36) What Is An Extension Of Entity Type?
Answer: The collections of entities of a particular entity type are grouped together into an entity set.
37) What Is Weak Entity Set?
Answer: An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.
Weak Entity Set is an entity that does not have a key attribute. A weak entity must participate in an identifying relationship type with an owner or identifying entity type.
Entities are identified by the combination of:
- A partial key of the weak entity type
- The particular entity they are related to in the identifying entity type.
A DEPENDENT entity is identified by the dependent’s first name, and the specific EMPLOYEE with whom the dependent is related.
Name of DEPENDENT is the partial key. DEPENDENT is a weak entity type.
EMPLOYEE is its identifying entity type via the identifying relationship type DEPENDENT_OF.
38) What Is An Entity? Differentiate Between Strong & Weak Entity?
Answer) An Entity is any object of interest to and organization or for the representation in the database. They represent objects in the real world which is distinguishable from all other objects. For Example: Every person in a college is an entity, Every room in a college is an entity.
An Entity which has a set of attributes which can uniquely identify all the entities is termed as Strong Entity whereas an entity whose primary key does not determine all the instance of the entity uniquely
termed as Weak entity.
39) What Is An Attribute? What Are The Types Of Attributes?
Answer) An Entity is represented by a set of properties called Attributes. The attributes are useful in describing the properties of each entity in the entity set.
The different types of attributes are:
- Simple Attribute.
- Composite Attribute.
- Single Valued Attribute.
- Multivalued Attribute.
- Stored Attribute.
- NULL Attribute.
40) Differentiate Between The Different Types Of Attributes?
Attributes which cannot be further divided into subparts are called Simple Attributes. Example: Roll Number of a student or say Employee No. is unique which cannot be further divided.
Attributes can be further divided into portions are called Composite Attributes. Example: The attribute name in the Student Database can be further divided into First Name, Middle Name, Last Name.
Attributes which at any instant contains only a specific value are called Single Valued Attributes. Example: PAN Card No. is always unique.
Certain attributes for example, the dependent name in the policy database may have set of values assigned to it. There may be more than one dependent for a single policy holder. Such attributes are called Multi-Valued Attributes.
Certain attributes for example, Consider a person entity, the value of age can be determined from the current date and the value of that person's birthdate. The Age attribute is hence Derived Attribute and is said to be derivable from the birthdate attribute, which is called a Stored Attribute.
A NULL value attribute is used when an attributes does not have any values.
ALSO CHECK THE BELOW FAQ's:
41) Define The Types Of Data Integrity Rules?
42) What Is A Table? What Is A Tuple? What Is A Relation?
43) What Are Extension & Intension?
44) What Is A View? How It Is Related To Data Independence?
45) What Is A View? Discuss The Difference Between A View & A Base Relation?
46) What Is A Key? What Are Different Types Of Keys In A Database?
47) What Is A Primary Key & Secondary Key?
48) What Is A Candidate Key & Alternate Key?
49) What Is A Super Key & Composite Key?
50) What Is Foreign Key?
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