[topicmapmail] <subjectIndicator> element not mandatory ?

[Steve Pepper]

At 17:43 30/01/02 +0100, Thomas Francart wrote:
>In the XTM DTD, the <subjectIdentity> element is not mandatory. It means
>that a topic element can be created without any subject... which is rather
>confusing.

No, it doesn't mean that a topic can be created without any subject (a 
topic, by definition, *always* represents some subject). All it means is 
that the author of the topic map is not forced to take the trouble to 
specify clearly and unambiguously what the identity of that subject is.

>In this case where no subjectIndentity is present, is the baseName playing
>the role of the subject Identity ? (something having to do the topic naming
>constraint ?) ?

In one sense you could say that the base name is now the only indication 
that either a human or software has of the "identity of the subject". But 
this is not "subject identity" in the formal sense as used in XTM.

>I suppose there is a good reason why the subjectIdentity element is not
>mandatory. Could anyone tell me why ?

Because it's not always necessary and we shouldn't force people to do 
unnecessary things! It's really only necessary if

1) human related:
    - the identity of a topic is not sufficiently clear to humans from the 
context

2) software related:
    - your software needs to be able to establish when two topics are about 
the same subject (e.g. when merging topic maps)
    - there is some other processing-related requirement to be able to 
unambiguously establish the subject identity of a topic

Having said that, I strongly encourage people to take subject identity 
seriously, to use published subject indicators wherever possible, and to 
participate actively in the work of the OASIS Topic Maps Published Subjects 
Technical Committee (see http://www.oasis-open.org/committees/tm-pubsubj/).

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