comments relax-ng 0.9

[Berthold Daum <bdaum@online.de>]

Hi,

 

I have a few points of concern regarding the Relax-NG 0.9 specifications:

 

1. Some operations seem not to conserve semantics. For example, given the pattern

 

<define name="example">
  <element name="firstName"><text/></element>
  <element name="lastName"><text/></element>
</define>

 

When we insert this pattern into some contexts, the intended semantics could be destroyed:

 

<choice>
  <ref name="example">
</choice>

 

matches only with instances that have either a firstName or a lastName.

 

<interleave>
  <ref name="example>
</interleave>

 

looses the intended order of elements. This is even true when the pattern is defined with a <group> clause.

 

While all the above operations are completely correct in terms of pattern substitution, they could
prove dangerous. Schema authors may with this pattern intuitively associate similar semantics as 
given by

 

<element name="name">
  <element name="firstName"><text/></element>
  <element name="lastName"><text/></element>
</element>

 

Here the definition of a sequence of child elements has the implicit meaning of an ordered sequence, a
meaning that could be associated with the above pattern definition by analogy.

 

To my opinion, schema validators should give a warning when such a pattern is referenced in a way as
shown in the examples above.

 

2. global="true"

 

I think this functionality is required, especially when referencing an external pattern with

 

<externalRef href="chameleon.rng" ns="http://www.example.org"/>

 

The global attribute would allow to cast also the attributes of such a "chameleon" pattern into the
specified namespace.
Maybe the name of the attribute should be revised though, for example, something like "parentNs".

 

3. Cross references

 

I think, in this point Relax-NG falls back behind XML Schema. The ability to define multi-field keys
and key references is, for example, required when we want to serialize databases into XML.

 

4. Brilliant. Love it!

 

Berthold Daum
bdaum industrial communications
bdaum@online.de