Bachman diagrams and E-R model

1)
When designing a database, we may use ( I’m not sure if at different or same stages of development ) each of the following three diagrams:
- bubble diagram

• e-r diagram
• data structure diagram ( bachman’s diagram )
  1. Are Bachman and bubble diagrams also used at conceptual level?
  2. So when do choose Bachman diagram, when bubble diagram and when E-R diagram?
  3. What are some major differences between Bachman and E-R diagrams?

2)
My book claims that Bachman diagram only knows one-to-one, one-to-many and many-to-many relationships. But then how do Bachman diagrams graphically represent zero-to-many relationships?

My question above is based on the assumption that 1:N relationship means that instance of entity type A can have zero, one or many connections to instances of entity type B, while each instance of entity type B must have exactly one connection to entity A  In other words, each instance of entity type B must have one ( zero connections is not allowed ) connection to instance of A entity. Am I correct?

thank you Received on Tue Jul 24 2007 - 03:01:52 CEST