RE: Sets and bags || UML and PUML going astray



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Daniel Jackson (dnj@lcs.mit.edu)
Wed, 24 Jan 2001 21:52:59 -0500


dov, let's get together and chat sometime. how about lunch one day? next monday (jan 29)? /daniel ....-----Original Message----- ....From: Dov Dori [mailto:dori@MIT.EDU] ....Sent: Wednesday, January 24, 2001 9:43 PM ....To: puml-list@cs.york.ac.uk ....Subject: Re: Sets and bags || UML and PUML going astray .... .... ....Hi Daniel, .... ....I share much of the views you express here, and see lots of ....problems in ....UML that I believe I solved with ....Object-Process Methodology. .... ....You can download a few papers from www.sightcode.com .... ....Best regards .... ....Dov .... ....Daniel Jackson wrote: ....> ....> i am struck by some comments in perdita's email that seem ....to be symptomatic ....> of why UML's gone astray. forgive my directness here, but ....i think these ....> issues are important, and i'm worried that the PUML group ....is exacerbating ....> the problem rather than solving it. ....> ....> first, this business about "static" vs "dynamic": ....> ....> ....I think _one_ of the root causes of UML's ambiguity is that ....> ....there is a confusion between static and dynamic ....associations. What do ....> ....we want to *use* associations for? ....> .... ....> ....Static: I want associations to tell me something ....about the structure ....> ....of the associated classes. If you want the presence of an ....> ....association between two classes to model the ....existence in one class of ....> an ....> ....attribute whose type is the other class, then you tend to view ....> ....associations as almost-classifiers. ....> .... ....> ....Dynamic: I want associations to tell me something about the ....> ....dynamics of my system. An association between A and B ....means simply that ....> an ....> ....object of one of the classes may send a message to an ....object of the ....> ....other, then it is more natural to view the ....(identity-free) links as ....> primitive with the ....> ....association seen as a relation. ....> ....> both of these seem wrong to me, because they're both ....hopelessly bound up ....> with the semantics of a particular programming language. ....if you don't have ....> classes, attributes, messages, etc, none of this makes ....sense; and if you ....> want to make it precise, you'll need to elaborate what ....you mean by these ....> terms, and thus bind the modelling language to a ....particular programming ....> language. do we really want to think of UML as a ....graphical notation for C++? ....> ....> this characterization of the static view is completely ....syntactic; to me, ....> this suggests it won't be of much use (since it's ....relationship to the ....> program text is trivial). the dynamic view doesn't appeal ....to me either; i ....> can't see what use cardinalities will be in such a context. ....> ....> a better approach, i think, is to give a semantics to the ....notation that maps ....> it to a domain of mathematical objects that is precise ....and simple. then, in ....> a second step, we interpret the artifacts of interest by ....mapping to this ....> domain. ....> ....> for object models, i take as the domain labelled graphs ....or relations. each ....> object model denotes a set (usually infinite) of such ....graphs. for an object ....> model of a program, we can interpret the heap as such a ....graph; the object ....> model is then a heap invariant. for an object model of a ....problem domain, we ....> can interpret the real world and its entities and their ....relations as such a ....> graph. ....> ....> the advantages of this approach are: ....> -- decoupling programming languages from modelling languages ....> -- getting a simpler semantics and making tool support possible ....> -- allowing a smooth transition from problem to solution ....object models ....> ....> it also makes it possible to use object models in more ....abstract settings. ....> we've used Alloy, our modelling language, to analyze ....naming schemes, ....> security domains, and network topologies, for example. ....doing this with a ....> language that has a "rich" notion of objects and ....associations would be ....> awkward at best. ....> ....> second, a response to a more general comment: ....> ....> ....*However*, I do think we need to work in the context of ....> ....UML, or at least in ....> ....the context of modelling languages, because that's where ....> ....the problem is. ....> ....> no it isn't! the problem is in the context of developing ....software. it may ....> well be the case that UML has become more of a problem ....than a solution, but ....> we should think carefully about whether it's a problem ....that's important ....> enough to work on. i wish instead we could focus our PUML ....discussions on ....> case studies and real practical problems and be less ....distracted by the ....> self-inflicted complexities of UML. ....> ....> /daniel ....> ....> To remove yourself from this list please mail ....puml-list-request@cs.york.ac.uk ....> with a message containing the word "unsubscribe". .... ....-- ....Dov Dori, Ph. D., Founder and CEO ....Sight Code, Inc. ....27A Mica Lane ....Wellesley, MA 02481 ....ddori@sightcode.com ....www.sightcode.com ....Tel. 781-431-0433, Mobile 781-858-2867, Fax 781-416-1841 .... ....Visiting Assoc. Professor ....Engineering Systems Division ....School of Engineering ....Massachusetts Institute of Technology ....77 Massachusetts Avenue, Building 37-447 ....Cambridge, MA 02139, USA ....dori@mit.edu ....Tel. 617-964-7930, Fax 617-253-8632 ....On sabbatical from Technion, Israel Institute of Technology ....http://ie.technion.ac.il/dori.phtml .... .... .... ....To remove yourself from this list please mail ....puml-list-request@cs.york.ac.uk ....with a message containing the word "unsubscribe". ....


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