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Re: Binding : Do I need a nodeset?

From: Mark Birbeck <mark.birbeck@webbackplane.com>
Date: Thu, 6 Aug 2009 16:42:26 +0200
Message-ID: <ed77aa9f0908060742h2e2067edte9f766abcb86e4c3@mail.gmail.com>
To: John Boyer <boyerj@ca.ibm.com>
Cc: adam.flinton@nhs.net, "www-forms@w3.org" <www-forms@w3.org>
Hi John,

I was careful to say "you always need a nodeset" rather than "you
always need @nodeset" for exactly the reasons that you said -- that
@nodeset is optional. I was just trying to emphasise that you need to
bind to something, and I thought I'd confuse the issue if I mentioned
nested binds.

However, I forgot all about the evaluation context for a top-level
bind being the first instance/node of the containing model, and that,
as you rightly point out, explains why Chiba was giving Adam some
results when he had @calculate with no @nodeset.

So it seems I couldn't get away with not mentioning nested binds after all. :)

Thanks for the much-needed clarification!

Regards,

Mark

On Thu, Aug 6, 2009 at 4:27 PM, John Boyer<boyerj@ca.ibm.com> wrote:
>
> Just to clarify for archival purposes, when Mark said you always need a bind
> nodeset even for calculate, that's not exactly true.  You always need to
> have a node to which you are attaching the model item property, which is
> what Mark is explaining.
>
> The nodeset binding on xf:bind is optional, but if you leave it off, then
> the other bind attributes are evaluated according to the inscope evaluation
> context.  This is handy when you are using inner binds.  So, for example,
> you can say
>
> <xf:bind nodeset="some/common/node">
>    <xf:bind relevant="some expression"/>
>    <xf:bind nodeset="some child" calculate="some expression"/>
> </xf:bind>
>
> Notice that the inner bind with the relevant attribute has no nodeset
> attribute.
>
> If you have an outermost bind with no nodeset, then the model item property
> is being attached to the default node, which is the root element of the
> default instance.
>
> Also, if you define the same model item property more than once for a given
> node, the processor is supposed to quit with an exception.   When you didn't
> use nodeset, you were attaching two relevant model item properties to the
> root element of the default instance, which is why your program wasn't
> working.  If you had tried to do a second calculate, you would have gotten
> the same error.
>
> As Mark explained, attributes like relevant and calculate are not applied to
> the bind itself, which is what I believe you were thinking.  Instead, the
> bind *binds* those properties to data nodes.  Then, your UI controls use
> "single node bindings" (e.g. ref) to refer to the same nodes in order to get
> at their value (whether or not calculated) and their other model item
> properties (like relevant).
>
> Cheers,
> John M. Boyer, Ph.D.
> STSM, Interactive Documents and Web 2.0 Applications
> Chair, W3C Forms Working Group
> Workplace, Portal and Collaboration Software
> IBM Victoria Software Lab
> E-Mail: boyerj@ca.ibm.com
>
> Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer
> Blog RSS feed:
> http://www.ibm.com/developerworks/blogs/rss/JohnBoyer?flavor=rssdw
>
>
>
>
> From: Mark Birbeck <mark.birbeck@webbackplane.com>
> To: adam.flinton@nhs.net
> Cc: "www-forms@w3.org" <www-forms@w3.org>
> Date: 08/06/2009 05:50 AM
> Subject: Re: Binding : Do I need a nodeset?
> ________________________________
>
>
> Hi Adam,
>
> You always need a nodeset, even with @calculate. I'm surprised that
> you are getting Chiba to output something using @calculate with no
> @nodeset value, so you might want to double-check that you really are
> seeing what you think you are seeing.
>
> One way to understand xf:bind is to see it as adding extra
> 'properties' to an instance node. I realise that in your particular
> example you want to have relevance based only on the result of an
> expression, but that's not possible; in XForms you have to make some
> existing node relevant, based on the expression you want. And if no
> obvious node exists, then unfortunately, as you have discovered, you
> usually need to invent one.
>
> So the minimum you will need is this:
>
>  <xf:bind
>   nodeset="instance('systemInformation')//@localEdit[1]"
>   relevant="
>    instance('OIDVals')//oids[1]/@active = 0
>     and
>    instance('systemInformation')//@nodeEditable[1] = 1
>   "
>  />
>
> The reason I say "minimum" is that I haven't added an @id value here.
> You only need the @id value if you want a shorthand for the node
> referred to by @nodeset. If all you want is the relevance mechanism
> itself, you can do this:
>
>  <xf:group ref="instance('systemInformation')//@localEdit[1]">
>    ...
>  </xf:group>
>
> I mention this only to draw attention to the two roles that xf:bind
> plays -- one to give a 'name' to a nodeset, and the other to add extra
> 'properties' to each node in that nodeset.
>
> Of course, in your example it's a good idea to use the named binding
> feature too, so that you don't need to worry about keeping the two
> XPath expressions in sync:
>
>  <xf:bind
>   id="bnd-oid-edit"
>   nodeset="instance('systemInformation')//@localEdit[1]"
>   relevant="
>    instance('OIDVals')//oids[1]/@active = 0
>     and
>    instance('systemInformation')//@nodeEditable[1] = 1
>   "
>  />
>
>  <xf:group bind="bnd-oid-edit">
>    ...
>  </xf:group>
>
> If you're wondering about the "bnd-oid-edit" ID value, by the way,
> it's because over the years we've discovered that a little Hungarian
> notation can go a long way to helping keep the numerous @id values
> that you need in XForms, distinct.
>
> It's also worth pointing out -- and I hope I'm not telling grandmother
> to suck eggs here :) -- that "//" usually causes quite a performance
> hit in XSLT/XPath engines, so it's often worth spelling out the full
> XPath for your instance data. (Especially if you are mapping that
> XPath to a named nodeset, via xf:bind.)
>
> Regards,
>
> Mark
>
> On Thu, Aug 6, 2009 at 1:58 PM, Adam Flinton<adam.flinton@nhs.net> wrote:
>> Dear All,
>>
>> I have a couple of groups one for editing (i.e. uses input fields) & one
>> for readonly (ie only uses output fields).
>>
>> Which to show is determined by binding to a bind which has a "relevant"
>> attrib set e.g.
>>
>>      <xforms:bind id="OID_EDIT"
>> relevant="instance('OIDVals')//oids[1]/@active = 0 and
>> instance('systemInformation')//@nodeEditable[1] = 1"
>> nodeset="instance('systemInformation')//@localEdit[1]"/>
>>       <xforms:bind id="OID_NO_EDIT"
>> relevant="instance('OIDVals')//oids[1]/@active = 1 and
>> instance('systemInformation')//@nodeEditable[1] = 1"
>> nodeset="instance('systemInformation')//@localNoEdit[1]"/>
>>
>> & then:
>>
>> <xforms:group appearance="minimal" bind="OID_EDIT"
>> id="OID_Group_Editable">
>>
>> etc.
>>
>> I can only seem to get it to work (in Chiba) is via having a nodeset
>> which is just there to bind to. I.e. I create 2 dummy/empty attributes
>> within an instance & use them as the nodeset reference.
>>
>> Do I need a nodeset ?
>>
>> e.g. should
>>
>>    <xforms:bind id="OID_EDIT"
>> relevant="instance('OIDVals')//oids[1]/@active = 0 and
>> instance('systemInformation')//@nodeEditable[1] = 1" />
>>    <xforms:bind id="OID_NO_EDIT"
>> relevant="instance('OIDVals')//oids[1]/@active = 1 and
>> instance('systemInformation')//@nodeEditable[1] = 1" />
>>
>> Work in the same way?
>>
>> It appears to work for calculated values e.g.
>>
>> <xforms:bind id="CountOv" calculate="count(instance('OIDVals')//ov)"/>
>>
>> So are there any rules wrt binding & when you need a nodeset & when you
>> don't?
>>
>> TIA
>>
>> Adam
>>
>>
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>
>
>
> --
> Mark Birbeck, webBackplane
>
> mark.birbeck@webBackplane.com
>
> http://webBackplane.com/mark-birbeck
>
> webBackplane is a trading name of Backplane Ltd. (company number
> 05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
> London, EC2A 4RR)
>
>
>
>



-- 
Mark Birbeck, webBackplane

mark.birbeck@webBackplane.com

http://webBackplane.com/mark-birbeck

webBackplane is a trading name of Backplane Ltd. (company number
05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
London, EC2A 4RR)
Received on Thursday, 6 August 2009 14:43:07 GMT

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