Domain
In data modeling, the construct used to organize and describe an attribute's set of possible values.
Primary key (PK)
An identifier composed of one or more attributes that uniquely identifies a row. Also, a can
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Domain
In data modeling, the construct used to organize and describe an attribute's set of possible values.
Primary key (PK)
An identifier composed of one or more attributes that uniquely identifies a row. Also, a candidate key
selected as a unique entity identifier. A minimal superkey.
Key
One or more attributes that determine other attributes.
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.
Determinant
Any attribute in a specific row whose value directly determines other values in that row.
Dependent
An attribute whose value is determined by another attribute.
Full functional dependence
A condition in which an attribute is functionally dependent on a composite key but not on any subset of
the key.
Composite key
A multiple-attribute key.
Key attributes
The attributes that form a primary key
Superkey
An attribute or attributes that uniquely identify each entity in a table.
Candidate key
A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey.
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.
Null
The absence of an attribute value.
Foreign key
An attribute or attributes in one table whose values must match the primary key in another table or
whose values must be null.
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.
Secondary key
A key used strictly for data retrieval purposes. For example, the combination of last name, first name,
middle initial, and telephone number will probably match the appropriate table row. Also called
an alternate key.
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. It is a container (variable) for holding relation
data, not the relation itself.
Closure
A property of relational operators that permits the use of relational algebra operators on existing tables
(relations) to produce new relations.
SELECT operator
An operator used to select a subset of rows. Also known as RESTRICT.
σ cus_code = 10010
PROJECT operator
An operator used to select a subset of columns. In other words, it yields a vertical subset of a table. This
operation retrieves all rows and some attributes of a table without using a WHERE clause to limit which
rows of the table are included.
π cus_fname, cus_lname
UNION operator
This set operator combines the result set of two or more SELECT statements, dropping the duplicate
rows.
supplier ∪ vendor
Union-compatible
Two or more tables that have the same number of columns and the corresponding columns have
compatible domains.
INTERSECT operator
This set operator combines the output of two SELECT queries and returns only the rows that appear in
both.
supplier ∩ vendor
DIFFERENCE
An operator used to yield all rows from one table that are not found in another union-compatible table.
supplier – vendor
PRODUCT
An operator used to yield all possible pairs of rows from two tables.
customer × agent
JOIN
In relational algebra, a type of operator used to yield rows from two tables based on criteria. There are
many types, such as natural, theta, equi, and outer.
Natural join (JOIN)
A relational operation that yields a new table composed of only the rows with common values in their
common attribute(s).
customer ⨝ agent
Equijoin
A join operator that links tables based on an equality condition that compares specified columns of the
tables. Is a special type of theta join
Theta join
A join operator that links tables using an inequality comparison operator (<, >, <=, >=) in the join
condition.
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). This join is the most
commonly used type of join.
OUTER JOIN
This join Returns a set of records that includes rows for which no corresponding match is found in the
other table. Unmatched values in the related table are left null. Three types LEFT, RIGHT and FULL
LEFT OUTER JOIN
In a pair of tables to be joined, a join that yields all rows in the left table, including those that have no
matching values in the other table.
SELECT *FROM T1 ____________ T2 ON T1.C1=T2.C1
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.
SELECT *FROM T1 ____________ T2 ON T1.C1=T2.C1
FULL OUTER JOIN
Returns rows with matching values and includes all rows from both tables (T1 and T2) with unmatched
values
SELECT *FROM T1 ____________ T2 ON T1.C1=T2.C1
DIVIDE operator
An operator that answers queries about one set of data being associated with all values of data in
another set of data. It uses one 2-column table as the dividend and one single-column table as the
divisor.
JOIN operation
This operation integrates data from two or more tables or combines them. It can be implemented in the
FROM and WHERE clauses.
Data dictionary
A DBMS component that stores metadata. It contains the data definition as well as their characteristics
and relationships. It may also include data that are external to the DBMS. Also known as an information
resource dictionary
System catalog
A detailed system data dictionary that describes all objects in a database.
Homonyms
The use of the same name to label different attributes. Some relational software automatically check for
these and either alerts the user to their existence or automatically makes the appropriate adjustments.
Synonym
The use of different names to identify the same object, such as an entity, an attribute, or a relationship;
For example, car and auto refer to the same object
The 1:M Relationship
This relationship is the relational modeling ideal. One record in a table can be associated with one or
more records in another table. For example, each customer can have many sales orders.
The 1:1 Relationship
This relationship should be rare in any relational database design. One entity can be related to only one
other entity, and vice versa.
The M:N Relationship
This relationship cannot be implemented as such in the relational model however, it can be
implemented by creating a new entity in 1:M relationships with the original entities.
Composite entity
An entity designed to transform an M:N relationship into two 1:M relationships. The entity's primary key
comprises at least the primary keys of the
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