A program that runs unattended to
perform a standard service. Some daemons are triggered automatically to
perform their task; others operate periodically.
DASD
Direct access storage device.
DASD fast write (DFW)
A form of fast write
where the data is written concurrently to cache and nonvolatile storage, and
is destaged to DASD when buffer space is needed or by operator-initiated
command.
DAT
Dynamic address translation.
data
Any type of information, not just
information contained in a database.
data area
An attribute (field) of an object
used to store data. This data can be other objects.
data area attribute
An field in an object
used to store generic data. Synonymous with data
area.
database ID (DBI)
The ECB field that
identifies which subsystem and subsystem user databases are being used by a
particular ECB.
database identification
See database ID
(DBI).
database management system (DBMS)
A software
system that has a catalog describing the data it manages. The DBMS
controls access to the data stored in it.
database ordinal number (DBON)
The
logical or relative record number of a record in a database.
database reorganization (DBR)
The
process whereby the user captures all or selected fixed file and pool records
from one system and reloads them on a different or reconfigured system.
database request module (DBRM)
A
DB2 data set member containing information about SQL commands. The DBRM
is created by the precompiler and used in the bind process. This file
contains information about all SQL commands in the user application program,
and includes information about how the SQL commands are processed and the DB2
access strategy.
DATABASE 2 (DB2)
An IBM relational database
management system for MVS operating systems.
data collection programs
The online programs
that collect the system activity data used to analyze system
performance.
Data collection/reduction
The TPF utility
used to tune the system and manage the sensitive balance between utilization
of resources and response to the users. See data collection
programs and data reduction programs.
data definition
(1) In TPF collection
support (TPFCS), a list of characteristics that are assigned to a collection
when the collection is created. The characteristics include record IDs,
shadowing, and collection lifetime. (2) A data definition describes a
data object and reserves storage. A data definition can also provide an
initial value. Definitions appear outside a function or at the
beginning of a block statement.
data element
A unit of storage in a data
entry for a coupling facility (CF). See also data
entry.
data entry
A part of a list entry that holds
user-defined data in a coupling facility (CF). A data entry contains
units of storage called data elements. See also data element
and list entry.
data event control block (DECB)
A control
block dynamically allocated from the private area of the entry control block
(ECB). A DECB is a logical extension of an ECB and ECB data levels, and
is used like a data level in FIND/FILE processing. See also entry
control block and ECB data levels.
datagram
In TCP/IP, the basic unit of
information passed across the Internet environment. A datagram contains
a source and destination address along with the data. An Internet
Protocol (IP) datagram consists of an IP header followed by the transport
layer data. See also packet.
data host
Synonym for data host
node.
data host node
In a CMC configuration, a
type 5 host node that is dedicated to processing applications and does not
control network resources, except for its channel-attached devices.
Synonymous with data host.
data link control (DLC)
The SNA protocols
that initiate, control, check, and stop data transfer over a data link between
2 adjacent nodes.
data loader
The program that loads pilot
tape data onto the online modules.
data loss exposure
A term describing the
potential for a fast write data loss condition. An exposure exists as
long as there is fast write data in the cache for a device attached to a 3990
caching control unit with the record cache subsystem RPQ.
data macro
A declarative macro that
generates dummy control sections (DSECT)s defining records that may be called
by any TPF source program by using the data macro name.
data object
A storage area used to hold a
value.
data record
A pool record where the actual
data elements for the collection are stored. A data record often
contains more than one data element for a given collection.
data record information library (DRIL)
A
file, used by the system test compiler (STC), containing an
entry for all system data records and message formats.
data reduction programs
The offline programs
that process data collection records stored on the data collection tape to
generate the reports required for system performance analysis.
data save area (DSA)
An area in the ISO-C
stack that is dynamically allocated at function entry and deallocated on
return. It contains a register save area, all of the automatic storage
for the function, and other data.
data store
A repository for persistent
collections. A data store name is subsystem-common, but the data in a
data store is subsystem-unique.
data type
(1) A generic description of an
elementary unit of information in a particular software system. Common
data types include whole numbers, decimal numbers, dollar amounts, dates, and
text. Higher-level data types may also be defined if abstract data
types are supported. (2) A category that specifies the interpretation
of a data object such as its mathematical qualities and internal
representation.
DATXPAGE envelope
A record that serves as a
package in which TPF collection support (TPFCS) stores all the other objects
it wants to file in that record.
DB2
DATABASE 2.
DBCS
Double-byte character set.
DBF
A symbolic name, reserved to TPF, for a
general tape denoting the database reorganization capture tape for fixed
files.
DBI
Database ID.
DBMS
Database management system.
DBON
Database ordinal number.
DBP
A symbolic name, reserved to TPF, for a
general tape denoting the database reorganization capture tape for pool
files.
DBR
Database reorganization.
DBRM
Database request module.
DCL
Dispatch control list.
DCR
Dispatch control record.
DDM
Distributed Data Management is an
architected data management interface used for data interchange between like
or unlike systems.
DDR
Dynamic device reconfiguration.
deactivate
The process by which all programs
in a particular active E-type loader loadset become inactive.
deactivate function
The E-type loader
function that prevents new ECBs from entering the programs contained in
specified loadsets.
dead-letter queue (DLQ)
A queue to which a
queue manager or application sends messages that it cannot deliver to their
correct destination.
deadlock
An error condition in which
processing cannot continue because each of two elements of the process is
waiting for an action by or a response from the other. Unresolved
contention for the use of a resource. An impasse that occurs when
multiple processes are waiting for the availability of a resource that does
not become available because it is being held by another process that is in a
similar wait state. A condition that occurs if processes simultaneously
attempt to get semaphores (locks) held by the other.
DECB
Data event control block.
debug
To detect, locate, and correct
mistakes in a program.
decimal
A base 10 numbering system;
decimal digits range from 0 to 9.
decimal constant
A number containing any
digits 0 to 9 that does not begin with
0.
declaration
A description that makes an
external object or function available to a function or a block.
declarator
An identifier and optional
symbols that describe the data type.
dedicated resources
The resources owned by
one processor in a loosely coupled complex. Dedicated resources are not
shared or switched to other processors. VFA is an example of this type
of resource.
default
A value that is used when no
alternative is specified by the programmer.
default clause
In a switch
statement, a default label followed by one or more
statements. When the none of the conditions of the specified case
clauses are met, the default clause is executed.
default initialization
The initial value of
the data object if an initializer is not specified. extern
and static variables receive 0 as their default initial
values. autoand register variables receive
undefined default initial values.
deferred list
The lowest priority CPU loop
list; used to delay processing of an entry (ECB) until higher priority
work is completed.
deferred queue
A mail queue of mail items
for which delivery has been attempted but was unsuccessful. Delivery
will be attempted again.
define
See #define.
definition
A data description which reserves
storage and may provide an initial value.
definition side-deck
A directive file
that contains an IMPORT control statement for each function and
variable exported by the dynamic link library (DLL). When you build a
DLL, a definition side-deck is automatically created and written to the
SYSDEFSD DDname by the prelinker. You must include this
definition side-deck when you prelink a DLL application that imports
any of those functions or variables from a DLL.
delay-file
A VFA attribute. When a
file-type macro is issued for a record that has the delay-file attribute, the
record is not written out to DASD until (1) the record is not currently
accessed by 1 or more Entries and space is needed in the VFA buffer, (2) the
system is cycling down, or (3) cycle up after a catastrophic software error
has occurred and recovery is a software IPL. Contrast with
immediate-file.
demand counter
An area that indicates the
number of entries (ECBs) currently using a particular program. The
higher the demand count the more likely that the program will remain in main
storage.
descriptor
A small, nonnegative integer that
is used to identify an object such as a file or other input/output (I/O)
stream.
destage
The asynchronous writing of new or
updated data from cache or nonvolatile storage to DASD.
device driver
A collection of subroutines
that control the interface to an input/output (I/O) device (such as a line
printer), a logical subdevice (such as a large section of a disk drive), or a
pseudo-device (such as the null file, /dev/null).
User-defined device drivers can be written to access data that exists in a TPF
database.
device level selection (DLS)
A DASD function
available with 3380 DASD. With DLS, 2 DASD strings can each be attached
to 2 storage paths on a DASD control unit. Using this configuration,
any 2 devices on the same DASD string can read or write data
simultaneously.
device level selection enhanced (DLSE)
A
DASD function available with 3390 DASD. With DLSE, a DASD string can be
attached to 4 storage paths on a DASD control unit. Using this
configuration, as many as 4 devices on the same DASD string can read or write
data simultaneously.
device type
As many as 4 physically
different DASD device types can be used in a TPF system. The logical
device types of DEVA, DEVB, DEVC, and DEVD are assigned to physical device
types 1, 2, 3, and 4 respectively at system generation time.
DFAD
FACE driver.
DFW
DASD fast write.
DFW attribute
A user-specified caching
attribute that allows a data record to be written as DASD fast write
data. Access to data with this attribute has performance benefits for
both read and write operations. This attribute is specified for a given
record ID through the RIAT.
diagnostic output formatter (DOF)
The
programs that convert the system error data on RTA tapes and RTL tapes into
readable dump listings used for debugging purposes.
digit
Any of the numerals from 0
through 9.
direct access storage device (DASD)
A device
on which access time is effectively independent of the location of the
data.
direct attachment support
The support of a
computer console directly attached to a subchannel.
directional capability
The capability of
data flow on a communication line: simplex transmissions flow in one
direction; half-duplex transmissions flow in either direction at a
time; full-duplex transmissions flow in both directions
simultaneously.
directory
(1) A type of file containing the
names and controlling information for other files or other directories.
(2) A construct for organizing computer files. As files are analogous
to folders that hold information, a directory is analogous to a drawer that
can hold a number of folders. Directories can also contain
subdirectories, which can contain subdirectories of their own. (3) A
file that contains directory entries. No two directory entries in the
same directory can have the same name. (POSIX.1) (4) A file that
points to files and to other directories. (5) An index used by a
control program to locate blocks of data that are stored in separate areas of
a data set in direct access storage. (6) In coupling facility (CF)
cache support, a directory for the CF cache structure where the TPF system
keeps control information about data shared among cache users. The
directory contains one directory entry for each piece of data that users
share.
directory entry
A field with two
formats. The first format is used mainly to contain the file addresses
of both the primary as well as the shadow copy of a record. The second
format contains the next available relative record number (RRN) that TPF
collection support (TPFCS) will use for the associated collection.
directory-only cache
A coupling
facility (CF) cache structure that contains directory entries but no pieces of
shared data. Directory-only cache users do not store data in the
CF cache structure. The directory-only users use the CF cache
structure to maintain the consistency of data in their local caches.
directory record
A special type of pool
record used to store directory entries.
directory reordering
See directory
replenishing.
directory replenishing
The storage
management process that retrieves a new pool directory record when the pool
directory record currently in use is nearly depleted. Synonymous with
directory reordering.
directory update program
The offline program
that creates input records required to update the online file copies of the
pool directory records. This procedure returns pool records no longer
needed to the list of available pool records.
dirty-read cursor
A nonlocking type of
cursor for read-only operations.
disk formatter
An offline program used to
format a disk module to TPF system requirements.
disk pack initialization
The system
initialization program that checks the tracks assigned to each disk pack and
initializes the necessary volume labels.
dispatch control list (DCL)
The 3rd-level
record in the centralized list handling (CLH) routines. There is 1 DCL
for each CPU list; it contains the addresses of work items to be
dispatched.
dispatch control record (DCR)
The 2nd-level
record in the centralized list handling (CLH) routines. There is 1 DCR
for each CPU list. This record contains a pointer to the DCL as well as
status information for that list.
dispatch management table (DMT)
The
1st-level record in the centralized list handling (CLH) routines. There
is 1 such record in a system. This record contains pointers to the
2nd-level information for each of the CPU loop list types in the
system.
dispense mode
In a FACE table that supports
FARF3/FARF4 addresses or FARF4/FARF5 addresses, the file address format
(FARF3, FARF4, or FARF5) that is returned to you when the system requests a
file address.
A
relational database connection protocol consisting of protocols for
communication between an application and a remote database, and communications
between databases.
DLC
Data link control.
DLL
Dynamic link library.
DLM
Dynamic load module.
DLQ
Dead-letter queue.
DLS
Device level selection.
DLSE
Device level selection enhanced.
DMT
Dispatch management table.
DNS
Domain Name System.
DOBT
Dynamic override bitmap table.
Document Object Model (DOM)
The
specification that allows an application to interact with XML data in memory
as a tree structure. It allows you to dynamically traverse and update
the XML document.
Document Type Definition (DTD)
A type of
schema. See also Schema.
DOF
Diagnostic output formatter.
DOM
Document Object Model.
domain name
In the Internet suite of
protocols, a name of a host system. A domain name consists of a
sequence of subnames separated by a delimiter character. For example,
if the fully qualified domain name (FQDN) of a host system is
ralvm7.vnet.ibm.com, each of the following is a domain
name:
ralvm7.vnet.ibm.com
vnet.ibm.com
ibm.com
Domain Name System (DNS)
In the Internet
suite of protocols, the distributed database system used to map domain names
to IP addresses.
dormant subsystem user
A subsystem user that
was included at initialization but has been deactivated because of an
unsuccessful global load. A dormant subsystem user cannot be
reactivated without reinitializing the system.
do statement
A C-language looping statement
that contains the word do followed by a statement (the action), the
word while, and an expression in parentheses (the
condition).
DOT
Dump override table.
dot
A symbol (.) that indicates the
current directory in a path name. The file name consisting of a single
dot character (.). This file name refers to the directory
specified by its predecessor. (POSIX.1)
dot-dot
A symbol (..) in a
path name that indicates the parent directory. The file name consisting
solely of two dot characters (..). This file name refers
to the parent directory of its predecessor directory. For the TPF file
system, dot-dot in the root directory refers to the root directory
itself.
dotted decimal notation
A common notation
for Internet host addresses that divides the 32-bit address into four 8-bit
fields. The value of each field is specified as a decimal number and
the fields are separated by periods (for example,
010.002.000.052 or
10.2.0.52). See also network byte
order.
double-byte character set (DBCS)
A set of
characters in which each character is represented by two bytes.
Languages such as Japanese, Chinese, and Korean, which contain more symbols
than can be represented by 256 code points, require double-byte character
sets. Since each character requires two bytes, entering, displaying,
and printing DBCS characters requires hardware and supporting software which
are DBCS capable.
double precision
Pertaining to the use of
two computer words to represent a number in accordance with the required
precision.
DRDA
Distributed Relational Database
Architecture.
DRIL
Data record information library.
DSA
Data save area.
DTD
Document Type Definition.
dump override table (DOT)
A table containing
both the static override bitmap table (SOBT) and the dynamic override bitmap
table (DOBT). These tables contain information that determines which
large storage areas are to be included in dumps for particular system
errors.
duplicate module
In a fully duplicated
system or a partially duplicated system, the disk module that contains the
duplicate copies of records from the corresponding prime module.
duplicate record
When DASD records are
duplicated, the two copies of a data record are called the duplicate record
and the primary record. A duplicate record is synonymous with
backup record.
DWARF
A debugging information format used to
standardize the software interface for development tools across multiple
operating environments.
dynamic address translation (DAT)
In IBM
virtual storage systems, the change of a virtual storage address to a real
storage address during the processing of an instruction.
dynamic device reconfiguration (DDR)
The
process of recovering the contents of a tape control unit buffer so that the
data can be written to a new tape.
dynamic link library (DLL)
A collection of
one or more functions or variables gathered in a load module and executable or
accessible from a separate DLL application load module.
dynamic link library (DLL) application
An
application that can reference imported functions or imported variables in a
DLL.
dynamic load module (DLM)
A load module with
a single entry point.
dynamic load module (DLM) stub
A small
object-code file that allows a DLM to call another real-time program. A
DLM stub is created by the DLM stub generator tool (STUB).
dynamic LU resource
A remote LU resource
that is defined to the TPF system using dynamic LU support.
dynamic LU support
Support that enables the
TPF system to automatically create resource definitions for new remote LU
resources and new ALS resources.
dynamic override bitmap table (DOBT)
A table
containing dump override bitmaps used to override the static override bitmap
table. Entries in the DOBT are created by the ZIDOT command.