Monday, 28 March 2016

Transactions in Database Management Systems - Definition

Transactions in DBMS, Define transaction in database, Explain database transactions with example


Transactions


Transaction is a logical unit of work carried out by a single execution (of a program or an application) that reads or writes (updates/changes) the contents’ (one or more data items) values of the database.

Discussion:
Example 1

Assume that you have a savings account with account number ‘A101’ and you want to check your latest account balance. Here,

Data Item(s): Your account with account number ‘A101’ is the data item.
Operation (Read/Write): You want to access your balance. That means you like to read the balance.
Program/Application: You may use, for example, the ATM machine interface. That is the application/program which does read your balance from database.

Example 2

Assume that you want to transfer money from your account ‘A101’ to your friend’s account ‘A345’. Here,

Data Item(s): Your account with account number ‘A101’ is one data item. Your friend’s account ‘A345’ is another data item.
Operation (Read/Write): You want to transfer fund from your account to others. This action reduces your balance and increases your friend’s. This means you have to write new balances in both data items.
Program/Application: You may use, for example, the internet banking facility. Here, internet banking is the application/program which does change (write) your balances in the database.

Other definitions:

A transaction is a unit of program execution that accesses and possibly updates various data items – Silberschatz, Korth, Sudarshan - Database System Concepts.

A transaction symbolizes a unit of work performed within a database management system (or similar system) against a database, and treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in database - Wikipedia.

A transaction is an executing program that forms a logical unit of database processing. A transaction includes one or more database access operations—these can include insertion, deletion, modification, or retrieval operations - Ramez Elmasri, Shamkant B. Navathe - Fundamentals of Database Systems.

A transaction is defined as any one execution of a user program in a DBMS. A transaction is seen by the DBMS as a series, or list, of actions. The actions that can be executed by a transaction include reads and writes of database objects. A transaction can also be defined as a set of actions that are partially ordered. That is, the relative order of some of the actions may not be important – Raghu Ramakrishnan, Johannes Gehrke – Database Management Systems.



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