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  1. #1
    Join Date
    Aug 2007
    Posts
    2

    Unanswered: ERD from existing Data Model

    Hi,

    I have been given the assignment to come up with an Entity Relationship diagram of an existing database. The database wasn't designed by me. I was wondering if there is a standard scientific way of displaying the relationships between the various tables at a functional level on Visio. Since, I didn't design the database in the first place, I don't know how to take a step backward and recreate the ERD from the given database.

    Any help will be appreciated.

    thanks

  2. #2
    Join Date
    Apr 2002
    Location
    Toronto, Canada
    Posts
    20,002
    do a search for "reverse engineer ERD from database"

    lots of software out there will build the skeleton diagram -- even the products that cost money will let you download and try, which is sufficient to get you started

    started, because you will then have to take over and tweak the model itself

    say, doesn't visio do this too?

    as for "standard scientific way", yes, there are a couple of standards

    my advice is to use the technique recommended by your teacher
    rudy.ca | @rudydotca
    Buy my SitePoint book: Simply SQL

  3. #3
    Join Date
    Feb 2004
    Location
    Burbank & Santa Cruz de la Sierra
    Posts
    3,716
    Yep, visio can provide a start. Actually not a bad start, it actually shows all the defined relationships in the database.

    Note that this can be different from showing the design of the database, since the original design can also include relationships and keys that are not enforced in the database, but are conceptually "enforced" in the design.

    This is a pet peeve of mine, btw
    aka "Paul"
    Non est ei similis.

    I just read "100 Things To Do Before You Die". I was surprised that "Yell for help!!" wasn't one of them

  4. #4
    Join Date
    Aug 2007
    Posts
    2
    Hi,

    I reverse engineered the database on visio. But the problem is to interpret those 50-60 tables and establish the relationship at the functional level, something as follows:
    If we have an Employee table and a document table, I have to establish a relationship using the proper symbols something like:
    Employee --->Can have--->Document, how do I interpret relationships such as these from the data model on visio?

    Thanks

  5. #5
    Join Date
    Feb 2004
    Location
    Burbank & Santa Cruz de la Sierra
    Posts
    3,716
    I'm going from memory, but can't you right-click on the relationship line to see what the relationship is? As for the symbology used, I think they are pretty standard in ERD diagrams. Not to be patronizing, but have you looked online for "ERD symbols" or the like? Also Visio's help file should also provide a legend and description of the symbols.

    Sorry I can't be more help on the specifics, but I have not yet installed Visio on my new PC here, so I'm going from memory and paper ERD's hanging on my cube wall.
    aka "Paul"
    Non est ei similis.

    I just read "100 Things To Do Before You Die". I was surprised that "Yell for help!!" wasn't one of them

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