Kingsley Idehen's Blog Data Space

As per usual I am writing this post with the aim of killing a number of meme-birds with a single post in relation to the emerging Linked Data Web.

*On* the ubiquitous Web of "Linked Documents", HREF means (by definition and usage): Hypertext Reference to an HTTP accessible Data Object of Type: "Document" (an information resource). Of course we don't make the formal connection of Object Type when dealing with the Web on a daily basis, but whenever you encounter the "resource not found" condition notice the message: HTTP/1.0 404 Object Not Found, from the HTTP Server tasked with retrieving and returning the resource.

*In* the Web of "Linked Data", a complimentary addition to the current Web of "Linked Documents", HREF is used to reference Data Objects that are of a variety of "Types", not just "Documents". And the way this is achieved, is by using Data Object Identifiers (URIs / IRIs that are generated by the Linked Data deployment platform) in the strict sense i.e. Data Identity (URI) is separated from Data Address (URL). Thus, you can reference a Person Data Object (aka an instance of a Person Class) in your HREF and the HTTP Server returns a Description of the Data Object via a Document (again, an information resource). A document containing the Description of a Data Object typically contains HREFs to other Data Objects that expose the Attributes and Relationships of the initial Person Data Object, and it this collection of Data Objects that is technically called a "Graph" -- which is what RDF models.

What I describe above is basic stuff for anyone that's familiar with Object Database or Distributed Objects technology and concepts.

URI and URL confusion

The Linked Document Web is a collection of physical resources that traverse the Web Information Bus in palatable format i.e documents. Thus, Document Object Identity and Document Object Data Address can be the same thing i.e. a URL can serve as the ID/URI of a Document Data Object.

The Linked Data Web on the other hand, is a Distributed Object Database, and each Data Object must be uniquely defined, otherwise we introduce ambiguity that ultimately taints the Database itself (making incomprehensible to reasoning challenged machines). Thus we must have unique Object IDs (URIs / IRIs) for People, Places, Events, and other things that aren't Documents. Once we follow the time tested rules of Identity, People can then be associated with the things they create (blog posts, web pages, bookmarks, wikiwords etc). RDF is about expressing these graph model relationships while RDF serialization formats enables the information resources to transport these data object link ladden information resources to requesting User Agents.

Put in more succinct terms, all documents on the Web are compound documents in reality (e.g. mast contain a least an image these days). The Linked Data Web is about a Web where Data Object IDs (URIs) enable us to distill source data from the information contained in a compound document.

Examples:

1. <http://community.linkeddata.org/dataspace/person/kidehen2#this> - the ID (URI minted from URL via addition of #this) of a Data Object of Type Person that Identifies me. The Person definition I use comes from the FOAF vocabulary/schema/ontology/data dictionary
2. <http://community.linkeddata.org/dataspace/person/kidehen2> - the URI (also a URL) of a FOAF file that contains a description of the Data Object ID: <http://community.linkeddata.org/dataspace/person/kidehen2#this> (me)
3. As an information resource <http://community.linkeddata.org/dataspace/person/kidehen2> can be dispatched from an HTTP server to a User Agent in (X)HTML, RDF/XML, N3/Turtle representations via HTTP Content Negotiation (note: Look at the "Linked Data" tab to see one example of what Data Links facilitate re. Data Discovery and Exploration)
4. If I choose an Object ID of <http://community.linkeddata.org/dataspace/person/kidehen2/this> instead of <http://community.linkeddata.org/dataspace/person/kidehen2#this> then the HTTP Server should not return an information resource (i.e provide 200 OK response) when a User Agent requests a resource via HTTP using the URI: <http://community.linkeddata.org/dataspace/person/kidehen2/this>, because a Data Object ID (URI) and the Data Object Address (URL) cannot be the same when my Data Object isn't of Type Document; the sever has to use response code 303 to redirect the user agent to the URL of an information resource that matches the Content-type designated in the HTTP Request or determine representation based on it's own quality of service rules for the information resource associated with the Object ID (URI).

The degree of unobtrusiveness of new technology, concepts, or new applications of existing technology, is what ultimately determines eventual uptake and meme virulence (network effects). For a while, the Semantic Web meme was mired in confusion and general misunderstanding due to a shortage of practical use case scenario demos.

The emergence of the SPARQL Query Language has provided critical infrastructure for a number of products, projects, and demos, that now make the utility of the Semantic Web vision mush clearly via the simplicity of Linked Data, as exemplified by the following:

1. Linking Open Data Community - collection of People and Linked Data Spaces (across a variety of domains)
2. DBpedia - Ground zero for experiencing and comprehending Linked Data
3. OpenLink Data Spaces - a simple solution for creating Linked Data Web presence via from existing Web Data Sources (Blogs, Wikis, Shared Bookmarks, Tag Spaces, Web Sites, Social Networking Services, Web Services, Discussion Forums etc..)
4. OpenLink Virtuoso - a Universal Server for generating, managing, and deploying RDF Linked Data from SQL, XML, Web Services based data sources

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