iCalendar was first created in 1998 by the Calendaring and Scheduling Working Group of the Internet Engineering Task Force, chaired by Anik Ganguly of Open Text Corporation, and was authored by Frank Dawson of Lotus Development Corporation and Derik Stenerson of Microsoft Corporation. iCalendar is heavily based on the earlier vCalendar by the Internet Mail Consortium (IMC). iCalendar data files are plain text files with the extension codice_1 or codice_3 (for files containing availability information only). RFC 5545 replaced RFC 2445 in September 2009 and now defines the standard.