Stephen Mellor and Sally Shlaer established the Shlaer-Mellor Method of object-oriented analysis and recursive design in the late 80s and early 90s. The Method was considered the most precise and semantically complete of the software design methodologies of the era. The primary tenets of model execution and translation have gradually been adopted or co-opted in other methodologies through the years. xtUML remains the purest form of Shlaer-Mellor still in popular use.
A session at xtUML 2015 will honor Stephen and Sally and briefly cover the 25 years or so of Shlaer-Mellor and xtUML.