Thread: Home Work

  1. #1
    Its not rocket science vasanth's Avatar
    Join Date
    Jan 2002

    Home Work

    Hi Everyone,
    Ok this is my home work.. but i am not gona ask you guys to do it..

    It is for the database class... I have modeled a Entity Relation Diagram (ER Diagram) for a given problem for which a database has to be created... I want to get the model right before i proceed to the next step.. i have created a model which i think is ok.. but i would like you guys to have a look and recommend any modifications which might improve the model.. or a better way of doing it..

    thanx in advance

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Well your double ended relationships seem wrong (and confusing)

    For example
    +============+                   +============+
    |            | 1               + |            |
    |   Site     |-------------------| Grid Ref   |
    |            |                   |            |
    +============+                   +============+
    A site is composed of many grid references
    A grid reference belongs to one site

    Depending on what your local conventions are on multiplicity, you might consider
    {m,n} - between m and n
    {m,} - at least m
    {,n} - at most n
    * - zero or more, same as {0,}
    + - one or more, same as {1,}

    For me, I would remove Species_Ref_No from Site_record (a site record will contain many species, so it can't really be here), and remove SiteID from Site_Species_Record, and replace it with a Site_record (so you can easily get date and recorder).

    So it would read
    A Site has many Site Records
    A Site Record has many Site Species Records
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Its not rocket science vasanth's Avatar
    Join Date
    Jan 2002
    thanks... for the valuable response.. i am working on that now.. I think a grid reference can belong to more than one site since sites overlap..

    any way will post the new model.. hope to get some review again..


Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Problem in accessing root home folder....
    By Bargi in forum Linux Programming
    Replies: 1
    Last Post: 02-13-2008, 05:50 AM
  2. getline() don't want to work anymore...
    By mikahell in forum C++ Programming
    Replies: 7
    Last Post: 07-31-2006, 10:50 AM
  3. Why don't the tutorials on this site work on my computer?
    By jsrig88 in forum C++ Programming
    Replies: 3
    Last Post: 05-15-2006, 10:39 PM
  4. C++ software for home work
    By rgk44 in forum C++ Programming
    Replies: 12
    Last Post: 02-15-2006, 04:00 AM
  5. Problems in getting OpenGL to work
    By zonf in forum C Programming
    Replies: 5
    Last Post: 02-13-2006, 04:48 AM