Re: [xsl] XSLT/XPath 2.0 (was "Identifying two tags...")

Subject: Re: [xsl] XSLT/XPath 2.0 (was "Identifying two tags...")
From: Dan Holmsand <holmsand@xxxxxxxxxxxxx>
Date: Sun, 12 May 2002 20:41:10 +0200
Hi Jeni,

Jeni Tennison wrote:
> I have the feeling that much of what makes XPath/XSLT 2.0 seem
> complicated is simply that it hasn't been described well. If you're
> had your head buried in the details for months, then it's often hard
> to write it down without skipping over the assumptions that you've
> come to take for granted, or spending too long on the exceptional,
> difficult cases. Again, we can help here by asking the dumb questions,
> like "what's the difference between 'treat' and 'assert'?"

You're probably right. I feel I have some ways to go until I reach dumb questions like that, though. Good one.

> The PSVI is the stuff that you get out of validating an instance
> document with an XML Schema. You know that if you validate an instance
> against a DTD, it's different from what you get if you look at the
> instance without the DTD? With the DTD, you get additional defaulted
> attributes, plus you get information about the types of attributes,
> like "this is an ID attribute". In some data models, you also get the
> element and attribute declarations, so you can refer to them later on.

Well, I think I've got these basics on the PSVI. It seems to me that the spec describe using an XML Schema to define a transformation from XML to some other language, with some sort of named "structs" and an abundance of "properties" for these structs and their members. Sort of like JAXB does, but to "PSVI" instead of to "Java", and at the same time keeping the underlying infoset (I may be totally wrong here, I admit...).

I guess that I have two problems in understanding this: this other language seems to be designed by descendants of Heidegger and Roland Barthes, or someone else feeling that using words already used by others is a sign of weakness (I mean: "in the post-schema-validation infoset the attribute information item may, at processor option, have a property attribute declaration" which is "An item isomorphic to the declaration component itself."). Heidegger couldn't have said it better.

But I guess that my big problem is that I don't get what this new (and apparently rich) language is good for. That, of course, does make understanding impossible (in the same way you can't very well understand what a chair is if you're not familiar with "sitting").

> I found that looking at the PSVI output of XSV
> (, which is described at
>, helped to
> visualise what it looked like; just remember that it wouldn't normally
> be passed around as an XML structure!

Thanks! That helps a bit (and, yes, I do hope that this representation doesn't become canonical :-) ).

But it doesn't really help me cry out neither that "Wow, this is really useful. I wish all xml could be transformed into this." nor that "Gee. I really, really wish that this could become the foundation of XPath/XSLT. That would really make XSLT simpler to understand and use.". If anything, it makes the question "What on earth is this good for?" come to mind.

I do hope that this will dawn on me, eventually... (And I must admit that it is a tempting intellectual challenge: as a book title "XML and Data Structures the Heidegger Way: Being-in-the-world as it relates to post-schema-validation infosets" is almost irresistible...).

Thanks again,


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