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In a project network, a dependency is a link amongst a project's terminal elements. The A Guide to the Project Management Body of Knowledge (PMBOK Guide) does not define the term dependency, but refers for this term to a logical relationship, which in turn is defined as ''dependency between two activities, or between an activity and a milestone''.〔 == Standard types of dependencies == There are four standard types of dependencies: # Finish to start (FS) # * ''A'' FS ''B'' means "B can't start before A is finished", or in other words, "activity A must be completed before activity B can begin".〔 # * image:Dependency-FS.png # * ''(Foundations dug) FS (Concrete poured)'' # Finish to finish (FF) # * ''A'' FF ''B'' means "B can't finish before A is finished" or in other words "activity A must be complete before activity B can finish".〔 # * image:Dependency-FF.png # * ''(Last chapter written) FF (Entire book written)'' # Start to start (SS). # * ''A'' SS ''B'' = ''B can't start before A starts'' or in other words ''Activity B can start after Activity A has started''.〔 # * image:Dependency-SS.png # * ''(Project work started) SS (Project management activities started)'' # Start to finish (SF) # * ''A'' SF ''B'' = ''B can't finish before A starts'' # * image:Dependency-SF.png # * ''(New shift started) SF (Previous shift finished)'' Finish-to-start is considered a "natural dependency". The Practice Standard for Scheduling recommends, that "Typically , each predecessor activity would finish prior to the start of its successor activity (or activities)(known as finish-to-start (FS) relationship). Sometimes it is necessarily to overlap activities; an option may be selected to use start-to-start (SS), finish-to-finish (FF) or start-to-finish (SF) relationships....Whenever possible, the FS logical relationship should be used. If other types of relationships are used, they shall be used sparingly and with full understanding of how the relationships have been implemented in the scheduling software being used. Ideally, the sequence of all activities will be defined in such a way that the start of every activity has a logical relationship from a predecessor and the finish of every activity has a logical relationship to a successor".〔 SF is rarely used, and should generally be avoided. Microsoft recommends to use SF dependency for just-in-time scheduling.〔 It can be easily shown however, that this would only work in case resource levelling is not used, because resource levelling can delay a successor activity (an activity, which shall be finished just-in-time) in such a way, that it will finish later than the start of its logical predecessor activity, thus not fulfilling the just-in-time requirement. There are three kinds of dependencies with respect to the reason for the existence of dependency: # Causal (logical) # * ''It is impossible to edit a text before it is written'' # * ''It is illogical to pour concrete before you dig the foundations of a building'' # Resource constraints # * ''It is logically possible to paint four walls in a room simultaneously but there is only one painter'' # Discretionary (preferential) # * ''I want to paint the living room before painting the dining room, although I could do it the other way round, too'' Early critical path-derived schedules often reflected only on causal (logical) or discretionary (preferential) dependencies because the assumption was that resources would be available or could be made available. Since at least the mid-1980s, competent project managers and schedulers have recognized that schedules must be based on resource availability. The critical chain method necessitates taking into account resource constraint-derived dependencies as well. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dependency (project management)」の詳細全文を読む スポンサード リンク
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