A nice pattern

stéphane ducasse ducasse at iam.unibe.ch
Mon Aug 21 10:21:21 UTC 2006


On 21 août 06, at 10:00, Klaus D. Witzel wrote:

> Hi Stef,
>
> this pattern is bread and butter in practice, what is it that you  
> find so important about it (perhaps besides that is gets a new name  
> every now and then ;-)

Because a good pattern is about simple practice and important ones.

> You work in a Department which has a Location in a Building. All  
> these departments belong to the same University which has Location  
> (superlocation of the departments' location) and Web site  
> (superpage of the departments' Web pages). Et cetera. Of course the  
> Movie / VideoTape example is nicer, even kids would understand it  
> when "tape" would be replaced by "game" 8-)
>
> Students of database normalization even (hopefully :) know the  
> value i of the pattern's corresponding i-th normal form. In its  
> most general form, the pattern is B.O.M. (a pre-computer age name  
> for it), see 4th entry on
>
> - http://en.wikipedia.org/wiki/BOM
>
> and it is indispensable in the construction business (yeah, also in  
> the software construction business :)
>
> But it also has drawbacks: say you have a B.O.M. for the A380  
> monster and you ask, how many of the constituent parts do we have  
> to purchase for assembling one instance of that beast. Then you  
> will see, that "S" in SQL stands for "simple", because SQL alone  
> cannot explode a B.O.M. (regardless of how you design the  
> corresponding database): the system (a data language) MUST be  
> extended (i.e. by a computer language) for to obtain that solution  
> (OT: has some form of G"odel's incompleteness).
>
> And large B.O.M's are typically maintained by many people (in a  
> collaborative fashion, like Squeak source code) and time dictates  
> that they are often inconsistent. IMHO they are the "mother" of  
> inconsistent designs (sw, hw, etc) in the construction business.
>
> /Klaus
>
> On Sun, 20 Aug 2006 21:02:26 +0200, Stéphane Ducasse wrote:
>
>> I'm happy to find it on the web
>> for this is a nice pattern that is the first level towards  
>> metamodeling.
>>
>> http://www.ksc.com/article3.htm
>>
>> (as an old CLOS Moper I do not like the aka MetaObject because the  
>> typeObject is not really that
>> but this is a really cool and important pattern).
>>
>> Stef
>>
>>
>>
>>
>
>
>




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