Hi Yongnian,

Le, Yongnian <yongnian.le@i...> writes:

> That's a pity that there is no real application having identity
> constraints, maybe because that feature is quite advanced.

I did a quick search over our schema repository. The following
two "real" schemas appear to use identity constrains:

3DXML                                             http://www.3ds.com/3dxml
Open Vulnerability and Assessment Language (OVAL) http://oval.mitre.org/


> 1.     Identity constraint processing creates dependence between
> validations in different SAX events, which make it hard for further
> advanced optimization; while regular expression in schema validation
> can be processed in a single SAX event validation.

This is not entirely correct. SAX can deliver content for an element
or attribute over several calls to characters().


> 2.     Identity constraint requires typed based comparison, which
> might involve a lot of table/value-object/memory management, type
> conversion and string operations during validation;

That's another reason why it is a good idea to do validation and
data extraction as one step. Luckily the element/attribute that is
specified in the field declaration should be of a simple type. This
way you only need to handle a handful of built-in XML Schema simple
types when it comes to comparing the values. Figuring out if types
are related by inheritance could be tricky though.


hth,
-boris


-- 
Boris Kolpackov
Code Synthesis Tools CC
http://www.codesynthesis.com
Open-Source, Cross-Platform C++ XML Data Binding

From mike@s... Sun May 13 21:13:44 2007
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