Let R12 be a many-to-many relationship between E1 and E2. Participation of both E1 and E2 in R12 is total.
The minimum number of relations required to convert the ER model into relational model (assuming there is no other functional dependency) where each relation is in third normal form (3NF) is __________ . (Answer in integer)
Converting ER Model to Relational Model
The conversion process requires creating relations for entities, multi-valued attributes, and relationships, ensuring they are in 3NF.
Relation for Entity E1
Entity E1 has attributes (A11, A12, A13), where A11 is the primary key (PK). This converts directly into one relation.
- Relation 1: E1_Relation(A11, A12, A13)
Relations for Entity E2 with Multi-valued Attribute
Entity E2 has attributes (A21, A22, A23), where A21 is the PK and A22 is a multi-valued attribute.
The entity's regular attributes form one relation, and the multi-valued attribute requires a separate relation linked by the entity's PK.
- Relation 2: E2_Base(A21, A23)
- Relation 3: E2_MultiValue(A21, A22)
(Stores pairs of PK from E2 and values of A22)
Relation for Many-to-Many Relationship R12
R12 is a many-to-many relationship between E1 and E2 with total participation from both.
A many-to-many relationship is converted into a separate relation containing the primary keys of the participating entities.
- Relation 4: R12_Relation(A11, A21)
(A11 is FK to E1_Relation, A21 is FK to E2_Base. Total participation implies NOT NULL constraints on FKs.)
Total Relations Calculation
Combining the relations derived:
- 1 relation for E1
- 2 relations for E2 (base + multi-valued attribute)
- 1 relation for the R12 relationship
Total minimum number of relations required = 1 + 2 + 1 = 4.
All derived relations are in 3NF as there are no transitive dependencies beyond the primary keys.
Important Questions from ER Model
______ are some problems that can occur when creating an entity-relationship model.
Relations produced from E - R Model will always be in ______
Consider the following statements:
Statement I: Composite attributes cannot be divided into smaller subparts.
Statement II: Complex attribute is formed by nesting composite attributes and multi- valued attributes in an arbitrary way.
Statement III: A derived attribute is an attribute whose values are computed from other attribute.
Which of the following is correct?
A company is consuming parts in the manufacturing of other products. Each of the part is either manufactured within the company or purchased from the external suppliers or both. For each part, partnumber, partname is maintained. Attribute batchnumber is maintained if the consumed part is manufactured in the company. If part is purchased from external supplier, then supplier name is maintained. Which of the following constraints need to be considered when modelling class/subclass concepts in ERD for the given problem.
Which of the following key constraints is required for functioning of foreign key in the context of relational database?
