Architectural Guidelines for Naming

1.   Architecture of the World Wide Web

• A grandiose concept
  • In practice an ongoing post-hoc analysis project with respect to a vast, messy, poorly delimited real-world phenomenon
• A document
  • The first publication from the Technical Architecture Group of the W3C (World Wide Web Consortium)
  • Architecture of the World Wide Web, Volume One
  • The goal of the document is to "preserve [the properties underlying the success] of the information space as the technologies evolve"
  • It contains a number of "Principles, Constraints and Good Practice Notes"

2.   Grandmother observations about the Web

• "Global naming leads to global network effects"
  • A prerequisite for citation
  • A challenge for many existing schemes
• "To benefit from and increase the value of the World Wide Web, agents should provide [http:] URIs as identifiers for resources"
  • I.e. not just any global name, but a particular kind of global name

3.   A terminological pause

• URIs identify resources
• Resources whose essential characteristics can by stored and transmitted over the Web are information resources
• Servers may deliver representations of information resources in messages in response to requests.
• [The ontological sophistication of this picture is modest, compared to e.g. Goodman or FRBR, but it has proved to be of reasonable utility none-the-less]
• Another way to look at this is that for information resources, the retrievable representations are (isomorphic to) the information resource itself -- consider
  • Beethoven's Symphony No. 6: http://downloads.bbc.co.uk/rmhttp/radio3/symphony6_beethoven_radio3.mp3
  • The Charge of the Light Brigade: http://eserver.org/poetry/light-brigade.html
  • The XML 1.0 Recommendation: http://www.w3.org/TR/REC-xml/
  • The W3C at 10 logo: http://www.w3.org/2004/09/logos/W3C10_logo_short_fc.png

4.   Back to grandma

• It's good for the ownership of a name (URI) to be manifest in the form of that URI
  • We need to know who is responsible for the name and its use
• "A URI owner should not associate arbitrarily different URIs with the same resource."
• "Agents do not incur obligations by retrieving a representation."
  • HTTP 'GET' is side-effect free (c.f. cookies)
• "A URI owner should provide representations of the resource it identifies"

5.   More on terminology and technology

• Retrieved representations are always accompanied by one crucial kind of metadata:
  • Its media type, e.g.
    • text/html
    • image/png
    • audio/mp3
    • See the IANA registry for a full list
  • That is, information sufficient to enable an agent to interpret the representation.
    • Some agents, e.g. web browsers, present the interpreted representations to human beings
    • Others, e.g. search engines, process the interpreted representations automatically for their own purposes
  • Retrieval may involve content negotiation
    • When multiple representations are available
      • JPG vs. PNG vs. SVG vs. GIF . . .
      • French vs. German vs. Chinese vs. . . .
      • DTD vs. XML Schema vs. . . .
• So information resources are not necessarily concrete
  • It's perfectly coherent to get real value from a URI which indentifies an abstraction
  • For example, http://www.guardian.co.uk/uklatest

6.   Connection with "persistent indentifiers"

• The TAG is concerned not only to protect the Web as it is
  • but also to extend its reach and value
• This often amounts to strenuous efforts to combat the NIH syndrome
  • It's so hard to accept that the solution to your problem is already available, off the shelf, but with someone else's name on it
• "No scheme or syntax guarantees persistence of any kind" (John Kunze most succinctly, but many others today)
  • Accordingly persistent identifier efforts can and should save huge amounts of fuss by focussing on the non-technology substrate issues involved in producing persistence
  • Just use http: URIs as the technology substrate

7.   Lookup plus hierarchy

• Virtually all public distributed naming system proposals we have seen have these properties
  • Some kind of global lookup to establish a context
  • Some kind of navigation through a structured space determined by that context
• These properties address the fundamental needs of such a naming system
  • It's distributed (no single central source of name bindings)
  • It's scalable (no intrinsic upper bound on what can be named)
• The http URI scheme is such a system
  • The domain name part (e.g. www.w3.org) can be resolved by appeal to a distributed lookup mechanism (DNS)
  • The path part (e.g. /2001/tag/webarch/) provides for scalable navigation to a particular name binding within that context
• There are huge benefits to using an existing, well-tried approach, that is, http URIs
  • So you need a very good reason to attempt to launch a new public distributed naming story

8.   (Parenthesis on distributed, secure and human-readable)

• You can have any two :-(
• See SFS (Self-certifying File System)
• The simplest kind of secure names are names which include a one-way unique hash of the thing that they name.

9.   Versioning and extensibility

• The scandal of computer science
• None-the-less, try not to forget that none of what you build will last forever
  • or even until next year

10.   Some folk wisdom

• The Web works because you can
  • View Source
  • Follow your nose
  • Write URIs on the side of a bus
  • Use generic tools
  • Redirect, cache and proxy
• The Web is hands-down the most successful distributed name-based system the world has yet seen
  • Postal addresses and the telephone system are not counterexamples
• Ergo anyone designing a persistent identifier system should start from the assumption that http: URIs are sufficient for their technology needs.