Consider the relationship R between two entity sets E_1 and E_2. Let K_1 and K_2
ID: 3832105 • Letter: C
Question
Consider the relationship R between two entity sets E_1 and E_2. Let K_1 and K_2 be the sets of key attributes of E_1 and E_2, respectively. Assume that R has no attributes and is one-one between E_1 and E_2. What are the keys for the relation R? If R is one-many from E_1 to E_2 what are the keys for the relation R? If R is many-many between E_1 and E_2, what are the keys for the relation R? If R is many-many between E_1 and E_2 and has an attribute A, what are the keys for the relation R? Assume that R is a multiway relationship between three entity sets, E-1, E_2 and E_3, with K_1, K_2, and K_3 as the respective sets of their key attributes. Further, assume that in the E/R diagram there is one arrowhead pointing to E_1 and no arrowheads pointing to E_2 and E_3. What are the keys for the relation R? Is the following interpretation correct: "Given E_2 entity and E_3 entity, there is at most one related E_1 entity"? Explain your answer. If incorrect, give the correct interpretation. Continuing; assume that in the E/R diagram there is one arrowhead pointing to E_1, one arrowhead pointing to E_2; and no arrowhead pointing to E_3. What are the keys for the relation R? Is the following interpretation correct: "Given E_3 entity, there is at most one related E_1 entity and at most one related E2 entity"? Explain your answer. If incorrect, give the correct interpretation. Continuing; assume that in the E/R diagram there is one arrowhead pointing to each of the entity sets. What are the keys for the relation R? Continuing; assume that in the E/R diagram there are no arrowheads pointing to any of the entity sets. What are the keys for the relation R?Explanation / Answer
a)Foreign key is used to define the relationship between two entity is one to one
b)Canditate or composite key is the key that defines the one to many relationship
c)Composite key is also used to mention many to many relationship
e) k1 is the foreign key
F)the arrow head usually represents one to many relationship
The E3 without any arrow head show one to one relationship
Thr arrow head denotes that the entity with foreign vkey points to the refernce key entity .
G) if every entity has an arrow then the relationship is one to many and every entity has a primary key which is reference to any other entity that is foreign key.
h)if there is no arrow head pointing then every thing is one to one relationship