UNSW Entity-relation diagram Q! (1 Viewer)

[MEOW123]

I had a few questions about this and wondering if anyone who knows can help!

http://i.imgur.com/HEjpRZ9.png

In the picture before the above we were asked make a Courses-<enrols>-Programs and enrols points down to Student (ternary relationship) but in this example we had to make it a composite entity (to make it from M-M to 1-Ms) but why and where did they get the "offering" part (was not given or drawn before)?

also
http://i.imgur.com/tdX5fh8.png


In the pic before the above pic, I was given Exercise class as having a many to many relationship with the Members entity. I know when you have M-N relationship it isn't good and must be split up into two 1-M relationships but I don't know why it is 1-M <enrols> M-1 and I don't get how they find the 4 cardinalities between Exercise class and Members.

similar in http://i.imgur.com/dVNZgTg.png. if you can can also explain (the 4 cardinalities in this one and what the green circle means). thank you so much for your help, it is very much appreciated!

thanks so much!

Thanks!

 

[obliviousninja]

Wasnt the exam today? Lol

 

[obliviousninja]

1) If you don't create the composite entity for offering, the entities don't logically flow

2) I never really understood the cardinalities for that, i just r0te it

 

[MEOW123]

1) If you don't create the composite entity for offering, the entities don't logically flow

2) I never really understood the cardinalities for that, i just r0te it

thanks! can you tell me what is meant by the green circle in the 3rd pic?

 

[obliviousninja]

Class entity is dependent on student, ie a class cannot exist without students

 

[MEOW123]

Class entity is dependent on student, ie a class cannot exist without students

Ah i see. Btw for the first pic I meant that the relationship was ternary with only "enrols" as a composite entity but for some reason they added "offerings". i know M-M needs to be convert to two 1-Ms but why couldn't they do with it with just "enrols"?