More Use Cases

[Graham_Labdon]

Hi All

In my system the system is configured from a set of files that will characterise how the system will operate. Therefore we have a requirement that says

The system will be characterised from data stored externally. Upon initialisation this data will be read and used to configure the system.

I am having trouble coming up with actors/use cases that can realise this requirement

Does anyone have any ideas

Thanks

Graham

[jeshaw2]

I don't think I would consider trying to write a use case for this;  There is no goal for a business or External System actor.  The requirement is more software implementation stuff.  I would first consider developing a PSM class diagram, based upon the GoF "Factory Pattern".  Guess I would also treat this as a Non-functional Business Requirment rather than a Functional Business requirement.

Use Cases are more of, but not exactly like, a contract between users and the system; they are not a substitute for Software Engineering Specifications.

[sargasso]

The system will be characterised from data stored externally. Upon initialisation this data will be read and used to configure the system.

Appears at first glance to be a DESIGN DECISION or at worst a Design Constraint.  Now I wonder why someone would try to put such a thing in a requirements document.

Perhaps they were too lazy to come up with :

1) The system run time must obey a static but changeable set of rules.  These rules must be persisted between invocations of the system.
2) The system must allow a user, possessing the correct amount of magic, to manipulate and save such rules.

Does the use case model start to appear yet?

hth
the ghost  

[Graham_Labdon]

The system I am working on can be configured to work with a variety of hardware components. Currently this configuration is read from a file but may change. I was trying to come up with a requirement that satisfies this need as the system won't work without this data.
Maybe the requirement as I wrote it is a design descision but there must be a requirement (maybe non functional) to make the system operate I just don't know what it is

[«Midnight»]

OK so far Graham, but I think you've already got all the pieces.

I have edited your post as follows:

The system...can be configured to work with a variety of hardware components. ...This configuration is read from a file but may change. ...The system won't work without this data.

...

...This...is a design descision [sic] ...There must be a requirement (maybe non functional) to make the system operate.

Which seems to be addressed above.

And now...

I just don't know what it is

...seems to be answered. You can take it from here.

David

[Graham_Labdon]

Thanks David

Do you agree with jeshaw that this is a non functional requirement and therefor it it is not possible to write a use case

Graham

[«Midnight»]

Yes. Pay attention to Jim; he knows of what he speaks!

That's the point. [It bears repeating.] You've described a requirement, not a use case.

These two concepts are not necessarily mutually exclusive, but non-functional requirements are generally poor candidates for use cases. You could always twist things around and contrive a viewpoint that might appear to suggest a use case, but such an exercise would obscure an otherwise simple point. The system you describe is case in point.

You've described what the system expects and requires in a few sentences. Stop there; the job is done at that point. Later, and in a different part of your documentation, you can describe the form and format of the input instructions - whether a file, an XML stream, the songs of a chorus of budgies, whatever - and you'll have finished the detailed design of this function.

As far as use cases are concerned, go on to the next design issue. There's nothing for you here. This seems to be a repeating theme in your system, but you are making progress. It can be a difficult lesson, but it only needs to be learned once.

David