This book constitutes the refereed proceedings of the 4th InternationalConference on Software and Data Technologies, ICSOFT 2009, held inSofia, Bulgaria, in July 2009. The 19 revised full papers presented together with two invited paperswere carefully reviewed and selected as best papers from 212submissions. The papers are organized in topical sections on enterprisesoftware technology; software engineering; distributed systems; datamanagement; knowledge-based systems.