Please answer the following questions about ER diagram and translation to the re
ID: 3841172 • Letter: P
Question
Please answer the following questions about ER diagram and translation to the relational model. a) When translating an ER diagram to the relational model, do all relationships end up as relations in the relational model? Explain your answer. b) What are the three categories of relationships in ER diagrams? c) What distinguishes relationships in "roles" from all other relationships in an ER diagram? d) When ISAs in the ER diagram are translated to the relation model, what types of translations are possible? e) When an attribute to a relationship needs to be multiple valued, i.e. a list of values, to match the natural language description of a database, how must the ER diagram be restructured?Explanation / Answer
Find the Answers below.
a.
b. The three types of relationships or
otherwise we can say like below.
c. Roles: The function that an entity plays in a relationship is called its role.
Roles are normally explicit and not specified. They are useful when the meaning of a relationship set needs clarification.
d. Let us assume the relationship is mandatory (for ex. a person has to be a student or a teacher) and disjoint (a person is either a student or a teacher, but not both), the best solution is with 2 tables, one for students and one for teachers.
If the participation is instead optional, then the 3 tables option is the way to go, with a Person(PersonID, Name) table and then the two other tables which will reference the Person table, e.g. Student(PersonID, GPA), with PersonID being PK and FK referencing Person(PersonID).
The 1 table option is probably not the best way here, and it will produce several records with null values (if a person is a student, the teacher-only attributes will be null and vice-versa).
e. Solution to Multi valued attribute by adding new entity with 1:M relation to an Entity