这个按照一个规范来吧，PMBOK，你可以查到定义 ss ，sf,ff,fs https://project-management.info/pdm-precedence-diagramming-method/
Start-to-Finish Relationship (SF) This logical relationship requires that a predecessor activity must have started before the successor activity can be finished. In practice, this type of dependency does not occur very often which is also acknowledged by the PMBOK.