Julian Reschke wrote:
Arun Ranganathan wrote:
The latest revision of the FileAPI editor's draft is available here:


4. A suggestion to *not* have a separate scheme ("filedata:") in lieu of urn:uuid:<uuid>[2] has been the basis of a rewrite of that feature in this version of the specification.

Is there a particular reason why a specific URI scheme needs to be called out at all?

(there are other schemes that may be more flexible, for instance because they allow using a UUID/String pair for identification).

This is a useful question to answer :)

I assume everyone understands use cases for this identifier. Ian's email discusses a few [1] which have been supplemented with a few more.
There are a few ways to proceed:

1. We could coin a new scheme such as the originally proposed filedata: scheme. This has the advantages of associating behavior (and semantics) with a scheme, so that existing schemes aren't confused or co-opted inappropriately. However, actually registering a new scheme used by browsers seemed problematic (with overhead due to coordination with multiple groups). I'm willing to revisit this idea given enough feedback, but to date, haven't really received enough of it.

2. We could reuse an existing scheme. This seemed desirable if there was little chance of confusion and collision, and it avoids multi-group coordination. Using urn:uuid was an obvious choice given assumptions on UUID uniqueness, but it is hardly a "pave the cowpaths" choice since it isn't currently used on the web platform in any way I can recognize. Also, "urn" isn't used on the web platform as an attribute on interfaces, but "url" is, so we once again have a consistency argument. While consistency is desirable, I don't think we should be too hung up on it. To make a longer story shorter, urn:uuid addressed the use case fairly well, and seemed a useful starting point.

[ Now between 1. and 2., I'd say the deciding factor might be implementation feedback. For instance, Firefox's code is such that 1. and 2. are both (pretty much) *equally* feasible. We also got some feedback from Microsoft [2], but that feedback seems to be preliminary, with more to come. I'm also not sure concern over origin issues are valid here [2], since a perusal of the issues with jar: (which urn:uuid has been compared to) doesn't reveal any cogent origin effrontery. I'd really like *more* implementor feedback on this issue. ]

3. We could not directly call out a URI scheme at all. The benefit of doing this is we can specify *behavior* without actually getting into details about the actual identifier scheme used. But, the chief reason to not take this course of action is that leaving *anything* unspecified on the web platform leads to reverse engineering in ways that we can't envision currently. Developers may rely on quirks within one implementation and incompatibly use them with other implementations. Having to "mimic" another user agent's behavior has been a common outcome on the web, due to lack of specifications -- *many* examples of this exist on the web throughout its history. One lesson from the browser competition of the past is to avoid leaving things to guesswork. I'd like us to agree on something, and I'd like that agreement to be bolstered with concrete implementor feedback.

-- A*

[1] http://lists.w3.org/Archives/Public/public-webapps/2009AprJun/1110.html

[2] http://lists.w3.org/Archives/Public/public-webapps/2009OctDec/0462.html

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