A Dictionary of Computer Science by Unknown

Author:Unknown
Language: eng
Format: mobi
ISBN: 9780199688975
Publisher: Oxford University Press
Published: 2015-12-15T00:00:00+00:00

http://www.w3.org/Graphics/JPEG/itu-t81.pdf

• The JPEG standard (CCITT recommendation T.81)

JSD (Jackson system development) A proprietary structured method for the analysis and design of data processing and real-time systems, originally devised by Michael Jackson in 1983. JSD is fully integrated with *JSP (Jackson structured programming). The JSD notation covers entity structures (similar to *SSADM entity life histories), and network diagrams connecting entity and process structures. Rules assist the designer to iteratively structure and sequence the design and to transform and trace requirements into the software design.

JSP 1. (Jackson structured programming) A proprietary brand of *structured programming, developed by the British consultant Michael Jackson specifically for use in *data processing. He observed that the inputs and outputs of programs could be defined in terms of particular data structures, which are mostly static and easier to define than programs. He then proposed that programs should be constructed by a systematic method based on data structure diagrams.

Two main problems arise. First, it may not be possible to combine the separate data structure diagrams involved in a program because of what are called structure clashes; this is solved by a form of program decomposition called inversion. Second, error handling is not accommodated by the simple method, and gives rise to a technique called backtracking, which is programmed by using *assertions and the notation posit/quit/admit.

JSP is used in conjunction with Cobol and PL/I. Translators exist to convert from textual equivalents of Jackson data-structure diagrams into the required target language. It is claimed that the same code will always be produced from a given data specification. 2. See JAVASERVER PAGES.

JTMP (Job Transfer and Manipulation Protocol) See RED BOOK.

jukebox Informal name for optical disk library.

jump 1. A departure from the normal sequential execution of program instructions. The departure is achieved during execution by means of a jump instruction. (Jump instruction is usually regarded as synonymous with *branch instruction.) A jump may be *conditional or *unconditional. See also GOTO STATEMENT. 2. (transfer) To undergo such a departure.

jump instruction (branch instruction) See JUMP.

junction The area of contact between two *semiconductor materials having different electric properties, or between a semiconductor and a metal. Junctions play a fundamental role in semiconductor devices. The most frequently used is the p-n junction, which is formed between n-type and p-type *semiconductors. A p-n junction has rectifying properties as a result of the potential barrier built up across the junction by the diffusion of electrons from the n-type to the p-type material.

justify 1. To achieve uniform vertical edges to pages or columns of material printed or displayed on a screen. Information can be aligned along the left or right margin or centred between the margins. In the latter case, the space between words and/or letters is increased until the line fills the distance between the margins. 2. To move the bit pattern stored in a register so that either the least or most significant bit is at the appropriate end of the register.

Just-in-time compiler See JIT COMPILER.

JVM Abbrev. for Java Virtual Machine.

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