W3C logo
slanted W3C logo

									 Cover page images (keys)

Identifying Resources on the Web and Beyond

Felix Sasaki, <fsasaki@w3.org>

This presentation



I am responsible for the materials and opinions expressed in this talk. I do not claim that there is consensus about them within W3C.

Key background documents

Published by the W3C Technical Architecture Group (TAG)



Key concepts: URIs, Resources, Representations

Resource, URI, Representation

Three architectural bases of the Web

Can http: URIs be used for things which are not web pages?

Example: An http: URI for Alice

The 303 HTTP response code helps to identify Alice as a person, and to provide RDF data about her (for machines) or a Web page:

The 303 URI solution

(From Cool URIs for the Semantic Web)

Dereferencing http: URIs? Not always


Do I need to invent a new scheme?



If at all possible, please don't:


Metadata used during HTTP-based interaction to decide about representations

Media type information in the HTTP content-type header tells a user agents what type of content to expect:

Metadata - who has precedence?

(From The use of Metadata in URIs)

Metadata in URIs: Document your Assignment Policies

"For the best weather information for your city, visit http://example.org/weather/your-city-name-here."


(From The use of Metadata in URIs)

Identification of related resources with the same http: URI

GET /weather/
Host: example.org
Accept: text/html
Accept-Language: de, en

Identification of related resources with various http: URIs


(Based on On Linking Alternative Representations To Enable Discovery And Publishing)

Identification of related resources via RDDL

RDDL example

From the W3C namespace document for ITS 1.0

<p>This document describes the namespace of the
    id="Core_Spec" xlink:title="Internationalization Tag Set (ITS) Version 1.0"
xlink:type="simple" xlink:show="none" xlink:actuate="none">
<a href="http://www.w3.org/TR/2007/REC-its-20070404/">
Internationalization Tag Set (ITS) Version 1.0</a></rddl:resource>
specification (November 2006 version).[...]</p>


[http:] URI Persistence - a social challenge

From URNs, Namespaces and Registries:

"URIs don't change: people change them." (Tim Berners-Lee)

Examples of policies related to persistence in W3C

Various policies and guidelines:

Example tools for checking persistence of W3C resources

Persistency policies for URIs in various organizations

http: URIs are cheap! Too cheap?

Persistence, Delegation and URIs

How to assure persistent access of representations of resources? Proposals from Henry Thompson:

  1. Delegation as centralisation ("Put all your eggs in one basket, and watch that basket!"): all participants in the community agree on one repository for representations and one domain name
  2. Delegation as replication ("Split up, one of us is bound to survive!") via two lookups:
    • naming-system-specific naming authority; implements the
    • second lookup, which identifies the repository

After all:


How to identify various resource types and sub resources?

Internationalization of identifiers

URIs (not only http: URIs) have found some answers to these questions over the years

Identifiers for objects versus identifiers for services



Personal conclusion about persistent identifiers on the Web