How to model variant data structures in XML Schema

How would you model a variant data structure in XML Schema, without using xsi:type? My goal is to define a schema for an element named <property> whose attributes and attribute types depend on the datatype attribute; for example:

<property datatype="integer" default="1234"/>
<property datatype="string" default="Abcde" maxlength="255"/>

Here, the default attribute of the integer-typed property shall only accept valid integer values, whereas the default attribute of the string-typed property sh开发者_StackOverflowall accept any characters.

Furthermore, the maxlength attribute shall be allowed only if datatype="string".

I.e. a schema validation error should occur on both of the following properties:

<property datatype="integer" default="NotAnInteger"/>
<property datatype="integer" default="12345" maxlength="100"/>  <!-- maxlength not allowed -->

I know that if I would use xsi:type instead of datatype, this would be easy to model in XML Schema. There are, however, at least two reasons, why I do not want to use xsi:type here:

• I have read in many places that it is not considered good style to use xsi:type, e.g. xsi:type is Evil or Smart but useless, part 3.

• The name xsi:type simply does not express the purpose of the attribute precisely enough. I rather would prefer datatype.

You can do this using Conditional Type Assignment in XSD 1.1, which is implemented in current releases of Xerces and Saxon. It can't be done in XSD 1.0 - it's a well known restriction (often referred to under the label "co-occurrence constraints").