General talk about software patterns

[Cruz Farfan <cruzfarfan AT yahoo.com>]

Hi Steve,

 

That's part of the question I'm trying to answer.

 

Cruz

Steve Schow <steve AT bstage.com> wrote:

> Hi all.
>
> I have one question. Is there any particular reason why this needs to
> be categorized into any one particular pattern? If its recurring
> "pattern" of any kind...and it doesn't quite fit the mold of of one of
> the existing patterns that have been identified in the existing books on
> the subject, then might this be a NEW pattern?
>
> -steve
>
> > -----Original Message-----
> > From: patterns-discussion-admin AT cs.uiuc.edu 
> > [mailto:patterns-discussion-admin AT cs.uiuc.edu] On Behalf Of 
> > oleg shteynbuk
> > Sent: Wednesday, June 11, 2003 9:05 AM
> > To: Cruz Farfan
> > Cc: gang-of-4-patterns AT cs.uiuc.edu; patterns-discussion AT cs.uiuc.edu
> > Subject: Re: [patterns-discussion] Re: [gang-of-4-patterns] 
> > MVC, PAC or Layers in J2EE applications?
> > 
> > 
> > I agree that behavior of controller is different too. After!
>   
> >
>  looking at 
> > PAC pattern again I can see your point that Module 2 is more close to 
> > PAC then MVC but I have hard time seeing it as the Layers pattern. It 
> > might be difficult to pin down exact match to existing 
> > patterns; after 
> > all there were no servlets at the time when POSA 1 was 
> > published. Intent 
> > of MVC in POSA 1 is close to Model 2 except for the last sentence on 
> > change-propagation mechanism. Intent of PAC looks different to me, as 
> > you noted there is no hierarchy of agents, but if you reduce 
> > hierarchy 
> > to one then implementation of PAC is close to Model 2, but it is my 
> > understanding that intent is what matters and implementations 
> > could be 
> > different.
> > 
> > 
> > Having a cool name like MVC might have played a role too :)
> > 
> > oleg
> > 
> > 
> > Cruz Farfan wrote:
> > 
> > > Thanks for your reply Oleg.
> &!
>  gt;
>  >
> > > Certainly, the Model-2 variant theory takes care of the notification
> > > issue. However, that's not my only issue. When I read Sun's 
> > > description of Model-2:
> > >
> > > 
> > http://java.sun.com/blueprints/guidelines/designing_enterprise_applica
> > > tions_2e/web-tier/web-tier5.html
> > >
> > > I can't help thinking the Controller servlet they're describing is
> > > acting as a Mediator and not as a Strategy. Thus even by Sun's 
> > > description the pattern looks more like PAC 
> > > (Presentation-Abstration-Control) and less like MVC.
> > >
> > > Well, I guess that puts me in the MVC purists list :)
> > >
> > > Thanks again,
> > >
> > > */oleg shteynbuk /* wrote:
> > >
> > > I believe that Sun and Apache when first mention this pattern
> > > refer to
> > > it as a Model 2 that is a!
>   variant
>  of the MVC pattern 
> > but probably
> > > because Model 2 doesn't sound as good as MVC they use 
> > MVC most of the
> > > time. My first impression was similar to yours, where is the
> > > notification part of MVC. There was a discussion on 
> > this issue, I
> > > do not
> > > remember if it was on apache site or sun's or in some book, that
> > > if you
> > > are the MVC purist then it is not MVC but if you are 
> > not a purist
> > > then
> > > it is an MVC variant. And actually the MVC structure is 
> > there but
> > > behavior is different, does it qualify it is a variant 
> > is a separate
> > > question. Model 2 probably sounds more like sun's internal
> > > codename and
> > > not a pattern name but it is used too.
> > >
> > > oleg
> > >
> > >
> > > Cruz Farfan wrote:
> > >
> > > > Hello everyone,
> &!
>  gt; >
>  >
> > > > I apologize if you already receive this email! . I 
> > sent it to the
> > > > siemens-patterns mailing list, but didn't get a lot 
> > of feedback.
> > > I'll
> > > > really appreciate your comments. This was the 
> > original message:
> > > >
> > > > Most Java experts recommend applying the MVC pattern 
> > to design J2EE
> > > > applications. However, the examples they show don't seem to
> > > follow the
> > > > MVC pattern of Smalltalk and the first POSA book. In 
> > that book, the
> > > > "Siemens" group describes a change-propagation mechanism as a
> > > > fundamental step to write an MVC-based application 
> > and suggests the
> > > > Observer pattern to implement such a mechanism. That 
> > element is
> > > seldom
> > > > present in J2EE applications because is too expensive to
> > > imple!
>  ment
>  in
> > > > terms of performance. In addition, Views and 
> > Controllers components
> > > > are bundled together in J2EE applications as in the 
> > Document-View
> > > > variant of MVC. Because of that, a group of people in 
> > the pattern
> > > > community has suggested that really what J! 2EE 
> > applications are
> > > > implementing is the PAC pattern, but I also have my 
> > doubts about
> > > that.
> > > > Certainly, the Presentation component ! of PAC is a bundle of
> > > the View
> > > > and Controller of MVC, but PAC defines a hierarchy of top,
> > > middle, and
> > > > bottom level cooperating agents. Each agent consists 
> > of its own
> > > > Presentation, Abstraction and Control components. In fact, the
> > > > political elections example in the POSA book implements a pie
> > > chart as
> > > > a vie!
>  w for MVC
>  and as a bottom-level agent for PAC. 
> > Thus, a simple
> > > > agent like a pie chart consists of its own Presentation,
> > > Abstraction
> > > > and Control components. Although this is closer to J2EE
> > > architectures,
> > > > the notion of the hierarchy of agents is not. Of 
> > course, one can
> > > argue
> > > > that the hierarchy is implicitly present, but I think this is
> > > forcing
> > > > things to fit in place. In contrast, J2EE 
> > architectures seem to
> > > follow
> > > > the mu! ch simpler Layers pattern. A minimalist 
> > example could be
> > > the
> > > > following three-layer architecture:
> > > >
> > > > 1. Presentation Layer (JSP, HTML, etc.)
> > > > 2. Control or Mediator Layer (Servlets, Session EJB, etc.)
> > > > 3. Abstraction or Model Layer (Entity EJB, JDO, etc.)
> > >
>  >
> > > > I'm using the same PAC terminology on purpose because 
> > I realized
> > > that
> > > > one can see the whole J2EE system as one big PAC 
> > agent, but I'll
> > > still
> > > > argue that most J2EE applications follow neither MVC nor PAC,
> > > but the
> > > > Layers pattern.
> > > >
> > > > Your thoughts?
> > > >
> > > >
> > > 
> > --------------------------------------------------------------
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