[topicmapmail] occurence role and its type

[Steve Pepper]

Hi Dan,

At 09:49 30/01/02 -0600, Dan Wu wrote:
>I was reading "the TAO of topic map"
>I am confused by the terms
>occurrence role,& occurrence role type.
>
>The paper said the diference is subtle but important.
>
>I do not think I got the difference.
>Could anyone explain a little bit to me the difference?

The TAO of Topic Maps describes topic maps as defined in ISO 13250, which 
uses SGML and HyTime concepts. As you probably know, there is also 
something called XTM (XML Topic Maps) which adapted ISO 13250 for use on 
the web. There are certain (minor) differences between the two and ISO 
13250 is now being revised to cater for this. (The XTM DTD has already been 
added to ISO 13250 as an Annex and now the text is being revised.)

So the first thing to be said is that, if you are interested in XTM rather 
than HyTM (which people seem to be), then you don't even need to bother 
about the distinction between "occurrence role" and "occurrence role type". 
Occurrence role is essentially a legacy of the HyTime-based meta-DTD used 
to define an architecture for interchanging topic maps.

All you need to understand (while reading The TAO), is that occurrence role 
type corresponds to "occurrence type" in XTM, and that occurrence role has 
gone away.

Now, if you *really* want to know the difference, say so once again, and 
I'll try and explain as clearly as I can. That difference is still subtle, 
but it is no longer so important :-)

Best regards,

Steve

--
Steve Pepper, Chief Executive Officer <pepper@ontopia.net>
Convenor, ISO/IEC JTC1/SC34/WG3  Editor, XTM (XML Topic Maps)
Ontopia AS, Waldemar Thranes gt. 98, N-0175 Oslo, Norway.
http://www.ontopia.net/ phone: +47-23233080 GSM: +47-90827246