Are URIs really names?
Henry S. Thompson
School of Informatics, University of Edinburgh
Markup Systems
16 Oct 2010
1. Introduction
URIs are at the heart of the Web
Like much of the computational universe
- They arose pragmatically
- And were only specified after-the-fact
Their official definitions have never quite matched actual practice
- And this can cause problems
Three examples:
- The 'httpRange-14' issue
- The semantics of the HTTP response codes
- The composition of redirection and fragment identifiers
2. Why ask "Are URIs really names"?
One of the primary roles of "the philosophy of ..."
- Help the subject discipline by identifying parallels
- "Your problem is not new"
- And, good news, the solution is ...
- Alternatively, bad news, the prognosis is not good, sorry
Within the web community discussions about URIs use words such as 'identify' and 'denote', as well as 'name' itself
These are terms of art within the Philosophy of Language
- Is there a parallel here that can be helpful?
- Or is the implied connection mistaken and irrelevant?
- Or at worst even harmfully misleading?
3. A previously unsolved problem?
The status of names within the Philosophy of Language is by no means settled
We can identify at least three positions:
- Description
- A name is short for some collection of descriptive
properties which pick out its referent(s)
- Baptism
- A name is attached to its referent by a (typical
ostensive) act of baptism
- The result is then a so-called rigid designator
- Use
- The referent of a name is determined by its (evolving) use
by a community of speakers
4. The official story about URIs
There is a moderately clear official consensus about URIs
Here's a summary of the WebArch version:
- URIs are, as the third initial says, identifiers, that is, names.
- They identify resources
- They often (although not always) allow you to access representations of those resources.
(Here, as in WebArch, http:
URIs are the kind of URIs most
clearly in focus)
5. Parallel number 1
'Resource' names a role in a story, not an intrinsically distinguishable subset of things
- just as 'referent' does in ordinary language.
Things are resources because someone created a URI to identify them
- not because they have some particular properties in and of themselves
Things are referents because some word or phrase refers to them
- not because they have some particular properties in and of themselves
6. Representations?
'Representation' names a pair: a character sequence and a media type.
- The media type specifies how the character sequence should be interpreted
- For example JPG or HTML or MP3
would be likely media types for representations of, respectively
- an image of an apple
- a news report about an orchard
- a recording of a Beatles song
Just as, in order to
interpret utterances or enscriptions, we need to know the language they are expressed in
7. Russell or Kripke?
Compare this illustration from WebArch:
With a Fregean view
Or Kripkean view
On the face of it, the AWWW view seems to be very close to the Kripkean one.
- Even the terminology is parallel
- URIs are 'minted'
- New names are 'coined'
8. What about meaning-as-use?
This certainly looks attractive from the perspective of "computation in
the wild"
- Virtually all users of URIs do so in complete ignorance of the
official story
- And more to the point, an "experimental epistemology" would surely
emphasise behaviour, rather than reference or anything like it
- A URI is what you click on
- A URI is what you give a browser
- Even for the average sophisticated developer
- A URI is what you do an HTTP 'GET' with to retrieve [something]
Does the Wittgensteinian position distinguish names from any other kind
of referring expression?
Consider the XHTML namespace URI http://www.w3.org/1999/xhtml
- Jonathan Rees has argued that it will continue to be that
- Regardless of what, if anything, the W3C serve in response to
access requests to it
- At least in part because of what browsers and other user agent software will
do when they encounter that string in certain contexts
9. Resources and identity
Resources are not immutable
- Both in principle and in practice
The idea of a 'home page', whether for persons or institutions, has been
an important part of the Web since very near its beginning
And home pages not only may change
- They should change
- Out-of-date information is worse than no information at all
Some mutability is clearly part of e.g. the Kripkean story for names
- Venus has undoubtedly changed in many ways since the 19th century
- And living beings, those most literally baptised of all name-bearers,
change a lot
But, is the time-varying nature of the resource in some way too flexible for the rigid designator view?
- 'Henry the VIII' seems to be an acceptable rigid designator
- But I suspect http://www.lemonde.fr/ is not
10. The paradox
The thing which most distinguishes URIs from other referring symbols
- Namely that you can also use (some of) them to access representations
Is also the thing you can rely on the least
- In principle, the utility/relevance of the representation depends on
the good practice of the minter
- In practice, the persistence of the 'original' representation depends
on institutional continuity
11. Two Webs, two kinds of URIs?
Maybe we should treat OFW URIs as distinct from SemWeb URIs
- OFW for Old Fashioned Web
SemWeb URIs are (Kripkean moving towards Wittgensteinian) names
- You don't (or at least should not) access
representations from them
- Only their minter knows for sure what they mean
Namespace URIs and other "not accessed" URIs similarly
But most OFW URIs are not names
- There are generalisations to be made over their accessable representations
- But it's not in practice terribly helpful to think of them as
identifying those abstractions
Perhaps our manifest inability to define "information resource" is
trying to tell us something
12. More, different, history
The thing we're interested in on the Web has a complex history
- And just as for names, more than one story has been told
It's worth noting that name-URIs (URIs which refer, which don't respond
to access attempts) are quite old
13. What are names for?
Names function as names within propositions
Even on non-strictly-analytic accounts
- Names occur in sentences
- Their referents participate in assertions/commands/questions/. . .
The primary propositions OFW URIs occur in are HTTP requests
- Which are a kind of speech act
- But a pretty marginal one
SemWeb URIs do occur in sentences
- And their referents participate in assertions
14. Names are discoverable
We know what to call things
- This is why even the Kripkeans can't dispense with descriptions
There is nothing corresponding to this for URIs
- Except search engines!
- Do I hear you say "aha, the extended mind"?
15. notes
Some (syntactic) names are indexicals: e.g. 'Air France 5050'
- Also systematically vague "AF5050 has a 75% on-time record"
History (My email of Date: Mon, 24 Nov 2008 12:54:51 +0000 to Kunze,
Fielding and Masinter, Replies to history query), Three phases: pre-theoretic; OFW (2616); SW
(3986).
Apparent differences: retrieval of representations
Apparent similarities: Kripkean parallel: baptism, indefeasability (maybe)
Indexicality---useful or marginal? It is hard to think of using a file:
URI for other than an information resource---what about file:///
16. References and further reading
- AWWW
The architecture of the World Wide Web, Volume
1, Jacobs, I. and N. Walsh eds. 2004. World Wide Web Consortium,
Cambridge, Tokyo, Sophia Antipolis. Available online at http://www.w3.org/TR/2004/REC-webarch-20041215/
- TBL09
Historical - Re: Proposed IETF/W3C task force: "Resource meaning" Review
of new HTTPbis text for 303 See Other, email from Tim Berners-Lee. Available
online at http://lists.w3.org/Archives/Public/www-tag/2009Aug/0000.html
- RFC3986
Uniform Resource Identifier (URI): Generic
Syntax, Berners-Lee et al., 2005. IETF RFC 3986, available online at http://www.apps.ietf.org/rfc/rfc3986.html
- PhiLang
Philosophy of Language, Michael P. Wolf,
2006. Available online at http://www.iep.utm.edu/lang-phi/, as retrieved 2010-10-11.
- meaning
Theories of meaning, Speaks, J., 2010. Stanford
Encyclopedia of Philosophy. Available online at http://plato.stanford.edu/entries/meaning/, retrieved 2010-10-11.
- names
Names, Cumming, S., 2008. Stanford
Encyclopedia of Philosophy. Available online at http://plato.stanford.edu/entries/names/