(3) The Realational Database Model Flashcards
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.
Primary key (PK)
In the relational model, an identifier composed of one or more attributes that uniquely identifies a row. Also, a key selected as a unique entity identifier.
Composite key
A multiple-attribute key
Key
One or more attributes that determine other attributes.
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.
Foreign key (FK)
An attribute or attributes in on e table whose values must match the primary key in another table or whose values must be null.
Dependent
An attribute whose value is determined by another attribute.
Prime attribute
A key attribute; that is, an attribute that is part of a key or is the whole key.
Secondary key
A key send 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.
Super key
An attribute or attributes that uniquely identify each entity in a table.
Unique index
An index in which the index key can have only one associated pointer value (row).
Linking table
In the relational model, a table that implements an M:M relationship.
Domain
In data modeling, the construct used to organize and describe an attribute’s set of possible values.
Null
The absence of an attribute value. Note that this is not a blank.
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.
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.
Key attribute
The attribute see that form a primary key.
Flags
Special codes implemented by designers to trigger a required response, alert end users to specified conditions, or encode values. They may be used to prevent nulls by bringing attention to the absence of a value in a table.
Index
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.
Fully functional dependence
A condition in which an attribute is functionally dependent on a composite key but not on any subset of the key.
Composite entity
An entity to transform an M:N relationship into two 1:M relationships. It’s primary key comprises at least the primary keys of the entities that it connects. Also known as a bridge entity or associative entity.
business rule
A description of a policy, procedure, or principle within an organization. For example, a pilot cannot be on duty for more than 10 hours during a 24 hour period.
Candidate key
A minimal super key; that is, a key that does not contain a subset of attributes that is itself a super key.
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.
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.
