INTRODUCTION TO RDBMS

Chapter 8: RDBMS & MySQL – A Review  Database-A well organized collection of inter-related data that ensures safety, security and integrity of data is called Database. It works like is a container which contains the object like Tables, Queries, Reports, Procedures in organized way.  Database Management System (DBMS)-DBMS is aSoftware tool that provides the essential services to create, storing, maintain and utilize the databases in efficient way. They also provide security tools that ensure the safe accessibility of the data. Example of RDBMS software are- Oracle, MS SQL Server, MS Access, Paradox, DB2 and MySQL etc.  Advantages of Data Base Management System:  Database reduces Redundancy- Database removes duplication of data because data are kept at one place and all the application refers to the centrally maintained database.  Database controls Inconsistency- When two copies of the same data do not agree to each other, then it is called Inconsistency. By controlling redundancy, the inconsistency is also controlled.  Database facilitates Sharing of Data- Data stored in the database can be shared among several users.  Database ensures Security - Data are protected against accidental or intentional disclosure to unauthorized person or unauthorized modification.  Database maintains Integrity- It enforces certain integrity rules to insure the validity or correctness of data. For example a date can’t be entered like 25/25/2000.  Structure Query Language (SQL) - A non-procedural Query Language used for querying the database.  DDL (Data Definition Language) – These SQL command facilitates defining creation/modification etc. of database object such as tables and indexes etc. These commands are- CREATE, ALTER, DROP etc.  DML (Data Manipulation Language)-Type of SQL command, thatfacilitatesmanipulation of stored records like retrieval, additions, deletions and modification etc. Some commands are- SELECT, INSERT, DELETE & UPDATE etc.  TCL (Transaction Control Language)- A transaction is a one complete unit of work. To manage and control the transactions, the transaction control commands are used. e.g COMMIT, ROLLBACk etc.  Data Dictionary - A file containing facts/data about the data stored in table, generally it refers the structure of the table.  Data Model- Data model refers ‘ how data are organized and stored in the database’.Commonly used models are-  Relational Data Model - In this model data is organized into tables i.e. Rows and columns. These tables are called relations.  The Network Data Model - In this model data are represented by collection of records & relationships among data. The collections of records are connected to one another by means of links.  The Hierarchical Data Model - In this model records are organized as trees rather than arbitrary graphs.  Object Oriented Data Model - Data and associated operations are represented by objects. An object is an identifiable entity with some characteristics and behavior.  Relation –A table in Database, which contains data in the form of rows and columns, is called relation.  Domain - Pool of values from which the actual values are derived for a column in the table.  Tuple - A row of a relation/table is called record or Tuple.  Attribute - A column/Field of relation/table is called Attribute.  Degree - Number of columns in a table is called Degree of the table or relation.  Cardinality - Number of records/tuples stored in the table is called Cardinility.  View - Virtual table that does not really existin the database.  Primary Key - Set of one or more attributes/columns that can uniquely identify a record in the table.  Candidate Key - A Candidate Key is the one that is capable of becoming Primary key i.e., a field or :: 68 :: attribute that has unique value for each row in the relation and can act as a Primary key.  Alternate Key - A candidate key that is not primary key is called alternate key.  Foreign Key - A non-key attribute, whose values are derived from the primary key of some other table.  Integrity Constraints - Integrity Constraints are the rules that a database must comply all the times to ensure the correctness or validity of data.It determines what all changes are permissible to a database.