The URI, URL, and Linked Data Meme's Generic HTTP URI (Updated)

Situation Analysis

As the "Linked Data" meme has gained momentum you've more than likely been on the receiving end of dialog with Linked Open Data community members (myself included) that goes something like this:

"Do you have a URI", "Get yourself a URI", "Give me a de-referencable URI" etc..

And each time, you respond with a URL -- which to the best of your Web knowledge is a bona fide URI. But to your utter confusion you are told: Nah! You gave me a Document URI instead of the URI of a real-world thing or object etc..

What's up with that?

Well our everyday use of the Web is an unfortunate conflation of two distinct things, which have Identity: Real World Objects (RWOs) & Address/Location of Documents (Information bearing Resources).

The "Linked Data" meme is about enhancing the Web by unobtrusively reintroducing its core essence: the generic HTTP URI, a vital piece of Web Architecture DNA. Basically, its about so realizing the full capabilities of the Web as a platform for Open Data Identification, Definition, Access, Storage, Representation, Presentation, and Integration.

What is a Real World Object?

People, Places, Music, Books, Cars, Ideas, Emotions etc..

What is a URI?

A Uniform Resource Identifier. A global identifier mechanism for network addressable data items. Its sole function is Name oriented Identification.

URI Generic Syntax

The constituent parts of a URI (from URI Generic Syntax RFC) are depicted below:

What is a URL?

A location oriented HTTP scheme based URI. The HTTP scheme introduces a powerful and inherent duality that delivers:

Resource Address/Location Identifier
Data Access mechanism for an Information bearing Resource (Document, File etc..)

So far so good!

What is an HTTP based URI?

The kind of URI Linked Data aficionados mean when they use the term: URI.

An HTTP URI is an HTTP scheme based URI. Unlike a URL, this kind of HTTP scheme URI is devoid of any Web Location orientation or specificity. Thus, Its inherent duality provides a more powerful level of abstraction. Hence, you can use this form of URI to assign Names/Identifiers to Real World Objects (RWO). Even better, courtesy of the Identity/Address duality of the HTTP scheme, a single URI can deliver the following:

RWO Identfier/Name
RWO Metadata document Locator (courtesy of URL aspect)
Negotiable Representation of the Located Document (courtesy of HTTP's content negotiation feature).

What is Metadata?

Data about Data. Put differently, data that describes other data in a structured manner.

How Do we Model Metadata?

The predominant model for metadata is the Entity-Attribute-Value + Classes & Relationships model (EAV/CR). A model that's been with us since the inception of modern computing (long before the Web).

What about RDF?

The Resource Description Framework (RDF) is a framework for describing Web addressable resources. In a nutshell, its a framework for adding Metadata bearing Information Resources to the current Web. Its comprised of:

Entity-Attribute-Value (aka. Subject-Predictate-Object) plus Classes & Relationships (Data Dictionaries e.g., OWL) metadata model
A plethora of instance data representation formats that include: RDFa (when doing so within (X)HTML docs), Turtle, N3, TriX, RDF/XML etc.

What's the Problem Today?

The ubiquitous use of the Web is primarily focused on a Linked Mesh of Information bearing Documents. URLs rather than generic HTTP URIs are the prime mechanism for Web tapestry; basically, we use URLs to conduct Information -- which is inherently subjective -- instead of using HTTP URIs to conduct "Raw Data" -- which is inherently objective.

Note: Information is "data in context", it isn't the same thing as "Raw Data". Thus, if we can link to Information via the Web, why shouldn't we be able to do the same for "Raw Data"?

How Does the Link Data meme solve the problem?

The meme simply provides a set of guidelines (best practices) for producing Web architecture friendly metadata. Meaning: when producing EAV/CR model based metadata, endow Subjects, their Attributes, and Attribute Values (optionally) with HTTP URIs. By doing so, a new level of Link Abstraction on the Web is possible i.e., "Data Item to Data Item" level links (aka hyperdata links). Even better, when you de-reference a RWO hyperdata link you end up with a negotiated representations of its metadata.

Conclusion

Linked Data is ultimately about an HTTP URI for each item in the Data Organization Hierarchy :-)

History of how "Resource" became part of URI - historic account by TimBL
Linked Data Design Issues Document - TimBL's initial Linked Data Guide
Linked Data Rules Simplified - My attempt at simplifying the Linked Data Meme without SPARQL & RDF distraction
Linked Data & Identity - another related post
The Linked Data Meme's Value Proposition
So What Does "HREF" stand for anyway?
My Del.icio.us hosted Bookmark Data Space for Identity Schemes
TimBL's Ted Talk re. "Raw Linked Data"
Resource Oriented Architecture
More Famous Than Simon Cowell .

Comments

Re:The URI, URL, and Linked Data Meme's Generic HTTP URI

Kingsley,

Thank you for sharing the thoughts and the memo. They are very interesting. URI and URL are certainly confusing terms and we often mix them when using in real time. To migrate to the web of linked data, however, it seems the issue become critical for people to know well.

Another thought I have, however, is that we may have three, in contrast to two, fundamental definitions on describing the Web. The two well-known ones are data and service; or in RDF we define Class and Property respectively. Until now, we assert the third one---link---to be nothing but a special form of data. The reality is, however, that this special form is so special that we may consider to give it a little bit honor so that it becomes the third member of the fundamental building block of the Web. That is, a link is not a data, and nor is it a service, but a link. Or with respect to your post, a URI is not a data, but a form of link, PERIOD.

I believe that this distinction, once it is made, could be important as well as valuable. A trick thing here is that, following this distinction we can start to think of other forms of links that is beyond URI (which is just a binary model). By contrast, we may start to invent the links in higher order, such as the link of links (metalink) or the thread of links (group link). Be honest, if the Web is moving towards a web of linked data (and I believe so since the Web data is more and more interconnected), we must breakthrough this traditional thinking of the link model. The key is, however, from today we start to think link to be link but not a data.

Anyway, your posts are always thoughtful and knowledgeable. I appreciate reading them, as usual.

cheers,

yihong

Posted by Yihong Ding on 08/08/2009 14:42 GMT-0500

Re:The URI, URL, and Linked Data Meme's Generic HTTP URI

Yihong Ding wrote:

<<<

>>>>

Yihong,

Nice to hear from you! I still awaityourtriptoCambridge:-)

Yes,wehaveanewdimensiontotheWebthatmanifestsasa"specialkindoflink";

inaasense,we are talking about "links with metadata benefits".

Ultimately, It's all about a new kind of Hypermedia Link, but we need to find a way to get people to understand how and why this new kind of Link is the fundamental conduit to the "Mind Society" or in your words: Mind Asset oriented Web.

Let's see what we can do (collectively) re. simplification of this 3rd critical component of the Word Wide Web :-)

Posted by kingsley Uyi Idehen on 08/09/2009 13:26 GMT-0500

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