Regarding predessors & Sucessors

The problem with using too many SS linkes as successors is that any delay to the firsty activity, will not lead to a delay in the second activity, and so on throughout the whole network.

FS links are the ideal relationships as they will have a consequential affect upon subsequent activities due to delays, or duration elongations earlier in the network. However, SS & FF links are equally valid if there is a degree of parallelism between activities.

As SS successors are effectively open-ends, it's good practice to also include a corresponding FF successor for every SS successor.

As per GAO most of the relationships in  a detailed schedule should be  Finsh to Start. Generally  more than 90% activites with FS relationship without any lag is preferable. Other relationships SS and FF also can be used for paralel works without any dangling logic ( Open ends ). 

not only does the GSA use a 90% threshold but the DCMA 14 point schedule asessemtn also states that 90% of the activity relationship types should be of the FS type. That means that there can be 10% of the SS or FF relationship.

Techanically using only a ss will flag the activity has not having a successor. What you can do is create a compound or combination relationship. On the activities where you know only have a SS successor and add successor of the same activity id but with a FF relationship. The SS successor will tie down the start of the activity while the FF successor will tie donw the end of the activity.

not only does the GSA use a 90% threshold but the DCMA 14 point schedule asessemtn also states that 90% of the activity relationship types should be of the FS type. That means that there can be 10% of the SS or FF relationship.

Techanically using only a ss will flag the activity has not having a successor. What you can do is create a compound or combination relationship. On the activities where you know only have a SS successor and add successor of the same activity id but with a FF relationship. The SS successor will tie down the start of the activity while the FF successor will tie donw the end of the activity.

Thanks all of you