices 16 …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”