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Sequence Diagram...emphasis on 'what' or 'how'?

Parag Doshi
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Joined: Jun 29, 2004
Posts: 317
What is the main emphasis of sequence diagram? Is it what messages are passed btw objects or is it how an object figures things out.
For example, a DAO can return a complex VO which might hold a bunch of other objects in it. So, do we just show that a DAO creates a complex VO or also show the different objects which are part of that composite object construction?
In other words, how detailed should one go in creating a sequence diagram?

Parag
Tomi Tuomainen
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Joined: Jun 13, 2004
Posts: 86
I don't think it's necessary to go into details. For example showing FlightListVO should be enough, I'm not planning to show any FlightVO's. There's just 12 points to gain.. (somebody correct me if I sound too lazy ).

Tomi
Parag Doshi
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Joined: Jun 29, 2004
Posts: 317
Originally posted by Tomi Tuomainen:
I don't think it's necessary to go into details. For example showing FlightListVO should be enough, I'm not planning to show any FlightVO's. There's just 12 points to gain.. (somebody correct me if I sound too lazy ).

Tomi


Tomi,
Yeah,Even I agree on that. I first created the loop of creating Flights and adding it to the list etc, then I realised, its really too much emphasis on implementation when this should also be more on high level. The implementation strategy on populating the list should be left on the developers. Atleast that seems a quicker way to get rid of the sequence diagram creation.

Parag
Dan Drillich
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Joined: Jul 09, 2001
Posts: 1180
Parag,

What is the main emphasis of sequence diagram?


UML Distilled defines it as:
"Typically, a sequence diagram captures the behavior of a single scenario. The diagram shows a number of example objects and the messages that are passed between these objects within the use case."

Is it what messages are passed btw objects or is it how an object figures things out.


I think it's the chicken and the eggs thing

By showing the messages among the participants, you clearly demonstrate how the participants interact.

Regards,
Dan


William Butler Yeats: All life is a preparation for something that probably will never happen. Unless you make it happen.
Parag Doshi
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Joined: Jun 29, 2004
Posts: 317
Originally posted by Dan Drillich:
Parag,



I think it's the chicken and the eggs thing

By showing the messages among the participants, you clearly demonstrate how the participants interact.

Regards,
Dan


Dan,
Thanks for your reply. I understand the participation and passing of messages, but do we also need to show how the receipient acts on the message to implement the functionality requested?

For eg. if a facade asks a DAO to get some data, the message btw the 2 objects would be getSomeData(), but do we stop there or do we also show how the DAO assembles the data(which could be complex and be composed of multiple other objects) and returns to the facade?

So, the getSomeData() is the 'what' part of the participation and the assembly of the object is the 'how' part of it. What is given more emphasis?

Parag
H. Hafer
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Joined: Aug 23, 2004
Posts: 108
Originally posted by Parag Doshi:

So, the getSomeData() is the 'what' part of the participation and the assembly of the object is the 'how' part of it. What is given more emphasis?


Cade clarifies this topic in his book (emphasis by me):
When does the creation of an architecture stop and the design process begin? There is not a definitive answer for every system. This issue of architecture and design can be summed up in terms of focus and control. Architecture defines what is going to be built and design outlines how you will build it. Architecture is controlled by one or a few individuals who focus on a big picture and design is controlled by many individuals who focus on the details of how to achieve the big picture.

As a consequence I'm not going to go into details of "how" for part II

Harbo
 
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