W3C home > Mailing lists > Public > www-forms@w3.org > August 2001

Levels of XForms (was: RE: Form function and presentation - Schema usage)

From: Sebastian Schnitzenbaumer <schnitz@mozquito.com>
Date: Tue, 21 Aug 2001 14:57:39 +0200
Message-ID: <D0F1529EE943B3449F755CA1A40887461116B6@winserver.windomain.mozquito.com>
To: "joern turner" <joern@webman.de>, <www-forms@w3.org>
Joern,

you know what? I think the points you make are
absolutely valid and need further consideration
by the Working Group.

I don't see us go down the path again to define
yet another "Simple Syntax" for the model. Been 
there, done that. It is also important to point
out that whilst your points in favour of such
freedom for the model part in XForms are totally
valid (really!), others do favour a concrete 
permutation of the model defined in the spec.

If we as the W3C XForms WG go down the path of
specifying a concrete model for XForms, we are
obliged to re-use existing W3C technology - that
is just the way it is - therefore we have to take 
a subset of Schema (XForms Basic) or Schema as it 
is (XForms Full). We simply don't have the 
freedom of defining a completely "self-contained" 
XForms spec - and I think that makes total sense 
too: to build upon tested, pre-existing 
components instead completely re-inventing the
wheel.

However, as I said, you have some valid points:
If you have to "break the spec" to make an
"xformisch" implementation happen, and for
resource reasons you cannot even implement 
the schema subset simply because of the verbose
syntax - we have to take this serious.

Would the following solve your problem:

We define a new level of XForms conformance next
to the two existing ones:

XForms Core: The basic XForms concept of 
  Model-View-Controller, the binding mechanism
  and the core XForms module(s) (<xform>, <model> &
  <instance>). You may yourself choose and use any 
  pre-existing or custom model language and any
  UI language as well as of course any arbitrary
  XML instance for data.

XForms Basic: XForms Core + Concrete Model as 
  W3C XML Schema Subset (Part 2 Datatypes) 
  + XForms UI.

XForms Full: XForms Core + Concrete Model as 
  Full W3C XML Schema + XForms UI.


Food for thought. Others on this list: Opinions?

Thanks,

- Sebastian

 
> -----Original Message-----
> From: joern turner [mailto:joern@webman.de]
> Sent: Tuesday, August 21, 2001 10:48 AM
> To: www-forms@w3.org
> Subject: Re: Form function and presentation - Schema usage
> 
> 
> Hello Josef,
> 
> excuse my late reply (but my collegues and me are actually in the
> deadline for delivering a basic, working 'XFormish' implementation, so
> that's why) and thanx for your detailed reply but it seems to me that
> maybe i somewhat haven't made clear our/my intensions:
> 
> let me try to clarify...
> 
> Josef Dietl wrote:
> 
>  > Hello Joern,
>  >
>  >
>  >>the former WD still defined a 'Simple Syntax' for defining
>  >>XForms-models,which was removed in the last WD. For my
>  >>personal opinion
>  >>this was an unlucky move...
>  >>Let me explain:
>  >>- it may be a personal issue but the removal left a gap 
> which makes it
>  >>harder to imagine how the pieces (model,instance,ui) fit 
> together. i
>  >>finally returned to a kind of 'simple syntax' for internal 
> processing.
>  >>
> 
>  >
>  > The current perceived gap is IMO mostly an editorial issue (nothing
>  > against our editor here :-): We have removed the simple 
> syntax when we
>  > knew that we couldn't sustain it, but we hadn't had the 
> replacement yet.
>  > A joint task force was founded between the Schema Working 
> Group and the
>  > XForms Working Group, and that task force has delivered its results
>  > recently. We are currently preparing a new draft that 
> among others fills
>  > the gap. Usual disclaimers apply, from what I can see 
> holdig your breath
>  > is in order.
> 
> 
> 
> i think i understand the status of a Working Draft but as 
> i've committed
> to the basic ideas of XForms and try to deliver a xformsish 
> ;) thing as
> soon as possible,  we had to 'guess' something in the 
> meantime in order
> to meet this goal (and adapt later). we would be happy to integrate a
> well-defined Schema syntax as soon as it's fixed.
> 
> 
> Our struggles/experiences with down-to-the-ground problems of the
> implementation brought up some differences/extensions to the 
> current WD
> and i've tried to transfer these back...
> 
> 
>  > True, Schema is said to be complicated. But looking 
> closely we found
>  > that
>  >  - given our requirements, the thinking process is the 
> difficult part,
>  > the actual syntax is "just syntax". Maybe we could have 
> simpliefied the
>  > syntax, but we could never have simplified the thinking.
>  >  - we have to support Schemas anyway. Simply because the 
> use case that
>  > someone has a Schema for his or her data already is so 
> overwhelmingly
>  > significant.
> 
> 
> Agreed, the thinking is the hard part - but after thinking 
> when it comes
> to implementation efficiency and real-world constraints 
> (limitations in
> clients/protocol/robustness of tools) are the other. sure, it's only
> syntax but it even brings a reasonable powerful machine into sweat if
> you implement all this server-side. so why hang the apple so
> un-necessarily high?
> 
> if you're really reject the idea of an 'abbreviated syntax' you
> should better skip the following, but i think there are arguments ;)
> that go much beyond.
> ---
> everything in the following is induced through some kind of real-world
> constraint that exists TODAY, so some issues will solve through newly
> delivered technology in the future while other issues will 
> remain. some
> can be overcome with common solutions while others may not. to list a
> few when you want to deliver for today:
> 
> - support for CSS is in most cases either incomplete and unreliable.
> this makes the layout part in XForms hard.
> 
> - only really advanced clients can deliver the 'XForms Full' 
> conformance
> level in networked applications - with DOM-Events, the
> 'immediate'-functions and such. this implies use of RPC of 
> some kind and
> some really serious processing...
> 
> - ... or the use in an stand-alone client. but which client could not
> network today, if it's so powerful, that it can deliver full XForms
> processing?
> 
> - ...otherwise the client must understand XML. unluckily it's likely
> that for some time (maybe one maybe two years, doesn't 
> matter) from now
> it will be senseless to send XML directly to your client, cause they
> will not or only partially understand it.
> 
> - so it maybe not completely wrong to assume a 'devided' 
> architecture to
> become common: some processing and advanced functions server-side and
> styling, interactivity, simple validation client-side for example.
> 
> - a lot of clients rely on http for simple to medium, even complex
> networked applications today and is IMHO one of the most interesting
> environment for XForms-processing, cause http often is used 
> not only for
> browsers but for small devices too. but unfortunately this 
> leads to all
> this well-known (and already mentioned) problems which i don't want to
> repeat here.
> 
> 
> the 'abbreviated' syntax lowers the memory consumption of our 
> processor
> by degrees through the simple fact that we use three times 
> less tags for
> expressing the same semantics; the memory consumption slowly reaches
> acceptable sizes: one testcase contains one example for most of the
> XForms UI elements and is about 500 lines of XML. these would 
> have been
> easily about at least the double in full Schema syntax.
> 
> - this memory consumption has naturally some unwanted effects on
> processing-time, searches and evaluations on the tree.
> 
> - fully! Schema-aware, robust and open technology will be some time
> away, as is common support for CSS, XPath, XML, XSL on the client
> (sorry, if i repeat myself)
> 
> 
>  >
>  > Essentially, there are two dominant use cases, probably 
> with not much in
>  > between:
>  >  - the really-simple form, say, a search form. Doesn't need input
>  > validation to begin with
> 
>  >  - the user interface to an XML-based application. In all 
> likelihood,
>  > already has a Schema: the Schema attached to the application in the
>  > background.
>  >
>  > You will find the details of the solution in the next 
> draft, roughly
>  > what we've done is a tiered approach:
>  >  - if you don't know about validation, don't worry - you 
> don't have to
>  > provide it.
>  >  - if you do, you may live with just Schema Datatypes (part 2).
>  >  - if you have a Schema, use it.
>  >  - if you have someone who knows how to handle Schemas, 
> work with him:
>  > the interface between the UI and the Schema is as lean as can be.
> 
> 
> i'm really looking forward to that!
> 
> 
>  >
>  > Again, it's not the solution that is difficult but the 
> problem that is
>  > hard, and by using XPath we have at least the people who know about
>  > XPointer and the people who know about XSL-T on our side. 
> We also leave
>  > the door open for future developments in the area of XPath 
> together with
>  > XML Query, which is a extremely exciting prospect to me. 
> Ideally, one
>  > day in the future, your form fields could adress directly into the
>  > database...
>  >
>  > XPath is currently the only know-how bottleneck.
>  >
>  > With all due respect, but tasked with writing something 
> for XML I take
>  > XML for granted, and tons of Web designers have managed to 
> master CSS so
>  > far. You can live well in an XForms context without 
> knowing anything
>  > about Schemas, it just shouldn't surprise you that you can't access
>  > Schema's features in that case.
>  >
> 
> 
> i don't really intended to make this an 
> 'all-or-nothing'-case. for one,
> i widely agree that new technologies offer new possibilities 
> but for the
> price of learning. we are in the lucky situation to have all these
> xml,xsl,Schema,xpath, java expert ready, so that's not the problem to
> us. but even then the solution should scale to meet a wide 
> range of needs.
> 
> second, but i believe that a spec also gains through
> 'self-containedness' - maybe one reason why html was adapted so fast.
> 
> 
>  >>- a lot of the power of XForms comes from its abstractions:
>  >>e.g. the UI
>  >>abstracts a concrete representation in a UI-toolkit. Why 
> not let the
>  >>model abstract the concrete usage of a schema (with little s)
>  >>mechanism?
>  >>This would nicely solve the issue with different clients: like the
>  >>processor maps the UI to the clients-format it could map a XForms
>  >>model-syntax to a version compatible with the client (may it
>  >>be Schema,
>  >>Relax,T-Rex, DTD, instance-attributes,..., according to needs).
>  >>
>  >
>  > Interesting approach. But as far as I can tell, it is difficult to
>  > realize and will not provide an XForms author with the necessary
>  > reliability. For example, if (s)he writes a form and 
> assumes that the
>  > model takes care of checking that a date-of-birth is 
> actually a date,
>  > then a translation to DTDs will just not cut it. Faced with that
>  > prospect, the designer would have to write the code for the date
>  > validation again anyway, so under these circumstances the 
> model doesn't
>  > add value.
> 
>   >
>   > If we provide the feature, we want people to be able to 
> depend on it.
>   >
> 
> absolutely.
> 
> on the contrary a transformation from an internal 
> representation to some
> kind of client-schema allows some advanced uses:
> 
> consider following scenario:
> a client connects to a server and requests an XForms session. through
> user-agent recognition the server may fetch a XForm and the 
> appropriate
> transformation for the client. for the server a 
> transformation to Schema
> will be used to validate the incoming-data. for the client another
> transformation will map all validations that the client 
> supports into an
> appropriate schema syntax and transfer it to it. this allows to reduce
> the contacts during the form-filling session and allows to delegate at
> least some immediate validations to the client.
> 
> to cut it short it would allow to plugin a schema mechanism into the
> processor may it be Schema (very likely in the future), some 
> lightweigth
> mechanism to support PDAs,DTDs when your application just 
> requests that.
> just imagine to map even to database-models directly. this way a
> processor could also export different model-representations for
> data-consumers.
> 
> 
> this scenario has surely some more interesting aspects which
> 
> allow a flexible adaptation to the clients capabilities and would go 
> beyond all-or-nothing.
> 
> 
> 
>  >
>  >>- we've been building some test-forms with repeats and
>  >>switches and even
>  >>in our simplified syntax, the appropriate model-markup 
> becomes really
>  >>complicated (we're using just one element where Schema 
> syntax needs at
>  >>least 3).
>  >>
>  >
>  > As I said earlier: the tricky thing is not the markup, the 
> tricky thing
>  > is the thinking behind. Repeat and switch are extremely powerful
>  > constructs, and exploiting that power takes some thought. 
> A switch in
>  > the UI for example is pretty much equivalent to a choice 
> in the Schema,
>  > and repeat corresponds to maxOccurs>1. So, fundamentally, 
> it's easy. But
>  > you can nest and recurse these constructs - that is where the power
>  > comes from, but it's also where the brainware is challenged.
>  >
> 
> 
> the power of XForms is why we committed us to it and i can only agree
> that it really challenged us but we managed to walk through all this
> recursions and get it running but not without the price of 'breaking
> some rules' of the spec.
> 
> with all respect for the WD and their authors, i can only sum up our
> experience: it's not only the thinking it's also the thinking 
> of how to
> implement it!
> 
> 
> Joern
> 
> 
>  >
>  > Josef
>  >
>  >
>  >
> 
> 
> 
> 
> 
Received on Tuesday, 21 August 2001 08:58:11 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Saturday, 10 March 2012 06:21:49 GMT