Hey guys, I'm a student in an intro to databases class and I'd like to make sure I've done this problem correctly. Here is the problem text:

This is the E-R Diagram I came up with using name and city as the candidate key for "Team":

http://img5.imageshack.us/img5/8348/hw1m.jpg
I've also attached my solution in-case image shack doesn't work.

Also, if things are changed where t1 and t2 and can play multiple times, I'd simply have to make "home_score", "visitor_score", and "date" all multi-valued...right?

I appreciate you guys looking over my solution, want to make sure I hand it in correct

everything looks okay except for the arrows between Team and Plays

NOOOOOOOOOOOooooooooooo.......

maybe your class hasn't covered first normal form yet

Thanks for the quick reply! Looking over the arrows again, I think I need to make the lines between Team and Plays have arrow heads on BOTH ends. To indicate that this is a one to one relationship, and not a one to many. Is this correct?

And you're right, we haven't covered first normal form yet. But there is another lecture before this homework is due so I'll hold out till then for that part of the question.

Thanks again.

what exactly does the arrowhead ~mean~ in your relationships?

and yes, both of these are one-to-many -- one team plays many games as home team, and one team plays many games as away team

first normal form basically says never to use multiple values in a single attribute, all attributes must be atomic

The cardinality is confusing me. I think because, this relationship set only includes one type of entity. It's not a relationship between a team and a game, but a relationship between a team and a team.

Since, for the initial condition of the problem, a team can only plan another time at most once in its home stadium...argh...the solution is in my head I just can't put together

For reference as you asked, the arrows are defined as follows:

One To Many: E1 <------ Relation ------ E2
Many to One: E1 ------> Relation ------- E2
Many to Many: E1 ------- Relation ------ E2

There is another, "Total participation" which is defined by double lines. It means that, at the very least EVERY entity in a set must participate in the relationship. As opposed to the three above, where an entity could possibly not be partaking in the relationship.

Change the diamond Plays to a square since it will be a table. Give it attributes of HomeTeamKey, VisitorTeamKey, HomeTeamScore, VisitorTeamScore, and DatePlayed.

I have never seen a diagram like yours, but the relationship between Team and Plays is many to many. A team would play multiple times, either as the home team or the visitor team. Based on your description of the arrows above that means you would have two lines between Team and Plays: -----Home----- and -----Visitor-----