OGC (re)discovers URLs, but let’s tighten up the terminology a bit

I had seen this tidbit that Sean Gillies writes about in the recent OGC newsletter. My thoughts were along the lines of Sean’s. I never understood the big deal behind URNs.

EDIT: Forget the semi-rant, see the comments, and then go read about URI…

But in re-reading Sean’s post and the OGC news coming out of the June 2010 meetings, I think the terminology is a bit imprecise. Too bad the source document, 10-124r1 isn’t available on the OGC web site (promised for mid-July, I see) to see if the issue is in the document or in the news page. Here’s the news page version:

OGC Identifiers – the case for http URIs’

The OGC Members approved release of ‘OGC Identifiers – the case for http URIs’ [OGC 10- 124r1] as an OGC Whitepaper. .According to the current OGC policy either URNs or http URIs may be used in OGC standards. However, the use of http URIs (a) resolves some deployment challenges and (b) provides an opportunity for easier engagement with broader communities. So OGC should now consider taking the next step, and mandate the use of http URIs for persistent identifiers in OGC specifications. This whitepaper canvasses a number of issues around this proposal.

http URI Policy

The OGC Members approved the following as official OGC policy to be included in the OGC Policies related to OGC standards [OGC 06- 135rN]:

  • OGC TC directs the OGC-NA that all new OGC identifiers issued for persistent public OGC resources shall be http URIs, instead of URNs
  • New standards and new major versions of existing standards shall use http URIs for persistent public OGC resources to replace OGC URN identifiers defined in previous standards and versions, unless OGC- NA approves an exception

Operational Implications: OGC should carefully manage (maintain for the long term) the http://www.opengis.net domain and identifiers in this domain

So what’s wrong? Refer to RFC3986 (or the html version). Section 1.1.3 talks about URI, URL, and URN:

A URI can be further classified as a locator, a name, or both. The term “Uniform Resource Locator” (URL) refers to the subset of URIs that, in addition to identifying a resource, provide a means of locating the resource by describing its primary access mechanism (e.g., its network “location”). The term “Uniform Resource Name” (URN) has been used historically to refer to both URIs under the “urn” scheme [RFC2141], which are required to remain globally unique and persistent even when the resource ceases to exist or becomes unavailable, and to any other URI with the properties of a name.

A URN is a kind of URI. What is called an “http URI” is really a “just” a URL in RFC3986. And, a URN need not (or I should say “need no longer”) be something with “urn:” in the scheme. A URL could be a URN based on the last part of the definition above, “any other URI with the properties of a name”

Therefore, an “http URI” (from the OGC wording) can be either a URL or a URN, based on section 1.1.3 of RFC3986. Of course, the URN is really a URL with the additional uniqueness and persistence properties. So let’s just call OGC’s newly mandated URIs URLs.

There are two primary motivations for using RFC2141 URNs. One is as a globally unique name managed by some authority. The other is as a persistent identifier, sometimes used to map onto a URL with a resolver. The trouble with the latter is that URLs really work better in the first place, and I’m guessing that’s what 10-124r1 says.

So here’s what I think they should have said in the TC:

URI Policy

The OGC Members approved the following as official OGC policy to be included in the OGC Policies related to OGC standards [OGC 06- 135rN]:

  • OGC TC directs the OGC-NA that all new OGC identifiers issued for persistent public OGC resources shall be http URLs, instead of RFC2141 URNs
  • New standards and new major versions of existing standards shall use http URLs for persistent public OGC resources to replace OGC RFC2141 URN identifiers defined in previous standards and versions, unless OGC- NA approves an exception

Sorry to be so pedantic. Back in the day, there would have been half a dozen people at any given TC who would have been able to argue the finer points of this for hours….

(And I just figured out what the OGC-NA is. I guess it’s the “Naming Authority”.)

Posted in Geo
4 comments on “OGC (re)discovers URLs, but let’s tighten up the terminology a bit
  1. Adrian Custer says:

    Hey,

    What are you trying to say? Are you merely worried about the name ‘http URIs’ or am I missing some larger contribution to this discussion?

    As you say, Simon Cox used ‘http URIs’ as a way of saying ‘URIs which have the property of being resolvable over the HTTP protocol.’ His terminology strikes me as a nice compromise since it is (1) new, and therefore unlikely to be confused with any earlier terms and (2) combines ‘identifier’ with the location protocol. Despite having pushed Simon far on this issue, I do not see why adopting your slightly more precise but less neutral ‘http URLs’ would change. Everyone present at the two conferences knew these were ‘http URLs’ since Simon said that whenever he used the term; however we avoided running into people’s naive assumptions about URLs.

    OGC documents and standards cater to a wide array of audiences; unless the terminology is wrong, it is generally safe to assume terms have been picked with precision, possibly relative to a particular literature or to diffuse possible confusion. Names are hard but let us not fight over the details of names unless there is an overarching reason to do so.

    cheers,
    –adrian

  2. Allan says:

    Adrian,

    I have to say, I do know a thing or two about OGC specs and how they are written, having been a fairly active participant in the first 50+ TC meetings. I’m sure that the authors of this spec chose their words with care. I’m certainly not fighting over the names. It’s not my document so I don’t have a stake in what it’s called.

    I think the term URI is much misunderstood and there was something about the wording that seemed slightly off kilter. Today, by researching this I learned a little more about URIs. If you look at the progression from RFC2396 to RFC3986, you can see that the IETF/W3C’s understanding of the term evolved a little.

  3. Sean Gillies says:

    Allan, I think “URI” fits. There are things we’d like to identify that can’t be located: Benjamin Franklin, Colorado North State Plane, for example. The linked data community uses the term in the same way, and I’m hopeful that this is a sign that the OGC will be following their lead.

  4. Allan says:

    I think you’re right, and thanks, Adrian, for helping me think this through better.