Database Concepts
Database Management Software (DBMS) simplifies the task of managing the data and extracting useful information out
of it.
Data is a collection of raw facts which have not been processed to reveal useful information. Information is produced by
processing data.
Need for a Database
Database Management System (DBMS)
In traditional file processing, data is stored in the form of files. A number of application programs are written by
programmers to insert, delete, modify and retrieve data from these files. New application programs will be added to the
system as the need arises.
A database management system is a software package with computer programs that controls the creation,
maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications.
A database is an integrated collection of data records, files, and other objects. A DBMS allows different user application
programs to concurrently access the same database.
Well known DBMSs include Oracle, IBM DB2, Microsoft SQL Server, Microsoft Access, PostgreSQL, MySQL, FoxPro, and
SQLite.
Data can be organized into two types:
• Flat File: Data is stored in a single table. Usually suitable for less amount of data.
• Relational: Data is stored in multiple tables and the tables are linked using a common field. Relational is suitable for
medium to large amount of data.
Database Servers
Database servers are dedicated computers that hold the actual databases and run only the DBMS and related software.
A database has the following properties:
1) A database is a representation of some aspect of the real world also called mini world. Whenever there are changes in
this mini world they are also reflected in the database.
2) It is designed, built and populated with data for specific purpose.
3) It can be of any size and complexity.
4) It can be maintained manually or it may be computerized.
RDBMS
A relational database management system (RDBMS) is a database management system that is based on the relational
model as introduced by E. F. Codd , of IBM’s San Jose Research Laboratory. The purpose of the relational model is to
provide a declarative method for specifying data and queries: users directly state what information the database
contains and what information they want from it, and let the database management system software take care of
describing data structures for storing the data and retrieval procedures for answering queries.
Characteristics of Database Management Systems
The main characteristics of a DBMS are as follows:
1. Self-describing Nature of a Database System
2. Insulation Between Programs and Data
3. Sharing of Data
Advantages of using DBMS Approach
1. Reduction in Redundancy
2. Improved Consistency
3. Improved Availability
4. Improved Security
5. User Friendly
Limitations of using DBMS Approach
1. High Cost
2. Security and Recovery Overheads
In relational model,
A row is called a Tuple. A column is called an Attribute.
A table is called as a Relation. The data type of values in each column is called the Domain.
The number of attributes in a relation is called the Degree of a relation.
The number of rows in a relation is called the Cardinality of a relation.
Relation Schema R is denoted by R (A, A, A …, A) where R is the relation name 1 2 3, n and A, A, A,….A is the
list of attributes. 1 2 3 n
Relation State is the set of tuples in the relation at a point in time. A relation state r of relation schema R (A,
A, ..., A), denoted r(R) is a set of n-tuples r = {t, 1 2 n 1 t,...., t}, where each n-tuple is an ordered list of values
t = <v , v , ...,v >, where v 2 m 1 2 n i is in domain of A or is NULL. Here n is the degree of the relation and m is
the cardinality of i the relation
Relational Model Constraints
Constraints, are restrictions on the values, stored in a database based on the requirements. For example, in the
relation EMPLOYEE, the Employee_ID must be a 4-digit number, the Date_of_Birth must be such that the birth year
> 1985.
1. Domain Constraint: It specifies that the value of every attribute in each tuple must be from the domain of that
attribute. For example, the Employee_ID must be a 4-digit number.
2. Key Constraint:
Super key is a set of attributes in a relation, for which no two tuples in a relation state have the same
combination of values. Every relation must have at least one super key which is the combination of all attributes
in a relation.
Candidate Key - is a set of attributes that uniquely identify tuples in a table. Candidate Key is a super key with no
repeated attributes.
Primary Key: One of the candidate keys may be designated as Primary key. Primary key is used to identify tuples
in a relation. If a relation has many candidate keys it is preferable to choose that one as primary key which has
least number of attributes.
3. Null Value Constraint: Sometimes it is required that certain attributes cannot have null values.
4. Entity Integrity Constraint: This constraint specifies that primary key of a relation cannot have null value.
5. Referential Integrity Constraint: This constraint is specified between two relations. Foreign key in a relation R1 is
the set of attributes in R1 that refer to primary key in another relation R2
R1 is called the referencing relation and R2 is called referenced relation, and a referential integrity constraint holds
from R1 to R2.
The main purpose of this constraint is to check that data entered in one relation is consistent with the data entered
in another relation.
ASSESSMENT
Fill in the blanks:
1. A __________ is an organized collection of data.
2. A ________________ is a software package that can be used for creating and managing databases.
3. A ____________ is a database management system that is based on the relational model.
4. Three popular DBMS software are ________, ________, & _______.
5. A ____________is a unique value that identifies a row in a table.
Short Answer Questions
1. What does DBMS stands for?
2. What does RDBMS stands for?
3. How is data organized in a RDBMS?
4. State the relationship and difference between a primary and foreign key?
