link



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Joaquin Miller (miller@joaquin.net)
Wed, 24 Jan 2001 09:02:54 -0500


Arend Rensink's analysis and Stuart's approach are excellent. Let me bump this up a level, though. (To avoid 'link,' i'll pick an arbitrary name. The following would be much more natural if i used 'link' but i do not want to bring in any presuppositions about what a link is. Warning: by 'class' i do not mean programming language or UML class, but the ordinary English meaning of 'class.') A foo is a set of objects together with an invariant that mentions those objects. Here are two options for 'association:' a. An association is a type of a foo. [type: http://uml.fsarch.com/RM-ODP/Part2/9.html#9.7 ] b. An association is a class of foos. [class: http://uml.fsarch.com/RM-ODP/Part2/9.html#9.8 ] b. may be represented by Arend's 1. thru 3d., Stuart's queries and other options (with various resulting restrictions on the generality of a. and b.). ..... Yes, the given definition of 'class' may limit the possibilities with b. But we get the full range again if we change the 'set' of class to 'bag.' a. does not limit the possibilities. ....... At 12:35 PM 1/24/2001 +0000, Stuart Kent wrote: >An association is a pair of association ends, each comprising a query and cardinality constraint... At 11:17 AM 1/24/2001 +0100, Arend Rensink wrote: >Hm. Let's see what options we have here. > >1. An association is a set of links. Each link has (at least) an identity > and a data content yielding a tuple of objects. > >2a. An association is a set of object tuples. > >2c. An association is a list of object tuples. > >Let me throw in some more possibilities: > >3a. An association is a set-valued object function - that is, a function > yielding for every object of a given "source" class (the left-hand > side of the association) a (possibly empty) set of objects of a "target" > class (the right hand side of the association) > >3b. An association is a bag-valued object function. > >3c. An association is a list-valued object function, where the lists may > not contain duplicates. > >3d. An association is an arbitrary list-valued object function. Cordially, Joaquin ................................................ Joaquin Miller Chief Architect Financial Systems Architects mailto:joaquin@acm.org San Francisco phone: +1 (510) 336-2545 fax: +1 (510) 336-2546 PGP Fingerprint: CA23 6BCA ACAB 6006 E3C3 0E79 2122 94B4 E5FD 42C3


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