[topicmapmail] multidirectional property of association role

[Jan Algermissen]

Dan Wu wrote:
> 
> Hello again,
> 
> In the same paper, The TAO of Topic Maps,
> that I was reading.
> 
> On page 12, it argued that
> "....associations are inherently multidirectional. In topic maps
> it does not make sense to say that A is related to B but that
> B is not related to A; If A is related to B, then B must, by definition,
> be related to A...."
> 
> For example, in the assocation born_in,
> I can have an association born_in(John, Canadan) to indicate
> that John was born in Canada.
> 
> The association between John and Canada, expressed
> in topic map as an association born_in(John, Canada)
> is differnent than the association born_in(Canada, John).
> 
> Furthermore, on page 12, it said
> 
> This is another way of warning against believing that the names
> assigned to association types (such as "was influenced by") imply any kind
> of directionality. THEY DO NOT!..."
> 
> Does the above sentence mean born_in(John, Canada) is the same
> as born_in(Canada, John)?

Dan,

it all depends on what roles John and Canada play. Also, I strongly
suggest that you DO NOT use names for association types that imply a
direction, it's just too misleading!

In your example I would do this:

association role played by Canada:  "Birthplace"
association role played by John:    "Living Being" or "Born-Being"
association type:                   "Association-Type-Living-Being"

(Well, this is of course not very readable, but I hope it shows
you the idea behind roles and association types.

Also note that  "Association-Type-Living-Being" is in fact a
class and that all associations of type "Association-Type-Living-Being"
are instances of that class.

Also, it might be very helpfull to think about associations with three or more
roles, that keeps you away from thinking in terms of binary relationships
and directions.

Hope that helps,

Jan

-- 
Jan Algermissen,
Consultant & Programmer
http://www.topicmapping.com