A lightning talk at the tech plenary is about 3 minutes long and introduces something very specific to the W3C.
I gave a lightning talk on the effecs of adding or changing the stuff in a namespace. You can see the diagram and notes here: http://www.w3.org/2006/03/01-Boyer-Lightning/SignaturesAndNamespaces_Boyer.html
Basically, got a lot of nods all the way up to TimBL himself when I said you either have to use a new namespace, or you have to internally version the language so that old processors for a vocabulary don't try to render new documents with graceful degradation of unrecognized content when the documents have been signed.
Too bad this is exactly what happened with xml:id. It got added to the XML namespace rather than some other namespace, and the version of XML didn't change. Lo' and behold, it broke something. When doing a C14N of a document subset containing orphaned nodes, C14N copies XML namespaced attributes into orphaned nodes when they don't contain their own settings for the nodes.
This is good for xml:space, xml:lang and xml:base, but it isn't good for xml:id.
Truth be told, it's kind of an edge case. In XFDL, we don't even allow you to orphan nodes when signature filtering because the structure of the language is such that an orphaned node is useless without its ancestral chain.
Still, while the problem doesn't affect Workplace Forms, we (in W3C capacity) will still endeavor to fix the problem.
Since the ship has already saled on what namespace xml:id lives in, we're going to be doing a new C14N algorithm that doesn't do the inheritance behavior on xml:id OR one that doesn't do the inheritance behavior except for lang, space and base.
Actually, it's a little more complicated than that, since either of the above choices means that C14N will again be broken in the future when either a non-heritable or a heritable attribute, respectively, is added to the XML namespace.
I think we may have to add a parameterization to the new C14N that allows the author to specify the heritable attributes. This will allow document authors to keep up with adjustments to the XML namespace.
The core WG feels that further additions to the XML namespace are highly unlikely, but I'm not convinced. Just at this tech plenary alone, I heard calls for xml:role (like HTML's role) and xml:profile (like DOM's hasFeature, it would declare that a document has a feature so the processor needs to have the feature or the document won't work). In the past, I've heard a need for xml:src (like HTML src, except HTML's default is wrong-- content should override the attribute rather than the reverse). And my personal fave would be xml:compute to express that the content of an element is computationally derived from other content. The list really does go on once you start to think about XML as an intelligent object...
Smarter Everyone, Smarter Everything, Smarter Everywhere
John M. Boyer 060000VMNY 1,173 Views
John M. Boyer 060000VMNY 880 Views
XForms 1.0 Second Edition has been published today at http://www.w3.org/TR/xforms/
To get an idea of the quality and quantity of improvements made to XForms, please see http://www.w3.org/2003/10/REC-xforms-10-20031014-errata.html
Based on this improved foundation, the XForms working group will now be focusing its energies on the completion of XForms 1.1. To get an idea of what will be available, check here: http://www.w3.org/TR/xforms11/
The one comment I would make about the above working draft is that the we will almost certainly revert to using the same namespace currently used for XForms 1.0, and instead use some mechanism within the language to do versioning.
In keeping with my prior post about signatures and namespaces, it is important to version a language either internally or by updating the namespace URI. Previously, we chose the namespace route because XForms is designed to be hosted within another language, so it has no root element of its own to which a version could be attached.
However, XForms 1.1 is using some special schema wizardry that allows it to have a "chameleon" namespace, which will make it easier to import XForms into a host language like XHTML without namespace qualification. I'm not a big fan of doing this, especially for host languages other than XHTML because it becomes harder to find the XForms within another document and host the XForms functionality separately from the original host language.
Nonetheless, the feature is there and it occurred to me during the W3C tech plenary that the chameleon namespace could be used to put XForms 1.1 back into the XForms 1.0 namespace. That means that XForms processors trying to determine what semantics to attach to the vocabulary need some other way to make their decisions. So we simply have to solve the versioning problem without using a change of namespace URI.
The camp that wanted us not to change namespaces will be happy. My own XSLTs will be happy too.[Read More]
Well, no blogs from me next week, so seems a good idea to knock off another one this week...
XML namespaces rec (pardon the pun) states that an attribute which is namespace unqualified is 'local' to an element and is uniquely identified by a combination of the attribute local name and the type and namespace URI of the containing element.
The word identify really should be used more sparingly, as here is a case where its misuse has caused years of confusion and acrimony in the XML community. An identifier is something that established the identity of something else. You cannot have two things associated with the same identifier unless they are identical things.
I am often frustrated by seasoned W3C folks who say that "this depends on your definition of identify" and honestly believe this is a defense of the confusion in the namespaces rec. This is like saying ot me, "Well you're right unless you have a definition for identify that doesn't identify things, which is what we did at the W3C."
To see the problem, you have to look earlier in the spec where a namespace n1 is associated with a URI and then the following code appears:
<good a="1" n1:a="2" />
The problem is that the element 'good' is in the same namespace as n1. So now you have local attribute a that is essentially given meaning by an element that is in the same namespaces as the 'global' attribute n1:a. Yes the two attributes have different values.
From this we have to infer that, although a local attribute is given meaning based on the containing element and its namespace, a global attribute with the same local name and namespace qualified into the same namespace can actually mean something totally different..
In other words, we have two attributes with the same local name, contained by the same element, and given meaning by the same namespace URI, but they are not identical. This is the local attribute not being 'identified' (in my sense) by local name and containing element type and namespace.
The technically subtle W3Cer will tell you that there was no reason to spell out using words in the normative part of the spec the fact that the two attributes are different things because the spec says that local attributes are in a different partition than global ones. Problem is, this partitioning info is in a non-normative part of the spec, and particularly in the same part that has the language about how local attributes are 'identified' by local name and containing element type and namespace.
Anyway, the upshot is that an XML vocabulary does not need to but is allowed to say that local and global attributes with the same local name can mean different things. If they're supposed to mean the same thing, then the XML language has to define a precedence rule for what happens if the two attributes differ in value. Here's an example:
Question: Is the price in USD or Euros?
Answer: Depends on who designed the language.
Second answer: Don't do that.
Interestingly, the XHTML working group came up with a fascinating example where it is legitimate and sensible to have a global and local attribute with the same local name but completely different meanings. It has to do with the next version of XML events. After hours of discussion, the decision was that they weren't going to do that (second answer above). Not because it's illegal, but because it's too subtle for most XML people.
Well, the XHTML group may change their minds, but even if they don't, the example is really worth understanding because it actually makes sense why you'd want to have the two attributes mean something different. Stay tuned, I'll tell you all about it when I get back...[Read More]
John M. Boyer 060000VMNY 1,822 Views
Continuing from the last post, here is a reasonable use case for having a global (namespace qualified) attribute with the same local name as a local (unqualified) attribute, where the attributes do not have the same meaning and the global attribute is in the same namespace as the containing element.
The current version of XML Events allows you to declare a listener for an event on a node. There are multiple ways to do this, but the easiest is to use a global attribute in the events namespace (signified by the prefix ev below):
An xforms:trigger can be represented, for example, by a button widget, and pressing the button results in a DOMActivate event on the trigger.
The ev:event declares the name of the event to listen for, and the default value for ev:target (when it's not specified) is the parent element of the one containing the ev:event. So, the above declaration causes a listener to be created for the occurrence of the DOMActivate on the trigger. The handler for the event is given by the content of the xforms:action that bears the ev:event. An example of an action to be performed would be inserting a node of data (which would likely correspond to adding a row to a repeat table).
All of this is just plain vanilla XForms so far. But at the W3C tech plenary, the XHTML working group began discussing upgrades to XML events. The reason is that the current version of XML events declares listeners that are created at the moment when the DOM node being listened to is created. There's no way to create a listener later in the life time of a document, possibly contingent on some condition or the occurrence of some event.
Syntax for this could look something like this:
In this example, ev:listener is an action handler for the DOMActivate event that happens on the trigger. So when you activate the trigger (press the button), a listener for event Y is created on the node with id="X".
The local, namespace unqualified attribute 'event' tells the event that the listener will listen for. The global, namespace qualified event 'ev:event' tells the event whose occurrence causes the ev:listener action to be performed.
This is a very neat and compelling example where a local attribute (event) which is given meaning by a namespace (XML Events) might legitimately have a completely different meaning than a global attribute with the same local name and same namespace as the containing element (ev:event).
Although the XHTML working group quite liked this solution, they had a lengthy discussiona and concluded that this aspect of XML namespaces is not understood well enough to rely on the feature without confusing document authors. Of course, they are free to change their minds later, I would say that the above syntax is not likely to see the light of day in a W3C recommendation.
That's why I'm blogging it. Because even if it goes away, we still need to try to increase understanding of this aspect of namespaces and attributes, and nothing does that better than a good example, and this is the first one I've seen.
And we can thank Steven Pemberton for it![Read More]