Subject: Re: [xsl] xsd- abstract definition|
From: "Laura Jenkins" <xsl_list@xxxxxxxxxxx>
Date: Wed, 02 Oct 2002 14:11:58 +0000
From: Jeni Tennison <jeni@xxxxxxxxxxxxxxxx> Reply-To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx To: "Laura Jenkins" <xsl_list@xxxxxxxxxxx> CC: xsl-list@xxxxxxxxxxxxxxxxxxxxxx Subject: Re: [xsl] xsd- abstract definition Date: Wed, 2 Oct 2002 14:18:33 +0100
> forgive me this is a bit off topic.
It is really -- you should send queries about W3C XML Schema to xmlschema-dev@xxxxxxx
> I have an xsd file, with one of the elements with an attribute > abstract = "true". and i used XML spy to generate an xml file out of > it. and the generated xml can not be validated w.r.t. it says that > the problem is with the abstract value being set to true. However i > changed the value of abstract to false and it is perfectly a valid > file .. I have no clue of the XSD file because it is passed on to me > by one of our clients. Can anyone explain me what "abstract=true" > means?
It means that the element itself can't actually appear in the document. For example, if you had:
<xs:element name="_inline" abstract="true" />
then a document couldn't actually have a <_inline> element in it.
So what's the point? Well, in W3C XML Schema you can provide element substitution groups which basically say that wherever a particular element is specified within a content model, a whole bunch of other elements can appear in their place. For example, you could do:
<xs:element name="emph" substitutionGroup="_inline" /> <xs:element name="strong" substitutionGroup="_inline" /> <xs:element name="code" substitutionGroup="_inline" /> <xs:element name="span" substitutionGroup="_inline" /> ...
and it means that when you had a content model like:
<xs:sequence> <xs:element ref="_item" minOccurs="0" maxOccurs="unbounded" /> </xs:sequence>
it would be interpreted as being exactly the same as:
<xs:choice minOccurs="0" maxOccurs="unbounded"> <xs:element ref="emph" /> <xs:element ref="strong" /> <xs:element ref="code" /> <xs:element ref="span" /> ... </xs:choice>
It also has a kind of conceptual advantage in that it says "these elements are all inline elements".
Usually when you create substitution groups, you don't want the "head element" (like _inline in this example) to actually be allowed in a document. Making it abstract forces one of the members of the substitution group to be used in its place.
I hope that explains things a bit; do post follow-ups to xmlschema-dev@xxxxxxx
--- Jeni Tennison http://www.jenitennison.com/
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
_________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com