Linked Data - Connect Distributed Data across the Web

plenty of questions, more answers on their way...

General

What is Linked Data?

The Web enables us to link related documents. Similarly it enables us to link related data. The term Linked Data refers to a set of best practices for publishing and connecting structured data on the Web. Key technologies that support Linked Data are URIs (a generic means to identify entities or concepts in the world), HTTP (a simple yet universal mechanism for retrieving resources, or descriptions of resources), and RDF (a generic graph-based data model with which to structure and link data that describes things in the world).

(Contributor: Tom Heath, including excerpts from Bizer, Heath and Berners-Lee (2009) (PDF))

What is RDF?

RDF, the Resource Description Framework, is one of the key ingredients of Linked Data, and provides a generic graph-based data model for describing things, including their relationships with other things. RDF data can be written down in a number of different ways, known as serialisations. Examples of RDF serialisations include RDF/XML, Notation-3 (N3), Turtle, N-Triples, RDFa, and RDF/JSON.

(Contributor: Tom Heath)

Further reading:

What is the relationship between Linked Data and the Semantic Web?

Opinions on this topic do differ somewhat, however a widely held view is that the Semantic Web is made up of Linked Data; i.e. the Semantic Web is the whole, while Linked Data is the parts. Tim Berners-Lee, inventor of the Web and the person credited with coining the terms Semantic Web and Linked Data has frequently described Linked Data as "the Semantic Web done right", e.g. in these slides.

(Contributor: Tom Heath)

Further reading:

Linked Data? Web of Data? Semantic Web? WTF? - by Tom Heath

What is the Semantic Web really all about? - by Jim Hendler

What is the relationship between Linked Data and RDFa?

RDFa is one of several ways of writing down, or serialising, RDF data. Specifically, RDFa enables RDF data to be embedded in HTML documents, which makes it very useful for publishing RDF in contexts where Web publishing is limited to HTML, for example where a legacy content management system prevents publication in other formats. As simply another serialisation of RDF, RDFa is ideally suited to publishing Linked Data.

(Contributor: Tom Heath)

What is the relationship with Microformats?

coming soon...

Does all Linked Data need to be Linked Open Data?

In a word, no, and it will likely never be so. The label "Linked Open Data" is widely used, but often to refer to Linked Data in general, rather than to Linked Data that is explicitly published under an open license. Not all Linked Data will be open, and not all Open Data will be linked. Therefore care should be taken to use the appropriate term, depending on the licensing terms of the data in question.

(Contributor: Tom Heath)

How is Linked Data different from Web 2.0 mashups?

coming soon...

Creating Linked Data

How do I create Linked Data?

If you want to get started creating and publishing Linked Data, the definitive introductory resource is the tutorial How to Publish Linked Data on the Web, by Chris Bizer, Richard Cyganiak and Tom Heath.

• Does everything in my dataset need a URI?
• How do I create URIs for things in my dataset?
• Should I reuse existing URIs or create my own and set sameAs links?
• Should I make my URIs human readable?
• How do I discover URIs for a thing?
• Which URI should I choose if several are available?
• Which vocabularies should I use for describing my dataset?
• Where do I find vocabularies?
• How should I choose between two or more existing vocabularies for describing my dataset?
• Where do I find vocabularies?
• How do I make a vocabulary?
• Should I use RDFS or OWL?
• How do I create links between datasets?
• Do links need to be bidirectional?
• What is the role of rdfs:seeAlso?

Publishing Linked Data

How do I publish Linked Data?

See How do I create Linked Data? above...

Should I replace my Relational Database with a native Triple Store?

Which is the best RDF serialization for publishing RDF?

This depends on the context, as different serializations are better suited to different usage scenarios. For example, if humans need to read and write the data, then Turtle is probably the easiest serialization to use. For publishing data then RDF/XML is a good choice as it has widespread support in tools for consuming Linked Data. If the publishing infrastructure is limited to producing HTML documents, then RDFa is the preferred serialization. By contrast, if data needs to be interchanged between systems at large volumes, such as when producing data dumps that may be loaded into a triple store, N-Triples are typically the best choice as they can be processed in a streaming fashion, one line at a time, without loading the whole data file into memory.

(Contributor: Tom Heath)

How do I publish Linked Data from existing tools such as MediaWiki, Drupal, Wordpress, etc?

How can I validate that my Linked Data is published correctly?

Which organizations publish Linked Data?

How do I express licensing terms of a dataset?

What are the incentives for publishing Linked Data?

Datasets

• How many datasets are in the Linked Data cloud?
• How many are published by the dataset owners?
• How do you know that a dataset is reliable and trust?
• How do I discover a dataset on a particular topic?
• How do I know what links a dataset has?

Consuming Linked Data

In The Web, one huge database ... you'll find a screen-cast and examples how to consume linked data with SPARQL.

• How do I consume Linked Data?
• Can I combine Linked Open Data with private or closed data?

Linked Data Applications

In case you want to get an overview and introduction have a look at the Technical Report Linked Data Applications - The Genesis and the Challenges of Using Linked Data on the Web. There is also a maintained, live list of linked data apps available via ESW Wiki.

• What existing applications use Linked Data?

Business with Linked Data

• What is the business value of Linked Data?