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Re: [xml-dev] 'is-a' Relationships in XML?

I belive XSD's  complexType along with extension provide "isa" at the schema level.
I certainly use them that way.

Example:  author_type "is a" person_type"

<xsd:complexType name = "person_type">
            <xsd:element ref = "name"/>
            <xsd:element name = "degree" type = "xsd:string" minOccurs = "0"/>
            <xsd:element name = "title_affil">
                        <xsd:element ref = "para" minOccurs = "0" maxOccurs = "unbounded"/>
    <xsd:complexType name = "author_type">
            <xsd:extension base = "person_type">
                    <xsd:element name = "disclosures" type = "xsd:string"/>

You can also declare pure abstract types like eg.

monograph "is a" abstract element of type monograph_type

<xsd:element name = "monograph" type = "monograph_type" abstract = "true"/>

David A. Lee

On 5/3/2010 2:25 PM, stephengreenubl@gmail.com wrote:
4bdf1551.0c07560a.7185.44aa@mx.google.com" type="cite">

There seems to be no shortage of ways, thankfully, to express 'has-a' relationships with XML (even without using a schema, it seems there is an implicit 'has' relationship between parent element and a child element or atttibute). There could be said to be an implicit semantic 'has' relationship declared between 'document' an 'date' when we write <document><date>...</date>...</document>. Is there any way to express the other key relationship of 'is-a' in XML? Is this something a schema language can express? Can we say that element (or even type) A 'is-an' element (or type) B? Any plans to add this 'feature' to the XML technologies if it isn't one already? It might be a key gap to fill. I might want to somehow imply that my <invoice/> is a <document/>. Are substitution groups (with, apparently, some inadequacies) the only way to express such a relationship in XML?

Best regards

Stephen D Green


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