C170 Data Management Application Questions and Answers Graded A+

C170 Data Management Application Questions and Answers Graded A+ AREA In DB2, a named section of permanent storage space that is reserved to store the database. associative entity See composite entity. Brainpower Read More Previous Play Next Rewind 10 seconds Move forward 10 seconds Unmute 0:07 / 0:15 Full screen 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. inner join A join operation in which only rows that meet a given criterion are selected. The join criterion can be an equality condition (natural join or equijoin) or an inequality condition (theta join). The inner join is the most commonly used type of join. Contrast with outer join. INTERSECT In relational algebra, an operator used to yield only the rows that are common to two union-compatible tables. JOIN In relational algebra, a type of operator used to yield rows from two tables based on criteria. There are many types of joins, such as natural join, theta join, equijoin, and outer join. join columns Columns that are used in the criteria of join operations. The join columns generally share similar values (have a compatible domain). key One or more attributes that determine other attributes. See also superkey, candidate key, primary key (PK), secondary key, and foreign key. key attribute The attributes that form a primary key. See also prime attribute. left outer join In a pair of tables to be joined, a join that yields all the rows in the left table, including those that have no matching values in the other table. For example, a left outer join of CUSTOMER with AGENT will yield all of the CUSTOMER rows, including the ones that do not have a matching AGENT row. See also outer join and right outer join. linking table In the relational model, a table that implements an M:M relationship. See also composite entity. natural join A relational operation that yields a new table composed of only the rows with common values in their common attribute(s). null The absence of an attribute value. Note that a null is not a blank. outer join Returns a set of records that include what an inner join would return but also includes other rows for which no corresponding match is found in the other table. Contrast with inner join. See also left outer join and right outer join. predicate logic Used extensively in mathematics to provide a framework in which an assertion (statement of fact) can be verified as either true or false. primary key (PK) In the relational model, an identifier composed of one or more attributes that uniquely identifies a row. Also, a candidate key selected as a unique entity identifier. See also key. prime attribute A key attribute; that is, an attribute that is part of a key or is the whole key. See also key attributes. PRODUCT In relational algebra, an operator used to yield all possible pairs of rows from two tables. Also known as the Cartesian product. PROJECT In relational algebra, an operator used to select a subset of columns. referential integrity A condition by which a dependent table's foreign key must have either a null entry or a matching entry in the related table. relational algebra A set of mathematical principles that form the basis for manipulating relational table contents; the eight main functions are SELECT, PROJECT, JOIN, INTERSECT, UNION, DIFFERENCE, PRODUCT, and DIVIDE. relvar Short for relation variable, a variable that holds a relation. A relvar is a container (variable) for holding relation data, not the relation itself. RESTRICT See SELECT. right outer join In a pair of tables to be joined, a join that yields all of the rows in the right table, including the ones with no matching values in the other table. For example, a right outer join of CUSTOMER with AGENT will yield all of the AGENT rows, including the ones that do not have a matching CUSTOMER row. See also left outer join and outer join. secondary key A key used strictly for data retrieval purposes. For example, customers are not likely to know their customer number (primary key), but the combination of last name, first name, middle initial, and telephone number will probably match the appropriate table row. See also key. SELECT A SQL command that yields the values of all rows or a subset of rows in a table. The SELECT statement is used to retrieve data from tables. In relational algebra, an operator to select a subset of rows. Also known as RESTRICT. set theory A part of mathematical science that deals with sets, or groups of things, and is used as the basis for data manipulation in the relational model. superkey An attribute or attributes that uniquely identify each entity in a table. See key. synonym The use of different names to identify the same object, such as an entity, an attribute, or a relationship; synonyms should generally be avoided. See also homonym. system catalog A detailed system data dictionary that describes all objects in a database. theta join A join operator that links tables using an inequality comparison operator (<, >, <=, >=) in the join condition. UNION In relational algebra, an operator used to merge (append) two tables into a new table, dropping the duplicate rows. The tables must be union-compatible. union-compatible Two or more tables that have the same number of columns and the corresponding columns have compatible domains. unique index An index in which the index key can have only one associated pointer value (row). binary relationship An ER term for an association (relationship) between two entities. For example, PROFESSOR teaches CLASS. cardinality A property that assigns a specific value to connectivity and expresses the range of allowed entity occurrences associated with a single occurrence of the related entity. composite attribute An attribute that can be further subdivided to yield additional attributes. For example, a phone number such as may be divided into an area code (615), an exchange number (898), and a four-digit code (2368). Compare to simple attribute. composite identifier In ER modeling, a key composed of more than one attribute. derived attribute An attribute that does not physically exist within the entity and is derived via an algorithm. For example, the Age attribute might be derived by subtracting the birth date from the current date. existence-dependent A property of an entity whose existence depends on one or more other entities. In such an environment, the existence-independent table must be created and loaded first because the existence-dependent key cannot reference a table that does not yet exist. existence-independent A property of an entity that can exist apart from one or more related entities. Such a table must be created first when referencing an existence-dependent table. identifiers One or more attributes that uniquely identify each entity instance. iterative process A process based on repetition of steps and procedures. mandatory participation A relationship in which one entity occurrence must have a corresponding occurrence in another entity. For example, an EMPLOYEE works in a DIVISION. (A person cannot be an employee without being assigned to a company's division.) multivalued attributes An attribute that can have many values for a single entity occurrence. For example, an EMP_DEGREE attribute might store the string "BBA, MBA, PHD" to indicate three different degrees held. non-identifying relationship A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity. optional attribute In ER modeling, an attribute that does not require a value; therefore, it can be left empty. optional participation In ER modeling, a condition in which one entity occurrence does not require a corresponding entity occurrence in a particular relationship. participants An ER term for entities that participate in a relationship. For example, in the relationship "PROFESSOR teaches CLASS," the teaches relationship is based on the participants PROFESSOR and CLASS. recursive relationship A relationship found within a single entity type. For example, an EMPLOYEE is married to an EMPLOYEE or a PART is a component of another PART. regular entity a strong entity: An entity that is existence-independent, that is, it can exist apart from all of its related entities. Also called a regular entity. relational schema The organization of a relational database as described by the database administrator. relationship degree The number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher.