Limit the value of an element based on existing XML data

[daddyjones]

I'm fairly sure what I want to do can't be done, but I thought I'd ask on here just in case.

If I have the following XML:

Code: Select all

<foo>
<bar name="lorem" />
<bar name="ipsum" />
<bar name="dolor" />
<bar name="sit" />
...
</foo>

Is it possible, in XML Schema to restrict a new element to the existing values of the name attribute? For example, I would define a new element called <foobar> which had an attribute called "name" and the value of the attribute could only be, in this case, lorem, ipsum, dolor or sit - and that's based on the XML and not an <xs:enumeration />. So if I added elements to the XML I would increase the possible values allowed.

I hope that all makes sense!

[tavy]

Hello,

If you want to restrict the values from an attribute based on some exiting values from the XML, you can use Schematron rules inside XSD or as a separate Schematron schema file. The Schematron rule in your case can be something like this:

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<sch:rule context="foobar/@name">
    <sch:let name="values" value="//bar/@name"/>
    <sch:assert test=". = $values"> Invalid value "<sch:value-of select="."/>",
        should be one of: "<sch:value-of select="$values"/>"
    </sch:assert>
</sch:rule>


Best Regards.
Octavian

[daddyjones]

thanks for the reply - so there's no way of doing this built into XML Schema itself? Would most standard parsers be able to validate based on both XML Schema and Schematron?

[daddyjones]

Could XPointer be used to achieve this?

[daddyjones]

Or XInclude? I think I could use XInclude to include an XML fragment - which might do, although I'm struggling to figure out how to get Oxygen to work with this...

[Radu]

Hi,

I second Octavian's post that Schematron is the only way to do this.

Regards,
Radu