U

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UA: See unnumbered acknowledgment.; See user agent.
UCS: See universal character set.
UCS-2: A 2-byte (16-bit) encoding scheme based on ISO/IEC specification 10646-1. UCS-2 defines three levels of implementation: Level 1-No combining of encoded elements allowed. Level 2-Combining of encoded elements is allowed only for Thai, Indic, Hebrew, and Arabic. Level 3-Any combination of encoded elements are allowed.
UDC: See user-defined character.
UDDS: See user-defined data stream.
UDF: See user-defined function. See also function, table function, routine, built-in function.
UDFS disk pool: An independent disk pool that contains only user-defined file systems. It cannot be a member of a disk pool group unless it is converted to a primary or secondary disk pool.
UDP: See User Datagram Protocol.
UDT: See user-defined type.
UEP: See user entry procedure. See also program entry procedure.
UI: See user interface.
UID: See user identification. The first part of a two-part network name used in the system distribution directory and in the office applications to uniquely identify a user. The network name is usually the same as the user profile name, but does not need to be. See also common user identification.
uid: See user identification number. See also group identification number.
UIM: See user interface manager.
UIM tag language: A System i® language supported by the user interface manager to define panels, menus, and help items.
U interface: In the reference model for the integrated services digital network (ISDN), the interface that includes the transmission line between the network terminator 1 (NT1) and the line transmission termination (LT).
Ultimedia Business Conferencing: An IBM® licensed program that provides a solution for desktop business conferencing. Ultimedia Business Conferencing is a cooperative processing application that manages the conference from scheduling to completion.
unacknowledged service: In communications, a data transfer service that does not provide for an acknowledgment from data receiver to data sender that the data was received. An active data link connection does not need to be established between receiver and sender before sending the data. See also acknowledged service.
unary expression: An expression that contains one operand.
unary operator: In COBOL, a plus sign (+) or a minus sign (-) that precedes a variable or a left parenthesis in an arithmetic expression, which has the effect of multiplying the expression by +1 or -1, respectively.
unattended mode: In Operations Console, a state of the system when the local controlling system can automatically grant access to a remote request for control of the System i system as long as the local controlling system does not have control at the time of the request.
unattended mode IPL: An IPL mode that automatically takes the system to the IBM i operating system without any user interaction. This is the most commonly used IPL mode. See also attended mode IPL.
UNBIND command: In SNA, a command used to reset the protocols for a session. See also BIND command.
unblocked signal: In POSIX, a condition that allows a signal-handling action associated with a signal to be performed. See also blocked signal.
UNC: See Universal Naming Convention.
uncommitted read (UR): An isolation level that allows any row that is read to be changed by other applications. UR also allows any row changed by other applications to be read, even if the change has not been committed. For updatable cursors, the UR isolation level is upgraded to CS. See also cursor stability, read stability, repeatable read, isolation level.
unconfirmed service: In OSI, a service that does not indicate to the sender whether or not data or control information was properly received. An unconfirmed service involves only request and indication service primitives. See also confirmed service.
undelivered message queue: See dead-letter queue.
underrun: Loss of data caused by the inability of a transmitting device or channel to provide data to the communications control logic at a rate that is fast enough for the attached data link or loop.
unformatted: Pertaining to something that is not defined, organized, or arranged in a required manner.
unformatted system service (USS): A communications function that translates a character-coded command, such as a LOGON or LOGOFF command, into a field-formatted command for processing by formatted system services. See also formatted system service.
unicast: Transmission of data to a single destination. See also multicast.
Unicode: A character encoding standard that supports the interchange, processing, and display of text that is written in the common languages around the world, plus some classical and historical texts. The Unicode standard has a 16-bit character set defined by ISO 10646. See also multibyte character set.
unidentified user: A user of the IBM i licensed program who uses the services of IBM i but who is not automatically reported on by the license management function of IBM i. An example of an unidentified user is one who accesses a IBM i system through a gateway server that is not a IBM i system.
Uniform Resource Locator (URL): The unique address of an information resource that is accessible in a network such as the Internet. The URL includes the abbreviated name of the protocol used to access the information resource and the information used by the protocol to locate the information resource.
uninterruptible power supply: A source of power from a battery installed between the commercial power and the system that keeps the system running, if a commercial power failure occurs, until it can complete an orderly end to system processing.
union: A variable that can hold any one of several data types, one data type at a time.; An SQL operation that combines the results of two select statements. Unions are often used to merge lists of values that are obtained from several tables.
unique constraint: The rule that no two values in a primary key or key of a unique index can be the same.
unique index: An index that ensures that no identical key values are stored in a column or a set of columns in a table.
unique key: A key that is constrained so that no two of its values are equal. See also primary key, foreign key.; A field or set of fields in a database file that must be unique, ascending, and cannot contain a null value. A unique key can become a parent key.
unique product: A product that is uniquely identified to the IBM i operating system by a product identifier (product ID) and version, release, and modification identifiers (Vx, Rx, Mx).
unique-weight sort sequence: A sort sequence in which each graphic character in the sequence has a weight different from the weight of every other graphic character in the sequence.
unit: The defined space within disk units that is addressed by the system.
unit number: The unique identifier of a storage unit within a disk unit or a disk unit subsystem configured on the system.
unit of recovery: A sequence of operations within a unit of work between sync points.
unit of work (UOW): A recoverable sequence of operations performed by an application between two points of consistency. A unit of work begins when a transaction starts or at a user-requested syncpoint. It ends either at a user-requested syncpoint or at the end of a transaction.; In advanced program-to-program communications, the amount of processing that is started directly or indirectly by a program on the source system. See also unit of recovery.; A recoverable sequence of operations within an application process. At any time, an application process is a single UOW, but the life of an application process can involve many UOWs as a result of commit or rollback operations. In a multisite update operation, a single UOW can include several units of recovery. See also unit of recovery, remote unit of work, transaction.
unit-of-work identifier: In advanced program-to-program communications, a unique label assigned to the unit of work. The ID is established when the program on the source system is started and is associated with each job started by that source system on the target system. The unit-of-work identifier provides a beginning-to-end audit trail within an APPC network.
unit reference code (URC): A group of numbers displayed on the console or control panel that identifies failing parts, system or device states, or system or device status conditions.; The last 4 characters of the SRC.
universal character set (UCS): The ISO standard that allows all data to be represented as 2 bytes (UCS-2) or 4 bytes (UCS-4). Encoding in the UCS-2 form can accommodate the necessary characters for most of the world's written languages.
Universal Naming Convention (UNC): The server name and network name (netname) combined. These names together identify the resource on the domain.
Universal Serial Bus (USB): A serial-interface standard for telephony and multimedia connections to personal computers.
UNIX: A highly portable operating system that features multiprogramming in a multiuser environment. The UNIX operating system was originally developed for use on minicomputers, but was adapted for mainframes and microcomputers. The AIX® operating system is IBM's implementation of the UNIX operating system.
unlike: Pertaining to two or more different operating environments. For example, unlike distribution is distribution between DB2® for IBM i and DB2 environments.
unlink: In IDDU, to remove the association between a database file on disk and a file definition in a data dictionary. See also link.
unload: To remove a volume from a tape unit or a direct access device.
unloaded: Pertaining to a status where the optical image associated with the selected image catalog entry that is not active or not loaded in the active virtual optical device. Only image catalog entries with a status of mounted or loaded can be accessed through the virtual optical device.
unlock: To release an object or system resource that was previously locked and return it to general availability.
unnumbered: In communications, pertaining to a frame format that provides additional control functions, such as XID, DISC, DM, SABM, SABME, UA, and FRMR.
unnumbered acknowledgment (UA): In communications, a data link command or response that acknowledges the receipt and acceptance of the SABM, SABME, and DISC command protocol data units.
unordered: In binary floating-point, describing the relationship that exists between two values when they cannot be arranged according to relative value. The relationship between two values is unordered either when a not-a-number is compared to any value or when infinity is compared to any value other than infinity.
unpacked decimal format: See also packed decimal format. See zoned decimal format.
unprotected conversation: An LU 6.2 conversation that has a synchronization level of none or confirm. If conversation errors or failures occur, the resources used by the application might be in inconsistent states.
unprotected field: A displayed field in which a user can enter, modify, or delete data.
unprotected logical unit of work: The logical unit of work that is used in an unprotected conversation. See also unit of recovery.
unprotected logical unit of work identifier: The logical unit of work identifier that is used in an unprotected conversation.
unprotected storage: The part of the system auxiliary storage pool (ASP) that is not protected by mirrored protection or device parity protection.
unresolved import: An import whose type and name do not yet match the type and name of an export.
untrusted system: A system in a network over which you do not have control of security.
unusable: In cross-site mirroring, pertaining to the mirror copy data state that indicates that the mirror copy contains incoherent data. This occurs (a) during synchronization because synchronization does not preserve the order of writes and (b) if a failure occurs while performing geographic mirroring in asynchronous mode.
UOW: See unit of work. A recoverable sequence of operations within an application process. At any time, an application process is a single UOW, but the life of an application process can involve many UOWs as a result of commit or rollback operations. In a multisite update operation, a single UOW can include several units of recovery. See also unit of recovery, remote unit of work, transaction.; See unit of work. A recoverable sequence of operations performed by an application between two points of consistency. A unit of work begins when a transaction starts or at a user-requested syncpoint. It ends either at a user-requested syncpoint or at the end of a transaction.
update authority: A data authority that allows the user to change the data in an object, such as a journal, a message queue, or a data area.
update file: In RPG, a file from which a program reads a record, changes data fields in the record, and writes the record back to the location from which it came.
update lock: A lock that limits concurrently executing application processes to read-only operations on the data if these processes have not declared that they might update the row.
update operation: An I/O process that changes the data in a record.
update rule: A condition enforced by the database manager that must be met before a column can be updated.
update trigger: A trigger that is activated by an update operation on the table or view that is specified in the trigger definition. See also delete trigger, insert trigger, trigger, instead of trigger, read trigger.
upgrade: Any hardware or software change to a later release, or any hardware addition or software addition.; To install a new version or release of a product to replace an earlier version or release of the same product.
upline: Pertaining to controllers that are above devices, and lines that are above controllers in a communications configuration. See also downline.
upload: To transmit data from a computer to a central computer or network, or to an attached device such as a printer.
upstream: Pertaining to the direction opposite to data flow, which is toward the source of a transmission. See also downstream.
UR: See uncommitted read. See also cursor stability, read stability, repeatable read, isolation level.
URC: See unit reference code.
URL: See Uniform Resource Locator.
usable: In cross-site mirroring, pertaining to the mirror copy data state that indicates that the correct order of updates to the mirror copy from the production copy is being preserved, but the mirror copy may be outdated. The usable mirror copy data state occurs (a) when the system performs geographic mirroring in synchronous mode, (b) after successfully suspending geographic mirroring, and (c) when the mirror copy is successfully detached.
usage type: In IBM i, a license management function that monitors usage by tracking the number of license users. Concurrent usage type indicates the usage limit is for the number of unique jobs using the product at the same time. Registered usage type indicates the usage limit is for the number of unique license users registered to use the product.
USB: See Universal Serial Bus.
use authority: An object authority that allows the user to run a program or to display the contents of a file. Use authority combines object operational authority, read authority, and execute authority.
user agent (UA): In OSI X.400, one of two basic parts of electronic mail. A user agent is a program that provides access to the mail system. This program allows users to compose, send, and receive mail.
user ASP: One or more auxiliary storage pools used to isolate journals, journal receivers, and save files from the other system objects stored in the system ASP. See also system ASP, auxiliary storage pool.; One or more storage units used to isolate some objects from the other objects that are stored in the system ASP and other user ASPs. User ASPs are defined by the user.
user-based pricing: A pricing option that provides the capability for the customer to pay for the licensed program on the basis of the number of users.
user class: The classification of a user by the system task, such as security officer, security administrator, programmer, system operator, and user. Each user class has a set of special authorities depending on the security level of the system. The user class determines which options are shown on the IBM-supplied menus.
user configuration: In System i Access, the set of files, created by the System i Access administrator, that define the user's System i Access configuration and the functions used. The files include the configuration file and the command file.
user-controlled environment: An extended program model (EPM) environment that is explicitly created using the QPXXCALL program.
user-created data stream: A data stream that has not been validated by a system program on the system when the data was spooled.
User Datagram Protocol (UDP): An Internet protocol that provides unreliable, connectionless datagram service. It enables an application program on one machine or process to send a datagram to an application program on another machine or process.
user-defined character (UDC): A character that is created through the Character Generator Utility (CGU). CGU is an extension of the code page with special user-defined ideographic characters, symbols, or logos. User-defined characters may be present in some of the Japanese, Chinese, and Korean code pages.
user-defined collating sequence: In Query, a collating sequence defined by the user that replaces the EBCDIC collating sequence provided by the system for sorting fields in a query report.
user-defined communications support: An IBM i function that provides an application program interface (API). User-defined communications support allows user-written application programs to call routines to set up and use a communications protocol over a token-ring, Ethernet, or X.25 network.
user-defined data stream (UDDS): A data stream in which the user has defined and embedded all device control characters.
user-defined edit code: A number (5 through 9) indicating that editing should be done on a numeric output field according to a pattern predefined to the system program. User-defined edit codes can take the place of edit words, so that repetitive coding of the same edit word is not necessary.
user-defined function (UDF): A function that is defined to the DB2 database system by using the CREATE FUNCTION statement and that can be referenced thereafter in SQL statements. A UDF can be an external function or an SQL function. See also function, table function, routine, built-in function.
user-defined type (UDT): A mechanism that can be used to create new data types. A UDT can extend the capabilities of the built-in data types and capture the unique semantics of user data.
user-defined word: In COBOL, a word, required by a clause or a statement, that must be supplied by the user in a clause or statement.
user domain object: An object on the system that can be accessed directly by a user state program. The object types that can be either system domain or user domain are: *USRSPC, *USRIDX, *USRQ, *PGM, *SQLPKG. All other object types are system domain. See also domain.
user entry procedure (UEP): The entry procedure, written by the application programmer, that is the target of a dynamic program call. This procedure gets control from the program entry procedure (PEP). See also program entry procedure.
user exit: In Backup, Recovery, and Media Services, a special operation (*EXIT) available in the control group to permit automatic processing of predefined user routines during control group processing.
user ID: See user identification. The name used to associate the user profile with a user when a user signs on to a system.
user ID/address: The two-part network name used in the system distribution directory and in the office applications to uniquely identify a user and send electronic mail.
user identification (UID, user ID): In the UNIX operating system, a string that uniquely identifies each user to the operating system.; The first part of a two-part network name used in the system distribution directory and in the office applications to uniquely identify a user. The network name is usually the same as the user profile name, but does not need to be. See also common user identification.; The name used to associate the user profile with a user when a user signs on to a system.
user identification number (uid): A 4-byte, unsigned integer (uid) used to identify a user profile. See also group identification number.
user index: In IBM i application programming interfaces, an object that provides a specific order for byte data according to the value of the data. User index objects reside in the user domain. The system-recognized identifier for the object type is *USRIDX.
user interface (UI): The hardware, or software, or both that enables a user to interact with a system, program, or device.
user interface manager (UIM): A function of the operating system that provides a consistent user interface by providing comprehensive support for defining and running panels (displays), dialogs, and online help information.
user message queue: A user-created object used to receive messages sent from the system, other users, and application programs.
user name: A string of characters that uniquely identifies a user to a system. See also user identification.
user password: A unique string of characters that a system user enters to identify that user to the system, if the system resources are secured.
user profile: An object with a unique name that contains the user's password, the list of special authorities assigned to a user, and the objects the user owns. The system-recognized identifier for the object type is *USRPRF.
user profile name: The name or code that the system associates with a user when the user signs on the system.
user queue: In IBM i application programming interfaces, an object consisting of a list of messages that communicate information to other application programs. The system-recognized identifier for the object type is *USRQ.
user registry: A collection of user information, such as user IDs and passwords, that is used as the basis for security control by a system such as a Web application server.
user shell: An interactive shell. The user's CICS® application program runs directly under this CICS facility.
user space: In IBM i application programming interfaces, an object consisting of a collection of bytes that can be used for storing any user-defined information. The system-recognized identifier for the object type is *USRSPC.
user state program: A program that can access objects in the user domain. All user programs on the system are user domain. A user state program can call only another user state program.
user table: A list of user IDs authorized to a System i finance job.
USS: See unformatted system service. See also formatted system service.
UTC: See Coordinated Universal Time.