The term round-trip is used in document conversion particularly involving

markup language A markup language is a Encoding, text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate au ...

s such as

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...

and

SGML The Standard Generalized Markup Language (SGML; International Organization for Standardization, ISO 8879:1986) is a standard for defining generalized markup languages for documents. ISO 8879 Annex A.1 states that generalized markup is "based on t ...

. Round-tripping 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 In computer science, a data structure is a data organization and storage format that is usually chosen for Efficiency, efficient Data access, access to data. More precisely, a data structure is a collection of data values, the relationships amo ...

to another.

Common use cases

# Databases: When migrating data between different database systems or formats, round-tripping validates that data remains consistent after conversion. # File Formats: Converting documents between formats, such as from

Microsoft Word Microsoft Word is a word processor program, word processing program developed by Microsoft. It was first released on October 25, 1983, under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platf ...

OpenDocument The Open Document Format for Office Applications (ODF), also known as OpenDocument, standardized as ISO 26300, is an open file format for word processor, word processing documents, spreadsheets, Presentation program, presentations and ...

Format and back, to ensure document fidelity. Converting a document from

HTML Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...

Markdown Markdown is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber created Markdown in 2004 as an easy-to-read markup language. Markdown is widely used for blogging and instant messaging, and also used ...

and back, checking for consistency. # Serialization and Deserialization: Converting objects to a storable or transmittable format (like JSON or XML) and back into objects without losing data. In the context of

graph databases A graph database (GDB) is a database that uses graph structures for semantic queries with nodes, edges, and properties to represent and store data. A key concept of the system is the graph (or edge or relationship). The graph relates the data ...

, round-tripping can validate conversions between different graph models, such as from the

Resource Description Framework The Resource Description Framework (RDF) is a method to describe and exchange graph data. It was originally designed as a data model for metadata by the World Wide Web Consortium (W3C). It provides a variety of syntax notations and formats, of whi ...

(RDF) to Property Graphs and back, ensuring the original semantics and structure are preserved.

Information loss

When a document in one format is converted to another there is likely to be information loss. For example, suppose an

document is saved as

plain text In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects ( floating-point numbers, images, etc.). It may also include a lim ...

(*.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 ( , short for Joint Photographic Experts Group and sometimes retroactively referred to as JPEG 1) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degr ...

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.

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.

Character encodings

Unicode Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...

has a principle to have round-trip compatibility with older standardized legacy encodings, so conversion of documents to Unicode do not lose information; they can be converted back. To achieve this,

Unicode compatibility characters In Unicode and the Universal Character Set, UCS, a compatibility character is a character that is encoded solely to maintain Round-trip format conversion, round-trip convertibility with other, often older, standards. As the Unicode Glossary says: ...

have been introduced.

Limitation

An application can claim to round-trip and be dishonest. For example, it may save the original data from docA as a field in docX, so the reverse transformation to docA′ simply extracts that field. While this may be needed for some cases, the idea of a round-trip conversion is to go through another format representation or data structure and back again. Such a strategy means that small changes in a document means that it can not be converted back to the original format.

Usage

The term appears to be common, but not reported in dictionaries. A typical usage occurs on a 1999 xml-dev thread but the term is likely to have been used before this.

References

{{reflist Markup languages File conversion software