C170 Data Management Application RATED A+

AREA - In DB2, a named section of permanent storage space that is reserved to store the database. associative entity - See composite entity. bridge entity - See composite entity. candidate key - A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey. See key. closure - A property of relational operators that permits the use of relational algebra operators on existing tables (relations) to produce new relations. composite entity - An entity designed to transform an M:N relationship into two 1:M relationships. The composite entity's primary key comprises at least the primary keys of the entities that it connects. Also known as a bridge entity or associative entity. See also linking table. composite key - A multiple-attribute key. dependent - An attribute whose value is determined by another attribute. determination - The role of a key. In the context of a database table, the statement "A determines B" indicates that knowing the value of attribute A means that the value of attribute B can be looked up. DIFFERENCE - In relational algebra, an operator used to yield all rows from one table that are not found in another union-compatible table. DIVIDE - In relational algebra, an operator that answers queries about one set of data being associated with all values of data in another set of data. domain - In data modeling, the construct used to organize and describe an attribute's set of possible values. entity integrity - The property of a relational table that guarantees each entity has a unique value in a primary key and that the key has no null values. equijoin - A join operator that links tables based on an equality condition that compares specified columns of the tables. flags - Special codes implemented by designers to trigger a required response, alert end users to specified conditions, or encode values. Flags may be used to prevent nulls by bringing attention to the absence of a value in a table. foreign key (FK) - An attribute or attributes in one table whose values must match the primary key in another table or whose values must be null. See key. full functional dependence - A condition in which an attribute is functionally dependent on a composite key but not on any subset of the key. functional dependence - Within a relation R, an attribute B is functionally dependent on an attribute A if and only if a given value of attribute A determines exactly one value of attribute B. The relationship "B is dependent on A" is equivalent to "A determines B," and is written as A-B. homonyms - The use of the same name to label different attributes. Homonyms generally should be avoided. Some relational software automatically checks for homonyms and either alerts the user to their existence or automatically makes the appropriate adjustments. See also synonym. index - An ordered array of key values and row ID values (pointers). Indexes are generally used to speed up and facilitate data retrieval. Also known as an index key. index key - See index.