Re: Class::DBI Beginner's Guide question on Many to many entity relationship diagram

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Terrence Brannon wrote:
> I was taking a look at a Class::DBI tutorial:
> 
>  
> 
> http://class-dbi.com/cgi-bin/wiki/index.cgi?BeginnersGuide
> 
>  
> 
> and I don’t understand one part of this diagram. Supposedly there is a 
> many to many relationship between artists and groups: an artist can have 
> many groups and a group can have many artists. But if this is the case, 
> then
> 
>  
> 
> 1/ why are the crow’s feet not drawn from artistgroup to band?

The idea (although it never caught on) was that and artist is either a 
solo person or band.  So the artist table is a supertype, and the band 
and person were sub-types.  Artistgroup is a table used for building 
hierarchies, so that you could do:

ArtistGroup
bandartistid, personid
----------------------
5,1
5,2
5,3
5,4

artist
artistid, name
-----------------
1,John Lennon
2,Paul McCartney
3,George Harrison
4,Ringo Starr
5,The Beatles

> 
> 2/ why is a 1-to-1 relationship between artist and band shown?
> 

Jay