Delta encoding is a way of storing or transmitting data in form of differences between sequential data rather than complete files. The differences are recorded in discrete files called "deltas" or "diffs". It is sometimes called delta compression, particularly where archival histories of changes are required (ie. SCM). Because changes are often small (only 2% total size on average), delta encoding greatly reduces data redundancy and thus collections of unique deltas are substantially more space-efficient than their non-encoded equivalents. Data is the plural of datum. ... In computing, diff is a utility that outputs the differences between two text files. ... In software configuration management (SCM), a delta is a type of file in which the difference (or diff) between two successive versions, is recorded. ... SCM is an acronym for Software Configuration Management, and relates to configuration management (CM). ...

Perhaps the simplest example is storing values of bytes as differences (deltas) between sequential values, rather than the values themselves. So, instead of 2, 4, 6, 9, 7, we would store 2, 2, 2, 3, -2. This is not very useful when used alone, but it can help further compression of data in which sequential values occur often. IFF 8SVX sound format applies this encoding to raw sound data before applying compression to it. Unfortunately, not even all 8-bit sound samples compress better when delta encoded, and the usability of delta encoding is even smaller for 16-bit and better samples. Therefore, compression algorithms often choose to delta encode only when the compression is better than without. However, in video compression delta frames can considerably reduce frame size, and are used in virtually every video compression codec. Interchange File Format (IFF), is a generic file format originally introduced by the Electronic Arts company in 1985 in order to ease transfer of data between software products produced by different companies. ... 8SVX is a subformat of the Interchange File Format. ... In music, sampling is the act of taking a portion of one sound recording and reusing it as an instrument or element of a new recording. ...

A delta can be defined in 2 ways,symmetric delta and directed delta. A symmetric delta can be expressed as , where v₁ and v₂ represent two successive versions.

A directed delta, also called a change, is a sequence of (elementary) change operations which, when applied to one version v₁, yields another version v₂ (note the correspondence to transaction logs in databases).

A variation of delta encoding which encodes differences between the prefixes or suffixes of strings is called incremental encoding. It is particularly effective for sorted lists with small differences between strings, such as a list of words from a dictionary. Look up prefix in Wiktionary, the free dictionary. ... Suffix has meanings in linguistics, nomenclature and computer science. ... Generally, string is a thin piece of fiber which is used to tie, bind, or hang other objects. ... Incremental encoding, also known as front compression or back compression, is a type of delta encoding compression algorithm whereby common prefixes or suffixes and their lengths are recorded so that they need not be duplicated. ... Look up word in Wiktionary, the free dictionary Word may mean: Word (linguistics), a unit of language that symbolizes or communicates a meaning Microsoft Word, a word processor Word (computer science), a small group of bits Word may also be: In hip hop slang, an exclamation indicating deep and complete... ...

In delta encoded transmission over a network where only a single copy of the file is available at each end of the communication channel special error control codes are used to detect which parts of the file has changed since its previous version. In computer science and information theory, error correction consists of using methods to detect and/or correct errors in the transmission or storage of data by the use of some amount of redundant data and (in the case of transmission) the selective retransmission of incorrect segments of the data. ...

The nature of the data to be encoded influences the effectiveness of a particular compression algorithm. Delta encoding performs best when data has small or constant variation; for an unsorted data set, there may be little to no compression possible with this method.

The following C code performs a simple form of delta encoding and decoding: The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a standardized imperative computer programming language developed in the early 1970s by Ken Thompson and Dennis Ritchie for use on the...

 void delta_encode(char *buffer, int length) { char t = 0; char original; int i; for(i = 0; i < length; i++) { original = buffer[i]; buffer[i] -= t; t = original; } } void delta_decode(char *buffer, int length) { char t = 0; int i; for(i = 0; i < length; i++) { buffer[i] += t; t = buffer[i]; } } 

Another instance of use of delta encoding is RFC 3229, "Delta encoding in HTTP," which proposes that HTTP servers should be able to send updated Web pages in the form of differences between versions (deltas), which should decrease Internet traffic, as most pages change slowly over time, rather than being completely rewritten repeatedly: HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...

This document describes how delta encoding can be supported as a compatible extension to HTTP/1.1.

Many HTTP (Hypertext Transport Protocol) requests cause the retrieval of slightly modified instances of resources for which the client already has a cache entry. Research has shown that such modifying updates are frequent, and that the modifications are typically much smaller than the actual entity. In such cases, HTTP would make more efficient use of network bandwidth if it could transfer a minimal description of the changes, rather than the entire new instance of the resource. This is called "delta encoding."

See also

• algorithm
• data compression
• data structure
• delta modulation
• encoding
• list of Amiths

• list of delta encoding software

Flowcharts are often used to represent algorithms. ... In computer science, data compression or source coding is the process of encoding information using fewer bits (or other information-bearing units) than a more obvious representation would use, through use of specific encoding schemes. ... A binary tree, a simple type of branching linked data structure. ... Delta modulation (DM): Analog-to-digital signal conversion in which (a) the analog signal is approximated with a series of segments, (b) each segment of the approximated signal is compared to the original analog wave to determine the increase or decrease in relative amplitude, (c) the decision process for establishing... The word encoding has a number of meanings. ... The following is a list of delta encoding software. ...

External links

• RFC 3229 - Delta Encoding in HTTP
• RFC 3284 - The VCDIFF Generic Differencing and Compression Data Format