Re: [Exist-open] [ANN] New Ajax-based XForms example using eXist

[<fre...@aj...>]

A bit Late, but an answer about XForms implementation of Orbeon.

Very nice answer, indeed.

> Disclaimer: I am not a huge fan of XML Schema!=20
> XML Schema is not
> that bad and does allow you to do some useful stuff, even if it is
> overly rigid and frustrating (compared, say, to Relax NG).

Some may need this precision.

> Now, you can be fairly declarative if you use types, for example:
>=20
>     <xs:simpleType name=3D"street-name-2">
>         <xs:restriction base=3D"xs:string">
>             <xs:pattern value=3D"([A-Z]|[a-z]|\-|\.|\/|\s){0,22}"/>
>         </xs:restriction>
>     </xs:simpleType>

such datatypes could also useful to write for Relax-NG
<http://books.xmlschemata.org/relaxng/relax-CHP-8-SECT-1.html>

> And you can also use those types from within XForms without thinking
> about structure, with for example:
>=20
> <xforms:bind nodeset=3D"my-street" type=3D"dmv:street-name-2"/>

You are right, it's clean.

> Also, since XForms allows you to modify the structure of a document
> (xforms:insert, xforms:delete, xforms:copy), you may want to check its
> structure, and in this case using XML Schema's ability to control
> structures is handy. Granted, in many cases you don't really need it.

[validation of relations]

>  > <customer id=3D"customer123">Name, FirstName</customer
>  > "check this customer before save this contract"

> OPS has an extension XPath function that allows you to call any XML
> pipeline. In XForms, you have other mechanisms to perform validation
> in addition to XML Schema: you have simple types, and constraints. You
> could say:
>=20
> <xforms:bind nodeset=3D"customer"
>   constraint=3D"string(xxforms:call-xpl(...)) =3D 'true'"/>
>=20
> Where the call to XPL passes the <customer> element, then runs the
> pipeline, which can do whatever you want, including calling up eXist
> to check the existence of the user.
>
>  > Xquery is needed here ?
>=20
> Yes if checking the existence of the particular user in eXist requires
> XQuery...

I guess that more complex Xquery could be embed in an OPS pipeline, not
a completely portable solution, but can save lots of bad code. This
validation writing seems also clear to maintain and debug.

>  > Is your implementation adapted to update for example, a leave in a b=
ig
>  > doc ?
>
> You can do that by using XUpdate and XQuery with eXist, right?  You
> should try to keep your XForms instances small for reasons of memory
> usage and performance (it takes time to create a DOM). Certainly, you
> can extract a subset of an eXist document with XQuery, then work on
> that with XForms, and finally update that leave with XUpdate in eXist
> again. I don't see any obstacle do doing that.

If it's a leave in a doc, you guess it needs reference validation, but
your answer upper provide a possible solution.

>  > I figure that the XML instance is stored as a DOM during client
>  > interaction ? And you save it as a resource in Exist ?
>=20
> We have a 2-state state keeping: one as string, where the entire
> XForms engine state is just an gzipped, encrypted string. This is in
> fact a key to a cache, where we keep a "live" version of the state. In
> that live version, that's correct, XForms instances are kept as DOM,
> in fact as dom4j instances. Note that you can have as many XForms
> instances as you want with XForms.

So I guess it could be very expensive for the server ? What are common
requirements in memory or CPU for OPS ?


This is a very convincing demonstration for Exist users.



--=20
Fr=E9d=E9ric Glorieux (AJLSM, http://ajlsm.com)