Comments on: REST design question #1: identification

By: Mark

Mark — Thu, 24 Feb 2005 02:23:41 +0000

PROBLEM: You cannot remember the source of the data you’ve just retrieved over an ambiguous duration or disposition through time.

SOLUTION{?}: Attribute an external identifier (the information may not need to care where its from after, you do.) I would elect: http://www.example.org.airports.ca.cyow.xml
or allow embedded paths: ‘www.example.org/airports/ca/cyow.xml’

By: Bo

Bo — Tue, 22 Feb 2005 23:05:20 +0000

Your intial assumptions are wrong. Identifiers, in the business sense that you mean, have nothing to do with URLs. Identifiers should be GUIDs and should never, ever change. URLs are not identifiers and trying to use them as such is silly. It’s common in many systems for a single resource to be located by several URLs and it’s also common for the business entity represented by a URL to change over time (eg http://www.weather.com/nyc results to a new business entity every 20 minutes). You’re not downloading a resource when you GET a URL, you’re downloading a representation of a resource. The representation of the resource should contain zero information about its URL (unless that makes sense for the RSS, for example RSS documents) but it should contain an identifer to prevent the need for conversational state.

By: Ryan Tomayko

Ryan Tomayko — Tue, 22 Feb 2005 21:41:17 +0000

It may be interesting to note that Atom accepted <link rel="self"> for identifying the location of a feed instead of xml:base. See PaceFeedLink and Discussion on atom-syntax mailing list. This is great stuff, btw, David.

By: Danny

Danny — Thu, 17 Feb 2005 09:17:22 +0000

I’m not 100% sure about RESTafarians considering identification and location one and the same thing - surely resources are identified (via URIs), representations are located (via HTTP).
The question of where the document identifier should go is spawned by your creating a new resource, albeit with the same representation as the original. A possible solution might be to wrap the content of the document to identify the resource which it represents, i.e.

By: Sjoerd Visscher

Sjoerd Visscher — Wed, 16 Feb 2005 11:14:19 +0000

The default base URI of the root element when there is not xml:base attribute is the base URI of the document, i.e. the URI used to retrieve the document. So you’re just asserting what is already the default.

Even when you don’t need a document identifier it seems good practice, as it makes your data location independent.

By: Mark Baker

Mark Baker — Wed, 16 Feb 2005 05:10:06 +0000

xml:base has, on occasion, the same value as the URL from which the document was retrieved, but that’s accidental. Consider that it makes no sense to have a base URI that ends with anything other than “/”, which most URLs do not do. rdf:about is the closest thing to what David’s looking for AFAICT.

Full response forthcoming on my weblog …

By: Sjoerd Visscher

Sjoerd Visscher — Tue, 15 Feb 2005 17:57:19 +0000

xml:base isn’t just a cute hack to set the base URI. From the very beginning of HTML [1] the base href is meant to provide the original URI of the document, to be used when the document is read out of context. XInclude extends this practice by providing with xml:base the url of the originating document.

So I’d expect that xml:base would usually contain a resolvable URI of a document, and not a URI like http://www.example.org/airports/ca/

[1] http://w3future.com/weblog/2005/01/13.xml#stillBugsInTheImplementationOfHtmlHyperlinks

By: Norman Walsh

Norman Walsh — Tue, 15 Feb 2005 16:37:40 +0000

Resolving cyyz.xml against a base URI of http://www.example.org/airports/ca/cyow.xml will result in http://www.example.org/airports/ca/cyyz.xml. That looks like a reasonable use of xml:base to me, though it seems like a slight extension. I’d have expected the xml:base to be http://www.example.org/airports/ca/ (the trailing slash is significant) but maybe that’s just narrow-minded of me.

By: Bob DuCharme

Bob DuCharme — Tue, 15 Feb 2005 14:13:32 +0000

XLink processors? What XLink processors?

By: Sjoerd Visscher

Sjoerd Visscher — Tue, 15 Feb 2005 09:32:03 +0000

I think this is exactly what xml:base is for. IMHO tools (like browsers) that allow XML documents to be retrieved from the web and stored somewhere else should automatically add an xml:base attribute.

XLink tools are either not xml:base aware or they will resolve the links correctly. I don’t think you’ll ever get cyow.xmlcyyz.xml.

Applications that are compatible with DOM Level 3 or with the XML Information Set should give you the base URI for every node.