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RE: changing final output while writing temporary tree

From: Andre Cusson <ac@hyperbase.com>
Date: Tue, 28 Jan 2003 10:22:21 -0500
To: "Kay, Michael" <Michael.Kay@softwareag.com>, "Kay, Michael" <Michael.Kay@softwareag.com>, public-qt-comments@w3.org
Cc: michael.h.kay@ntlworld.com, saxon-help@lists.sourceforge.net
Message-id: <5.2.0.9.0.20030128101959.03222830@pop.hyperbase.com>

Hi,

Thank you.

I am happy if this is useful.

Tell me if/how I can help.

Regards.
Andre Cusson
ac@hyperbase.com
01 Communications Inc.




At 02:30 PM 1/28/2003 +0100, Kay, Michael wrote:
>Thanks.
>
>The reason we produce public working drafts and the reason that I ship an
>early implementation of the drafts is precisely to get this kind of
>feedback.
>
>I think we need to take a look at the algorithms you are using, and come to
>a position on whether we regard this as being an appropriate use case for
>the language or not. It looks as if we have some studying to do.
>
>Michael Kay
>
>
> > -----Original Message-----
> > From: Andre Cusson [mailto:ac@hyperbase.com]
> > Sent: 28 January 2003 05:57
> > To: Kay, Michael; public-qt-comments@w3.org
> > Cc: michael.h.kay@ntlworld.com; saxon-help@lists.sourceforge.net
> > Subject: RE: changing final output while writing temporary tree
> >
> >
> > Hi,
> >
> > Thank you again for your time and interest.
> >
> > I would like to sit down with you and show you what we are
> > doing but since
> > that is not really possible now and since the code base is
> > relatively large
> > (and complex), I will try to describe some typical problems
> > we are trying
> > to solve, using result-document.  In essence, it is quite simple:
> >
> > 1. The principle : a possibly large and complex source xml
> > document that
> > needs to be traversed recursively and from which pages (ex:
> > web pages) are
> > to be published.
> >
> > 2.. A publishing use case : I have a source XML document of ,
> > lets say 50
> > to 100K lines, describing the structured content of a scientific
> > information web site, organized in volumes, sections,
> > chapters, and pages
> > (which are of course also organized into sections, sub-sections,
> > paragraphs, etc).  Further, the page contents, gathered from
> > the source
> > document have to be merged with XML defined layouts that
> > describe the page
> > layout.  Every time a page is to be published, the
> > page-publish template is
> > called and passed the corresponding contents.  It then merges
> > the contents
> > into specified layout(s) and then serializes the page to
> > html.  Note: this
> > is again a simplified model of a section of the application,
> > the publishing
> > module.
> >
> > As the publishing module is traversing the source document,
> > it figures out
> > what needs to be done and calls the page-publish template as
> > required.  Many cases happen.  A typical one could be, for
> > example, a test
> > page, a page that offers a test to the user:  so we start
> > building the page
> > tree and doing all kinds of calculations for the page,  on
> > this page we
> > also find information to build the answer page which uses a
> > lot of the same
> > data so we build the answer page, publish it and go on with
> > the publishing
> > of the test page, building hyperlinks and navigation between
> > the pages, and
> > so on.  The only issue is that since we are traversing down a
> > tree, the
> > leaves get output first and the root, last.
> >
> > 3. O-R mapping use case: Another example could come from our
> > O-R mapping
> > tool where we take a tree, any tree and map its contents to a
> > series of
> > hyperlinked editing forms, each with a table with the
> > children (or a group
> > of them) of a node and where each child that has children
> > will require
> > additional sub-pages, and so on recursively. So, as I am
> > building page 1, I
> > find that I also need to do pages 1a, 1b and 1c (all with
> > bidirectional
> > links (xpointers) between them).  Since everything is
> > recursive, as I start
> > building page 1a, but now I find that I also have to build
> > sub-pages 1a1,
> > 1a2 and 1a3 and so on.
> >
> > Every time that I have a page ready, I publish it but, because of
> > recursion, bottom pages (tree leaves) get publish first and
> > the root node
> > is still being build at that time so the result-document
> > instruction bombs out.
> >
> >
> > The way I see this, we are not using a side-effect, we are
> > doing plain
> > recursive processing, with no tricks or anything twisted.
> > The fact that
> > there is a tree (final) in a tree (temporary) can hardly (or maybe
> > academically) be called a side-effect.  In my view and for
> > the uses we have
> > of this, a tree in a tree is recursion.  Is recursion a side effect ?
> >
> > Now, I don't doubt that some people may want to abuse
> > recursion or the
> > result-document instruction and I believe that we should do
> > everything
> > reasonable to prevent these abuses, short of preventing the
> > development of
> > useful applications.  Personally, the price to pay for
> > side-effects is to
> > high for me to toy with.  On the other hand, blocking
> > recursion kills my
> > application.
> >
> > I am surprised that something so natural to (streaming) XSLT like
> > traversing a tree structure and building web pages as you go has not
> > brought up this issue before and I start to wonder, what are
> > others doing
> > with XSLT?
> >
> > Theoretically, I could process the structure iteratively but
> > I would loose
> > performance, maintainability and I would get sick looking at the code
> > because of its ugliness and illogical structure.  Comparatively,
> > (academical) side-effects are almost nice.
> >
> > Ever since we found out about the new restriction, a few
> > weeks ago, I have
> > been trying to find a viable alternative but I have not yet.
> > If you can think or suggest me one, I will be happy to try
> > it. If we can't, XSLT 2.0 might run into a problem when
> > people start using it
> > to generate web pages as opposed to simply rendering them or
> > building them
> > from flat structures.
> >
> > For now, and until a viable solution is found, the only way
> > we can advance
> > and deliver a product to our users is to stick to Saxon
> > v6.5.2 and forget
> > about XSLT 2.0.
> > It is a very high price to pay in the long run but it may be
> > better than
> > loosing everything.
> >
> > I hope that the case is getting clearer and I will be happy
> > to provide you
> > with additional information, try things out, talk on the
> > phone or anything
> > that will help resolve this.
> > I also hope that the mix of my passion and my frustration
> > does not blur the
> > issues.
> >
> > I thank you for everything and especially for your interest.
> > Please take care.
> >
> > Regards,
> > Andre Cusson
> > ac@hyperbase.com
> > 01 Communications Inc.
> >
> > PS: Whether I invoke result-document while building a
> > with-param tree or I
> > do it in a variable and then pass the variable as a parameter
> > does not
> > improve the problem because now I have additional variables
> > (which are
> > temporary trees also) and more "non streamable" steps, but I
> > still need to
> > recursively generate pages (from temporary trees).
> >
> > Recursion is designed to handle problems that are cannot
> > (easily) be solved
> > otherwise and it seems to me that generating html pages from
> > traversing a
> > hierarchical structure is one of them.
> >
> > I am very sorry that the committee might already have spent serious
> > resources debating (complex) output tree issues and that I am
> > trying to
> > stir things up again but the way I see it, either I am wrong
> > and there is a
> > better way to do this and I will be happy and I will grow as
> > a programmer
> > if I can find/learn it, or I am right and it is in XSLT's
> > best interest to
> > revisit the issue.  Consequently, If I have not been clear
> > enough in my
> > description of the problem, or anything else, please advise
> > me and I will
> > quickly try to fix up or provide more info.
> >
> >
> > PSS: we have a small test portal with some static html pages
> > generated like
> > described above, currently on the web.  One of the sites
> > there is a complex
> > document of close to 1000 web pages, dedicated to a
> > generative approach to
> > music theory.  This site can be accessed through
> > www.musicnovatory.com.  Please keep in mind that both the
> > sites and the
> > tools to generate them are still in construction.  Please
> > also note that
> > everything, including all portals, sites, pages, navigation,
> > sitemaps, etc
> > are automatically generated from pure content XML source
> > documents (and XML
> > layouts), all with XSLT.
> >
> >
> >
> >
> > At 02:42 AM 1/28/2003 +0100, Kay, Michael wrote:
> > >I think that the mental model we have used for multiple
> > result trees is
> > >that there is conceptually one combined tree, and that the actual
> > >result trees all have to be subtrees of this combined tree. The
> > >stylesheet logic for writing multiple result documents is therefore
> > >exactly the same as you would write if you were generating
> > the combined
> > >tree. If you can write the logic to produce the combined
> > tree, then it
> > >is trivial to modify it to produce multiple trees. What the facility
> > >for multiple result trees does not do is to free you from
> > the need to
> > >produce output in "result tree order" - that is, the order of
> > >instructions in the stylesheet reflects the order of nodes
> > written to
> > >the result.
> > >
> > >Its true that the restriction on when xsl:result-document
> > can be used
> > >appears somewhat draconian, and the problem it is solving
> > seems rather
> > >small in comparison. Arguably, we are applying the "no-side-effects"
> > >philosophy of the language rather strictly in this case. I'm sure we
> > >could relax the rules by leaving some edge cases implementation
> > >defined, but on the whole we have been reluctant to do that.
> > >
> > >We did have a different solution to this problem in earlier
> > drafts, but
> > >it required extra information in the data model and was very hard to
> > >understand. It still imposed substantial restrictions. The model was
> > >that a result document was effectively a child node attached to some
> > >other tree, invisible to XPath expressions, but still linked in the
> > >sense that the tree was written out only if and when the parent node
> > >was written to a result tree.
> > >
> > >We spent some time debating this and I'm reluctant to re-open it.
> > >Rather, I'd like to see whether we can use your problem as a
> > test case
> > >to see whether the existing language is up to solving the
> > problem. In
> > >the example you show, I find it very hard to understand why you are
> > >trying to produce a result document as a side-effect of
> > calculating a
> > >parameter to a named template. It seems a very odd way to do things,
> > >though I'm sure it makes sense to you.
> > >
> > >Michael Kay
> >
Received on Tuesday, 28 January 2003 10:06:32 GMT

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