Are URIs really names?

Henry S. ThompsonSchool of Informatics, University of Edinburgh

Markup Systems16 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:

1. The 'httpRange-14' issue2. The semantics of the HTTP response codes3. 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:

DescriptionA name is short for some collection of descriptive properties which pick out its referent(s)

BaptismA name is attached to its referent by a (typical ostensive) act of baptism – The result is then a so-called rigid designator

UseThe 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• Explicitly specified in RFC 3986• Summarised and extended in WebArch

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 inscriptions, 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]

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

Does the Wittgensteinian position distinguish names from any other kind of referring expression?

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. 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/