Results 1 to 9 of 9

Thread: EER models

  1. #1
    Join Date
    Nov 2007
    Posts
    4

    EER models

    Hi, I two questions regarding EER models that I would be grateful if anyone could help me out with.

    I'm designing an EER diagram at the moment, I was wondering if for example I had data stored on someone that contained name, age and id number would name , age and id number just be attributes of the entity "stored data" or could I use Generalisation/Specialisation where "stored data" would be the top entity and name age and id number would be disjoint constraints?

    Secondly, is it acceptable to draw seperate diagrams for the Generalisation/Specialisation part fo a databse model from the entity/relationship part or should all the parts of the EER model be drawn together?

    Thanks

  2. #2
    Join Date
    Apr 2002
    Location
    Toronto, Canada
    Posts
    20,002
    what to the initials EER stand for?

    "stored data" is not an entity

    if the attributes are name, age, and id number, i'm guessing the entity is Someones

    so each instance of the Someones entity would be an actual someone
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  3. #3
    Join Date
    Feb 2004
    Location
    One Flump in One Place
    Posts
    14,912
    Funny - I thoughts you didn't likes pluralised entities. Or is that another big cat?

  4. #4
    Join Date
    Nov 2007
    Posts
    4
    EER stands for extended entity relationship model. Its a model that incorporates all the elements of ER models along with gerneralisation/specialisation.

    Thanks for the replies. The example I gave was just made up so sorry if it was a bad example - but are name, age and id just attributes then? Can I link attributes?

  5. #5
    Join Date
    Apr 2002
    Location
    Toronto, Canada
    Posts
    20,002
    Quote Originally Posted by pootle flump
    Funny - I thoughts you didn't likes pluralised entities. Or is that another big cat?
    me? no, i always tell people to use plural entity/table names

    it is to remind you that you are dealing with a set of rows (e.g. select from employees)

    placing emphasis on the container (e.g. select from tblemp) is old school process-oriented thinking

    plural names help you remember that you are specifying values to qualify all desired rows at once, rather than the repetitive read-a-record-and-do-something-with-it mindset
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  6. #6
    Join Date
    Apr 2002
    Location
    Toronto, Canada
    Posts
    20,002
    Quote Originally Posted by cobijones
    Can I link attributes?
    you sure can

    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  7. #7
    Join Date
    Nov 2007
    Posts
    4
    so when drawing the actual models by hand - do I just link attributes with a line?

  8. #8
    Join Date
    Apr 2002
    Location
    Toronto, Canada
    Posts
    20,002
    yes, and of course attributes like name, age, and id number would be "related" inside the same box
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  9. #9
    Join Date
    Nov 2007
    Posts
    4
    Thanks for the answers I appreciate it. One last question - can I add generalisation/specialisation to attributes. Say for example I have sex as an attribute can I then add disjoint constraints of male/female to the attribute? And if so would I draw these in the same fashion as I would draw generalisation/specialisation constraints to an entity?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •