FORMA NORMAL DE BOYCE CODD * Determinante: uno o más atributos que, de manera funcional, determinan otro atributo o atributos. Transcript of Forma Normal de Boyce-Codd. Objetivos Se dice que el esquemaR (T, L) está en 2FN si y sólo si cumple: 1. Está en 1FN. 2. Forma normal de boyce codd by thiago_monteiro_
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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 Edgar F.
Codd as an integral 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. A basic objective boyde-codd the first normal form defined by Codd in was to permit data to be queried and manipulated using a “universal data sub-language” grounded in first-order logic.
When an attempt is made to modify update, insert into, or delete from a relation, the following undesirable side-effects may arise in relations that have not been sufficiently normalized:.
A fully normalized database allows its structure to be extended to accommodate new types of data without changing existing structure too much.
As a result, applications interacting with the database are minimally affected.
Boyce–Codd normal form – Wikipedia
Normalized relations, and the relationship between one normalized relation and another, mirror real-world concepts and their interrelationships. Querying and manipulating the data within a data structure that is not normalized, such as the following non-1NF representation of customers, credit card transactions, involves more complexity than is really necessary:.
To each customer corresponds a ‘repeating group’ of transactions. The automated evaluation of any query relating to customers’ transactions, therefore, would broadly involve two stages:. For example, in order to find out the monetary sum of all transactions that occurred in October for all customers, the system would have to know that it must first unpack the Transactions group of each customer, then sum the Amounts of all transactions thus obtained where the Date of the transaction falls in October One of Codd’s important insights was that structural complexity can be reduced.
Reduced structural complexity gives users, application, and DBMS more power and flexibility to formulate and evaluate the queries. A more normalized equivalent of the structure above might look like this:. Now each row represents an individual credit card transaction, and the DBMS can obtain the answer of interest, simply by finding all rows with a Date falling in October, and summing their Amounts. The data structure places all of the values on an equal footing, exposing each to the DBMS directly, so each can potentially participate directly in queries; whereas in the previous situation some values were embedded in lower-level structures that had to be handled specially.
Accordingly, the normalized design lends itself to general-purpose query processing, whereas the unnormalized design does not. The normalized version also allows the user to change the customer name in one place and guards against errors that arise if the customer name is misspelled on some records.
Codd introduced the concept of normalization and what is now known as the first normal form 1NF in Informally, a relational database relation is often described as “normalized” if it meets third normal form. From Wikipedia, the free encyclopedia. This article needs attention from an expert in Databases. See the talk page for details.
WikiProject Databases may be able to help recruit an expert. First normal form 2NF: Second normal form 3NF: Third normal form EKNF: Elementary key normal form BCNF: Boyce—Codd normal form 4NF: Fourth normal form ETNF: Essential tuple normal form 5NF: Fifth normal form DKNF: Domain-key normal form 6NF: A first-order predicate calculus suffices if the collection of relations is in first normal form.
Such a boyce-cocd would provide a yardstick of linguistic power for all other proposed data languages, and would itself be a strong candidate for embedding with appropriate syntactic modification in a variety of host languages programming, command- or problem-oriented.
Addison-Wesleypp. Communications of the ACM.
Republished in Randall J. Courant Computer Science Symposia Series 6.
An Introduction to Database Systems. Proceedings of the 15th International Conference on Database Theory.
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FORMA NORMAL DE BOYCE CODD by Mariachi Gala on Prezi
ID Date Amount Primary key no duplicate tuples. No partial dependencies values depend on the whole of every Candidate key. No transitive dependencies values depend only on Candidate keys. Every non-trivial functional dependency involves either a superkey or an elementary key’s subkey. No redundancy from any functional dependency. A component of every explicit join dependency is a superkey .
Every non-trivial join dependency is implied by a candidate key. Every constraint is a consequence of domain constraints and key constraints.