Database Reference
In-Depth Information
Permission The specification of the kind of access a
user has to the objects in a database.
Persistence The ability to have a program “remember”
its data from one execution to the next.
Physical-level design The step during database design in
which a design for a given DBMS is produced from the
final information-level design.
Polymorphism The use of the same name for different
operations in an object-oriented system.
Pop-up form A form that opens on top of other objects,
even when another object is active.
Presidential Records Act A federal law enacted in 1978
that regulates the data retention requirements for all
communications, including electronic communications,
of U.S. presidents and vice presidents.
Primary copy In a distributed database with replicated
data, the copy of the database that must be updated in
order for the update to be deemed complete.
Primary key A minimal collection of columns
(attributes) in a table on which all columns are
functionally dependent and that is chosen as the main
direct-access vehicle to individual rows. Also see
candidate key.
PRIMARY KEY The SQL clause that is used in a
CREATE TABLE or ALTER TABLE command to set a
table's primary key field(s).
Primary sort key When sorting on two fields, the more
important field; also called a major sort key.
Privacy The right of individuals to have certain
information about them kept confidential.
Private visibility In UML, an indication that only the
class itself can view or update the attribute value.
Procedural language A language in which a user
specifies the steps that are required for accomplishing a
task instead of merely describing the task itself.
Procedure A series of steps followed in a regular,
specified order to accomplish one end result.
Product The table obtained by concatenating every row
in the first table with every row in the second table.
Production system The hardware, software, and
database for the users. Also called a live system.
PROJECT The relational algebra command used to
select columns from a table.
Protected visibility In UML, an indication that only the
class itself or public or protected subclasses of the class
can view or update the attribute value.
Public visibility In UML, an indication that any class
can view or update the attribute value.
QBE See Query-By-Example.
Qualify To indicate the table (relation) of which a given
column (attribute) is a part by preceding the column
name with the table name. For example,
Customer.Address indicates the column named Address
in the table named Customer.
Query A question, the answer to which is found in the
database; also used to refer to a command in a nonpro-
cedural language such as SQL that is used to obtain the
answer to such a question.
Query-By-Example (QBE) A data manipulation lan-
guage for relational databases in which users indicate
the action to be taken by completing on-screen forms.
RAID (redundant array of inexpensive/independent
drives) A device used to protect against hard drive
failures in which database updates are replicated to
multiple hard drives so that an organization can
continue to process database updates after losing one
of its hard drives.
RDBMS See relational DBMS.
Record A collection of related fields; can be thought of
as a row in a table.
Recovery The process of returning a database to a state
that is known to be correct from a state known to be
incorrect.
Redundancy Duplication of data, or the storing of the
same data in more than one place.
Referential integrity The rule that if a table A contains a
foreign key that matches the primary key of table B,
then the value of this foreign key must either match the
value of the primary key for some row in table B or be
null.
Relation A two-dimensional table-style collection of
data in which all entries are single-valued, each column
has a distinct name, all the values in a column are
values of the attribute that is identified by the column
name, the order of columns is immaterial, each row is
distinct, and the order of rows is immaterial. Also called
a table.
Relational algebra A relational data manipulation
language in which new tables are created from existing
tables through the use of a set of operations.
Relational database A collection of relations (tables).
Relational DBMS (RDBMS) A DBMS that supports and
manipulates a relational database.
Relational operator An operator used to compare
values. Valid operators are ¼ , < , > , , , <> , and
! ¼ . Also called a comparison operator.
Relationship An association between entities.
Remote site From a user's perspective, any site other
than the one at which the user is working.
Repeating group More than one entry at a single
location in a table.
Replica A copy of the data in a database that a user can
access at a remote site.
Replicate A duplicate of the data in a database that a
user can access at a remote site.
Replication transparency The property that users do
not need to be aware of any replication that has taken
place in a distributed database.
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