Skip to main content

Define the following in term of relational model?

Domain


Domain denoted by D. Every attribute has some pre-defined value scope, known as attribute domain. Domain D is a set of atomic values (indivisible).Data type or format is to be specified for each domain.

Ex.
Name: set of characters strings that represent names of person.

Employee_ages: Possible age of employees must be integer values between 15 to 80.
Academic_department_codes: values must be ‘CS’, ’ECON’, ‘PHYS’.



Attribute 


In a relation table, each column is called by its column name or attribute name .
the name of a role played by a domain in that relation
Exa- s-name, s-id, s-add etc.


Tuple 


A single row of a table, which contains a single record for that relation is called a tuple.


Relation


A Database structured to recognize relation between stored items as information.


Relation schema 


Relation Schema denoted by R. A relation schema describes the relation name(table name), attributes, and their names.
R(A₁,A₂,…,An), relation name and list of attributes (each of which has a name and a domain)


Relation State 


A set of tuples. Each tuple is an ordered list of values, corresponding with the domain of their attribute, and representing a fact. A relation state is a subset of the Cartesian product of the domains defining the relation schema.
(r ) R set of n-tuples r={ t1+t2+………….tn } each n tuple is an ordered list of n values .
t={ v1+v2+……...vn }


Degrees of Relationship (Cardinality)


 The degree of relationship (also known as cardinality) is the number of occurrences in one entity which are associated (or linked) to the number of occurrences in another.
There are three degrees of relationship, known as:
  1. one-to-one (1:1)
  2. one-to-many (1:M)
  3. many-to-many (M:N)
The latter one is correct, it is M:N and not M:M.


Relation Database Schema



Set of relation schema S = (R1,R2……..Rn) an set of integrity constraints.

Relation Database State



Set of relation states DB ={r1,r2……..rn} each r is a state of Ri and such that the ri relation states integrity constraints specified in
Labels:

Comments

Post a Comment

Popular posts from this blog

Define the following terms: Entity, Attribute, Attribute Value, Relationship Instance, Composite Attribute, Multi-valued Attribute, Derived Attribute, Complex Attribute, Key Attribute, Value set(Domain), Recursive Relationships?

Entity – An entity can be a real-world object, either animate or inanimate, that can be easily identifiable. For example, in a school database, students, teachers, classes, and courses offered can be considered as entities. All these entities have some attributes or properties that give them their identity. Attribute – In general, an attribute is a characteristic. In a database management system (DBMS), an attribute refers to a database component, such as a table. It also may refer to a database field. Attributes describe the instances in the row of a database. Attribute Value – Attribute value is the real data of a particular entity for each of its attributes. In other word, associated with each real world entities are certain attributes that describe that entity; value of these attributes for any entity is called attribute value. For example, attribute value of first_name of attribute of student_name can be Gyanendra.  Relationship Instance – Each relationship instance ri...
Post a Comment
Read more

Compare the difference between the following:

i) Entities and Attributes – Entity -  An entity can be a real-world object, either animate or inanimate, that can be easily identifiable. For example, in a school database, students, teachers, classes, and courses offered can be considered as entities. All these entities have some attributes or properties that give them their identity. ii) an attribute is a characteristic. In a database management system (DBMS), an attribute refers to a database component, such as a table. It also may refer to a database field. Attributes describe the instances in the row of a database. ii) Composite and Atomic attributes –   Composite attribute − Composite attributes are made of more than one simple attribute. For example, a student's complete name may have first_name and last_name. Simple attribute (Atomic) − Simple attributes are atomic values, which cannot be divided further. For example, a student's phone number is an atomic value of 10 digits. iii) Single valued and Mu...
Post a Comment
Read more

Explain the four actors on the scene of Database?

For a small personal database, one person defines, constructs and manipulates the database . For a large organization, many people are involved in the design, use and maintenance of the large database Two types of actors of DBMS: 1. Actors on the Scene (day-to-day use of large database ) 2. Workers behind the Scene ( work to maintain database environment and are not involved in its contents ) Actors on the Scene Database administrators (DBA) are responsible for:  Authorizing access to the database  Coordinating and monitoring its use  Acquiring software and hardware resources Database designers are responsible for:  Identifying the data to be stored  Choosing appropriate structures to represent and store this data . End users - People whose jobs require access to the database.  Types of End Users • Casual end users • Naive or p...
Post a Comment
Read more