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RE: Separate data from rules ... is the XML Schema 1.1<assert>

• From: "Costello, Roger L." <costello@mitre.org>
• To: "'xml-dev@lists.xml.org'" <xml-dev@lists.xml.org>
• Date: Wed, 17 Jun 2009 09:28:54 -0400

Hi Michael,

> > First an example of a business rule: 
> > 
> >     A Level 1 manager has a maximum signature
> >     authority of $10K.
> > 
> >     An auto loan applicant, living in Ohio, is
> >     underage if he/she is under 18 years of age.
> > 
> >     If a customer has no outstanding invoices, 
> >     then the customer is of preferred status.
> > 
> I agree those are business rules and are best kept out of a schema.

I am concerned that schema designers will not recognize that this is bad practice:

    <element name="Level_1_Manager_Signoffs">
        <complexType>
            <sequence>
                <element name="purchase-request" maxOccurs="unbounded">
                    <complexType>
                        <sequence>
                            <element name="item" type="string" />
                            <element name="cost" type="decimal" />                                      
                        </sequence>
                    </complexType>
                </element>
            </sequence>
            <assert test="purchase-request/cost lt 10000"/>
        </complexType>
    </element>

How will a schema designer distinguish between "structural rules" versus "business rules?" (And put the former into XML Schema but not the latter)

What is a "structural rule?"

In XML Schema 1.0 the answer was clear: anything that required computation, if-then-else logic, inference, and co-constraints could not be placed in XML Schema, and was therefore placed in Schematron) All rules were expressed and managed by Schematron.

The XML Schema 1.1 <assert> element adds confusion to the task of building schemas: 

    Is this a structural rule or a business rule? 

    Should I express this using <assert> within 
    XML Schema, or manage it separately in a 
    rules document?

What do you think?

/Roger

• Follow-Ups:
  • RE: Separate data from rules ... is the XML Schema 1.1 <assert> element a step backwards?
    • From: "Michael Kay" <mike@saxonica.com>

• References:
  • Separate data from rules ... is the XML Schema 1.1 <assert> elementa step backwards?
    • From: "Costello, Roger L." <costello@mitre.org>
  • Re: Separate data from rules ... is the XML Schema 1.1<assert> element a step backwards?
    • From: Frank Manola <fmanola@acm.org>
  • RE: Separate data from rules ... is the XML Schema 1.1<assert> element a step backwards?
    • From: "Costello, Roger L." <costello@mitre.org>
  • RE: Separate data from rules ... is the XML Schema 1.1 <assert> element a step backwards?
    • From: "Michael Kay" <mike@saxonica.com>