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  1. #1
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    entity relationship diagram. require help plz.

    Hi. I dont even know if this is the right board for this so please dont go nuts at me if it isnt. I'm working on a question for uni. But I'm really having some difficulty trying to make sense of it so I tried to find some people who may know anything about it.

    Heres the description:

    The chemical plant described is one of several such operated by a company. Each plant specialises in one or more products, but each product is manufactured at a single plant. Several supervisors are allocated to each plant, and each supervisor is in sole charge of a single manufacturing run for the duration (each run typically being 1 - 10 days duration, and manufacturing a single product but using any number of gas components). Components are stored separately in the various gas containers, no container being ever used for a gas component other than the specific one for which it was designed. There may of course be several containers of a particular gas component being used in a single manufacturing run or in different manufacturing runs at any one time.



    Now i've drawn a diagram. But I know that i've made a mistake.

    The last line of the description makes me believe there is a many to many relationship between the component and the manufacturing run. This would then me I require an extra entity inbetween the two.

    I know this is very long winded but I would really appreciate help.
    Attached Thumbnails Attached Thumbnails work.jpg  

  2. #2
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    manufacturing run to gas container is many to many.

  3. #3
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    So my gas container and gas component would switch places?

    Meaning many "manufacturing runs" use many "gas containers" and many "gas containers" hold a "gas component"

    But if there is a many to many relationship would that not mean I require an extra entity inbetween there.

    Thats a part of it i cant figure out.

    Although thank you for that information. I will have to change that.

  4. #4
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    I have changed the design of the diagram so that it appears as you have said. Im still unable to get rid of the many to many relationship as i do not know what entity would go between the container and manufacturing run.

    Any thoughts on this?
    Attached Thumbnails Attached Thumbnails work.jpg  

  5. #5
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    Sorry, no.


    Run Components will be your associative entity for
    Manufacturing Run many to many Gas Containers.

    Manufacturing Run one to many Gas Components
    Gas Components one to many Gas Containers
    Gas Containers one to many Run Components
    Manufacturing Run one to many Run Components

    That should do it.

    Sorry, but I don't have time to create a graphic.
    Last edited by certus; 12-15-03 at 09:47.

  6. #6
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    Should we get another category added to the list of forums?

    It would be called "Help me with my homework, please!"

    blindman

  7. #7
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    "Meaning many "manufacturing runs" use many "gas containers" and many "gas containers" hold a "gas component" "

    The relationship between gas containers and gas components is completely independent of the many-many as indicated by your diagram.

    "But if there is a many to many relationship would that not mean I require an extra entity inbetween there"

    Correct, though this new relation is formed during the construction of tables, as described by your diagram.
    Last edited by r123456; 12-15-03 at 10:31.
    Bessie Braddock: Winston, you are drunk!
    Churchill: And Madam, you are ugly. And tomorrow, I'll be sober, and you will still be ugly.

  8. #8
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    Ive modified the diagram enlight of what you have said. I have spoken to my lecturer who says to me that there are infact 8 entities. You can imagine the frustration im feeling trying to find an 8th entity.

    Also some people still tell me that i cannot have loops like in my diagram. Ofcourse i dont believe them.

    The attributes for the run component would then be:

    (runcomponent_no, manufacturingrun_no, gascontainer_no)

    Thats just what im assuming. Heres the diagram. Is this correct?
    Attached Thumbnails Attached Thumbnails work.jpg  

  9. #9
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    Looks like you are on the right track.

    Now, for that eighth entity

    "The chemical plant described is one of several such operated by a company."

    Company has one to many Plants.

    "Each plant specialises in one or more products, but each product is manufactured at a single plant."

    Plant has one to many Products.

    "Several supervisors are allocated to each plant,"

    Plant has one to many Supervisors.

    "and each supervisor is in sole charge of a single manufacturing run for the duration"

    Supervisor has one to one Manufacturing Run.

    "(each run typically being 1 - 10 days duration, and manufacturing a single product but using any number of gas components)."

    Manufacturing Run has one to one product.

    Manufacturing Run has one to many Gas Components.

    "Components are stored separately in the various gas containers, no container being ever used for a gas component other than the specific one for which it was designed. "

    Gas Component has one to many Gas Containers.

    "There may of course be several containers of a particular gas component being used in a single manufacturing run or in different manufacturing runs at any one time."

    Gas Container has many to many Manufacturing Runs.


    You should find your eighth entity in there.

  10. #10
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    The 8th entity you speak of as you may think is the company but we are told that its a redundant entity and should not be included.

    I was told there are 6 obvious entites from the text and 2 which have to be created. The run component is created which makes 7.

    Although the lecturer said that having less than 8 is not incorrect as some people will break down a certain entity to gain 8.

    Im going to a class tomorow night to get more help with this. hopefully someone can shed some light on whether i require another entity.

    Thank you for the help i really appreciate it.

    Other than that do my attributes look ok for the run component that i stated in my above post. ?

  11. #11
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    Run Component should be Run Container. I'll take the hit for that.

    Your entities (not attributes), your relationships and your cardinality all look good.

    You should do well.
    Last edited by certus; 12-15-03 at 16:08.

  12. #12
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    So i'd be looking at:

    A manufacturing run has many run containers. Many run containers have a gas container.

    Somethin like that. Once again diagram change.
    Attached Thumbnails Attached Thumbnails work.jpg  

  13. #13
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    That's what you'd be looking at.

  14. #14
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    Dec 2003
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    Here is my final diagram. I went to a tutorial where only 6 people showed up. Asked my lecturer some questions and came about this diagram which i suspect is right because he went through it with me.


    Thanks for all the help. Now i gotta get on and get the rest of it done.

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