gtpd3m0gLibrary Guide with Master Index and Glossary

D

daemon
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.

Distributed Relational Database Architecture (DRDA)
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:

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.