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content addressable memory

(CAM, or "associative memory") A kind of storage device which includes comparison logic with each bit of storage. A data value is broadcast to all words of storage and compared with the values there. Words which match are flagged in some way. Subsequent operations can then work on flagged words, e.g. read them out one at a time or write to certain bit positions in all of them. A CAM can thus operate as a data parallel (SIMD) processor.

CAMs are often used in caches and memory management units.

Last updated: 1995-02-16

content-based information retrieval

<image, algorithm>

(CBIR, query by image content, QBIC, content-based visual information retrieval, CBVIR) A general term for methods using image analysis to try to identify objects and features in images to allow them to indexed and searched.

This contrasts with the use of image metadata such as keywords or tags associated with (and possibly stored in) the image.

[IEEE Computer, September 1995].

Last updated: 2017-12-12

content-based visual information retrieval

content-based information retrieval

Content Data Model

<standard, documentation, language>

(CDM) An SGML-based specification for interactive maintenance manuals, developed by the Air Force Human Resourceas Laboratory (AFHRL) with assistance from RJO Enterprises, Incorporated. CDM models data hierachically and data are identified by their content structure with SGML mark-up used to identify information classes such as "system information", "functions", "tasks" and "steps".

http://www.dtic.mil/dtic/tr/fulltext/u2/a205916.pdf.

["Final Report - Content Data Model of Organizational Maintenance Information for Automated Interchange of Technical Source Data.", Chicago, Illinois, Datalogics, Inc., 1998-07-07].

Last updated: 2014-10-20

content-free

<jargon>

1. (By analogy with "context-free") Used of a message that adds nothing to the recipient's knowledge. Though this adjective is sometimes applied to flamage, it more usually connotes derision for communication styles that exalt form over substance or are centred on concerns irrelevant to the subject ostensibly at hand. Perhaps most used with reference to speeches by company presidents and other professional manipulators.

contention slot

<networking>

In a communication system where only one node at a time may transmit successfully on a shared channel, the contention slot or contention period is the time a node must wait before it can be sure that no other node's transmission has collided with its transmission.

If node A starts to transmit at time t0 and then another node starts to transmit just before it recieves A's transmission at time t0 + T, then the transmissions will collide but node A will not detect the collision until time t0 + 2T. The contention slot, 2T, for nodes seperated by the maximum propagation delay thus determines how much data the node must be prepared to re-transmit in the event of a collision.

Last updated: 2014-11-06

Contents of Address part of Register

<programming>

(car) /kar/ The left-hand element of a Lisp cons cell.

Last updated: 2014-11-09

Contents of Decrement part of Register

<programming>

(cdr) /ku'dr/ or /kuh'dr/ The right-hand element of a Lisp cons cell.

Last updated: 2014-11-09

context

<grammar>

In a grammar, context refers to the symbols before and after the symbol under consideration. If the syntax of a symbol is independent of its context, the grammar is a context-free grammar.

Last updated: 2014-11-24

context clash

<grammar>

When a parser cannot tell which alternative production of a syntax applies by looking at the next input token ("lexeme"). For example, given syntax

 C -> A | b c

 A -> d | b e

If you're parsing non-terminal C and the next token is 'b', you don't know whether it's the first or second alternative of C since they both can start with b.

If a grammar can generate the same sentence in multiple different ways (with different parse tress) then it is ambiguous. An ambiguity must start with a context clash (but not all context clashes imply ambiguity). To see if a context clash is also a case of ambiguity you would need to follow the alternatives involved in each context clash to see if they can generate the same complete sequence of tokens.

Last updated: 1995-04-05

COntext Dependent Information Language

<language>

(CODIL) An early language for non-numerical business problems.

["CODIL, Part1. The Importance of Flexibility", C.F. Reynolds et al, Computer J 14(3):217-220, May 1971].

Last updated: 1994-12-23

context-free grammar

<grammar>

(CFG) A grammar where the syntax of each constituent (syntactic category or terminal symbol) is independent of the symbols occuring before and after it in a sentence. A context-free grammar describes a context-free language.

Context-free grammars can be expressed by a set of "production rules" or syntactic rules. For example, a language with symbols "a" and "b" that must occur in unequal numbers can be represented by the CFG:

 S → U | V
 U → TaU | TaT | UaT
 V → TbV | TbT | VbT
 T → aTbT | bTaT | ε

meaning the top-level category "S" consists of either a "U" or a "V" and so on. The special category "ε" represents the empty string. This grammar is context-free because each rule has a single symbol on its left-hand side.

Parsers for context-free grammars are simpler than those for context-dependent grammars because the parser need only know the current symbol.

Algol was (one of?) the first languages whose syntax was described by a context-free grammar. This became a common practice for programming languages and led to the notation for grammars called Backus-Naur Form.

Last updated: 2014-11-24

context-sensitive menu

<operating system>

A menu which appears in response to a user action (typically a mouse click) and whose contents are determined by which application window was clicked or has the input focus.

Most GUIs use a secondary mouse button (right or middle) to call up a context-sensitive menu as the primary mouse button is normally used to interact with objects which are already visible.

The context-sensitive menu often contains functions that are also available in a menu bar but the context-sensitive menu provides quick access to a subset of functions that are particularly relevant to the window area clicked on.

The RISC OS WIMP uses only context-sensitive menus (always invoked using the middle mouse button). This saves screen space and reduces mouse movement compared to a menu bar.

Last updated: 1999-09-22

context switch

<operating system>

When a multitasking operating system stops running one process and starts running another. Many operating systems implement concurrency by maintaining separate environments or "contexts" for each process. The amount of separation between processes, and the amount of information in a context, depends on the operating system but generally the OS should prevent processes interfering with each other, e.g. by modifying each other's memory.

A context switch can be as simple as changing the value of the program counter and stack pointer or it might involve resetting the MMU to make a different set of memory pages available.

In order to present the user with an impression of parallism, and to allow processes to respond quickly to external events, many systems will context switch tens or hundreds of times per second.

Last updated: 1996-12-18

Contextually Communicating Sequential Processes

<language>

(CCSP) A notation based on CSP.

["Contextually Communicating Sequential Processes - A Software Engineering Approach", M. Hull et al, Software Prac & Exp 16(9):845-864, Sept 1986].

Last updated: 1994-11-01

Nearby terms:

content addressable memory ♦ content-based information retrieval

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