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2015-11-19T15:47:37+05:30

ACID (atomicity, consistency, isolation, and durability) is an acronym and mnemonic device for learning and remembering the four primary attributes ensured to any transaction by a transaction manager (which is also called a transaction monitor). These attributes are:


Atomicity. In a transaction involving two or more discrete pieces of information, either all of the pieces are committed or none are.

Consistency. A transaction either creates a new and valid state of data, or, if any failure occurs, returns all data to its state before the transaction was started.


 Isolation. A transaction in process and not yet committed must remain isolated from any other transaction.

Durability. Committed data is saved by the system such that, even in the event of a failure and system restart, the data is available in its correct state.
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2015-11-19T16:48:31+05:30
An acid (from the Latin acidus/acēre meaning sour) is a chemical substance whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals (like calcium) to form salts. Aqueous solutions of acids have a pH of less than 7. Non-aqueous acids are usually formed when an anion (negative ion) reacts with one or more positively charged hydrogen cations. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in thesolution. Chemicals or substances having the property of an acid are said to be acidic.There are three common definitions for acids: the Arrhenius definition, the Brønsted-Lowry definition, and the Lewis definition. The Arrhenius definition defines acids as substances which increase the concentration of hydrogen ions (H+), or more accurately, hydronium ions (H3O+), when dissolved in water. The Brønsted-Lowry definition is an expansion: an acid is a substance which can act as a proton donor. By this definition, any compound which can easily be deprotonated can be considered an acid. Examples include alcohols and amines which contain O-H or N-H fragments. A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. Examples of Lewis acids include all metal cations, and electron-deficient molecules such as boron trifluoride and aluminium trichloride.
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