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ER Model

Lecture on Database Design Process
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This lecture explains the Process of Database Designing.

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Lecture on Entity, Entity Type, Entity Set
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This video explains the basic concepts of Entity, Entity Type, and Entity Set.

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Lecture on Attributes, Domain
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  • This lecture explains the concept of Attributes and its Domain.
  • Attribute: It is the property that describes an entity.
  • Domain: It is the set of permitted values.
    Example: Name can be made of letters A-Z , a-z,' '
    Age: can be made of 0-9.
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Lecture on Simple & Composite
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This lecture discusses about Simple and Composite Attributes in a relation.

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Lecture on Single-valued Vs Multivalued
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This lecture describes the concepts of Single-valued and Multivalued Attributes.
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Lecture on Stored Vs Derived
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This lecture concentrates on Stored and Derived attributes in a relation.

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Lecture on Null Values
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This lecture explains about Null Values in attributes.

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Lecture on Complex Attributes
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This lecture tells about Complex Attributes in a relation.

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Concept of Null Values
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What are different cases where we can come across null value for an attribute

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Lecture on Key Attribute
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KEY ATTRIBUTE:
An attribute or a set of attributes which can uniquely identify all the entities of an entity set (or each record of a relation) is called Key attribute.
Consider the below  table Student,

Name Subject Grade
A1 DBMS Excellent
B1 OS A
A2 DBMS C

Here we can uniquely identify any row by attribute 'Name'. but if later entry for a person with the same name as A1 is inserted in the table, our table will look like,

Name Subject Grade
A1 DBMS Excellent
B1 OS A
A2 DBMS C
A1 DBMS B

Here, you can see that 'Name' can not uniquely identify a row but a combination of 'Name' and 'Grade' can uniquely identify the rows of table.
But suppose a person with same name may have a same grade in different subject so this will not be a feasible way for key attributes. We will use some unique ids for such purpose. These ids will be unique throughout the table for example, we have different roll numbers in our class.
So our table will look like,

Roll No. Name Subject Grade
1 A1 DBMS Excellent
2 B1 OS A
3 A2 DBMS C
4 A1 DBMS B

Here 'Roll No.' is a key attribute of student table.
Note- Any superset of key attribute will also be a key attribute.
 

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Lecture on Notation for ER Diagram
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This lecture tells you about the different Notations used in ER Diagram.

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Lecture on Relationship Constraints
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This lecture explains the basics of Relationship Constraints in ER model.

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Lecture on Cardinality Ratio
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This lecture explains the concept of Cardinality Ratio in detail.

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Lecture on Participation Constraints
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This lecture explains Participation Constraints as appearing in ER Models.

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Lecture on Weak Entity
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  • This lecture explains the concept of Weak Entity in ER Diagram.
  • Weak Entity is the entity which doesn't  have any key attribute, we may have two instances of that entity with same record , we identify it through identifying relationship with strong entity and we may have a key among this entity to distinguish which is called partial key.
  • Example: 
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Lecture on Relationship Attribute
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This lecture explains about the concept of Attributes of Relations in ER model.

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Lecture on Specialization
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This lecture explains the concept of Specialization as an enhanced feature ER model.
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Lecture on Generalization
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This lecture describes the concept of Generalization as an enhanced feature of ER model.

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Lecture on Aggregation
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  • This lecture explains the concept of Aggregation in enhanced ER model.
  • Aggregation is an abstraction, it is a a way of hiding higher level details.
  • It is a way of avoiding data redundancy.
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Lecture on ER Model to Relational Table
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This lecture describes the process of deriving Relational Tables from a given ER Model.

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This video tells about a special case appearing while converting a given ER model to relational tables.

This video explains the step by step method to solve a problem on getting relational tables from a given ER model.

What is the type of relationship between weak and strong entity?

(A) 1:1
(B) 1:M
(C) M:1
(D) M:N

Consider the following entity relationship diagram (ERD), where two entities E1 and E2 have a relation R of cardinality 1:m.

The attributes of E1 are A11, A12 and A13 where A11 is the key attribute. The attributes of E2 are A21, A22, and A23 where A21 is the key attribute and A32 is a multivalued attribute. Relation R doesn’t have any attribute. A relational database containing minimum number of tables with each table satisfying the requirements of the third normal form (3NF) is designed from the above ERD. The minimum number of tables in the database is:

(a) 2                  (b) 3                       (c) 4                 (d) 5

 

The quiz covers the concepts of ER model in Database Management Systems. 

Difficulty Level:  intermediate
GATE 2012 Question on ER Diagram

Given the basic ER and relational models, which of the following is INCORRECT?

A) An attribute of an entity can have more than one value.

B) An attribute of an entity can be composite.

C) In a row of a relational table, an attribute can have more than one value.

D) In a row of a relational table, an attribute can have exactly one value or NULL value.

 

Things you need to know

Refer Techtud's lectures for DBMS.

For an ER diagram

A) True, an attribute can be composite.

B) True, an attribute can be composite.

C) False, an attribute can not have more than one value.

D) True, an attribute can have exactly one value or NULL value.

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GATE 1997 Question on Refrential Integrity Constraint ?

Let R(a,b, c) and S(d, e, f ) be two relations. 'd' is foreign key of S that refers to the primary key of R.

Consider the following four operations on 'R' and 'S'.

A) Insert into 'R'

B) Insert into 'S'

C) Delete from 'R'

D) Delete from 'S'

Which of these can cause the violation of referential integrity constraint?

Referential Integrity Constraint

Every record of table 'S' must be related to a record of table 'R'.

A) This will not violate any constraint

B) This can violate the referential constraint,  if the record inserted into the table 'S' does not refer to any record of table 'R' .

C) This can violate the refrential constraint, as if a record is deleted from 'R', then all the records of table 'S' that points to this record must also be deleted.

D) This will not violate refrential constraint.

 

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