Michael Henson's

Glossary of Computer Science Terms

Index | A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


abstract class: a class that cannot have direct instances but whose descendents can have instances; a class that has declared one or more methods for which it does not provide definitions (i.e. abstract methods)
abstract data type (ADT): a data declaration packaged together with the functions that operate on it
abstraction: a mental facility that permits humans to view real-world problems with varying degrees of detail depending on the current context of the problem; the process of focusing on the essential, inherent aspects of an entity and ignoring its accidental properties; the selective examination of certain aspects of a problem
absolute positioning: using pixel coordinates to position GUI components
access transparency: a type of transparency that enables local and remote information objects to be accessed using identical operations
action: an instantaneous operation. Actions are associated with events and are usually formal in nature.
active rendering: a technique often used in animation where an application manages its own visual updates rather than relying on the operating system's rendering thread
activity: an operation that takes time to complete. Activities are associated with states and represent real-world accomplishments.
activity diagram: a UML diagram that models the activity (workflow) of a portion of a software system
actor object: an active object that drives a data flow graph by producing or consuming values.
adapter class: a class in the java.awt.event package that provides empty implementations of event listener methods so that the programmer can write code for only relavant events
address space: a collection of ranges of virtual memory locations with specific memory access rights
ADT: See abstract data type
aggregation: a tightly coupled form of association, between a whole and its parts, in which the whole is composed of the parts; see also compositioni
algorithm: a finite sequence of unambiguous instructions which, when given the required input, produces the correct output and then stops;
a procedure for solving a problem in terms of the steps to be taken and the order in which the steps are to be carried out
ALU: Arithmetic/Logic Unit -- the part of the CPU responsible for performing arithmetic and Boolean operations
analysis: a stage in the development cycle in which a real-world problem is examined to understand its requirements without planning the implementation
anonymous class: a local class that is declared and instantiated in a single statement, often as a parameter to a method
API: Application Programming Interface -- the interface used by a program to access various services on the computer
applet: a Java program that runs in a web browser or other applet container
architecture: the overall structure of a system, including its partitioning into subsystems and their allocation to tasks and processors
array: a homogeneous collection of data items stored by a sequential ordinal index
ASCII: the American Standard Code for Information Interchange -- an encoding standard for text and control characters. ASCII is a subset of Unicode.
assignment: an operation that places a value in a variable
association: a relationship between objects and classes that describes a group of links with common structure and common semantics
asynchronous communication: communication in which the sending process can proceed as soon as the message has been sent out to a buffer
at-least-once call semantics: RPC semantics in which a caller sends a request message several times until a reply is received
at-most-once call semantics: RPC semantics in which duplicate messages are filtered out and replies are retransmitted without re-executing operations so that the remote procedure is executed once or not at all
atomic multicast: a multicast message that is either received by all intended recipients or none of them
attribute: a property of the objects in a class. Synonyms: Data member, member variable
authentication server: a server that provides a secure way for pairs of processes to obtain secret keys for secure encryption
automatic variable: a local variable
auxiliary carry flag (AC): a carry flag used by instructions that perform binary coded decimal (BCD) arithmetic; the second bit in the PSW register
See carry flag
availability: a measure of a proportion of time that something can be used