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Re: [ontolog-forum] MVC

To: Duane Nickull <dnickull@xxxxxxxxx>
Cc: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Edward Barkmeyer <edward.barkmeyer@xxxxxxxx>
Date: Tue, 23 Feb 2010 12:52:53 -0500
Message-id: <4B8415F5.60506@xxxxxxxx>
Duane Nickull wrote:
> I amn not sure if we are thinking the same here:
>       (01)

I think we are.  We just have very different ways of expressing ourselves.    (02)

> IMO, UML is an expression/view of the model, not the model itself.      (03)

I agree with what I think you mean.  I would have said:  A UML model of 
an MVC model is an expression/view of the MVC model, not the MVC model 
itself.     (04)

It is important to distinguish the entirely different concepts denoted 
by UML:model and MVC:model.  Per ISO 1087-1, a designation (the 
interpretation of a sign like "model") has context.    (05)

> An application using MVC has a model. The model can be expressed as UML as
> one possible view.      (06)

This is correct as long as we understand that the term "model" here is 
the MVC term, which means the information processing part of the 
application.  And yes, the MVC Model part of the application can have a 
UML model, just as the MVC "View" and "Control" parts can have UML models.    (07)

> UML can also be used to represent the metadata for the
> model independent of implementation of any instances of the model within the
> application instance (this is where a lot of people get confused).      (08)

Well, I'm confused, because (1) I have no idea what you mean by 
"metadata".  (2) I think "implementation of instances of the model 
within the application instance" means "implementation of the MVC:Model 
part of the application", but I'm not sure.  I would have said that the 
UML:model can be a representation of an MVC:Model instance, i.e., the 
MVC:Model part of an application implementation, at any of several 
levels of abstraction.  (That is the MDA concept.)  Is that what you mean?    (09)

> The application itself does not use UML as the format for the model    (010)

Agree.  Depending on what you mean by "the application itself", the 
format of the operational MVC:model part of the application is probably 
Java Byte Code, or native machine instructions.  At the engineering 
level, the implementation format is Java or C or VBasic.    (011)

> (UML is only 
> a two dimensional "view" of a model, not executable via an application.)
>       (012)

Well, I would agree that a UML model is not usually "executable", 
although the "executable UML" standard has added that possibility.  The 
point is that the UML model, even if it has a 1-to-1 mapping to Java, is 
not the form the software engineer will consider to be the 
"implementation form".    (013)

A "two dimensional view" of a UML model, however, is a "diagram".  A UML 
model is a representation of a concept network (which is the only reason 
this discussion is relevant to the Ontolog Forum).    (014)

> The control can be used to update the model or the view.  The view can also
> offer functionality that can trigger the control to do some forms of
> calculations which may also update either the view, the model or both.
> There are many variations of this.  For example, in Adobe Flex we have many
> frameworks for working with MVC.  Some are more complex than others and use
> secondary patterns such as mediators to register for events and relay
> communications (such as the Cairngorm framework).  PureMVC, Matte are much
> easier to digest for beginners.
>       (015)

All doubtless true.  So it seems we don't disagree.    (016)

I am still trying to understand the relevance of the MVC architectural 
pattern to knowledge engineering.  I think the relevant MVC idea is that 
one can have multiple display forms for the same underlying 
information/knowledge, to meet the needs of different audiences.  The 
MVC model component maintains that knowledge in some unspecified way.    (017)

In a similar way, a UML diagram is a display form for the knowledge that 
is captured in a UML model, and one can have multiple forms, using 
different diagrams and even diagram types, that display parts of the 
same UML model in different ways, for different audiences.  In that 
sense there is a parallel.  But the UML standard specifies a formal 
reference structure for the knowledge maintained in the UML model, and 
part of that knowledge is a concept network.  And John's original point 
was that a subset of that formal reference structure ("foundational 
UML") now has a semantics expressed in formal logic.    (018)

-Ed    (019)

"You may believe you understand what you think you heard, but
what you do not realise is that what I said is not what I meant."
        -- R. Alexander (Sandy) Tyndale-Biscoe    (020)

Edward J. Barkmeyer                        Email: edbark@xxxxxxxx
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Stop 8263                Tel: +1 301-975-3528
Gaithersburg, MD 20899-8263                FAX: +1 301-975-4694    (021)

"The opinions expressed above do not reflect consensus of NIST, 
 and have not been reviewed by any Government authority."    (022)

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