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Normal Forms (logic)
Database normalization or database normalisation (see American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences) is the process of structuring a relational database in accordance with a series of so-called Database normalization#Normal forms, normal forms in order to reduce data redundancy and improve data integrity. It was first proposed by British people, British computer scientist Edgar F. Codd as part of his relational model. Normalization entails organizing the column (database), columns (attributes) and relation (database), tables (relations) of a database to ensure that their Dependency theory (database theory), dependencies are properly enforced by database integrity constraints. It is accomplished by applying some formal rules either by a process of ''synthesis'' (creating a new database design) or ''decomposition'' (improving an existing database design). Objectives A basic objective of the first normal form defined by Cod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American And British English Spelling Differences
Despite the various List of dialects of English, English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography, the two most notable variations being British and American spelling. Many of Comparison of American and British English, the differences between American English, American and British English date back to a time before spelling standards were developed. For instance, some spellings seen as "American" today were once commonly used in Britain, and some spellings seen as "British" were once commonly used in the United States. A "British standard" began to emerge following the 1755 publication of Samuel Johnson's ''A Dictionary of the English Language'', and an "American standard" started following the work of Noah Webster and, in particular, his ''Webster's Dictionary, An American Dictionary of the English Language'', first published in 1828. Webster's efforts at spellin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First Normal Form
First normal form (1NF) is a property of a relation in a relational database. A relation is in first normal form if and only if no attribute domain has relations as elements. Or more informally, that no table column can have tables as values (or no repeating groups). Database normalization is the process of representing a database in terms of relations in standard normal forms, where first normal is a minimal requirement. SQL-92 does not support creating or using table-valued columns, which means that using only the "traditional relational database features" (excluding extensions even if they were later standardized) most relational databases will be in first normal form by necessity. Database systems which do not require first normal form are often called no sql systems. Newer SQL standards like SQL:1999 have started to allow so called non-atomic types, which include composite types. Even newer versions like SQL:2016 allow json. Overview In a hierarchical database like the IBM ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fifth Normal Form
Fifth normal form (5NF), also known as projection–join normal form (PJ/NF), is a level of database normalization designed to remove redundancy in relational databases recording multi-valued facts by isolating semantically related multiple relationships. A table is said to be in the 5NF if and only if every non-trivial join dependency in that table is implied by the candidate keys. It is the final normal form as far as removing redundancy is concerned. A 6NF also exists, but its purpose is not to remove redundancy and it is therefore only adopted by a few data warehouses, where it can be useful to make tables irreducible. A join dependency * on R is implied by the candidate key(s) of R if and only if each of A, B, …, Z is a superkey for R. The fifth normal form was first described by Ronald Fagin in his 1979 conference paper ''Normal forms and relational database operators''. Example Consider the following example: The table's predicate is: products of the type designated b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
