Dull thread of the day - Does anyone know about use cases?

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  • Mike_Hunt 29 Aug 2010 17:09:06 23,523 posts
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    I'm writting a dissertation, and one chapter covers the exciting topic of use cases.

    I've read various books and papers, but I'm confused by some of the terminology. In terms of the diagrams, is a 'use case' the entire diagram itself (the use case scenario)? Or, are the ovals within the system use cases (as more than one of my books suggests)?

    If anyone can help clarify what exactly a use case is in the UML diagram then I'd really appreciate it.

    [MH]
  • Jeepers 29 Aug 2010 17:12:12 13,181 posts
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    In my line of work, a 'use case' is a written description of the interaction, supported with a list of actors and a diagram which would display any logic/conditions. The whole parcel is - ime - 'the use case'.
  • ProfessorLesser 29 Aug 2010 17:14:00 19,357 posts
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    /head explode
  • Mike_Hunt 29 Aug 2010 17:22:16 23,523 posts
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    Thanks Jeepers. So if the whole package is the 'use case', then what would you call the ovals within the system in the diagram?

    [MH]
  • Mike_Hunt 29 Aug 2010 17:22:38 23,523 posts
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    ProfessorLesser wrote:
    /head explode
    Some Professor you are!

    ;)

    [MH]
  • Spectral 29 Aug 2010 17:32:21 4,997 posts
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    Mike_Hunt wrote:
    ProfessorLesser wrote:
    /head explode
    Some Professor you are!

    ;)

    [MH]

    Can you make your own head explode?
  • Deleted user 29 August 2010 17:35:10
    this is attacking me. I liked it when you almost turned up at the train station with a base ball bat. ps: chill out, life is too short.
  • convercide 29 Aug 2010 17:37:10 6,045 posts
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    Spectral wrote:
    Mike_Hunt wrote:
    ProfessorLesser wrote:
    /head explode
    Some Professor you are!

    ;)

    [MH]

    Can you make your own head explode?

    Suicide (1994) by Kurt Cobain has that information.

    If you can read this, you don't need glasses.

  • Phattso Moderator 29 Aug 2010 17:39:11 13,345 posts
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    The ovals in the diagram are the use cases - the actors and other entities around them just lend context.
  • Mike_Hunt 29 Aug 2010 17:39:29 23,523 posts
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    Spectral wrote:
    Mike_Hunt wrote:
    ProfessorLesser wrote:
    /head explode
    Some Professor you are!

    ;)

    [MH]

    Can you make your own head explode?
    I do believe I could achieve this. However, this is unproven and will remain so for the forseeable future.

    [MH]
  • Mike_Hunt 29 Aug 2010 17:40:16 23,523 posts
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    AltCtrlDelete wrote:
    this is attacking me. I liked it when you almost turned up at the train station with a base ball bat. ps: chill out, life is too short.
    Whatchootalkingaboutwillis?

    [MH]
  • Mike_Hunt 29 Aug 2010 17:43:15 23,523 posts
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    Phattso wrote:
    The ovals in the diagram are the use cases - the actors and other entities around them just lend context.
    So if the ovals are the use cases, what would you collectively call the elements and goal of the diagram?

    This is why I'm getting confused! :)

    [MH]
  • Deleted user 29 August 2010 17:44:15
    Mike_Hunt wrote:
    AltCtrlDelete wrote:
    this is attacking me. I liked it when you almost turned up at the train station with a base ball bat. ps: chill out, life is too short.
    Whatchootalkingaboutwillis?

    [MH]

    :D

    Post more.

  • Phattso Moderator 29 Aug 2010 17:46:20 13,345 posts
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    It's a Use Case Diagram. That's what it is.

    The purpose of this diagram is to identify the key actors in the scenario and the actions/activities they will be involved in.

    In application terms, you're identifying how external actors will interact with the system. Literally the valid Use Cases that the software (or system) would need to be architected to support. Each Use Case would then equate to a service or function of the final product.

    The Use Case Diagram is generally used up front to help define the scope of a project.
  • Deleted user 29 August 2010 17:47:46
    warlock say's fuck the diagram, then creates something brilliant. :p
  • Mike_Hunt 29 Aug 2010 17:55:18 23,523 posts
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    Phattso wrote:
    It's a Use Case Diagram. That's what it is.

    The purpose of this diagram is to identify the key actors in the scenario and the actions/activities they will be involved in.

    In application terms, you're identifying how external actors will interact with the system. Literally the valid Use Cases that the software (or system) would need to be architected to support. Each Use Case would then equate to a service or function of the final product.

    The Use Case Diagram is generally used up front to help define the scope of a project.
    Ok - so the requirements are ultimately derived from the use cases which are drawn up in the diagram? For example, sample use cases in a project tracking system would be:
    -Enter project details
    -Assign resources
    -Track progress
    -Print schedule

    That list of use cases would then be used to determine the requirements of the system (what it needs to do in order to help the actor achieve their goal). Is that right?

    [MH]
  • Mike_Hunt 29 Aug 2010 17:56:45 23,523 posts
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    AltCtrlDelete wrote:
    warlock say's fuck the diagram, then creates something brilliant. :p
    Great, well, thanks for clearing that up.

    /double thumbs up

    [MH]
  • warlockuk 29 Aug 2010 18:25:06 19,178 posts
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    AltCtrlDelete wrote:
    warlock say's fuck the diagram, then creates something brilliant. :p
    Leave me out of this, it's years since I ever had to look at anything resembling UML.

    I'm a grumpy bastard.

  • Mike_Hunt 29 Aug 2010 18:34:53 23,523 posts
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    warlockuk wrote:
    AltCtrlDelete wrote:
    warlock say's fuck the diagram, then creates something brilliant. :p
    Leave me out of this, it's years since I ever had to look at anything resembling UML.
    I envy you...

    [MH]
  • Phattso Moderator 29 Aug 2010 18:38:25 13,345 posts
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    That's the general gist, yeah. It's identifying the goals and intended operation of a system, as part of a larger requirements capture initiative. Use Cases in industry are often used to define contractual scope of the software - generally for a non-technical audience.

    If you put a technical requirements document in front of most customers, they'd shit themselves. A Use Case Diagram is a nice, non-threatening manner in which to enumerate the discrete areas of functionality within a system so all parties can review and agree that this defines the scope of the system in its entirety.

    When you get into software requirements on the technical side you will, of course, have to delve a lot deeper (you're into data flow diagrams, activity diagrams, etc. etc.) especially when there's a client/server system involved.
  • Mike_Hunt 29 Aug 2010 18:50:16 23,523 posts
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    That's great, cheers Phattos. Thankfully I don't have to go down the road of technical requirements documents. I'm trying to adapt use cases into the development of something non-tehnical. In this case, documentation such as policies and standards.

    [MH]
  • Phattso Moderator 29 Aug 2010 19:05:17 13,345 posts
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    The beauty of UML: doesn't matter what you're modelling. Best of luck with the dissertation.
  • mal 29 Aug 2010 20:10:01 22,605 posts
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    Never seen the point of use case diagrams personally. The most important thing with use cases is identifying the actors and just writing as many good use cases as you can. Diagrams don't help with the former, and they definitely don't help with the latter. Just write them out FFS.

    I guess the benefit of them in UML is you can link them to other diagrams like your activity diagrams which in turn map to your object diagrams and so on, but frankly I've yet to see an editor that does that well enough to make it worthwhile.

    On the other hand, managers like charts. If you can write your use case in a box then put a little stick man next to it that may be a good thing.

    Cubby didn't know how to turn off sigs!

  • Mike_Hunt 29 Aug 2010 20:29:45 23,523 posts
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    Hmm... maybe, but then some of the use case design documents which I've read are probably not that clear to a non-techie.

    The diagrams themselves are relatively simple. I've never used them myself, but I can envisage them being useful when drafting out the requirement - e.g working through what's occuring by drawing it out on a whiteboard and then filling in the detail in documentation later, once the diagram is finalised.

    [MH]
  • Phattso Moderator 29 Aug 2010 21:33:05 13,345 posts
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    When defining a system at the outset, there's nothing as good as just drawing the actors and the basic relationships and interactions. It's not much more effort than plain text and vastly more readable when doing anything above the most simple of projects.

    Certainly for the projects I've worked on they've been invaluable, even if only to give a suit a warm and fuzzy feeling that they're part of the process. Something that shouldn't be underestimated.

    But then we do follow through on most levels with the UML, so having a structured starting point is excellent. It has formed the basis for most SOW docs I've seen, so some people must be finding it useful.
  • coastal 29 Aug 2010 21:33:28 5,383 posts
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    I get so much fucking OCD over having straight lines in my UML diagrams I've had to give up and do most of my design on thick pads of A3 paper - and then transfer to t'puter.

    bf3: sergeant_shaftoe

  • Jeepers 29 Aug 2010 21:44:43 13,181 posts
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    Phattso wrote:
    When defining a system at the outset, there's nothing as good as just drawing the actors and the basic relationships and interactions. It's not much more effort than plain text and vastly more readable when doing anything above the most simple of projects. (Snip!)

    Agreed - sticking with diagrams scribbled on A3 is the easiest way I've found to make sure that you test your design models and don't just jump into the first solution that comes to mind. It means that the non-techy people can get involved in the requirements/high-level design phase and gather an understanding of the 'shape' of the system you're trying to build for them.
  • Mike_Hunt 30 Aug 2010 02:18:46 23,523 posts
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    Hmm... I've confused myself again.

    Ok, here's a video store example:

    Use Case: Rent video
    (other information)
    Main Success Scenario: 1. Customer takes video to counter, 2. Sales rep scans video, 3. sales rep takes payment, 4. Sales rep updates database, 5. Customer leaves with video.

    If the use case is in fact "Rent Video" then what are the five steps? Are they also use cases - as I would expect to see each of those steps depicted as ovals in a use case diagram.

    /confused

    [MH]
  • mwtb 30 Aug 2010 02:55:03 2,381 posts
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    The steps are often called "the steps", also the events, the event flow, detailed interactions etc. I'm not sure the UML spec says anything about the naming convention as last time I checked it didn't specify exactly how to document the use case itself. Based on what you're saying, you appear to be confusing different levels of detail. The oval with the main use case title is an instance of a use case diagrammatically but there would usually be something behind that (a document, series of flow-charts, whatever) that provides detail and which is also the use case.

    As for your question about steps being use cases, again, the spec allows sub-use-cases via inclusion relationships as well as extension relationships. Actual usage will vary though, especially considering that many people won't have any formal training to allow them to decipher the more esoteric stuff.
  • mal 30 Aug 2010 03:48:31 22,605 posts
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    Sounds like you want a state machine diagram, MH. But then I guess I may be missing something with UML use case diagrams - all the ones I've seen just have one oval per use case attached to actors. As I understand it, breaking down use cases into steps is beyond the scope of a use case diagram, but then as I say, I'm probably missing the point wrt. use case diagrams.

    Cubby didn't know how to turn off sigs!

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