Although this is not an apple to apple comparison and there is significant overlap i would like to know examples or specific cases where a data set falls into either category but not both. Can data be still called linked if it has a certain structure but is not a part of open web ?

up vote 18 down vote accepted

Data can be open but not linked, or linked but not open.

"Linked data" refers to data that is machine readable, semantic data, that a machine can 'understand'. The "semantic meaning" comes from the links, hence the names. "Open Data" refers to data that is accessible to anyone (e.g. without monetary cost to access) with a permissive license on reuse (e.g. public domain or CC0).

Development in linked data usually focuses on tools that provide meaning to data as microdata, RDFa, or RDF, and ontologies that provide meaning of terms. Open data focuses instead on tools that allow users to access the data conveniently, focusing on tools such as RESTful APIs, and formats that allow a user to query and subset data such as JSON or XML.

Tim Berners-Lee suggested this five star rating system to help think about linked data:

★ make your stuff available on the Web (whatever format) under an open license

★★ make it available as structured data (e.g., Excel instead of image scan of a table)

★★★ use non-proprietary formats (e.g., CSV instead of Excel)

★★★★ use URIs to denote things, so that people can point at your stuff

★★★★★ link your data to other data to provide context

In Tim's system, five-star linked data has to be open (first star, also open format, third star); The linking is really in stars four and five.

By contrast, most open data systems provide the first three stars (e.g. a RESTful API providing data in JSON format), but don't necessarily hit the fourth and fifth star. From this we might surmise that all linked data is open data, while all open data is not linked data.

One could arguably claim that they provide linked data (URIs, links to other data) behind some proprietary firewall for internal use only, and thus it is not open data.

  • Great info for linked-data tag wiki... – batpigandme May 22 '13 at 21:43
  • Tim's 5 star system is designed as a recommended step-by-step route to improving your data. I believe he (nor anyone else in linked data) claim that linked data has to be open. Two closed datasets can be linked together and that might well be a useful thing in a closed environment. – D Read May 24 '13 at 20:27
  • @DRead I believe my answer reflects that. You can follow the conditions stars 4 & 5 without getting star 1. However it quite clear that stars 1 & 3 emphasize openness. I'm not saying the closed environment version wouldn't count as linked data would be linked data, but it wouldn't get all 5 stars. – cboettig May 24 '13 at 21:28
  • 1
    @cboettig Your point might be expressed better as "Tim encourages people to make their data both linked and open". Which is sort of related to the question of whether being linked demands it being open, but actually I think is more of a red herring. – D Read May 28 '13 at 8:58

The Linked Data FAQ suggests that the 'open' portion has to do with licensing:

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)

"Open data" is data that is available for anyone to use, reuse and redistribute (see the Open Definition for more details and a precise description of the requirements for open data).

It therefore requires data to be available and either in the public domain or under license conditions that allow the user to use the data how they want without restriction (see for example the Open Data Handbook)

"Linked data" refers to datasets that make use of unambiguous identifiers that allow elements or relations in different datasets to be identified as referring to the same thing.

Big-L big-D Linked Data is often associated with the use of identifiers that take the form of URIs that, if dereferenced/resolved, displays a page that describes that thing. In addition, big-L big-D Linked Data data models often take the form of data triples that relate one entity to another via a relation and are serializable as RDF (or similar format like n3 or turtle).

So:

  • any kind of data (whether linked or otherwise) can be open data if is available and appropriately licensed.
  • Linked Data is more about the format of the data and, in particular, use of URIs as identifiers, use of triples and use of RDF or similar serialization
  • Linked Data need not be Open Data and Open Data need not be Linked Data
  • Open Data that is Linked Data is usually referred to as Linked Open Data

For more information, see Linked Data vs Open Data vs RDF Data

The currently unanswered part of your question is:

I would like to know examples or specific cases where a data set falls into either category but not both

Open but not Linked: Road Safety data. Open because the licence is open (OGL in this case). This is one chosen from many thousands on open data sites across the world.

Linked but not Open: (a much more interesting question!) BBC Sport's website is based on a Linked Data triple store, queried with SPARQL (e.g. Usain Bolt is linked to his news stories, linked to his results, linked to the medal table). Very cool stuff. But as far as I know (correct me if I'm wrong), the data is not Open (i.e. not openly licensed).

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