[news.eclipse.tools.uml2] Re: Why UML2 metamodel is "flattened" ?

["Antonio Carrasco Valero" <acv@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Thanks Kenn,

YES! Eclipse UML implementation is aligned with UML2.1 standard
(here I refer to the subject of merged packages).

The choice of flattening the whole metamodel into a single package,
is indeed a standard simplification that has been incrementally
added to UML2 in its various revisions over the last 3 years.
(for details, see paragraphs at the end of the message).

No (M1) modeler user with a "final" tool like Rational Architect
would ever notice the flattening, nor needs to concern him or herself with 
this.

Granted!


But as an Eclipse plug-in, where a great (and big) community
is in the business of metamodeling and tooling
the choice of Not Providing implementations of the merged/receiving packages
is in my opinion unfortunate:
As explained in previous message,
I fear their absence does not help in interoperability of DSLs,
and makes Metamodelling by specialization of Eclipse UML2.1 implementation,
a burden identical to that of Profiling
as one has to suffer the whole merged specifications,
and all their referenced elements,
as opposed to just the semantics needed.

I believe that it is possible and recommendable to supply to the community
an implementation with the result packages,
as well as the "intermediate" merged/receiving.

Any interested parties ? - or are all already in the non-UML, discrete DSL 
mindset ?

Cheers,
Antonio Carrasco Valero
Model Driven Development sl






Point 7.13.2 Package Merge of 2003´s OMG´s UML2.0 Superstructure Final 
Adopted specification document 03-08-02 stated in the third paragraph:

"A package merge is a relationship between two packages, where the contents 
of the target package (the one pointed at) is
merged with the contents of the source package through specialization and 
redefinition, where applicable.
This is a mechanism that should be used when elements of the same name are 
intended to represent the same concept,
regardless of the package in which they are defined. A merging package will 
take elements of the same kind with the same
name from one or more packages and merge them together into a single element 
using generalization and redefinitions.
It should be noted that a package merge can be viewed as a short-hand way of 
explicitly defining those generalizations and
redefinitions. The merged packages are still available, and the elements in 
those packages can be separately qualified.."



Then, point 7.3.40 Package Merge 2004´s OMG´s UML2.0 Superstructure Final 
Adopted specification document 05-07-04 stated in the first two paragraphs:

"A package merge between two packages implies a set of transformations, 
whereby the contents of the package to be
merged are combined with the contents of the receiving package. In cases in 
which certain elements in the two packages
represent the same entity, their contents are (conceptually) merged into a 
single resulting element according to the formal
rules of package merge specified below.
As with Generalization, a package merge between two packages in a model 
merely implies these transformations, but the
results are not themselves included in the model. Nevertheless, the 
receiving package and its contents are deemed to
represent the result of the merge, in the same way that a subclass of a 
class represents the aggregation of features of all of
its superclasses (and not merely the increment added by the class). Thus, 
within a model, any reference to a model
element contained in the receiving package implies a reference to the 
results of the merge rather than to the increment that
is physically contained in that package."




Then, point 7.3.40 Package Merge 2006´s OMG´s UML2.1 Superstructure Final 
Adopted specification document 06-04-02 stated in its first paragraphs:¨
"A package merge is a directed relationship between two packages that 
indicates that the contents of the two packages are
to be combined. It is very similar to Generalization in the sense that the 
source element conceptually adds the
characteristics of the target element to its own characteristics resulting 
in an element that combines the characteristics of
both.
This mechanism should be used when elements defined in different packages 
have the same name and are intended to
represent the same concept. Most often it is used to provide different 
definitions of a given concept for different purposes,
starting from a common base definition. A given base concept is extended in 
increments, with each increment defined in
a separate merged package. By selecting which increments to merge, it is 
possible to obtain a custom definition of a
concept for a specific end. Package merge is particularly useful in 
meta-modeling and is extensively used in the definition
of the UML metamodel.
Conceptually, a package merge can be viewed as an operation that takes the 
contents of two packages and produces a new
package that combines the contents of the packages involved in the merge. In 
terms of model semantics, there is no
difference between a model with explicit package merges, and a model in 
which all the merges have been performed."



"Kenn Hussey" <khussey@xxxxxxxxxx> wrote in message 
news:eh0i4a$6ro$1@xxxxxxxxxxxxxxxxxxxx
> Antonio,
>
> Just to be clear, the UML2 implementation of the UML specification IS in 
> fact fully alligned with, and conformant to, the UML 2.1(.1) standard...
>
> Kenn
>
> "Antonio Carrasco Valero" <acv@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in 
> message news:eh0gbv$q74$1@xxxxxxxxxxxxxxxxxxxx
>> Tas, Kenn, thanks a lot for the rationale and explainations,
>> fully consistent with with the reality of the problem and solutions of 
>> UML2 implementation
>> and indeed with comments from EdMerks and others at Eclipse Summit.
>>
>> - By the way, a most memorable event. Loved it!
>>
>>
>> --- Many Objects in Memory ---
>> I understand that using the composition/delegation approach to Java 
>> implementation of multiple inheritance, creates more complex object 
>> networks.
>>
>> I observe that the choice of approach (composition/delegation) is driven 
>> by the need to avoid duplicating method implementations (and data slots 
>> declaration) in multiple classes,
>> quite an important requirement in EMF, as developers must be able to 
>> customize code,
>> and do it in a single place - not everywhere a certain structure or 
>> behavior happens to be inherited into.
>>
>> But, I hope that we can find other technical solutions,
>> such that fully compliant UML2 implementations can be produced,
>> while preserving our investiment in current usages of UML2
>> - and ironing out one or two wrinkles in the alignment between Eclipse 
>> and OMG.
>>
>> I look forward to James work about UML2 extension.
>>
>>
>> --- Metamodels and Profiles ---
>> The rendering of Metamodels as Profiles of UML
>> is a common practice since the unification at the famous OOPSLA'95,
>> and mandatory in OMG standards.
>> Indeed, the last non-UML-aligned submission BOCA
>> (Business Object Component Architecture, 1998) was rejected,
>> and the following submissions had to include (and were in fact named 
>> after)
>> a UML Profile rendering of their Metamodels
>> (i.e. UML Profiles for CORBA, for EDOC, for EAI, and for SPEM, among 
>> others).
>>
>> Similarly, this reflected the duality of vendor camps,
>> the one partial to UML "final" (as in Java classes, not extensible) tool 
>> vendors,
>> and the MOF alternative.
>>
>> It was my understanding that OMG's UML2 effort tried to resolve both 
>> problems,
>> by enabling the goal of a family of UML languages,
>> with enhanced interopeability by commonality of reusable semantics,
>> and unequivocal adoption of MOF as the metamodelling language of choice.
>>
>> Today, Eclipse proves to the community at large,
>> how modelling tools can be extended with new semantics and syntax,
>> that become first class citizens of the tool, as the ones originally 
>> shipped by the vendor.
>>
>>
>>
>> ---  ---
>> In short:
>> I observe that most of the audience is being driven towards
>> non UML pure unrelated Domain Specific Languages
>> or to Profiling mechanisms in "final" UML tools.
>>
>> Therefore I see no real market or user need for "final" tools,
>> and that the choices made, about which approaches to enable and 
>> facilitate,
>> are strongly influenced by the market dominance efforts
>> that Microsoft, IBM and Sun must engage themselves in,
>> to better guarantee their long term success.
>>
>> On the other side, the community at large is now much better equipped 
>> than 10 years ago,
>> in a big part, thanks to these very same dominance efforts of the market 
>> leaders,
>> but also to many others that wanted interoperable domain specific 
>> modelling.
>>
>> After the amount of talent I've seen since July in
>> the ECDMA, JISBD and Eclipse Summit,
>> it won't surprise me a bit, if somebody comes up and publish
>> open source implementations of UML2 and MOF
>> that are fully aligned with the standards,
>> yet still righfully Eclipse.
>>
>> Cheers!
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> "Tas Frangoullides" <tas.frangoullides@xxxxxxxxxxxxxxxxxx> wrote in 
>> message news:egeg97$r7l$1@xxxxxxxxxxxxxxxxxxxx
>>> Hi Antonio,
>>>
>>>
>>>
>>> I'm not sure I can answer all your questions but I've done some 
>>> heavyweight and lightweight extensions using uml2/emf and so some of 
>>> what I've learnt might be useful.
>>>
>>>
>>>
>>> Kenn once attempted to explain all the pains of retaining the 
>>> hierarchical structure of UML2 in the implementation but my head 
>>> overheated before I could absorb all of it. If I rememeber correctly one 
>>> of the reasons the Eclipse UML2 implementation was flattened is because 
>>> it produced way too many objects in memory, even for moderate sized 
>>> models. I think the UML2 spec has since been updated to reflect this and 
>>> the flat structure of Eclipse UML2 is compliant. Personally I think this 
>>> was a good thing also because I find navigating the metamodel hard 
>>> enough without having several definitions of each element, and the API 
>>> would have been way more complex. Also, because the flattening is only 
>>> done at the final stage of generating the implementation you don't loose 
>>> any of the cherry-picking potential of the complete metamodel.
>>>
>>>
>>>
>>> If you want  you can define your meta model based on any part of the UML 
>>> superstructure or infrastructure and use the UML2 Codegen to generate 
>>> implementations. When I first starting learning about the UML metamodel 
>>> I was very interested in the prospect of reusing the infrastructure and 
>>> unmerged superstructure but in practice I've found extending complete 
>>> specification produces better and more flexible results.
>>>
>>>
>>>
>>> Although profiling is still not as flexible as metamodel extensions it 
>>> does have some advantages and is much improved in version 2.1 of the 
>>> spec, especially compared to UML 1.x.. The big advantage is you don't 
>>> have to write your own model editor and can reuse the UML diagramming 
>>> capabilities of your UML tool. However, profiles are trickier to extract 
>>> data out of when processing them but you can get round this by defining 
>>> both a heavyweight and lightweight extension. What I've done in the past 
>>> is define a nice clean metamodel (often based on UML2, at other times 
>>> just an EMF model) and then defined a UML2 profile equivalent. I then 
>>> implement a transformation between a profiled UML2 model an instance of 
>>> my metamodel. This gives me model instances that are clean and easy to 
>>> traverse without having to develop a new diagram editor. If you have 
>>> diagramming requirements beyond the UML2 diagrams then you've got lots 
>>> of work to do either way. If you are interested in this sort of thing 
>>> then I recommend taking a look at the GMF project.
>>>
>>>
>>>
>>> Hope that is of some use,
>>>
>>> Tas.
>>>
>>>
>>>
>>> "Antonio Carrasco Valero" <acv@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in 
>>> message news:eg8csf$2pv$1@xxxxxxxxxxxxxxxxxxxx
>>>>I am trying to produce a metamodel, not a Profile
>>>>  - as EMF provides such a rich metamodel implementation platform,
>>>>  that is not worth to put up with the lightweight profiling approach .
>>>>
>>>> My well-informed customers require their language to be as integrated 
>>>> as possible
>>>> with the UML Family of Languages promise of UML2,
>>>> and explicitly require to reuse as much reuse as possible of UML2 
>>>> semantics.
>>>>
>>>> But, Eclipse UML2 metamodel implementation has flattened all the UML 
>>>> modeling elements,
>>>> - therefore, their semantics and sintax -
>>>> and only offers the "leaf" specifications.
>>>> For example, in UML2 (infra & supra),
>>>> there are 4 (unless I missed some) Class specifications,
>>>> each incorporating selected semantics and syntax.
>>>>
>>>> My question is:
>>>>
>>>> How does Eclipse UML2 implementation support the OMG (and my 
>>>> customer's) requirement
>>>> of facilitating a UML2 family of languages,
>>>> as opposed to forcing most users to "profile" rather than metamodel ?
>>>>
>>>> My customer is specially sensitive to UML profiling,
>>>> because of their unfulfilled expectations in UML1.x profiling with 
>>>> RRose,
>>>> and perceive that it is a significant risk,
>>>> to expressing their semantically rich domain and technology models,
>>>> instantiating profiled vainilla UML elements,
>>>> rather than fully customized metamodels.
>>>>
>>>> How should I educate my customers about the profile-biased Eclipse UML2 
>>>> implementation ?
>>>>
>>>> Thanks,
>>>> ACV
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
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