Re: [xml-dev] RE: Abstraction in Science, Mathematics, Software, and Mar

[Stephen D Green <stephengreenubl@gmail.com>]

There needs to be a way, then, to point elements (and maybe complex
and simple types) at these crossProducts. Maybe just an attribute added
to xsd:element called something like 'crossProduct' or maybe something
more sophisticated like a combination of an element whose type is the
crossProduct and a substitution group in another element, I haven't thought
it through...  The simplest might be to see the crossProduct as orthogonal
to any association between element and its type and just to add a
'crossProduct' attribute I think. Hopefully it would allow an 'is-a'
relationship
to be defined in a schema between a concrete element and an abstract
crossProduct which might be very useful in

1) modelling using the XSD
2) defining semantics using the XSD

Maybe we need an initial feasibility study plus a temporary XSD extension
namespace for the crossProduct element and, maybe, attribute followed
by perhaps a more premanent namespace if it all proves to be useable. I
imagine there would be a lot of use for this even without adding anything
to any future W3C XML Schema standard since the two uses above do not,
I think, absolutely need anyhting more than a custom extension since tools
which execute a schema in versions 1.0 and 1.1 perhaps are more for
validation than modelling or semantics (perhaps the modelling aspects
could make use of the extension though).

----
Stephen D Green



On 12 March 2011 11:08, Costello, Roger L. <costello@mitre.org> wrote:
>> I'd add that a 'crossProduct' should be able to include ref's to not just
>> simpleTypes but also to other crossProducts.
>
> Excellent!
>
> Yes!
>
> /Roger
>
>
> -----Original Message-----
> From: Stephen D Green [mailto:stephengreenubl@gmail.com]
> Sent: Saturday, March 12, 2011 6:06 AM
> To: Costello, Roger L.
> Cc: xml-dev@lists.xml.org
> Subject: Re: [xml-dev] RE: Abstraction in Science, Mathematics, Software, and Markup
>
> +1
>
> I'd add that a 'crossProduct' should be able to include ref's to not just
> simpleTypes but also to other crossProducts.
>
> ----
> Stephen D Green
>
>
>
> On 12 March 2011 10:34, Costello, Roger L. <costello@mitre.org> wrote:
>> Hi Stephen,
>>
>>> Are you suggesting or even hinting that it should be possible
>>> to define a type whose contents are types rather than elements?
>>
>> Funny you should ask! Yes!
>>
>> A couple weeks ago I pitched that very idea on the xmlschema-dev list:
>>
>> --------------------------------------------
>>           Data Abstraction
>> Creating a User-Defined Data Type that is a
>>  Collection of User-Defined simpleTypes
>> --------------------------------------------
>>
>> Decoupling the definition of a simpleType from an element or attribute declaration is very useful. For example, here I define a family name simpleType:
>>
>>    <xs:simpleType name="Family-name">
>>        <xs:restriction base="xs:string">
>>            <xs:minLength value="1" />
>>            <xs:maxLength value="100" />
>>            <xs:pattern value="[a-zA-Z' \.-]+" />
>>        </xs:restriction>
>>    </xs:simpleType>
>>
>> Now that it is defined, I can declare any number of elements or attributes to be of that type; for example:
>>
>>    <xs:element name="Family-name" type="Family-name" />
>>
>>    <xs:element name="Surname" type="Family-name" />
>>
>>    <xs:element name="Last-name" type="Family-name" />
>>
>> That's nice!
>>
>> The definition of the user-defined simpleType and the declaration of the elements are completely decoupled. The Family-name simpleType is a reusable data type.
>>
>> Suppose I define 2 more simpleTypes. A simpleType for Middle initial:
>>
>>    <xs:simpleType name="Middle-initial">
>>        <xs:restriction base="xs:string">
>>            <xs:length value="1" />
>>            <xs:pattern value="[A-Z]+" />
>>        </xs:restriction>
>>    </xs:simpleType>
>>
>> And a simpleType for Given name:
>>
>>    <xs:simpleType name="Given-name">
>>        <xs:restriction base="xs:string">
>>            <xs:minLength value="1" />
>>            <xs:maxLength value="100" />
>>            <xs:pattern value="[a-zA-Z' \.-]+" />
>>        </xs:restriction>
>>    </xs:simpleType>
>>
>> Now there are 3 simpleTypes. Collectively, they make up a user-defined "Name" data type.
>>
>> Of course, this Name data type is not a simpleType. It is made up of three simpleTypes.
>>
>> XML Schema does not have a way to express this so I propose a new capability, <xs:crossProduct>. Here is how to define the Name data type:
>>
>>    <xs:crossProduct name="Name">
>>        <xs:componentType ref="Given-name" />
>>        <xs:componentType ref="Middle-initial" />
>>        <xs:componentType ref="Family-name" />
>>    </xs:crossProduct>
>>
>> That defines a data type that is a cross product of 3 simpleTypes.
>>
>> Now that it is defined, I can declare any number of elements to be of that data type; for example:
>>
>>    <xs:element name="Name" type="Name">
>>        <xs:element name="First" type="Name.Given-name" />
>>        <xs:element name="MI" type="Name.Middle-initial" />
>>        <xs:element name="Last" type="Name.Family-name" />
>>    </xs:element>
>>
>> Here's a different assignment of element names to the data type and its components:
>>
>>    <xs:element name="Customer" type="Name">
>>        <xs:element name="Given" type="Name.Given-name" />
>>        <xs:element name="MI" type="Name.Middle-initial" />
>>        <xs:element name="Surname" type="Name.Family-name" />
>>    </xs:element>
>>
>> Here's how the latter would appear in an XML instance document:
>>
>>    <Customer>
>>        <Given>Roger</Given>
>>        <MI>L</MI>
>>        <Surname>Costello</Surname>
>>    </Customer>
>>
>> The important thing to notice is that the data type definition is completely decoupled (abstracted) from the assignment of element names to the component fields of the data type.
>>
>> To recap: just like xs:simpleType enables the creation of reusable (simple) data types, xs:crossProduct enables the creation of reusable (cross product) data types.
>>
>> Comments?
>>
>> /Roger
>>
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>
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