Derivation by Restriction

[Henry S. Thompson]

"Fabio Arciniegas A." <l-arcini at uniandes.edu.co> writes:

> Hi all.
> During the definition of a schema for instances product of Object
> serialization, I begin to wonder about the implications of derivation
> by restriction in XML: Schema when used with OO apps...
> 
> Is derivation by restriction necessary/desirable? could anyone
> please explain the need behind it a bit? Is D by R a "threat" to
> the conformance[1] principle when using schema to define object
> hierarchies? 
> 
> just oblique thoughts... :) comments?
> 
> Fabio
> 
> 
> [1] loosely put, the traditional conformance principle in OO states: If B
> inherits from A, B can be used wherever A can be used.

That's precisely the intention of restriction.  Any element
information item (EII) which is valid per a type (R) derived by restriction
from a type (T) by construction contains all the required components
of T.  It follows that all such EIIs are valid per T.

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht at cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/

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