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C175 - Chapter 3
Terms in this set (28)
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 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 associative entity or composite entity.
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, or a professor may teach up to four classes during a semester.
A minimal superkey; that is, a key that does not contain a subset of attributes that is itself a superkey. See key.
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.
A multiple-attribute key.
An attribute whose value is determined by another attribute.
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.
In data modeling, the construct used to organize and describe an attribute's set of possible values.
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.
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.
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.
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.
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.
One or more attributes that determine other attributes. See also superkey, candidate key, primary key (PK), secondary key, and foreign key.
The attributes that form a primary key. See also prime attribute.
In the relational model, a table that implements an M:M relationship. See also composite entity.
The absence of an attribute value. Note that a null is not a blank.
Used extensively in mathematics to provide a framework in which an assertion (statement of fact) can be verified as either true or false.
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.
A key attribute; that is, an attribute that is part of a key or is the whole key. See also key attributes.
A condition by which a dependent table's foreign key must have either a null entry or a matching entry in the related table.
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.
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.
An attribute or attributes that uniquely identify each entity in a table. See key.
An index in which the index key can have only one associated pointer value (row).
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