DDK Glossary - H

handle: # An identifier that represents an object, such as a device or a window, to the Presentation Interface.; # In the Advanced DOS and OS/2 operating systems, a binary value created by the system that identifies a drive, directory, and file so that the file can be found and opened.

handshaking: A method by which two pieces of hardware, such as a personal computer and a plotter, can communicate. Depending upon the devices communicating, handshaking occurs either as a hardware function or through software, such as a device driver.

hard error: An error condition on a network that requires that the network be reconfigured or that the source of the error be removed before the network can resume reliable operation.

header: (1) System-defined control information that precedes user data.; (2) The portion of a message that contains control information for the message, such as one or more destination fields, name of the originating station, input sequence number, character string indicating the type of message, and priority level for the message.

heading tags: A document element that enables information to be displayed in windows, and that controls entries in the contents window, controls placement of push buttons in a window, and defines the shape and size of windows.

heap: An area of free storage available for dynamic allocation by an application. Its size varies according to the storage requirements of the application.

help function: (1) A function that provides information about a specific field, an application panel, or information about the help facility.; (2) One or more display images that describe how to use application software or how to do a system operation.

Help index: In SAA Common User Access architecture, a help action that provides an index of the help information available for an application.

help panel: A panel with information to assist users that is displayed in response to a help request from the user.

help window: A Common-User-Access-defined secondary window that displays information when the user requests help.

hexadecimal: Pertaining to a system of numbers to the base 16; hexadecimal digits range from 0 through 9 and A through F, where A represents 10 and F represents 15.

hidden file: An operating system file that is not displayed by a directory listing.

hide button: In the OS/2 operating system, a small, square button located in the right-hand corner of the title bar of a window that, when selected, removes from the screen all the windows associated with that window. Contrast with maximize button. See also restore button.

hierarchical inheritance: The relationship between parent and child classes. An object that is lower in the inheritance hierarchy than another object inherits all the characteristics and behaviors of the objects above it in the hierarchy.

hierarchy: A tree of segments beginning with the root segment and proceeding downward to dependent segment types.

high-performance file system (HPFS): In the OS/2 operating system, an installable file system that uses high-speed buffer storage, known as a cache, to provide fast access to large disk volumes. The file system also supports the coexistence of multiple, active file systems on a single personal computer, with the capability of multiple and different storage devices. File names used with the HPFS can have as many as 254 characters. Abbreviated as HPFS.

hit testing: The means of identifying which window is associated with which input device event.

hook: A point in a system-defined function where an application can supply additional code that the system processes as though it were part of the function.

hook chain: A sequence of hook procedures that are "chained" together so that each event is passed in turn to each procedure in the chain.

hot spot: The part of the pointer that must touch an object before it can be selected. This is usually the tip of the pointer. Contrast with action point.

hypergraphic link: A connection between one piece of information and another through the use of graphics.

hypertext: A way of presenting information online with connections between one piece of information and another, called hypertext links. See also hypertext link.