Re: Are circular relationships a bad thing in ER-modeling?

xlazyx wrote:

> Hey!

Hi
>
> If I have the following theatre system:
>
> A theater sets up _shows_, which is based on a _manuscipt/play_ written by a
> _person_ A show also has _persons_in differnent _roles_, based on the
> _manuscript_.
>
> And have the following entities:
>
> Theater(TheaterID, Name)
> Manuscript(ManuscriptID, Name, Year)
> Person(PersonID, Name)
> Show(ShowID, ManuscriptID, TheaterID, Date, Time)
> Role(RoleID, ManuscriptID, Name)
>
> How do I relate a Person to a show, so that a person can be an actor in a
> show, in multiple roles?

Maybe like so:
Performance(PersonID, ShowID, RoleID)

> And how do I relate a Person to a Manuscript, so that many people can write
> the same manuscript, and one person can write serveral manuscripts.

Author(ManuscriptID, PersonID)

> As I see it I would end up with something like:
>
> Person->Show->Manuscript->Person, which is a circle relationship. Isn't this
> bad? Or is it ok?

I don't think it's bad in general. Trees, hierarchies and networks are often represented by recursive associations (circle relationships). But I don't think it is appropriate in your program-booklet application.

> Of course, there has to be an entity between Person and Show because of the
> N:N relationship, but that's not a problem right?

HTH Received on Mon May 03 2004 - 16:13:58 CEST