DATA BASE MANAGEMENT SYSTEM CLASS 12 NOTES
What is database?
A database is an organized collection of information arranged in well defined tabular form. The purpose of a database is to collect, store, and retrieve related information for future purpose
What is DBMS?
The Software used to manage ,control ,storage, organize and retrieval) databases for future purpose is called Data Base Management System (DBMS).
Benefits of using a DBMS are:
a. Redundancy can be controlled (duplication)
b. Inconsistence can be avoided (uniqueness)
c. Data can be shared (portable)
d. Security restrictions can be applied
What is table ?
table is a two-dimensional representation of a relation in the form of rows and columns.
What is a Relational database?
A relational database is a database that stores data in relations (tables). In Other words relational database is collection of two or more tables.
What is RDBMS?
And the software used to manage control storage a relational database is called relational database system RDBMS . today's popular rdms are oracle,SQL server,my sql etc.
Terminology Used in a RDBMS
•Table A table is the basic storage structure of RDBMS. A table holds all the data necessary about something in the real world, e.g. employees, invoices or customers.
•Row A single row or tuple represents all data required for a particular entity.
•Column A column or attribute represents a specific type of data of different entities.
•Degree It represents the number of attributes in a relation.
•Cardinality It represents the number of tuples in a relation.
•Primary Key: A column or set of columns that uniquely identifies a row within a table is called primary key.
•Candidate Key: Candidate keys are set of fields (columns with unique values) in the relation that are eligible to act as a primary key.
Alternate Key: A candidate key that is not the primary key is called alternate key.
•Domain Refers to the description of an attribute’s allowed values. It is actually a set of values the attribute can have, and the semantic, or logical, description is the meaning of the attribute.
What is a transaction?
a Transaction is a unit of work that must be done in logical order and successfully as a group or not done at all.
different states of a database transaction.
Active- This is the initial state of every transaction, where a transaction is executed.
Partially Committed- When a transaction executes its final operation, it is said to be in a partially committed state.
Failed- A transaction is said to be in a failed state if any of the checks made by the database recovery system fails.
Aborted- If any of the checks fails, then the recovery manager rolls back all its write operations on the database to bring the database back to its original state where it was prior to the execution of the transaction.
Committed- If a transaction executes all its operations successfully,it is said to be committed. All its effects are now permanently established on the database system.
Properties of Transactions
Or define acidity of a transaction
Atomicity ensures that all operations within the work unit are completed successfully. Otherwise, the transaction is aborted at the point of failure and all the previous operations are rolled back to their former state.
Consistency ensures that the database properly changes states upon a successfully committed transaction.
Isolation enables transactions to operate independently of and
transparent to each other.
Durability ensures that the result or effect of a committed transaction persists in case of a system failure.
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