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A database is an organized collection of data, general stores, and accessed electronically from a computer system.

The Database Management System(DBMS) is the software that interacts with end-users, applications, and the database itself to capture and analyze the data.

The DBMS software additionally encompasses the core facilities provided to administer the database. The sum total of the database, the DBMS, and the associated applications can be referred to as a “database system”.

• Data redundancy and inconsistency.


• Difficulty in accessing data


• Data isolation


• Integrity problem


• Atomicity problem


• Concurrent access anomalies

Instance and Schemas

• The collection of information stored in the database at a particular moment is called an instance of the database.


• The overall design of the database is called the database schema.

• Commercial database


• Multimedia database


• Deductive database


• Temporal database


• Geological Info System

• Provides security and removes redundancy


• Self-describing nature of a database system


• Insulation between programs and data abstraction


• Support of multiple views of the data


• Sharing of data and multiuser transaction processing


• Database Management Software allows entities and relations among them to form tables.


• It follows the ACID concept ( Atomicity, Consistency, Isolation, and Durability).

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• To remove this partial execution problem, we increase the level of atomicity and bundle all the instructions of a logical operation into a unit called a transaction.


• So, formally - ‘A transaction is a set of logically related instructions to perform a logical unit of work’.

• When two or more transactions are executed together or one after another, then they can be bundled up into a higher unit of execution called schedule.


• A schedule of N transactions T1, T2, T3...TN, is an ordering of the operations of the transactions. Operations from different transactions can be interleaved in the scheduled S.


• However, the schedule for a set of transactions must contain all the instructions of those transactions, and for each transaction T, that participates in the schedule S, the operation of T, in S must appear in the same order in which they occur in T.

• The domain is a set of atomic values.


• By atomic we mean that each value in the domain is indivisible as far as the formal relational model is concerned.


• A common method of specifying a domain is to specify a data type from which the data forming the domain are drawn.


• 
  Table(Relation): A relation is a set of tupes/rows/entities/records.


• Tuple: Each row of a relation/table is called a tuple.


• Degree: Number of columns/attributes of a relation.


• Cardinality: Number of rows/types/record of a relational instance.

• Cells contain atomic values.


• Values in a column are of the same kind.


• Each row is unique.


• Each column has a unique name


• No two tables can have the same name in a relational schema.


• The sequence of rows is insignificant.


• The sequence of columns is insignificant.

• Database Testing


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