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Glossary
read committed access
read committed access. An access option for any DML statement that requires that the
data being accessed is from committed rows. SQL/MX requires that a lock can be
acquired on the data requested by the DML statement, but does not actually lock the
data, thereby reducing lock request conflicts. If a lock cannot be granted (implying that
the row contains uncommitted data), the DML statement request waits until the lock in
place is released. Contrast with read uncommitted access and serializable access.
read uncommitted access. An access option for the SELECT statement that gives users
immediate access to data when a transaction in progress might be changing the data.
The data accessed need not be from committed rows. With read uncommitted access,
a process does not acquire a lock on the data it accesses and does not test for existing
locks before reading data. Contrast with read committed access and serializable
access.
recompilation. See automatic SQL recompilation or explicit SQL compilation.
record. A unit of data that can be read from or written to a file; a record is represented as a
row in a relational table.
record locks. A lock held by a process on one specific record; corresponds to row lock.
recovery. The returning of a database file or files to a consistent state.
referential integrity. A SQL-92 feature that prevents users or applications from entering
inconsistent data. The SQL/MX ALTER TABLE statement allows you to set referential
constraints for tables to declare that a column or set of columns (called a foreign key)
can contain only values that match those in a column or set of columns specified in the
REFERENCES clause. The two columns or sets of columns must have the same
characteristics (data type, length, scale, precision). There must also be a UNIQUE or
PRIMARY KEY constraint on the column or set of columns specified in the
REFERENCES clause. The foreign key is the column or set of columns specified in the
FOREIGN KEY clause, immediately following the FOREIGN KEY keywords.
register. Establishing a catalog reference on a remote node for a catalog that is visible from
the local node.
regular identifier. Names beginning with a letter (A through Z or a through z), that can also
contain other letters, digits (0-9), or the underbar character (_). Regular Identifiers are
not case-sensitive. See also delimited identifier.
related catalogs. The relationship between catalogs when objects from one catalog depend
upon objects from another catalog because of a trigger, view, or constraint. Related
catalogs must have identical visibility; that is, be registered on the same set of nodes.
relational database. A database in which data is represented as tables.
Remote Duplicate Database Facility (RDF). An HP NonStop data replication product that
monitors changes made to a production database on a local (primary) system and
maintains a copy of that database on one or more remote (backup) systems.
HP NonStop SQL/MX Glossary— 523732-002
Glossary -29
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