Kerala Plus Two Computer Application Notes Chapter 8 Database Management System
DBMS means Data Base Management System. It is a tool used to store a large volume of data, retrieve and modify the data as and when required. DBMS consists of data and programs.
Advantages of DBMS
- Data Redundancy
- Inconsistency can be avoided
- Data can be shared
- Standards can be enforced
- Security restrictions can be applied
- Integrity can be maintained
- Efficient data access
- Crash recovery
Structure of DBMS
- Fields – Smallest unit of data. Eg: Name, age, sex, …
- Record – Collection of related fields.
- File – Collection of records
Components of DBMS
- Databases – It is the main component.
- Data Definition Language (DDL) – It is used to define the structure of a table.
- Data Manipulation Language (DML) – It is used to add, retrieve, modify and delete records in a database.
- Users – With the help of programs users interact with the DBMS.
Database Abstraction – Abstraction means hiding, it hides certain details of how data is stored and main-tained.
Levels of Database Abstraction:
- Physical Level (Lowest Level) – It describes how the data is actually stored in the storage medium.
- Logical Level (Next Higher Level) – It describes what data are stored in the database.
- View Level (Highest level) – It is closest to the users. It is concerned with the way in which the individual users view the data.
Data Independence – It is the ability to modify the scheme definition in one level without affecting the scheme definition at the next higher level.
- Physical Data Independence – It is the ability to modify the physical scheme without causing application programs to be rewritten.
- Logical Data Independence – It is the ability to modify the logical scheme without causing application programs to be rewritten.
Users of Database
- Database Administrator
- Application Programmer
- New users
Data models – It is a collection of tools for describing data, data relationship, data semantics and consistency problem. 3 models.
- Hierarchical model
- Network model
- Relational model
RDBMS – Relational DataBase Management System. It consists of a collection of relations as database.
Relation means table.
Domain – A pool of possible values from which col-umn values are drawn. ‘
Tuple means rows.
Attributes means columns.
Cardinality – The number of rows.
Degree – The number of columns
View – A view is a virtual table derived from one or more base tables.
Key is used to identify or distinguish a tuple in a relation.
Candidate key – It is used to uniquely identify the row.
Primary key – It is a set of one or more attributes used to uniquely identify a row.
Alternate key – Acandidate key other than the primary key.
Foreign key – A single attribute ora set of attributes, which is a candidate key in another table is called foreign key.
Relational Algebra – It consists of a set of opera¬tions that takes one or two relations as input and produces a new relation as a result.
- Select operation (σ)
- Project Operation (π)
- Cartesian Product
- Union Operation (∪)
- Intersection operation (∩)
- Set difference operation (-)