Abstract: In this paper,aiming at some classical conceptions in "overall planning" network,such as total float,node float,free float,safety float,interference float,the earliest start time and the latest finish time,limitations of these conceptions are analyzed and extended from single time area to length area,and from conceptions of floats which don't consider direction to ones which consider direction,et al.In addition,some applications of above classical conceptions are presented briefly,for instance,the properties which are reflected when those conceptions are extended,the simple method of simlifying time-cost tradeoff network equivalently,and the simple function of calculating result of scheduling.

Key words: overall planning , network planning , float