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   Re: [xml-dev] Objections to / uses of PSVI?

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On Wednesday 15 May 2002 21:45, Dare Obasanjo wrote:

> Forgive my ignorance but exactly what does isomorphic mean in lay terms?
> I am sure that I've been misinterpreting in the XSD spec.

Isomorphic literally means 'same shaped'.

In computing, we usually use this term to mean two different things that have 
the same fundamental structure.

Let me see... a function accepting an integer and returning either an integer 
or some kind of failure (NULL, -1, throwing an exception) is isomorphic to an 
SQL database table with an integer primary key field and another field which 
is also an integer. Since they both provide this service of converting an 
integer into another integer (for some subset of all integers, unless the 
database table is infinite :-)

Isomorphisms are usually dependent on the context. My table and my function 
are isomorphic to the programmer who uses them, but not to the computer's 
disk subsystem. They're also not isomorphic if you're considering update 
operations - the function's behaviour is fixed unless it's rewritten, while 
the table can have rows added and removed at will.

'Modulo' is often used as a corruption of its meaning in number theory, which 
I won't go into here, but it can be used to mean 'except' or 'barring'.

I am immortal (modulo being stabbed in the heart with a wooden stake).

Numbers in text consist of an optional + or -, one or more digits, and 
optionally a decimal point followed by one or more digits, modulo whitespace. 
In this case, it means that they are leaving whitespace considerations out of 
this definition of a number, probably meaning that whitespace can be added 
anywhere in the number and is to be ignored rather than saying '...consist of 
optional whitespace, and optional + or -, optional whitespace, one or more 
digits optionall seperated by whitespace, ...'.

> Thanks.

Hope that helps,


                               Alaric B. Snell
 http://www.alaric-snell.com/  http://RFC.net/  http://www.warhead.org.uk/
   Any sufficiently advanced technology can be emulated in software  


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