Ivar Hjalmar Jacobson (born 1939) is a Swedish computer scientist and software engineer, known as major contributor to UML, Objectory, Rational Unified Process (RUP), aspect-oriented software development and Essence. Biography Ivar Jacobson was born in Ystad, Sweden, on September 2, 1939. He received his Master of Electrical Engineering degree at Chalmers Institute of Technology in Gothenburg in 1962. After his work at Ericsson, he formalized the language and method he had been working on in his PhD at the Royal Institute of Technology in Stockholm in 1985 on the thesis Language Constructs for Large Real Time Systems. After his master's degree, Jacobson joined Ericsson and worked in R&D on computerized switching systems AKE and AXE including PLEX. After his PhD thesis in April 1987, he started Objective Systems with Ericsson as a major customer. A majority stake of the company was acquired by Ericsson in 1991, and the company was renamed Objectory AB. Jacobson developed the software method Object-Oriented Software Engineering (OOSE) published 1992, which was a simplified version of the commercial software process Objectory (short for Object Factory). In October, 1995, Ericsson divested Objectory to Rational Software and Jacobson started working with Grady Booch and James Rumbaugh, known collectively as the Three Amigos. When IBM bought Rational in 2003, Jacobson decided to leave, after he stayed on until May 2004 as an executive technical consultant. In mid-2003 Jacobson formed Ivar Jacobson International (IJI) which operates across three continents with offices in the UK, the US, Sweden, Switzerland, China, and Singapore. Work Ericsson In 1967 at Ericsson, Jacobson proposed the use of software components in the new generation of software controlled telephone switches Ericsson was developing. In doing this he invented sequence diagrams, and developed collaboration diagrams. He also used state transition diagrams to describe the message flows between components. Jacobson saw a need for blueprints for software development. He was one of the original developers of the Specification and Design Language (SDL). In 1976, SDL became a standard in the telecoms industry. At Objectory he also invented use cases as a way to specify functional software requirements. Rational Software At Rational, Jacobson and his friends, Grady Booch and James Rumbaugh, designed the UML and his Objectory Process evolved to become the Rational Unified Process under the leadership of Philippe Kruchten. Essential Unified Process In November 2005, Jacobson announced the Essential Unified Process or “EssUP” for short. EssUP was a