Re: [xml-dev] XML Schema complex type restriction

[Mukul Gandhi <gandhi.mukul@gmail.com>]

On 29 September 2017 at 14:09, Michael Kay <mike@saxonica.com> wrote:

More realistically, imagine you have a complex type whose content model is <element name="para" minOccurs="0" maxOccurs="unbounded"/>, and the assertion says test="exists(para)", then the assertion on its own would allow

<para/>

<fig/>

<fig/>

which the complex type's grammar does not allow.

Requiring the assertion to be true ONLY for content that satisfies the grammar would be a ridiculous burden on schema authors.

 

Thanks for sharing this example. In this, the assertion has violated the constraint defined by the grammar. I think, this is an anti-pattern for using an assertion.

Please consider the following example:

XML instance

<?xml version="1.0"?>

<speed>

   <from>10</from>

   <to>50</to>

</speed>

The corresponding XSD 1.1 schema

<?xml version="1.0"?>

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

   

   <xs:element name="speed">

     <xs:complexType>

        <xs:sequence>

           <xs:element name="from" type="xs:positiveInteger"/>

           <xs:element name="to" type="xs:positiveInteger"/>

        </xs:sequence>

        <xs:assert test="from lt to"/>

     </xs:complexType>

   </xs:element>

   

</xs:schema>

IMHO, these are the sort of use cases, where assertions are quite useful.

--

Regards,

Mukul Gandhi