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This site contains terms and definitions from many IBM software and hardware products as well as general computing terms.


A CCITT Recommendation that provides a method for the international numbering of X.25 packet-switching data networks.


  1. See Recommendation X.21.
  2. See specification X.21.

X.21 bis
In data communications, an interim specification of the CCITT that defines the connection of data terminal equipment (DTE) to an X.21 (public data) network using V-series interchange circuits such as those defined by CCITT V.24 and CCITT V.35.

A CCITT standard that defines an interface to packet-switched communication services. See also packet switching.

X.25 adapter
See X.25 Interface Co-Processor/2.

X.25 interface
An interface consisting of a data terminal equipment (DTE) and a data circuit-terminating equipment (DCE) in communication over a link using the procedures described in the CCITT Recommendation X.25.

X.25 Interface Co-Processor/2
A separately orderable adapter card that attaches a system unit to an X.25 packet switching data network.

X.25 line
In X.25 communications, the physical link between the DTE and the DCE, and the subscribed service.

X.25 link
The X.25 line from the X.25 adapter to the network terminating unit. In the X.25 API, a link is equivalent to an X.25 port.

X.25 NCP Packet Switching Interface (NCP Packet Switching Interface, NPSI)
An IBM licensed program that allows SNA users to communicate over packet switching data networks that have interfaces complying with CCITT Recommendation X.25. It allows SNA programs to communicate with SNA or non-SNA equipment over such networks.

X.25 network
A service providing packet-switched data transmission that conforms to Recommendation X.25 adopted by the CCITT.

X.25 port
A device in the /dev directory that corresponds to an X.25 link.

X.25 protocol
The connection-mode network service that the CCITT specifies in Recommendation X.25.

X.25 protocol ID
In OSI, a technique that OSI Communications Subsystem uses to pass an NSAP address when using the 1980 level of the X.25 protocol.

X.25 Public Data Network
A computer network that uses the X.25 transport method to send and receive data. Usually, an X.25 network provides local access phone numbers.

X.25 subnetwork
In OSI, a subnetwork that conforms to the X.25 protocols.

A CCITT Recommendation for international electronic mail (messages).

The directory services standard of ITU, ISO, and IEC.

X.509 certificate
A certificate that contains information that is defined by the X.509 standard.

In data communications, a specification that defines ways of connecting two X.25 networks.

A protocol from the American National Standards Institute (ANSI) for electronic data interchange (EDI).


  1. See extended architecture.
  2. A bidirectional interface between one or more resource managers that provide access to shared resources and a transaction manager that monitors and resolves transactions. See also distributed transaction, XA transaction.

See Extensible Access Control Markup Language.

Xalan processor
An XSLT processor that is part of the Apache project. See also XSL Transformation.

XA transaction

  1. A global transaction that adheres to the X/Open standard for distributed transaction processing (DTP).
  2. In an XA-enabled environment, a unit of work involving one or more resource managers that is coordinated by a transaction manager. See also XA.


  1. In printing, the axis perpendicular to the direction in which the paper moves through the printer. See also Y-axis.
  2. In a system of coordinates, the axis of the first component used to locate points in space (X-axis, Y-axis, and Z-axis).

See eXtensible Business Reporting Language.


  1. See X/Open Backup Services API.
  2. An industry-standard API set for backup and restore utilities.

See external communication adapter.

See XML common analysis structure.

See cross-system coupling facility.

XCF couple data set
A data set that is created through the cross-system coupling facility (XCF) couple data set (CDS) format utility and, depending on its designated type, is shared by some or all of the systems in a sysplex.

XCF group
The set of related members defined to SCF by a multisystem application in which members of the group can communicate with (send data to and receive data from) other members of the same group. All MERVA systems working together in a sysplex must pertain to the same XCF group.

XCF-local mode
The state of a system "..in which the cross-system coupling facility (XCF) provides limited services on one system and does not provide signaling services between MVS systems.

XCF member
A specific function of a multisystem application that is defined to XCF and assigned to a group by the multisystem application. A member resides on one system in a sysplex and can use XCF services to communicate with other members of the same group.

XCF PR/SM policy
In a multisystem sysplex on PR/SM, the actions that the cross-system coupling facility (XCF) takes when one MVS system in the sysplex fails. This policy provides high availability for multisystem applications in the sysplex.

X Client
An application program that uses the X protocol to communicate windowing and graphics requests to an X Server.

See extended common object file format.

The horizontal or inline position that defines a page origin or the starting point of a line or field.

See XML data area.

XDC file
See XML data configuration file.

In bar codes, the nominal dimension of the narrow bars and spaces in a bar code symbol.

See XQuery and XPath data model.

XDM instance
Data conforming to the XQuery and XPath data model (XDM). See also XML data, XQuery and XPath data model.

See extended data object.

An open, source code generation engine that uses special JavaDoc tags to parse Java source files and generate output such as XML descriptors or source code, based on templates.

See External Data Representation.


  1. See X/Open Directory Services.
  2. See XML data specifier.

A open-source virtualization environment for System x and similar platforms.

An XML parser, which is part of the Apache project.

A validating XML parser written in a portable subset of C++.

xerographic paper
A paper that is manufactured specially for the xerographic process, in which key paper qualities are carefully controlled.

See cross-system extended services.

X extent
A separate extent, part of the system log. During backout in emergency restart, system log records are written to the X extent. The presence of an X extent is mandatory if CICS Transaction Server is using a local DL/I system; otherwise, it is optional. The X extent can be used for audit purposes.

A measurement along the X-axis.

X field
The primary data field in a chart. In a line chart, typically the X field appears along the horizontal axis. For example, an X field can represent cost data for the elements that appear along the horizontal axis of the chart.

See Graphics Support Library.


  1. The nominal height above the baseline, ignoring the ascender, of the lowercase characters in a font. X-height is usually the height of the lowercase letter x.
  2. The body of a lowercase letter, which is equivalent to the height of the lowercase x in the selected type family.

See Extensible Hypertext Markup Language.


  1. See exchange identification.
  2. See transaction identifier.
  3. See exchange station ID.
  4. See X/Open identifier.

See XML Enhancements for Java.

An XML-based job control language that is used to define a batch job. See also job control language, results algorithm.

See transaction list table.

See XML Metadata Interchange.

See Extensible Markup Language.

XML attribute
A name-value pair within a tagged XML element that modifies certain features of the element.

XML catalog
A catalog that contains rules specifying how an XML processor should resolve references to entities. Use of a catalog eliminates the need to change URIs within XML documents as resources are moved during development.

XML classifier
A Content Platform Engine function that identifies a document type by examining the contents of XML documents. The XML classifier applies the script contained in the XML property mapping script to determine property mappings.

XML collection
A collection of relational tables from which XML documents can be composed or into which XML documents can be decomposed.

XML column
A column of a table that stores XML values and is defined using the SQL built-in data type XML.

XML common analysis structure (XCAS)
An XML representation of the CAS.It can be used for saving and restoring CASs to and from streams. See also Common Analysis Structure.

XML data

  1. Data of type XML, including serialized XML or XDM instances. See also serialized XML, XDM instance.
  2. A collection of hierarchical nodes, based on XML instance documents, that can be stored in an XML column or can be returned from an XML column by an SQL or XQuery statement.

XML data area (XDA)
See XML storage object.

XML data configuration file (XDC file)
A configuration file that defines the relationship between entities in a data source and columns in a relational table.

XML data source adapter
A data source adapter that reads XML data from strings and files, and reads XML data from web servers over HTTP.

XML data specifier (XDS)
A string specifying the name, location, and validation schema for a file containing stored XML data. The import, export, and load utilities use an XDS to identify XML-formatted content that must be stored separately from the main data file.

XML data type
A data type for XML values.

XML digital signature
A specification that defines the XML syntax and the processing rules to sign and verify the digital signatures for the digital content.

XML document
A well-formed XML artifact that conforms to the XML specification and contains markup tags along with the content, with exactly one root element.

XML document definition
A reference to either an XML DTD document definition or an XML schema document definition.

XML domain
The message domain that includes all messages that conform to the W3C XML standard. The XMLNS domain is an extension of the XML domain and contains messages that conform to the same standard and that can exploit the namespaces feature of the XML specification. Messages in this domain are processed by the XML parser. See also BLOB domain, DataObject domain, IDoc domain, JMS domain, MIME domain, MRM domain, SOAP domain, XMLNS domain, XMLNSC domain.

XML element
A logical structure in XML that is delimited by a start tag and an end tag.

XML encoder object
A compiled map that translates data from either the input or output side of a source map into XML. EDI, positional, and variable-length delimited data formats can be compiled into XML encoder objcts.

XML encoding declaration
The attribute of an XML or TEXT declaration named encoding and its value, which specifies the name of the encoding scheme of XML data.

XML encryption
A specification that defines how to encrypt the content of an XML element.

XML Enhancements for Java (XJ)
An extension to Java that supports XML, XML Schema, and XPath as first-class constructs. XJ introduces XML support to Java in a way that makes programs based on XML easier to develop.

XML index

  1. See index over XML data.
  2. An index on an XML column that provides efficient access to nodes within an XML document by providing index keys that are based on XML patterns.

XML lock
A column-level lock for XML data. The operation of XML locks is similar to the operation of LOB locks.

XML mapping template
This template processes inbound XML messages and translate them to WebSphere Commerce command parameters. The mapping template file defines how to map the elements of an incoming XML message into the target command parameters.

XML message mapper
A mechanism that converts the incoming XML message into a Java object that the target command expects. A message mapper can be registered with the instance_name.xml configuration file and is uniquely by a message mapper ID. The XML message mapper uses the mappings defined in the mapping template file to convert the XML message into the corresponding Java command parameter.

XML Metadata Interchange (XMI)
A model-driven XML integration framework for defining, interchanging, manipulating, and integrating XML data and objects. XMI-based standards are in use for integrating tools, repositories, applications, and data warehouses.

XML namespace
A collection of names, identified by a Universal Resource Identifier (URI) reference, used in XML documents as element types and attribute names. An XML namespace allows a user to include multiple XML vocabularies in a single XML document without ambiguity of names.

XML node
The smallest unit of valid, complete structure in a document. For example, a node can represent an element, an attribute, or a text string.

XML node ID index
An implicitly created index, on an XML table that provides efficient access to XML documents and navigation among multiple XML data rows in the same document.

XMLNSC domain
An extension of the XML domain that provides high-performance XML parsing and offers optional XML Schema validation. Messages in this domain are processed by the XMLNSC parser. To process a message, a message model for messages is created in this domain, but a model is only necessary when messages are validated. See also BLOB domain, DataObject domain, IDoc domain, JMS domain, MIME domain, MRM domain, SOAP domain, XML domain, XMLNS domain.

XMLNSC parser
A program that interprets a message that belongs to the XMLNSC domain, and generates the corresponding tree from the bit stream on input, or the bit stream from the tree on output. The bit stream is a representation of an XML file.

XMLNS domain
An extension of the XML domain that contains messages that conform to the W3C XML standard, and that can also exploit the namespaces specification. Messages in this domain are processed by the XMLNS parser. See also BLOB domain, DataObject domain, IDoc domain, JMS domain, MIME domain, MRM domain, SOAP domain, XML domain, XMLNSC domain.

XMLNS parser
A program that interprets a message that belongs to the XMLNS domain, and generates the corresponding tree from the bit stream on input, or the bit stream from the tree on output. The bit stream is a representation of an XML file.

XML parser
A program that reads XML documents and provides an application with access to their content and structure.

XML parsing
The process of converting a character string or binary string into an XML value. XML parsing is the inverse of serializing.

XML path index
A system-generated index that is associated with an XML column and contains all unique paths that exist in the XML documents that are stored in that XML column. Each XML column in a table has an XML path index.

XML Path Language (XPath)
A language that is designed to uniquely identify or address parts of source XML data, for use with XML-related technologies, such as XSLT, XQuery, and XML parsers. XPath is a World Wide Web Consortium standard. See also XML Path Language injection.

XML Path Language injection (XPath injection)
An attack technique used to exploit websites that construct XPath queries from user-supplied input. If an application embeds unsafe user input into the query, it may be possible for the attacker to inject data into the query so that the newly formed query will be parsed differently from the programmer's intention. See also XML Path Language.

XML pattern
A slash-separated list of element names that describes a path through an XML document and through specific node characteristics. The pattern selects elements that match the specifications. XML patterns are specified to create indexes on XML columns in a database.

XML property mapping script
A script that maps XML values in an incoming document to a target document class.

XML publishing function
A function that returns XML values from SQL values.

XML resource bundle
A group of XML properties that is bound in a package for ease of deployment. There is a separate resource bundle for each language.

XML root element
The implicit highest-level node of a parsed XML document. It may not always be possible to predict which element will be the document element of a parsed instance, but it will always have a root node that can be used for preliminary or setup processing.

XML Rule Language (XRule)
An XML text string that the scan should search for in a website.

XML Schema
The W3C specification that describes how to represent XML structures and XML data types in XML Schema language.

XML schema

  1. A means for defining the structure, content, and semantics of XML documents as defined by a World Wide Web Consortium (W3C) recommendation.
  2. A mechanism for describing and constraining the content of XML files by indicating which elements are allowed and in which combinations. XML schemas are an alternative to document type definitions (DTDs) and can be used to extend functionality in the areas of data typing, inheritance, and presentation.

XML Schema Definition (XSD)
An instance of an XML schema written in XML Schema definition language. An XML Schema Definition file has the extension .xsd. The prefix "xsd" is also typically used in the XML elements of the XSD file to indicate the XML Schema namespace.

XML Schema Definition Language (XSD, XSDL)
A language for describing XML files that contain XML schema.

XML schema document
An XML document with [schema] as the root element that defines the components in one namespace of an XML schema. An XML schema with components in more than one namespace consists of multiple XML schema documents.

XML Schema Infoset Model (XSD)
A library that provides an API for manipulating the components of an XML Schema, as described by the W3C XML Schema specifications.

XML schema model
An object that contains a schema-based definition of entities within an XML schema.

XML schema repository (XSR)
A repository that allows the DB2 database system to manage dependencies on externally referenced XML artifacts in XML instance documents within a database. Supported XSR objects include XML schemas, document type definitions (DTDs), and other external entities. When registered with the XSR, these objects have a unique identifier and can be used to validate XML instance documents. See also XSR object.

XML serialization function
A function that returns a serialized XML string from an XML value.

XML signature
A digital electronic, encrypted, stamp of authentication on digital information such as messages.

XML statistics
The statistics that are collected on XML data that is stored in an XML column. The information includes path distribution statistics, which show the frequency of all distinct root-to-node paths. The information also contains path-value distribution statistics, which show the frequency of XML value strings that are truncated to fixed-length prefixes to conserve space.

XML storage object
The object that is used by default to store XML documents contained in XML columns of a table.

XML subtype indicator
An indicator that specifies that a base LOB data type is used to hold XML data.

XML table
An auxiliary table that is implicitly created when an XML column is added to a base table. This table stores the XML data and the column in the base table points to it.

XML table space
A table space that is implicitly created when an XML column is added to a base table. The table space stores the XML table. If the base table is partitioned, one partitioned table space exists for each XML column of data.

XML token
A security token that is in an XML format, such as a Security Assertion Markup Language (SAML) token.

XML transform service
A data management service that can be used to apply the rule-based data privacy policies defined in an XSLT data privacy stylesheet to an XML data source.

XML value
See XDM instance.

XML Wire Format
The physical representation of a message in the MRM domain that can be parsed as XML.

Xmodem protocol
A communications protocol in which messages are sent in blocks of 128 characters, surrounded by control characters. This protocol also uses the checksum program for error checking.


  1. See execution object model.
  2. See X/Open Object Management.

An industrial consortium that produces specifications and test suites to resolve incompatibilities among different computer systems and software components.

X/Open Backup Services API (XBSA)
An API that provides a programming interface and functions that manage backup and restore operations. XBSA can connect storage managers with the database server.

X/Open Company, Ltd
An industrial consortium that produces specifications and test suites to resolve incompatibilities among different computer systems and software components.

X/Open Directory Services (XDS)
An application program interface (API) that Distributed Computing Environment (DCE) uses to access its directory service components.

X/Open identifier (XID)
A work ID that is a possible identifier for a distributed transaction used in the X/Open model.

X/Open Object Management (XOM)
An interface for creating, deleting, and accessing objects. Because XOM is object-oriented, each object belongs to a particular class, and classes can be derived from other classes, inheriting the characteristics of the original class. The representation of the object is transparent to the programmer; the object can be manipulated only through the XOM interface.

X/Open Transport Interface (XTI)
A library implementation that defines the set of transport-level services that are independent of any specific transport provider's protocol or its framework. The X/Open Transport Interface is specified by X/OPEN CAE Specification of X/Open Transport Interface and is fully conformant to X/OPEN and the XPG4 Common Application Environment (CAE) specification.

X/Open XA
The X/Open Distributed Transaction Processing XA interface. A proposed standard for distributed transaction communication. The standard specifies a bidirectional interface between resource managers that provide access to shared resources within transactions, and between a transaction service that monitors and resolves transactions.

See extreme programming.

Xp,Yp coordinate system
The logical-page coordinate system that describes the size, position, and orientation of a logical page.

A digital trunk processor implemented using DSP technology on the DTXA without the need for external hardware. One XPACK is directly equivalent to one SPACK. One DTXA provides up to four XPACKs on a PCI card. See also SPACK, VPACK.

See XML Path Language.

XPath expression
An expression that searches through an XML document and extracts information from the nodes (any part of the document, such as an element or attribute) in that document.

XPath injection
See XML Path Language injection.

See Extensible Program Call Markup Language.

Xp extent
In architecture, the size of a presentation space or logical page in the Xp-dimension.

Xpg,Ypg coordinate system
The coordinate system of a page presentation space. This coordinate system describes the size, position, and orientation of a page presentation space. Orientation of an Xpg,Ypg coordinate system is relative to an environment specified coordinate system; for example, an Xm,Ym coordinate system.


  1. See exit programming interface.
  2. See user exit programming interface.

See Extra Performance Linkage.

Xp orientation
In printing, the orientation of a font along the X-axis.

X-Press Update (XPU)
A software update that is issued between major releases to protect a network against the latest security vulnerabilites and threats.

See X-Press Update.

XQuery and XPath data model (XDM)
The abstract logical structure that defines all permissible values in the XSLT 2.0, XQuery 1.0, and XPath 2.0 languages. The XDM is described in terms of sequences of atomic values and nodes. See also atomic value, node, sequence, XDM instance.

XQuery constructor
See constructor.

XQuery expression
An expression that operates on instances of the XQuery and XPath data model (XDM) and returns instances of the data model.

XQuery language
An XML query language for interpreting, retrieving, and modifying data as defined by the XQuery and XPath data model, such as XML documents. XQuery Version 1.0 is an extension of XPath Version 2.0.

See extended remote copy.

X resource

  1. In Enhanced X-Windows, a named piece of data in a widget that can be set by a client, by an application, or by user defaults.
  2. In AIXwindows and Enhanced X-Windows, a unique characteristic of appearance or behavior that is associated with one specific class of graphical object. Resources can be passed downward (inherited) by each subclass that is downstream from a higher-level class in the class hierarchy.

X resource file
In AIXwindows, an ASCII file that includes the definition of all property values that were specified as Public in the Widget Property Editor. Such files are editable by the end user.

See extended recovery facility.

XRF complex
The central processor complexes (CPCs) and the licensed programs in the active and the alternate that provide the extended recovery facility (XRF) for IMS users.

XRF takeover
See takeover.

See extended restart.

See XML Rule Language.

See extended subarea addressing.


  1. See XML Schema Definition.
  2. See XML Schema Definition Language.
  3. See XML Schema Infoset Model.

See XML Schema Definition Language.

The product name of an IBM eServer product that emphasizes industry-standard server scalability and self-managing server technologies. It is the successor to the Netfinity family of servers.

X Server
A program that interprets the X protocol and controls one or more screens, a pointing device, a keyboard, and various resources associated with the X Window System, such as graphics contexts, pixmaps, and color tables.

See Extensible Stylesheet Language.

XSL Formatting Objects
An XML vocabulary for specifying formatting semantics.

XSL style sheet
Code that describes how an XML document should be rendered (displayed or printed).


  1. See Extensible Stylesheet Language Transformation.
  2. See XSL Transformation.

XSLT function
Function that is defined by the XSL Transform (XSLT) specification for the manipulation of numbers, strings, Boolean values, and node-sets.

XSL Transformation (XSLT)
A standard that uses XSL style sheets to transform XML documents into other XML documents, fragments, or HTML documents. See also Xalan processor.

See cross-site mirroring.

In i5/OS, a tool that can be used to learn about socket APIs and that can be used to re-create specific socket scenarios interactively to help in debugging.

See XML schema repository.

XSR object
An XML artifact that is registered in the XML schema repository (XSR) and is used to validate XML instance documents. Supported XSR objects include XML schemas, document type definitions (DTDs), and other externally referenced entities. See also XML schema repository.

See cross-site scripting.

A terminal emulator for the X Window System.

See X/Open Transport Interface.

Xt intrinsics
In the Enhanced X-Windows Toolkit, a set of management mechanisms that provides for constructing and interfacing between composite widgets, their children, and other clients. Also, intrinsics provide the ability to organize a collection of widgets into an application.

X Toolkit
See AIXwindows Toolkit.

See execution unit.

X Window System
A software system, developed by the Massachusetts Institute of Technology, that enables the user of a display to concurrently use multiple application programs through different windows of the display. The application programs can execute on different computers. See also Athena widget set, Enhanced X-Windows Toolkit.

XY format
The format of a pixmap organized as a set of bitmaps representing individual bit planes that appear in most-significant to least-significant bit order.