Second Normal Form (2NF)

Second Normal Form (2NF) : (l) A relation R is in second normal form (2NF) if and only if it is in 1NF and every nonkey attribute is fully functionally dependent on the primary key. (2) A table is in 2NF if each nonidentified attribute provides a fact that describes the entity identified by the entire primary key and not part of it. See Functional dependence.

[Category=Data Quality ]

Source: Larry English, http://www.iaidq.com/main/glossary.shtml , 09-Feb-2009 11:12

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Second Normal Form - The result of normalizing to ensure that a data model contains no partial key dependencies. In practice, when entities have compound keys, seek out any attribute that is dependent upon only part of the key. Whatever business thing isentifiable by that part of the key is an entity, and the 2NF violation is an attribute of that entity. (DMReview definition)

Source: The Data Governance Institute, 24 December 2009 13:10:36, http://www.datagovernance.com/glossary-governance/

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Second Normal Form - The result of normalizing to ensure that a data model contains no partial key dependencies. In practice, when entities have compound keys, seek out any attribute that is dependent upon only part of the key. Whatever business thing is identifiable by that part of the key is an entity, and the 2NF violation is an attribute of that entity.

[Category=Information Management ]

Source: Information-Management.com, 06 July 2010 12:54:25, http://www.information-management.com/glossary/m.html

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Second normal form (2NF) - In relational data analysis, a relation is in second normal form if it is in first normal form and every non-key attribute is fully functionally dependent on the primary key - there are no part-key dependencies.

[Category=Data Quality ]

Source: DAMA UK, 19 July 2011 10:17:44, http://www.damauk.org/glossary.php

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second normal form - [database structures] The second level of guidelines for designing table and data structures in a relational database. The second-normal-form guideline incorporates the guidelines of first normal form; in addition, it recommends removing data that applies to multiple rows in a table into its own table and using a foreign key to create a relationship to the original table. A database that follows these guidelines is said to be in second normal form.

[Category=Geospatial ]

Source: esri, 12 August 2012 08:55:54, http://support.esri.com/en/knowledgebase/GISDictionary/term/abbreviation

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2NF - In creating a database, normalization is the process of organizing it into tables in such a way that the results of using the database are always unambiguous and as intended. Normalization may have the effect of duplicating data within the database and often results in the creation of additional tables. (While normalization tends to increase the duplication of data, it does not introduce redundancy, which is unnecessary duplication.) Normalization is typically a refinement process after the initial exercise of identifying the data objects that should be in the database, identifying their relationships, and defining the tables required and the columns within each table.

A simple example of normalizing data might consist of a table showing:

   Customer Item purchased Purchase price
   Thomas   Shirt          $40
   Maria    Tennis shoes   $35
   Evelyn   Shirt          $40
   Pajaro   Trousers       $25

If this table is used for the purpose of keeping track of the price of items and you want to delete one of the customers, you will also delete a price. Normalizing the data would mean understanding this and solving the problem by dividing this table into two tables, one with information about each customer and a product they bought and the second about each product and its price. Making additions or deletions to either table would not affect the other.

Normalization degrees of relational database tables have been defined and include:

First normal form (1NF). This is the "basic" level of normalization and generally corresponds to the definition of any database, namely:

   * It contains two-dimensional tables with rows and columns.
   * Each column corresponds to a sub-object or an attribute of the object represented by the entire table.
   * Each row represents a unique instance of that sub-object or attribute and must be different in some way from any other row (that is, no duplicate rows are possible).
   * All entries in any column must be of the same kind. For example, in the column labeled "Customer," only customer names or numbers are permitted.

Second normal form (2NF). At this level of normalization, each column in a table that is not a determiner of the contents of another column must itself be a function of the other columns in the table. For example, in a table with three columns containing customer ID, product sold, and price of the product when sold, the price would be a function of the customer ID (entitled to a discount) and the specific product.

Third normal form (3NF). At the second normal form, modifications are still possible because a change to one row in a table may affect data that refers to this information from another table. For example, using the customer table just cited, removing a row describing a customer purchase (because of a return perhaps) will also remove the fact that the product has a certain price. In the third normal form, these tables would be divided into two tables so that product pricing would be tracked separately.

Domain/key normal form (DKNF). A key uniquely identifies each row in a table. A domain is the set of permissible values for an attribute. By enforcing key and domain restrictions, the database is assured of being freed from modification anomalies. DKNF is the normalization level that most designers aim to achieve.

Related glossary terms: BLOB (binary large object), data structure, catalog, data mart (datamart), ECMAScript (European Computer Manufacturers Association Script), Visual FoxPro, segment, block, flat file

[Category=Data Management ]

Source: WhatIs.com, 02 July 2013 09:01:59, http://whatis.techtarget.com/glossary/Data-and-Data-Management