TOPIC: Finish to Start Definition:Crashing or Fast Track

I understand that a Finish-Start (FS) relationship: Activity must finish before successor can start and this is the most common.

Also on the diagrams in samples or the prep cast, the assumption is that they are all FS relationship.

If there is a question like:
A schedule activity (Y) may begin X days before the predecessor (Z) activity finishes. If we are asked what type of logical relationship this is. How would we answer this?

I assume this is saying, Y can start before X days Z is complete.

Or is my interpretation of the definition not correct. We can have leads relatonships in a FS, so the predecessor activity does not have be finished before the successor can start, like when we crash?

Help me understand or what I am not getting correct in understanding FS and if the predessor activity needs to be complete before the successor can start, since I doesn't seem that would be the case in crashing or the above question.

Thanks again.

Dear Edward:
“A schedule activity (Y) may begin X days before the predecessor (Z) activity finishes”

You are right; this is a finish-to-start dependency with X days of lead. Read the key words here “begins when other finishes”.

However, this is neither fast-tracking nor crashing. This is just a dependency with a lead.

If you have a project that has two sequential activities in a strict FS relationship and you are running short of the project deadline. If you handle the deadline by giving the successor activity a head start of X days, you would change the FS dependency to FS – X days. In that case, this is an example of fast-tracking.

Hope this helps resolve your doubt.

Regards,

Khurram

Thanks. I understand what a lead is.
I guess, I am getting confused why the FS definition would be
"Activity must finish before successor can start and this is the most common."

Means "Z" must finish before "Y" can start?

But it seems that the FS definition does not take into account leads? I am confused, since I understand the concept but the definition is does not seem aligned.

Help!!

See the attached graphic for clarification. Here I have created four tasks 1,2,4 and 5 in a scheduling tool.

Task 1 has a FS relationship with Task 2

Task 4 has a FS – 3 days relationship with Task 5

As you can see, both of the relationships are FS. However the later has a lead of 3 days (i.e., - 3 days).

Your definition, "Activity must finish before successor can start", holds for a strict FS relationship. A FS relationship with a lead in the successor is not a strict FS relationship; it’s an adjustment of the FS relationship.

Does this help?

Regards,

Khurram

Here is the graphic:

Khurram:
Thank you for your help. I was curious how you systematically process this question, to get to the answer. Can you run me through your systematic thought process in your mind, if that makes sense.

“A schedule activity (Y) may begin X days before the predecessor (Z) activity finishes. If we are asked what type of logical relationship this is. How would we answer this?”

Here Y is depending on Z. Y can start when Z has finished. This means that the dependency is Finish to Start. However the question also say that Y can start X days before Z finishes, this means that a lead of X days has been assigned to Y so that for X days both Y and Z are being run in parallel. Since Y is dependent on the finish of Z minus X days, this is Finish to Start minus X days (X days of lead).

Let me change the question. “A schedule activity Y may being X days AFTER the start of predecessor Z. What type of logical relationship is this?”

Now Y can start when Z has already been started for X days. This means Y can start with the start of Z plus X days. This would be a start to start relationship with X days of lag on Y.

Does this help?

Khurram

Awesome.

Thank you very much for showing me how you logically process the question AND the similar question (SS) was VERY helpful!

When you show me your logical process it helps me see what are the key words or part of the question that I am missing or not interpeting correctly. Thanks again.