Question

I have simple XML format for metas

<?xml version="1.0" encoding="utf-8"?>

<metas>
<meta type="date">
    <code>storage_date</code>
    <value>12-02-1989</value>
</meta>
<meta type="int">
    <code>weight</code>
    <value>12</value>
</meta>
<meta type="bool">
    <code>foo</code>
    <value>true</value>
</meta>
<meta type="text">
    <code>bar</code>
    <value>Hello world</value>
</meta>    
</metas>

I want to have schema that takes into account my meta type and validate depending if it is an int bool date or text.

So far I have

<?xml version="1.0" encoding="utf-8"?>
<xsd:schema attributeFormDefault="unqualified" elementFormDefault="qualified" version="1.0" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="metas" type="metasType" />
  <xsd:complexType name="metasType">
    <xsd:sequence>
      <xsd:element maxOccurs="unbounded" name="meta" type="metaType" />
    </xsd:sequence>
  </xsd:complexType>

  <xsd:complexType name="metaType">
    ???
</xsd:schema>

Is what I am trying to do possible to validate with schemas ?

Answer 1

So you want the type attribute on the meta element to control the content of the meta element. One way to do that is to:

1. let metaType be an empty type
2. create a new type by extension from metaType for each possibility
3. have the type attribute on the meta element be xsi:type
4. the type attribute’s value should identify the actual subtype of metaType being used

E.g. you define meta_int as a subtype of metaType. When you define the value element there, it will be type xs:int. Then you will have in your XML:

<meta xsi:type="meta_int">
  <code>weight</code>
  <value>12</value>
</meta>

Another approach is to use different element names rather than the type attribute (e.g., a meta_int element). You can then use a choice group to choose between the various meta_* elements.

Yet another approach might be to use assertions, but that is a feature of XSD 1.1 which is not yet official (AFAIK).

I am not sure what you are doing, but I think it is fair to say that in XSD, the element names are generally what is most useful in controlling the content that follows, whereas you are trying to do that using an attribute.