WGU C170 - DATA MANAGEMENT - APPLICATIONS
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 uniqu...
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).
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