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

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

+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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