Developing CMS software documentation system

CMSSW (CMS SoftWare) is the overall collection of software and services needed by the simulation, calibration and alignment, and reconstruction modules that process data so that physicists can perform their analyses. It is a long term project, with a large amount of source code. In large scale and complex projects is important to have as up-to-date and automated software documentation as possible. The core of the documentation should be version-based and available online with the source code. CMS uses Doxygen and Twiki as the main tools to provide automated and non-automated documentation. Both of them are heavily cross-linked to prevent duplication of information. Doxygen is used to generate functional documentation and dependency graphs from the source code. Twiki is divided into two parts: WorkBook and Software Guide. WorkBook contains tutorial-type instructions on accessing computing resources and using the software to perform analysis within the CMS collaboration and Software Guide gives further details. This note describes the design principles, the basic functionality and the technical implementations of the CMSSW documentation