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  1. #1
    Join Date
    Aug 2004
    Posts
    7

    Allowed ORM design?

    Is the attached ORM diagram allowed in the world of information moddeling?

    Info:

    An action has a specific letter and number.
    An action occures in a process
    An action in one process is DIFFERENT to an action with the same letter/number combination in another process

    For the purposes of this, an action follows another action and is preceeded by another action within the process.

    For the above statement, is the red or the blue correct? I think it's the red because it's the combination of activity number, activity letter and process.

    Finally, completly OT but how do I do nested entities in M$ Visio? It has icons for almost everything else except nested. And I think for the purposes of this, a ternary is out of the question.
    Attached Thumbnails Attached Thumbnails orm.JPG  

  2. #2
    Join Date
    Aug 2004
    Posts
    7
    ok... it's been refined slightly. But I'm having huge problems modeling certian constraints.

    INFO: activities have a type dictated by a letter (A/B/C/D). This is constant throughout all processes.

    the constraint is:

    certian activities cannot be linked - activity D cannot follow activity A.
    ------------and---------------->activity B and activity C cannot be linked at all

    So is either of the red or the blue correct. Ignoring most else for now. I hate subtyping but to me it makes sence. Duno if it makes sence to anyone else.

    SO- according to the constrain above
    A can follow B, C and D
    B can follow A and D
    C can follow A and D
    D can follow B and C

    assuming my understand of subtyping is correct (that subtypes inherit the same fact types as their parent) and the following subtyping is allowed (legal in ORM worlds) then it "should" work out. hoepfully.

    Thanks alot for your help

    ps- if you're wondering. This is for uni. But I'm not asking you to DO my work rather asking if certain aspects of it are aceptable to knowledgable people such as yourselves.
    Attached Thumbnails Attached Thumbnails orm2.JPG  

  3. #3
    Join Date
    Apr 2004
    Location
    Toronto, Canada
    Posts
    249
    Hi,


    I think that you are looking for one main table, process_activity, that has the process, activity, sequence information.

    Of course, you will have tables for describing each of "process", "activity", etc.

    Additionally, to impose the constraint on successor activities, you can have a table called, say, next_activity_type, with the following columns:
    (current_activity_type, next_allowed_activity_type, ...)

    Write a small procedure (trigger) to validate that the activites in the main table (process_activity) obey these constraints.


    That should take care of this problem.

    There is no need for types and sub-types here. As an aside, in the OO world, types and sub-types are heavily mis-used.


    Ravi

  4. #4
    Join Date
    Aug 2004
    Posts
    7
    thanks but um... look the whole point is to display the constraints on the ORM diagram. which is what I'm confused about.

    I'm beginning to think the subtyping is wrong and that subtyping isn't needed at all.. .

  5. #5
    Join Date
    Apr 2004
    Location
    Toronto, Canada
    Posts
    249

    ORM Design

    Since you had posted to a forum titled "Database Concepts and Design", I assumed that you were looking for a database design to meet your requirements.

    Could you please explain what you mean by ORM modelling? Does ORM stand for Object relational mapping?

    And how does your post fit into a forum titled '"Database Design Concepts"?

  6. #6
    Join Date
    Aug 2004
    Posts
    7
    jesus. don't get narky. Simple mis-understanding.

    This is the closest relevant forum I could think of since ORM is one of the first stages of database design. and yes... orm is object role modeling/mapping (I guess i shouldn't say orm modeling. Kinda like saying ATM machine). If you think it belongs in another forum please tell me so I can get an admin to move it.

  7. #7
    Join Date
    Sep 2004
    Posts
    5
    Or PIN number. That one gets me.

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