Chapter Sixteen

Alias An alternative name given to an attribute.
Anomalies Errors or inconsistencies that may result when a user attempts to update a table that contains redundant data. There are three types of anomalies: insertion, deletion, and modification anomalies. See also Normalization.
First normal form (1NF) A relation that contains no repeating data. See also Normalization.
Foreign key An attribute that appears as a nonkey attribute in one relation and as a primary key attribute (or part of a primary key) in another relation.
Functional dependency A particular relationship between two attributes. For any relation R, attribute B is functionally dependent on attribute A if, for every valid instance of A, that value of A uniquely determines the value of B. The functional dependence of B on A is represented as A %gt; B. See also Partial functional dependency, Transitive dependency.
Homonym A single name that is used for two or more different attributes (for example, the term invoice to refer to both a customer invoice and a supplier invoice).
Logical database model A description of data using a notation that corresponds to an organization of data used by database management systems. See also Relational database model.
Normal form A state of a relation that can be determined by applying simple rules regarding dependencies to that relation. See also Functional dependency.
Normalization The process of converting com-plex data structures into simple, stable data structures.
Partial functional dependency A dependency in which one or more nonkey attributes are functionally dependent on part, but not all, of the primary key.
Recursive foreign key A foreign key in a relation that references the primary key values of that same relation.
Referential integrity An integrity constraint specifying that the value (or existence) of an attribute in one relation depends on the value (or existence) of an attribute in the same or another relation.
Relation A named, two-dimensional table of data. Each relation consists of a set of named columns and an arbitrary number of unnamed rows.
Relational database model A data model that represents data in the form of tables or relations.
Second normal form (2NF) A relation is in second normal form if it is in first normal form and every nonkey attribute is fully functionally dependent on the primary key. Thus no nonkey attribute is functionally dependent on part (but not all) of the primary key. See also Functional dependency, Partial functional dependency.
Synonyms Two different names that are used to refer to the same data item (for example, car and automobile).
Third normal form (3NF) A relation is in third normal form if it is in second normal form and no transitive dependencies exist.
Transitive dependency A functional dependency between two (or more) nonkey attributes in a relation. See also Third normal form.
Well-structured relation A relation that contains a minimum amount of redundancy and allows users to insert, modify, and delete the rows in a table without errors or inconsistencies. See also Normalization.

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