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 :-)
Related
-
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 .