ER Diagrams MCQ Quiz in தமிழ் - Objective Question with Answer for ER Diagrams - இலவச PDF ஐப் பதிவிறக்கவும்

In the ER model,

Double ellipses

It is a Multivalued attribute

Dashed ellipses

It is a Derived attribute

Double line and Double Rectangles

Double lines indicate total participation E₂ of an entity into a relation.         

Double Rectangles represent weak entity sets E₂.

Explanation:

Each department can manage more than one employee

It appears one to many relationships

And given no null values are allowed in any of the relations

Because of this 3 tables are required

Table1 =Departments(did, dname, budget)

Table2 =Manages(ssn, did, since)

Table3 =Employee(ssn, name, Iot)

The correct answer is option 4.

Concept:

An entity-relationship diagram (ERD) depicts the relationships between entity sets in a database. An ER diagram is a method of visualizing how the information produced by a system is related. An ERD is made up of some of the following major parts.

Entities:

Rectangles are used to represent entities. An entity is a physical object or concept about which you want to store data.

Weak entity:

A weak entity is one that cannot be uniquely identified by its own attributes and must be defined by a foreign key relationship with another entity.

Relationship:

Diamond shapes are used to represent relationships, which show how two entities share information in the database.

Attributes:

Ovals are used to represent attributes. A key attribute is the entity's unique, distinguishing feature.

Multivalued attribute:

A multivalued attribute can have multiple values. An employee entity, for example, can have multiple skill values.

Total Participation:

Each entity is involved in the relationship. Total participation is represented by double lines.

Partial participation:

Not all entities are involved in the relationship. Partial participation is represented by single lines.

Hence the correct answer is Hexagons.

The correct answer is option 3.

Concept:

In DBMS, a degree of relationship represents the number of entity types that associate in a relationship. There are three types of relationships that can exist between two entities.

The cardinality ratio is express the number of entities to which another entity can be associated via a relationship set.

• One-to-One Relationship
• One-to-Many or Many-to-One Relationship
• Many-to-Many Relationship

One-to-One Relationship:

Such a relationship exists when each record of one table is related to only one record of the other table.

Example:

One-to-Many or Many-to-One Relationship:

The relationship exists when each record of one table can be related to one or more than one record of the other table. This relationship is the most common relationship found. A one-to-many relationship can also be said as a many-to-one relationship depending upon the way we view it.

Many-to-Many Relationship:

A many-to-Many relationship in DBMS is a relationship between more than one instance of an entity with more than one instance of another entity i.e. both the entities can have many relationships between each other.

Hence the correct answer is A - (ii), B - (iii), C - (iv), D - (i).

Entity Relationship Diagram - It is a diagram that displays the relationship of entity sets stored in a database. In other words, ER diagrams help to explain the logical structure of databases. ER diagrams are created based on three basic concepts: entities, attributes and relationships.

Relationship - It is nothing but an association among two or more entities. Entities take part in relationships. We can often identify relationships with verbs or verb phrases. It is represented by a Diamond. 

Attributes - It is a single-valued property of either an entity-type or a relationship-type. It is represented by an Oval. 

Optional One - It represents a relationship between two entities that is NOT mandatory to exist. It is represented by a line intersected with a vertical line and an oval at one end. 

Mandatory One - It represents a relationship between two entities that is mandatory to exist. It is represented by a line intersected by two small vertical lines at one end 

Key PointsOption 1: Bank Account_Num is a candidate key

False, If two students hold a joint account then BankAccount_Num is not a candidate key and will not uniquely determine other attributes.

Option 2: Registration_Num can be a primary key

True, A Unique registration number of each registered student is a candidate key and uniquely determines other attributes.

Option 3: UID is a candidate key if all students are from the same country

True, Unique identity number, unique at the national level for each citizen is a candidate key and uniquely determines other attributes.

Option 4: If S is a superkey such that S∩UID is NULL then S∪ UID is also a superkey

True, Let's consider super key is  Registration_Num  and Registration_Num ∩UID is NULL then  Registration_Num ∪ UID is also a superkey.

Hence the correct answer is Bank Account_Num is a candidate key.

Diagram:

E1 (e11, e12, e13)                                 E2 R (e21, e22, e23, e11)

                                                              E2 R1(e21,e22)

                                                              E2 R2(e21,e23,e11)

Relation: 1: M (no need of extra table)

For mutlivalued attribute, extra table is required

So, total no. of tables is 3

The correct answer is Discriminator of W and primary key of O

Key Points

• In database design, a weak entity set is an entity set that does not have a primary key but has a partial key, known as the discriminator.
• The existence of a weak entity depends on another entity, referred to as its identifying or owner entity set (O).
• The primary key of the weak entity set (W) is composed of its discriminator (which ensures uniqueness within an entity set) along with the primary key of its identifying or owner entity set, not a foreign key, since the primary key of O directly participates in forming the primary key of W.

The correct answer is Hexagons.

Key Points

• Entity Relationship Diagrams (ERDs) are a graphical representation used to model the structure of a database.
• Common components of ERDs include entities, relationships, and attributes.
• In ERDs:
  • Double lines are often used to represent the participation constraints in relationships.
  • Double rectangles are used to denote weak entities.
  • Ellipses are used to represent attributes of entities or relationships.
• However, Hexagons are not a standard component of Entity Relationship Diagrams.

Additional Information

• Entities are represented by rectangles and are used to model objects or concepts in the domain.
• Relationships are represented by diamonds and depict the associations between entities.
• Attributes provide more information about entities and relationships and are represented by ellipses connected to their related entities or relationships.
• In some extended ERDs, additional symbols and notations might be used, but hexagons are not part of the standard notation.

The correct answer is option 1.

Concept:

Data Definition Language (DDL):

Data Definition Language (DDL) is a standard for commands that define the different structures in a database. DDL statements create, modify, and remove database objects such as tables, indexes, and users.

List of DDL commands:

• CREATE
• DROP
• ALTER
• TRUNCATE
• COMMENT
• RENAME

DQL(Data Query Language):

The DQL is used to implement queries on the database. The query will produce a result by fetching the data from the relation.

List of DQL commands:

• SELECT

The relational Model :

The relational model represents how data is stored in Relational Databases.  A relational database stores data in the form of relations (tables). Relational Data Model uses tables to represent the data and the relationship among these data. Each table has multiple columns and each column is identified by a unique name. It is a low-level model. The relationship model has records of data and these all records form a table. A relationship consists of an attribute, relation Schema, tuple or records, relation instance, degree, and cardinality ratio.

ER model:

ER model stands for an Entity-Relationship model. It is a high-level data model. This model is used to define the data elements and relationships for a specified system. It has Entity, attributes, relations.

Hence the correct answer is A - (iii), B - (iv), C - (i), D - (ii).