Use Cases, Procedures and Scenarios

[Keith Jeremy Posner <posner -at- SODALIA -dot- IT>]

Suzy Davis wrote:

> I'm hoping someone can provide me with:
> a) definitions for 'use case', 'procedure' and 'scenario', and
> b) advise whether tasks performed by a person can be a use case.
>
> I have a use case (I personally don't like the term for external docume=
> ntation
> but I'm stuck with it.) which includes the following step:
> "CSA performs Call Wrap Up procedure".
> I've been asked to change the word 'procedure' to 'use case', but it
> doesn't work for me.
>

Here are some incomplete answers from my own experience.

> a) definitions for 'use case', 'procedure' and 'scenario'

The terms Use Case and Scenario belong to the domain of system
requirements analysis. You should use these terms only if you are
developing requirements-type documentation. You should not use these
terms in user documentation.

Use Cases are developed by the analyst as part of an attempt to
formulate system requirements during the initial stages of a software
projects.

The Use Case has the form of a procedure, in that the Use Case is a
step-by-step specification of a process that occurs in the system.
Where the Use Case involves a user (or an actor in Use Case terminology)
and the system, you have a task.

A Scenario is "an instantiation of a Use Case", i.e. take the general
procedure described in the Use Case and plug in real values. If you
think of the Use Case as being close to the task descriptions in the
user guide, then you should think of the Scenario as being the
equivalent task in the training materials.

A procedure is a more general term which as far as I know does not have
a specific meaning in the requirements analsyis domain.

So the questions you should perhaps be asking are: Where are we in the
software process? In the analysis phase? Or towards the end of the
software cycle? Who's going to read this document, System Engineers or
users? Should my document have a requirements analsysis bent or will all
this analysis type terminology (Use Case, actor, Scenario) create a
semantic overhead for the people who have to read the document?


b) advise whether tasks performed by a person can be a use case

Yes! Use Cases can be performed by anyone or anything that is external
to the system being developed. Take the example of a piece of software
which manages e-mail. First define the boundaries of your system. Then
define anything external to that system which interacts directly with
your system. These are the Actors. In the case of the e-mail software
the Actors are:

the operating system on which the e-mail software resides

the user who sends/receives mail

the system administrator who monitors the performance of the e-mail
software, controls user access etc.


Each of these Actors can perform Use Cases. So the the user who
sends/receives mail is performing Use Cases. The system administrator
who monitors the performance of the e-mail software, controls user
access is performing Use Cases. But the purpose of identifying and
documenting these Use Cases is **primarily** to help identify system
requirements for you e-mail system.


I hope this helps.


Keith

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Keith Posner                     mailto:posner -at- sodalia -dot- it
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