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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