Reverse domain name notation
Reverse domain name notation (or reverse-DNS) is a naming convention for components, packages, types or file names used by a programming language, system or framework. Reverse-DNS strings are based on registered domain names, with the order of the components reversed for grouping purposes. For example, if a company making the product "MyProduct" has the domain name
example.com, they could use the reverse-DNS string
com.example.MyProduct as an identifier for that product. Reverse-DNS names are a simple way of eliminating namespace collisions, since any domain name is globally unique to its registered owner.
The first appearance of reversed DNS strings predated the Internet domain name standards. The UK Joint Academic Networking Team (JANET) used this order in its Name Registration Scheme, before the Internet domain name standard was established. For example, the name
uk.ac.bris.pys.as was interpreted as a host named
as within the UK (top level domain
.uk), while the Internet standard would have interpreted it as a host named
uk within the American Samoa top level domain (
.as). During the period while both JANET-style and Internet-style addresses were in use, mailers and gateway sites had ad-hoc workarounds to handle the differences, but could still be confused.
Examples of systems that use reverse-DNS notation are:
- Sun Microsystems' Java platform for class names
- Apple's Uniform Type Identifier (UTI)
- The Android operating system, for classifying applications (because the Dalvik virtual machine was based on Java)
- dconf, the configuration backend used by GNOME
- The freedesktop.org Desktop Entry Specification
Some examples of reverse-DNS strings are:
java.io.File, a Java class name
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
org.kde.dolphin.desktop, a desktop file name
- "Apple Developer Connection: Introduction to Uniform Type Identifiers Overview". 2005-11-09. Retrieved 2013-04-04.
- "Desktop Entry Specification". freedesktop.org. Retrieved 15 November 2020.