X-Schema syntax

Andy Dent dent at oofile.com.au
Mon Jun 28 23:07:45 BST 1999

At 17:17 -0400 27/6/99, Paul Prescod wrote:
>Although I am in favor of instance syntax in general I think that
>recasting regular expressions as nested elements is a big mistake from a
>usability point of view and a very small gain from an ease-of-parsing
>point of view.

I'm really not sure I understand what you're talking about here so 
the following comments may be totally inapplicable, but I think my 
point below is still valid.

 From a usability point of view (which drives a LOT of my API design) 
I think it is much easier for most people to understand definitions 
in context.

Many document types, and particularly database documents, will define 
elements that are only meaningful in a larger context (eg: LastName 
within Person).

The X-schema and DTD modes seem to support only defining all atomic 
elements separately from a context saying where they are used.

This requires the reader and writer of these schemae to build an 
abstract model in their heads that puts the definitions in context.

For both machine and human reading and writing of schemae, where 
nested contexts are meaningful, I found the following variation much 
easier to follow.

So did the programmers I tested it on - as a UI designer of several 
years experience I'm not so bold as to propose something on usability 
grounds without a focus group :-). The test group I picked range in 
programming experience, database experience and programming 
languages(VB, C & C++). The only common factor was their lack of XML 
or SGML background.

The contextual definition of elementTypes which are atomic 
(containing a dataTypeRef) also allows for reuse of element names 
which is essential for writing out database schemae.

       <elementType name='dbStudents'>
          <elementType name='Last_Name'>
             <datatypeRef name='string' length='25'/>
          <elementType name='First_Name'>
             <datatypeRef name='string' length='15'/>

Andy Dent BSc MACS AACM, Software Designer, A.D. Software, Western Australia
OOFILE - Database, Reports, Graphs, GUI for c++ on Mac, Unix & Windows
PP2MFC - PowerPlant->MFC portability

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