RE: What good is Restriction?

It is also perhaps worth noting that "derivation 
by restriction" is not supported in all OO environments.  
For example, most of what you can do in XSD restriction 
can only be accomplished using "constraints" in UML.  
And this requires an add-on constraint language, 
such as OCL, which is not part of UML itself.  

In fact the formal notion of derivation-by-restriction 
- a formally defined fully valid subset - 
might be seen as a significant additional capability 
provided by XSD which is an enhancement to standard 
object meta-models.   

_____
[This mail represents part of a discussion of work in progress 
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Simon.Cox@csiro.au  CSIRO Exploration & Mining
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http://www.csiro.au/page.asp?type=resume&id=CoxSimon

> -----Original Message-----
> From: Gary Cramblitt [mailto:garycramblitt@comcast.net]
> Sent: Tuesday, 9 July 2002 5:41 AM
> To: xmlschema-dev@w3.org
> Subject: What good is Restriction?
> 
> 
> 
> Quoting from the XML-Schema Primer, when deriving a new type 
> by restricting a base complex type...
> ---
> Notice that types derived by restriction must repeat all the 
> components of the base type definition that are to be included 
> in the derived type
> ---
> So if I must repeat everything in the base type as well as the 
> restrictions, what good is it?  Why not just create a new type 
> and be done with it?  My conclusion is that while XSD claims 
> to be object oriented, it doesn't support full inheritance, at least 
> not in this instance.  Maybe this is similar to Microsoft's  
> "Interface Inheritance"?  Anybody know why this requirement 
> was put in the spec?  Just wondering...
> 
> Thanks
> 
> --
> Gary Cramblitt
> garycramblitt@comcast.net
> 
>

Received on Monday, 8 July 2002 22:38:19 UTC