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Boyce–Codd Normal Form
Boyce–Codd normal form (or BCNF or 3.5NF) is a normal form used in database normalization. It is a slightly stronger version of the third normal form (3NF). BCNF was 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). If a relational schema is in BCNF then all redundancy based on functional dependency has been removed, although other types of redundancy may still exist. A relational schema ''R'' is in Boyce–Codd normal form if and only if for every one of its dependencies ''X → Y'', at least one of the following conditions hold: * ''X'' → ''Y'' is a trivial functional dependency (Y ⊆ X), * ''X'' is a superkey for schema ''R''. 3NF table always meeting BCNF (Boyce–Codd normal form) Only in rare cases does a 3NF table not meet the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Normalization
Database normalization or database normalisation (see spelling differences) 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 seriou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Candidate Key
A candidate key, or simply a key, of a relational database is a minimal superkey. In other words, it is any set of columns that have a unique combination of values in each row (which makes it a superkey), with the additional constraint that removing any column would possibly produce duplicate rows (which makes it a minimal superkey). Specific candidate keys are sometimes called primary keys, secondary keys or alternate keys. The columns in a candidate key are called prime attributes, and a column that does not occur in any candidate key is called a non-prime attribute. Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that isn't minimal, some subset of that will be minimal. There is a functional dependency from the candidate key to all the attributes in the relation. The candidate keys of a relation are all the possible ways we can identify a row. As such, they are an impo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chris Date
Chris Date (born 1941) is an independent author, lecturer, researcher, and consultant, specializing in relational database theory. Biography Chris Date attended High Wycombe Royal Grammar School (U.K.) from 1951 to 1958 and received his BA in Mathematics from Cambridge University (U.K.) in 1962. He entered the computer business as a mathematical programmer at Leo Computers Ltd. (London), where he quickly moved into education and training. In 1966, he earned his master's degree at Cambridge, and, in 1967, he joined IBM Hursley (UK) as a computer programming instructor. Between 1969 and 1974, he was a principal instructor in IBM's European education program. While working at IBM he was involved in technical planning and design for the IBM products SQL/DS and DB2. He was also involved with Edgar F. Codd’s relational model for database management. He left IBM in 1983 and has written extensively of the relational model, in association with Hugh Darwen. As of 2007 his b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ACM Transactions On Database Systems
The ''ACM Transactions on Database Systems'' (''ACM TODS'') is one of the scientific journal, journals produced by the Association for Computing Machinery. ''TODS'' publishes one volume yearly. Each volume has four issues, which appear in March, June, September and December. The editor-in-chief is Christopher Jermaine (Rice University). Abstracting and indexing According to the ''Journal Citation Reports'', the journal had a 2020 impact factor of 1.086. It is indexed in the following bibliographic databases: *Ei Compendex *SCImago Journal Rank, SCImago *Scopus *ProQuest SciTech Premium Collection *Web of Science References External links Journal homepage Computer science journals Association for Computing Machinery academic journals, Transactions on Database Systems Hybrid open access journals {{compu-journal-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NP-complete
In computational complexity theory, a problem is NP-complete when: # it is a problem for which the correctness of each solution can be verified quickly (namely, in polynomial time) and a brute-force search algorithm can find a solution by trying all possible solutions. # the problem can be used to simulate every other problem for which we can verify quickly that a solution is correct. In this sense, NP-complete problems are the hardest of the problems to which solutions can be verified quickly. If we could find solutions of some NP-complete problem quickly, we could quickly find the solutions of every other problem to which a given solution can be easily verified. The name "NP-complete" is short for "nondeterministic polynomial-time complete". In this name, "nondeterministic" refers to nondeterministic Turing machines, a way of mathematically formalizing the idea of a brute-force search algorithm. Polynomial time refers to an amount of time that is considered "quick" for a de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Referential Integrity
Referential integrity is a property of data stating that all its references are valid. In the context of relational databases, it requires that if a value of one attribute (column) of a relation (table) references a value of another attribute (either in the same or a different relation), then the referenced value must exist. For referential integrity to hold in a relational database, any column in a base table that is declared a foreign key can only contain either null values or values from a parent table's primary key or a candidate key. In other words, when a foreign key value is used it must reference a valid, existing primary key in the parent table. For instance, deleting a record that contains a value referred to by a foreign key in another table would break referential integrity. Some relational database management systems (RDBMS) can enforce referential integrity, normally either by deleting the foreign key rows as well to maintain integrity, or by returning an error and n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elementary Key Normal Form
Elementary key normal form (EKNF) is a subtle enhancement on third normal form, thus EKNF tables are in 3NF by definition. This happens when there is more than one unique compound key and they overlap. Such cases can cause redundant information in the overlapping column(s). A table is in EKNF if and only if all its elementary functional dependencies In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database. In other words, a functional dependency is a constraint between two attributes in a relation. Given a relation ' ... begin at whole keys or end at elementary key attributes. For every full non-trivial functional dependency of the form X→Y, either X is a key or Y is (a part of) an elementary key. In this definition, an ''elementary functional dependency'' is a full functional dependency (a non-trivial functional dependency X → A such that there is no functional dependency X' → A that also holds w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transitive Dependency
A transitive dependency is a functional dependency which holds by virtue of transitivity among various software components. Computer programs In a computer program a direct dependency is functionality exported by a library, or API, or any software component that is referenced directly by the program itself. A transitive dependency is any dependency that is induced by the components that the program references directly. E.g. a call to a function will usually induce a transitive dependency to a library that manages the I/O to write the log message in a file. Dependencies and transitive dependencies can be resolved at different times, depending on how the computer program is assembled and/or executed: e.g. a compiler can have a link phase where the dependencies are resolved. Sometimes the build system even allows management of the transitive dependencies. Similarly, when a computer uses services, a computer program can depend on a service that should be started before to execute ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 the primary 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 included a column for the telephone number of their doctor. The phone number is dependent on the doctor, rather than the patient, thus w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Second Normal Form
Second normal form (2NF) is a Database normalization#Normal forms, normal form used in database normalization. 2NF was originally defined by E. F. Codd in 1971.Codd, E. F. "Further Normalization of the Data Base Relational Model". (Presented at Courant Computer Science Symposia Series 6, "Data Base Systems", New York City, May 24–25, 1971.) IBM Research Report RJ909 (August 31, 1971). Republished in Randall J. Rustin (ed.), ''Data Base Systems: Courant Computer Science Symposia Series 6''. Prentice-Hall, 1972. 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 Functional dependency, functionally dependent on any proper subset of any candidate key of the relation. 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 is in 2NF if it is in 1NF and every non-prime attribute of the relatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Candidate Key
A candidate key, or simply a key, of a relational database is a minimal superkey. In other words, it is any set of columns that have a unique combination of values in each row (which makes it a superkey), with the additional constraint that removing any column would possibly produce duplicate rows (which makes it a minimal superkey). Specific candidate keys are sometimes called primary keys, secondary keys or alternate keys. The columns in a candidate key are called prime attributes, and a column that does not occur in any candidate key is called a non-prime attribute. Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that isn't minimal, some subset of that will be minimal. There is a functional dependency from the candidate key to all the attributes in the relation. The candidate keys of a relation are all the possible ways we can identify a row. As such, they are an impo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Normalization
Database normalization or database normalisation (see spelling differences) 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 seriou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
