Task needs to be driven by earliest of 4 independent tasks

[Gene]

Task A must be completed before Tasks 1, 2, 3, or 4 can begin. Tasks 1-4 all
have different start dates and are independent of each other. How can I set
up a relationship so that Task A will be scheduled to start and finish before
the first of Tasks 1-4 begins? I tried a SS with a lag time that worked for
a single task but when I added the other tasks, Task A was driven by the task
that started last. Thanks for any help!

 

[Mike Glen]

Hi Gene,

Welcome to this Microsoft Project newsgroup

Don't enter any dates. Link the 4 tasks to Task A with a Finish-to-Start
(FS) relationship.

You might like to have a look at my series on Microsoft Project in the
TechTrax ezine, particularly #1 giving a link to Network Analysis, at this
site: http://tinyurl.com/2xbhc or this:
http://pubs.logicalexpressions.com/Pub0009/LPMFrame.asp?CMD=ArticleSearch&AUTH=23
(Perhaps you'd care to rate the article before leaving the site,
Thanks.)

FAQs, companion products and other useful Project information can be seen at
this web address: <http://www.mvps.org/project/>

Hope this helps - please let us know how you get on

Mike Glen
MS Project MVP

 

[Steve House]

Well, there are a couple of problems here. First, one way to think of what
links do is to use the words "controlling" and "controlled" instead of
predecessor and successor. The schedule of the predecessor task controls
the schedule of the successor task. But it's not quite that simple - it's a
permissive control rather than an obligatory one. The predecessor says when
the successor CAN start but it doesn't mean that is when it WILL start
because there are other things that control the schedule as well. Say the
predecessor says the task in question can start on Tuesday but it so happens
that the only person qualified to do that particular thing has booked the
day as a day off - so it can't start on Tuesday after all but will have to
wait till Wednesday when the resource will be back in to work. Now an
additional problem with your schedule is it requires a good bit of
clairvoyance, something in rather short supply. You've said that Task A
must start so that it will finish 7 days before the earliest of tasks 1, 2,
3, or 4 starts. Well and good. But that assumes can can know with some
certainty when those 4 tasks will start and in fact there's never going to
be a way for you to know that. You might THINK that Task 1 will start on
Feb 1st but you won't know that as a fact until it really happens. Let's
say Task A is expected to take 3 days to complete. So you assume Task 1
will start the 1st, make it the predecessor, make Task A the successor and
link them Start-Finish, where the start of the predecessor controls the
Finish of the successor. Since you want Task A to finish 7 days before Task
1 starts, you also enter a -7day lead time in the link. That puts Task 1
starting 01 Feb, Task A finishing 23 Jan, and starting 18 Jan. But what
happens if you do Task A on those dates and then about the 25th something
happens to force a delay in the start of Task 1? It could happen - the
resource calls in sick at the last minute, all sorts of things. So your
mandatory gap of 7 days between the finish of Task A is now going to be
violated. Since Task 1 is now starting later than 01 Feb, we really need a
time machine to go back and 'undo' Task A and start it over again on a date
later than 18 Jan so that it will now finish 7 days before the NEW start of
Task 1. Obviously we can't do that.

 

[Mike Glen]

You're welcome, Gene But beware! ALAP constraints are very severe in
that you've lost all flexibility and any delay on ony one of those 4 tasks
will delay their successors. If they're on the critical path, then such
delay will delay the whole project. It might also affect the result of
levelling when Project tries to move tasks with overallocated resources with
such constraints. Make sure you analyse the result to see if it is what you
want before committing your project to begin.

Mike Glen
Project MVP



Mike Glen
MS Project MVP
See http://tinyurl.com/2xbhc for Project Tutorials