Re: Sets and bags / Identity of a link



Date view Thread view Subject view Author view

Kerry Raymond (kerry@dstc.edu.au)
Thu, 25 Jan 2001 11:44:43 +1000


> Mmmm. On this topic, is it not the case that the only way one can invoke a > message on another object is if you have a reference to it through one of your > own queries (could be an attribute, could be a function, could be tied to an > association - see my previous email on this topic) or through a temporary > variable, such as a method parameter or a variable locally declared in the > invoking method. Indeed. The whole basis of the problem seems to be that having decided to draw associations (in their static sense of being structural relationship) as a line in a UML diagram, it then "follows" that anything drawn as a line must therefore be an association. Clearly, structural relationships and communication paths are completely different things, and conceptually we should keep them so with their own properties and not attempt some "unified theory" merging two entirely different concepts, just because we draw them the same way. On the subject of association classes, I am always a little uneasy with treating them as a true class. An instance of an association class comes into existence with the creation of a link in the association, and should disappear when the link goes. Personally, I prefer to think of them as being part of the tuple-space represented by the asssociation. So an association between classes X and Y with an association class Z with attribute A is to me just a set of <X,Y,a> triples. That is, I unroll the association class into its constituent elements. Kerry =========================================================================== Dr Kerry Raymond, Distinguished Research Fellow kerry@dstc.edu.au CRC for Enterprise Distributed Systems Technology Ph: +61 7 3365 4310 University of Queensland 4072 Australia Fax: +61 7 3365 4311 ===================================================== www.dstc.edu.au/kerry


Date view Thread view Subject view Author view