Availability Guide for Application Design

Glossary
Availability Guide for Application Design—525637-004
Glossary-6
DDL
DDL. See data definition language (DDL).
defensive programming. The process of enhancing a software design methodology by
adding checks that test that the program is operating the way it was designed or by
adding checks that catch anomalous conditions where the program is not operating as
designed.
design outage class. An outage class that includes bugs in design and design failures in
hardware and software. For example, an application change that introduces
unexpected problems could cause a design outage.
deterministic error. A hardware or software error that occurs in a predictable way and is
easy to reproduce. For example, a software error that occurs every time a line of code
is executed is said to be deterministic. Deterministic errors are sometimes known as
hard errors. Contrast with transient error.
disk process. In the HP environment, the portion of the operating-system software that
performs read, write, and lock operations on disk volumes and creates audit records.
distinguished bulletin board liaison (DBBL). The NonStop Tuxedo System /T
administrative process that communicates with the BBL processes to coordinate
updates to the bulletin boards replicated throughout the application. The DBBL resides
on the master machine of the application. See also bulletin board (BB), bulletin board
liaison (BBL), and master machine.
distributed application. An application whose modules or associated data reside on more
than one system in a network of systems.
distributed database. A database whose objects reside on more than one system in a
network of systems and whose objects can be accessed from any system in the
network.
Distributed Name Service (DNS). An HP product that provides a mapping of logical device
names to physical device names.
distributed processing. A type of processing environment in which resources are
distributed among processors within a single system or spread across a network of
systems. A user on any network node can, if properly authorized, access resources
and database files anywhere within the network.
Distributed Systems Management (DSM) products. A set of software tools that facilitate
management of NonStop systems and networks. These tools include the Distributed
Name Service (DNS), the Event Management Service (EMS), the Subsystem Control
Facility (SCF) for communications subsystems, the Subsystem Programmatic Interface
(SPI), and the ViewPoint and NonStop NET/MASTER management applications.
Distributed Systems Management Solutions (DSMS). An HP application package with
two interfaces—NetStatus and NetCommand—and an underlying management service
layer—Distributed Systems Network Management (DSNM)—that enables a user to