Round-trip format conversion
Encyclopedia
The term round-trip is commonly used in document conversion
particularly involving markup language
s such as XML
and SGML. A successful round-trip consists of converting a document in format A (docA) to one in format B (docB) and then back again to format A (docA′). If docA and docA′ are identical then there has been no information loss and the round-trip has been successful. More generally it means converting from any data representation and back again, including from one data structure
to another.
document is saved as plain text
(*.txt). Then all the markup (structure, formatting, superscripts, …) will be lost. Compound documents will frequently lose information on images and other embedded objects. If the text file is converted back to the original format, information will necessarily be missing.
A similar effect happens with image formats. Some formats such as JPEG
achieve compression through small amount of information loss. If a lossless file
, such as a BMP or PNG file, is converted to JPEG and back again then the result will be different from the original (although it may be visually very similar).
Just because the initial and final documents are not bitwise identical does not mean there is information loss. Some formats have undefined fields, or fields where the contents have no impact on the result.
The XML document should contain identical information to the legacy format. An important condition is that the roundtrip (legacy → XML → legacy') should result in effectively identical documents. Because some document structures allow some flexibility in content order, whitespace, case-sensitivity, etc. it is useful to have a means of canonicalizing the legacy format. The full roundtrip may then be:
If canonicalLegacy = canonicalLegacy′ then the roundtrip has been successful.
Document conversion
Document conversion is the act of converting one document's format to another, which allows the document to be read in many more applications. Documents can be converted into* other source document formats* consumer formats* structured data- How it works :...
particularly involving markup language
Markup language
A markup language is a modern system for annotating a text in a way that is syntactically distinguishable from that text. The idea and terminology evolved from the "marking up" of manuscripts, i.e. the revision instructions by editors, traditionally written with a blue pencil on authors' manuscripts...
s such as XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
and SGML. A successful round-trip consists of converting a document in format A (docA) to one in format B (docB) and then back again to format A (docA′). If docA and docA′ are identical then there has been no information loss and the round-trip has been successful. More generally it means converting from any data representation and back again, including from one data structure
Data structure
In computer science, a data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently.Different kinds of data structures are suited to different kinds of applications, and some are highly specialized to specific tasks...
to another.
Information loss
When a document in one format is converted to another there is likely to be information loss. For example, suppose an HTMLHTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
document is saved as plain text
Plain text
In computing, plain text is the contents of an ordinary sequential file readable as textual material without much processing, usually opposed to formatted text....
(*.txt). Then all the markup (structure, formatting, superscripts, …) will be lost. Compound documents will frequently lose information on images and other embedded objects. If the text file is converted back to the original format, information will necessarily be missing.
A similar effect happens with image formats. Some formats such as JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
achieve compression through small amount of information loss. If a lossless file
Lossless data compression
Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. The term lossless is in contrast to lossy data compression, which only allows an approximation of the original data to be reconstructed, in exchange...
, such as a BMP or PNG file, is converted to JPEG and back again then the result will be different from the original (although it may be visually very similar).
Just because the initial and final documents are not bitwise identical does not mean there is information loss. Some formats have undefined fields, or fields where the contents have no impact on the result.
Markup languages
Markup languages such as XML can, in principle, hold any information and so the process docA → docX → docA' could be designed to avoid information loss. It is now common to convert legacy formats to XML formats because they have greater interoperability and a wider set of available tools. Thus it is possible to convert Word documents to an XML format and reimport them.The XML document should contain identical information to the legacy format. An important condition is that the roundtrip (legacy → XML → legacy') should result in effectively identical documents. Because some document structures allow some flexibility in content order, whitespace, case-sensitivity, etc. it is useful to have a means of canonicalizing the legacy format. The full roundtrip may then be:
- legacy → canonicalLegacy → XML → legacy′ → canonicalLegacy′
If canonicalLegacy = canonicalLegacy′ then the roundtrip has been successful.