Reverse domain name notation
This article relies largely or entirely on a single source. (May 2011)
Reverse domain name notation (or reverse-DNS) is a naming convention for the components, packages, and types used by a programming language, system or framework. A characteristic of reverse-DNS strings is that they are based on registered domain names, and are only reversed for sorting purposes. For example, if a company making a product called "MyProduct" has the registered domain name "example.com", they could use the reverse-DNS string "com.example.MyProduct" to describe it. Reverse-DNS names are a simple way of reducing name-space collisions, since any domain name is registered by only one party at a time.
Most of the world follows the Internet standard and writes email addresses starting with the name of the computer and ending up with the name of the country. In the U.K. the Joint Academic Networking Team (JANET) had decided to do it the other way round before the Internet domain standard was established. Most gateway sites have ad-hockery in their mailers to handle this, but can still be confused. In particular, the address email@example.com could be interpreted in JANET's big-endian way as one in the U.K. (domain uk) or in the standard little-endian way as one in American Samoa (domain as) on the opposite side of the world.
Examples of systems that use reverse-DNS are Sun Microsystems' Java platform and Apple's Uniform Type Identifier or UTI. The Android operating system also makes use of the notation for classifying applications, as the Dalvik virtual machine made use of Java.
Example of reverse-DNS strings are:
- com.adobe.postscript-font (UTI string for Adobe Systems's PostScript fonts)
- com.apple.ostype (UTI string for Apple's OSType)
- org.omg.CORBA (Java library for CORBA)
- org.w3c.dom (Java library for W3C's DOM)
- ar.com.mydomain (for International domains)
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- Jargon File: Big-endian
- "Apple Developer Connection: Introduction to Uniform Type Identifiers Overview". 2005-11-09. Retrieved 2013-04-04.