Cis-1200 Chapter 3

Front 1

associative entity

Back 1

See composite entity.

Front 2

attribute domain

Back 2

See domain.

Front 3

bridge entity

Back 3

See composite entity.

Front 4

candidate key

Back 4

A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey. See key.

Front 5

closure

Back 5

A property of relational operators that permits the use of relational algebra operators on existing tables (relations) to produce new relations.

Front 6

composite entity

Back 6

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. See also linking table.

Front 7

composite key

Back 7

A multiple-attribute key.

Front 8

data dictionary

Back 8

A DBMS component that stores metadata—data about data. Thus, the data dictionary contains the data definition as well as their characteristics and relationships. A data dictionary may also include data that are external to the DBMS. Also known as an information resource dictionary.

Front 9

dependent

Back 9

An attribute whose value is determined by another attribute.

Front 10

determinant

Back 10

Any attribute in a specific row whose value directly determines other values in that row.

Front 11

determination

Back 11

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.

Front 12

domain

Back 12

In data modeling, the construct used to organize and describe an attribute’s set of possible values.

Front 13

entity integrity

Back 13

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.

Front 14

equijoin

Back 14

A join operator that links tables based on an equality condition that compares specified columns of the tables.

Front 15

flags

Back 15

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.

Front 16

foreign key (FK)

Back 16

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.

Front 17

full functional dependence

Back 17

A condition in which an attribute is functionally dependent on a composite key but not on any subset of the key.

Front 18

functional dependence

Back 18

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 AB.

Front 19

homonym

Back 19

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.

Front 20

index

Back 20

An ordered array of index key values and row ID values (pointers). Indexes are generally used to speed up and facilitate data retrieval. Also known as an index key.

Front 21

index key

Back 21

See index.

Front 22

inner join

Back 22

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.

Front 23

join column(s)

Back 23

Columns that join two tables. The join columns generally share similar values.

Front 24

key

Back 24

An entity identifier based on the concept of functional dependence; keys may be classified in several ways. See also superkey, candidate key, primary key (PK), secondary key, and foreign key.

Front 25

key attribute

Back 25

The attributes that form a primary key.

Front 26

left outer join

Back 26

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.

Front 27

linking table

Back 27

In the relational model, a table that implements an M:M relationship. See also composite entity.

Front 28

natural join

Back 28

A relational operation that links tables by selecting only the rows with common values in their common attribute(s).

Front 29

null

Back 29

In SQL the absence of an attribute value. Note that a null is not a blank.

Front 30

outer join

Back 30

A relational algebra JOIN operation that produces a table in which all unmatched pairs are retained; unmatched values in the related table are left null. Contrast with inner join. See also left outer join and right outer join.

Front 31

predicate logic

Back 31

Used extensively in mathematics to provide a framework in which an assertion (statement of fact) can be verified as either true or false.

Front 32

primary key (PK)

Back 32

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.

Front 33

referential integrity

Back 33

A condition by which a dependent table’s foreign key must have either a null entry or a matching entry in the related table. Even though an attribute may not have a corresponding attribute, it is impossible to have an invalid entry.

Front 34

relational algebra

Back 34

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.

Front 35

right outer join

Back 35

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.

Front 36

secondary key

Back 36

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.

Front 37

set theory

Back 37

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.

Front 38

superkey

Back 38

An attribute or attributes that uniquely identify each entity in a table. See key.

Front 39

synonym

Back 39

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.

Front 40

system catalog

Back 40

A detailed system data dictionary that describes all objects in a database.

Front 41

theta join

Back 41

A join operator that links tables using an inequality comparison operator (<, >, <=, >=) in the join condition.

Front 42

tuple

Back 42

In the relational model, a table row.

Front 43

union-compatible

Back 43

Two or more tables that share the same column names and have columns with compatible data types or domains.

Front 44

unique index

Back 44

An index in which the index key can have only one associated pointer value (row).