[Year 12 SofDev] Use Case Questions

Tue Apr 17 19:31:26 EST 2012

A belated thanks to Mark for the input.

I've been giving similar instructions to my students... there are many ways to present the UCD as long as it makes sense and covers all of the functions then you're good.
Perhaps I'll give them some guidelines in the future based on what seems to be the general convention (from the UCDs I've seen... which isn't much) limiting the total number of Use Cases (maybe about 8 to 12) and the number of different Use Cases that should be linked together in a chain (I'm thinking maybe 3 or 4). This might also serve to reduce the number of trivial tasks that get included as Use Cases.

Cheers,

Nick

From: sofdev-bounces at edulists.com.au [mailto:sofdev-bounces at edulists.com.au] On Behalf Of Mark KELLY
Sent: Sunday, 15 April 2012 11:06 AM
To: Year 12 Software Development Teachers' Mailing List
Subject: Re: [Year 12 SofDev] Use Case Questions

Hi Nick. Use cases are relatively new to SD so there's not really an established understanding of our 'rules' for them, unlike (say) DFDs which have been on the course and in exams for quite some time.

1. I would include printing the invoice as a system functional requirement. After all, if the system does not generate the invoice, who does? If it must be generated as part of the system's functionality, it should be in the UCD.  Putting invoices into a tray, on the other hand, is not something the software is expected to do - unless robots are part of the system.

2. How far you go separating use cases into separate <<includes >> is a matter of judgement, I think. You have to use common sense to ask "Is this functional requirement a significant discrete action or is it a trivial part of a larger use case (e.g. "Print the heading on the invoice").  <<Extends>> are different because they are conditional, and if they are not always carried out, they can't be lumped in with other activities that are always carried out.

I give my kids latitude in their interpretation of how a UCD is built - it's a bit of an art form, I think. As long as the functional requirements are really CLEAR, I give my kids credit.  The main role of a UCD is to be comprehensive and easy to understand.

At least that's what I reckon.

Regards
Mark
On 14 April 2012 22:53, Stebbing, Nicholas N <stebbing.nicholas.n at edumail.vic.gov.au<mailto:stebbing.nicholas.n at edumail.vic.gov.au>> wrote:
Hi all,

                I've spent much of today going through the archives of this list trying to glean as much info as I can about use case diagrams and Outcome 1 in general. I have to say this list is outstanding, the knowledge and resources shared is awesome.

                I am left with some questions about use case diagrams to help me assessing SAC 1...

1.       Should things like "Printing invoice" and "Place printout in tray" be considered as use cases to go on a UCD?
(I've been telling my students no because they are not important functions of the system. They can be thought of as steps that are taken to complete the functions. Is this right? Could I be explaining it better?)

2.       Many of my students have linked all of the different use cases up into a tangled web of includes and extends. At what point should they be separated?
(I've been thinking about this and have a couple of ideas. Firstly it seems that if an actor is associated with a use case then we can assume they are associated with any use cases that extend from or are included in it. So one point at which we need to separate cases is when one use case could be considered to extend from another but is performed by a different actor. For example if one person prepares an invoice but another person prints it they would have to be entirely separate use cases. Does this sound right?)

Thanks in anticipation of any advice,

Nick Stebbing
ICT Teacher
Bayside P-12 College

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