Database Processing 3

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attribute

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1. A column of a relation; also called a column, field, or data item.

2. A property in an entity

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Boyce-Codd Normal Form

(BCNF)

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A relation in which every determinant is a candidate key.

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candidate key

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An attribute or group of attributes that identifies a unique now in a relation. One of the candidate keys is chosen to be the primary key.

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composite key

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In database design, a key with two or more attributes.

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data integrity problems

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A table that has inconsistencies that create insert, update, or deletion anomalies is said to have data integrity problems

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database integrity

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The state of a database in which all constraints are fulfilled. Usually refers to interrelation constraints in which the value of a foreign key is required to be present the table having that foreign key as its primary key.

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decomposition rule

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later

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deletion anomaly

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In a relation, the situation in which the removal of one row of a table deletes facts about two or more themes.

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determinant

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One or more attributes that functionally determine another attribute or attributes, In the functional dependency (A. B)-->C, the attributes (A. B) are the determinant.

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domain

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A name set of all possible values that an attribute can have, rules for determining allowed values.

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domain integrity constraint

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Also called a domain constraint, a data constraint that limits data values to a particular set of values.

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domain/key normal form

(DK/NF)

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A relation in which all constraints are logical consequences of domains and keys

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entity

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1. In the entity-relationship model, a representation of something that users want to track.

2. In a generic sense, something that users want to track. In the relational model, an entity is stored in one row of a table.

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entity integrity constraint

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The constraint that the primary key column or columns must have unique values so that each row can be uniquely identified.

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fifth normal form

(5NF)

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A normal form necessary to eliminate an anomaly where a table can be split apart but not correctly joined back together. Also know as Project-Join Normal Form(PJ/NF)

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first normal form

(1NF)

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Any table that fits the definition of a relation.

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fourth normal form

(4NF)

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A relation in Boyce-Codd normal form in which there are no multivalued dependencies or in which all attributes participate in a single multivalued dependency

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functional dependency

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A relationship between attributes in which one attribute or group of attributes determines the value of another.

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functionally dependent

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The term that describes the right-hand side of a functional dependency, The right-hand values of a functional dependency are said to be functionally dependent upon the left-hand table side values of the functional dependency.

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insertion anomaly

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In a relation, the condition that exists when ,to add a complete row to a table, one must add facts about two or more logically different themes.

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key

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1. Group of one or more attributes identifying a unique row in a relation. Because relations may not have duplicate rows , every relation must have at least one key, which is the composite of all of the attributes in the relation, A key is sometime called a logical key.

2. With some relational DBMS products, an index on a column used to improve access and sorting speed, sometime called Physical key.

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multivalued dependency

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A condition in a relation with three or more attributes in which independent attributes appear to have relationships they do not have.

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non-prime attribute

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In normalization, an attribute that is not contained in any candidate key.

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normal forms

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A rule or set of rules governing the allowed structure of relations. The rules apply to attributes, functional dependencies, multivalue dependencies, domains, and constraints.

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null value

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An attribute value that has never been supplied. Such values are ambiguous and can mean that 1. the value is unknown 2. the value is not appropriate or 3. the value is known to be blank.

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overlapping candidate key

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Two candidate keys are said to be overlapping candidate keys if they have one or more attributes in common.

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partially dependent

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In normalization, a condition where an attribute is dependent on only part of a composite primary key instead of on the whole key.

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Project-Join Normal Form

(PJ/NF)

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Anohter name for 5NF.

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referential integrity constraint

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A relationship constraint on foreign key values, A referential integrity constraint specifies that the values of a foreign key must be a subset of the values of the primary key to which it refers.

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relation

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A two-dimensional array containing single-value entries and no duplicate rows.Values for a given entity are shown in rows; values of attributes of that entity are shown in columns. The meaning of the columns is that same in every row. The order of the rows and columns is immaterial.

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second normal form

(2NF)

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A relation in first normal form in which all non-key attributes are dependent on all of the key attributes.

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surrogate key

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A unique, system supplied identifier used as the primary key of a relation. It is created when a row is created, it never changes, and it is destroyed when the row is deleted. The values of a surrogate key have no meaning to the users and are usually hidden within forms and reports.

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third normal form

(3NF)

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A relation in second normal form that has no transitive dependencies.

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transitive dependency

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In a relation having at least three attributes , for example, R (A. B. C),the situation in which A determines B, B determines C, but B does not determine A.

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tuple

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same as row.

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union rule

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later

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update anomaly

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A data error created in a non normalized table when an update action modifies one data value without modifying another occurrence of the same data value in the table.