You are currently browsing the tag archive for the ‘linked data’ tag.

Blank Node

A blank node is an unnamed node, whose name is set by the underlying RDF software and cannot be guaranteed to have the same name for different sessions. Within a graph, it is guaranteed to resolve to the same thing (not a resource/URI but a separate way to represent a node), and between graphs, “it would be incorrect to assume that blank nodes from different graphs having the same blank node identifiers are the same” (see RDF Primer). If you want multiple independent graphs to refer to the same resource, you have to give it an explicit URI.

The most authoritative source for named graphs (being a W3C Recommendation) is SPARQL. Serialization syntaxes, such as RDF/XML or Turtle, allow you to assign an explicit name (a “blank node identifier”) to a blank node, but this is only to distinguish between different blank nodes or to refer to the same blank node from different triples within the same graph. If you give the same blank node identifier to blank nodes in different graphs, these blank nodes are still different from each other; in fact, there will be no relationship or interaction between them at all.

 

Named Graph

Named Graphs is the idea that having multiple RDF graphs in a single document/repository and naming them with URIs provides useful additional functionality built on top of the RDF Recommendations.

Named Graphs turn the RDF triple model into a quad model by extending a triple to include an additional item of information. This extra piece of information takes the form of a URI which provides some additional context to the triple with which it is associated, providing an extra degree of freedom when it comes to managing RDF data. The ability to group triples around a URI underlies features such as: Tracking provenance of RDF data, Access Control and Versioning.

There’s some useful background available on Named Graph Provenance and Trust,  on Named Graphs in general in a paper about NG4J, and specifically on their use in OpenAnzo.

Named Graphs are an important part of the overall technical framework for managing, publishing and querying RDF and Linked Data, and its important to understand the trade-offs in different approaches to using them.

Advertisements

The Web is increasingly understood as a global information space consisting not just of linked documents, but also of linked data. The term Linked Data was coined by Tim Berners-Lee in his Linked Data Web architecture note. The goal of Linked Data is to enable people to share structured data on the Web as easily as they can share documents today. More specifically, Wikipedia defines Linked Data as “a term used to describe a recommended best practice for exposing, sharing, and connecting pieces of data, information, and knowledge on the Semantic Web using .

More than just a vision, the Web of Data has been brought into being by the maturing of the Semantic Web technology stack, and by the publication of an increasing number of datasets according to the principles of Linked Data. Today, this emerging Web of Data includes data sets as extensive and diverse as DBpedia, Geonames, US Census, EuroStat, MusicBrainz, BBC Programmes, Flickr, DBLP, PubMed, UniProt, FOAF, SIOC, OpenCyc, UMBEL and Yago. The availability of these and many other data sets has paved the way for an increasing number of applications that build on Linked Data, support services designed to reduce the complexity of integrating heterogeneous data from distributed sources, as well as new business opportunities for start-up companies in this space.

The basic tenets of Linked Data are to:

  • use the RDF data model to publish structured data on the Web
  • use RDF links to interlink data from different data sources

Applying both principles leads to the creation of a data commons on the Web, a space where people and organizations can post and consume data about anything. This data commons is often called the Web of Data or Semantic Web.

In summary, Linked Data is simply about using the Web to create typed links between data from different sources. It is important to know that Linked Data is not the Semantic Web, it’s the basement for it.

For more information, you may refer to:

The Tabulator Extension is an extension for Firefox that provides a human-readable interface for linked data. It is based on the Tabulator, a web-based interface for browsing RDF. Using Tabulator’s outline mode, query views, and back-end code, the Tabulator Extension integrates the browsing of linked data directly into the Firefox browser, making for a more natural and seamless experience when browsing linked data on the Web.

A primary goal of the Tabulator Extension is to explore how linked data could be displayed in the next generation of Web browsers. The Tabulator aims to make linked data human-readable by taking a document and picking out the actual things that the document describes. The properties of these things are the displayed in a table, and then the links in that table can be followed to load more data about other things in other documents.

A link to the latest version of the extension can be found on the Tabulator Extension site: The Tabulator Extension. Moreover, Tabulator is now hosted on addons.mozilla.org. If you download and install from there, it will provide automatic updates through the Firefox Addon Manager.

 

Once the extension file is downloaded, it should automatically install. After restarting Firefox, all documents served as application/rdf+xml and text/n3 (and for a while legacy documents served as text/rdf+n3) will be automatically loaded in the Tabulator’s outline view. It may be necessary to disable other RDF-related extensions that could override the Tabulator’s capture of these documents.

 

For more information, read this article : Tabulator: Exploring and Analyzing linked data on the Semantic Web