OCLを用いた記述

action Calendar::removeEvent (e: Event)

pre schedule->includes(e)

post not schedule->includes(e) and

not e.instructor.schedule@pre->includes(e)

function Calendar::calendarFor(i: Instructor): Enumeration

pre true

post result: Enumeration.new [unvisited = i.schedule]

inv start <= end

inv Event::overlaps(d: Date) = (start <= d & end >= d)

Object Constraint Language ： UMLの一部