expression

n 1: the expression on a person's face; "a sad expression"; "a

look of triumph"; "an angry face" [syn: {look}, {aspect},

{facial expression}, {face}]

2: expression without words; "tears are an expression of

grief"; "the pulse is a reflection of the heart's

condition" [syn: {manifestation}, {reflection}, {reflexion}]

3: the communication (in speech or writing) of your beliefs or

opinions; "expressions of good will"; "he helped me find

expression for my ideas"

4: a word or phrase that particular people use in particular

situations; "pardon the expression" [syn: {saying}, {locution}]

5: the style of expressing yourself; "he suggested a better

formulation"; "his manner of expression showed how much he

cared" [syn: {formulation}]

6: a group of symbols that make a mathematical statement [syn:

{formula}]

7: a group of words that form a constituent of a sentence and

are considered as a single unit; "I concluded from his

awkward constructions that he was a foreigner" [syn: {construction}]

compression

1. (Or "compaction") The coding of data to save

storage space or transmission time. Although data is already

coded in digital form for computer processing, it can often be

coded more efficiently (using fewer bits). For example,

{run-length encoding} replaces strings of repeated characters

(or other units of data) with a single character and a count.

There are many compression {algorithms} and utilities.

Compressed data must be decompressed before it can be used.

The standard {Unix} compression utilty is called {compress}

though {GNU}'s {gzip} is better. Other compression utilties

include {pack}, {zip} and {PKZIP}.

When compressing several similar files, it is usually better

to join the files together into an {archive} of some kind

(using {tar} for example) and then compress them, rather than

to join together individually compressed files. This is

because some common compression {algorithm}s build up tables

based on the data from their current input which they have

already compressed. They then use this table to compress

subsequent data more efficiently.

See also {TIFF}, {JPEG}, {MPEG}, {Lempel-Ziv Welch}.

There is a compression {FAQ} at

{(ftp://rtfm.mit.edu/pub/usenet/news.answers/compression-faq/)}.

{Usenet} newsgroups: {news:comp.compression},

{news:comp.compression.research}.

2. Reducing the dynamic range of an audio signal,

making quiet sounds louder and loud sounds quieter. Thus,

when discussing digital audio, the preferred term for reducing

the total amount of data is "compaction". Some advocate this

term in all contexts.

(1999-10-22)