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Normal Forms (logic)
Database normalization is the process of structuring a relational database in accordance with a series of so-called '' normal forms'' in order to reduce data redundancy and improve data integrity. It was first proposed by British computer scientist Edgar F. Codd as part of his relational model. Normalization entails organizing the columns (attributes) and tables (relations) of a database to ensure that their 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 Codd in 1970 was to permit data to be queried and manipulated using a "universal data sub-language" grounded in first-order logic. An example of such a language is SQL, though it is one that Codd regarded as seriously flawed. The objectives of normalization ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Relational Database
A relational database (RDB) is a database based on the relational model of data, as proposed by E. F. Codd in 1970. A Relational Database Management System (RDBMS) is a type of database management system that stores data in a structured format using rows and columns. Many relational database systems are equipped with the option of using SQL (Structured Query Language) for querying and updating the database. History The concept of relational database was defined by E. F. Codd at IBM in 1970. Codd introduced the term ''relational'' in his research paper "A Relational Model of Data for Large Shared Data Banks". In this paper and later papers, he defined what he meant by ''relation''. One well-known definition of what constitutes a relational database system is composed of Codd's 12 rules. However, no commercial implementations of the relational model conform to all of Codd's rules, so the term has gradually come to describe a broader class of database systems, which at a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Communications Of The ACM
''Communications of the ACM'' (''CACM'') is the monthly journal of the Association for Computing Machinery (ACM). History It was established in 1958, with Saul Rosen as its first managing editor. It is sent to all ACM members. Articles are intended for readers with backgrounds in all areas of computer science and information systems. The focus is on the practical implications of advances in information technology and associated management issues; ACM also publishes a variety of more theoretical journals. The magazine straddles the boundary of a science magazine, trade magazine, and a scientific journal. While the content is subject to peer review, the articles published are often summaries of research that may also be published elsewhere. Material published must be accessible and relevant to a broad readership. From 1960 onward, ''CACM'' also published algorithms, expressed in ALGOL. The collection of algorithms later became known as the Collected Algorithms of the ACM. CA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Third Normal Form
Third normal form (3NF) is a database schema design approach for relational databases which uses normalizing principles to reduce the duplication of data, avoid data anomalies, ensure referential integrity, and simplify data management. It was defined in 1971 by Edgar F. Codd, an English computer scientist who invented the relational model for database management. A database relation (e.g. a database table) is said to meet third normal form standards if all the attributes (e.g. database columns) are functionally dependent on solely a key, except the case of functional dependency whose right hand side is a prime attribute (an attribute which is strictly included into some key). Codd defined this as a relation in second normal form where all non-prime attributes depend only on the candidate keys and do not have a transitive dependency on another key. A hypothetical example of a failure to meet third normal form would be a hospital database having a table of patients which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Second Normal Form
Second normal form (2NF), in database normalization, is a normal form. A relation is in the second normal form if it fulfills the following two requirements: # It is in first normal form. # It does not have any non-prime attribute that is functionally dependent on any proper subset of any candidate key of the relation (i.e. it lacks partial dependencies). A ''non-prime attribute of a relation'' is an attribute that is not a part of any candidate key of the relation. Put simply, a relation (or table) is in 2NF if: # It is in 1NF and has a single attribute unique identifier (UID) (in which case every non key attribute is dependent on the entire UID), or # It is in 1NF and has a multi-attribute unique identifier, and every regular attribute (not part of the UID) is dependent on ''all attributes'' in the multi-attribute UID, not just one attribute (or part) of the UID. If any regular (non-prime) attributes are predictable (dependent) on another (non-prime) attribute, that is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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First Normal Form
First normal form (1NF) is the simplest form of database normalization defined by English computer scientist Edgar F. Codd, the inventor of the relational database. A Relation (database), relation (or a Table (database), ''table'', in SQL) can be said to be in first normal form if each field is ''atomic'', containing a single value rather than a set of values or a nested table. In other words, a relation complies with first normal form if no attribute domain (the set of values allowed in a given column) has relations as elements. Most relational database management systems, including standard SQL, do not support creating or using table-valued columns, which means most relational databases will be in first normal form by necessity. Otherwise, normalization to 1NF involves eliminating nested relations by breaking them up into separate relations associated with each other using foreign keys. This process is a necessary step when moving data from a non-relational (or NoSQL) database, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Unnormalized Form
In database normalization, unnormalized form (UNF or 0NF), also known as an unnormalized relation or non-first normal form (N1NF or NF2), is a database data model (organization of data in a database) which does not meet any of the conditions of database normalization defined by the relational model. Database systems which support unnormalized data are sometimes called non-relational or NoSQL databases. In the relational model, unnormalized relations can be considered the starting point for a process of normalization. "Unnormalized form" should not be confused with denormalization, where normalization is deliberately compromised for selected tables in a relational database. History In 1970, E. F. Codd proposed the relational data model, now widely accepted as the standard data model. At that time, office automation was the major use of data storage systems, which resulted in the proposal of many UNF/NF2 data models like the Schek model, Jaeschke models ( non-recursive and recur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Sixth Normal Form
Sixth normal form (6NF) is a normal form used in relational database normalization which extends the relational algebra and generalizes relational operators (such as join) to support interval data, which can be useful in temporal databases. The term 6NF has historically also been used to refer to another normalization degree, which today is more commonly known as domain-key normal form (DKNF) (see Other meanings). Definition Christopher J. Date and others have defined sixth normal form as a normal form, based on an extension of the relational algebra. Relational operators, such as ''join'', are generalized to support a natural treatment of interval data, such as sequences of dates or moments in time, for instance in temporal databases. Sixth normal form is then based on this generalized join, as follows: A relvar R ableis in sixth normal form (abbreviated 6NF) if and only if it satisfies no nontrivial join dependencies at all — where, as before, a join dependency i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Christopher J
Christopher is the English version of a Europe-wide name derived from the Greek name Χριστόφορος (''Christophoros'' or '' Christoforos''). The constituent parts are Χριστός (''Christós''), "Christ" or "Anointed", and φέρειν (''phérein''), "to bear"; hence the "Christ-bearer". As a given name, 'Christopher' has been in use since the 10th century. In English, Christopher may be abbreviated as " Chris", "Topher", and sometimes " Kit". It was frequently the most popular male first name in the United Kingdom, having been in the top twenty in England and Wales from the 1940s until 1995, although it has since dropped out of the top 100. Within the United Kingdom, the name is most common in England and not so common in Wales, Scotland, or Northern Ireland. Cognates in other languages *Afrikaans: Christoffel, Christoforus * Albanian: Kristofer, Kristofor, Kristoforid, Kristo *Arabic: كريستوفر (''Krīstafor, Kristūfar, Krístufer''), اصطفر (''ʔ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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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 designa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Fourth Normal Form
Fourth normal form (4NF) is a normal form used in database normalization. Introduced by Ronald Fagin in 1977, 4NF is the next level of normalization after Boyce–Codd normal form (BCNF). Whereas the second, third, and Boyce–Codd normal forms are concerned with functional dependencies, 4NF is concerned with a more general type of dependency known as a multivalued dependency. A table is in 4NF if and only if, for every one of its non-trivial multivalued dependencies ''X'' \twoheadrightarrow ''Y'', ''X'' is a superkey—that is, ''X'' is either a candidate key or a superset thereof."A relation schema R* is in fourth normal form (4NF) if, whenever a nontrivial multivalued dependency X \twoheadrightarrow Y holds for R*, then so does the functional dependency X → A for every column name A of R*. Intuitively all dependencies are the result of keys." Multivalued dependencies If the column headings in a relational database table are divided into three disjoint groupings ''X'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Ronald Fagin
Ronald Fagin (born 1945) is an American mathematician and computer scientist, and IBM Fellow at the IBM Almaden Research Center. He is known for his work in database theory, finite model theory, and reasoning about knowledge. Biography Ron Fagin was born and grew up in Oklahoma City, where he attended Northwest Classen High School. He was later elected to the Northwest Classen Hall of Fame. He completed his undergraduate degree at Dartmouth College. Fagin received his Ph.D. in Mathematics from the University of California, Berkeley in 1973, where he worked under the supervision of Robert Vaught. He joined the IBM Research Division in 1973, spending two years at the Thomas J. Watson Research Center, and then transferred in 1975 to what is now the IBM Almaden Research Center in San Jose, California. He has served as program committee chair for ACM Symposium on Principles of Database Systems 1984, Theoretical Aspects of Reasoning about Knowledge 1994, ACM Symposium on Theor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Boyce–Codd Normal Form
Boyce–Codd normal form (BCNF or 3.5NF) is a normal form used in database normalization. It is a slightly stricter version of the third normal form (3NF). By using BCNF, a database will remove all redundancies based on functional dependencies. History Edgar F. Codd released his original article "A Relational Model of Data for Large Shared Databanks" in June 1970. This was the first time the notion of a relational database was published. All work after this, including the Boyce–Codd normal form method was based on this relational model. The Boyce–Codd normal form was first described by Ian Heath in 1971, and has also been called Heath normal form by Chris Date. BCNF was formally developed in 1974 by Raymond F. Boyce and Edgar F. Codd to address certain types of anomalies not dealt with by 3NF as originally defined.Codd, E. F. "Recent Investigations into Relational Data Base" in ''Proc. 1974 Congress'' (Stockholm, Sweden, 1974). New York, N.Y.: North-Holland (1974). As ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |