Task Start Dates

[Diane]

How do I create a start date that is 2 weeks prior to another task?

 

[Rick Roszko]

By 2 weeks you mean 10 business days I assume?

Let's say you have task 100 and task 101

In predecessors for the second task (101), put in 100SS-10d
which means task 100 will start 10 days befor task 100 starts

 

[Trevor Rabey]

I hate to split hairs, but I think that's not quite what it means, without
qualification, and the exact meaning can be important.
It means, that:
if we are scheduling forwards iaw with good Critical Path Method (you would
have to like pain to do anything else)
and if there are no date constraints to consider on either Task (Task
Properties, Constraint Type and Date)
and if both Tasks use the same Calendar and there are no other Calendar
considerations (eg Resource Calendars, Working Time)
and bearing in mind that we are talking about working days rather than edays
and if there is no progress recorded in Actuals along with Tasks having been
re-scheduled and perhaps split, depending on calculation options,
and if there are no other Predecessor Links with other Tasks
and if there is no Resource Leveling involved

... and we may as well throw in Task Type and effort driven as a
consideration except that it would seem to be the only thing that doesn't
have to be kept in mind here because it can only affect duration which also
doesn't come into this case.

Then Task 101 will be scheduled to start as soon as possible (Day 1), but NO
SOONER than 10 days before Task 100 starts, because, according to what you
have put into your model, it can't (due to something immutable like the law
of gravity). So it means don't expect to be able to do it sooner than this
(and if it is on the critical path make sure you do it no later).

When you actually come to do it the condition may not be so strict after all
and you can do it sooner, and choose to or not, or other events not modeled
may prevent it from happening that soon anyway.

However, after all this arduous thinking, unless start of Task 100 is a
fixed Date (like the opening ceremony of the olympic games or a solar
eclipse) in which case Task 101 is also a fixed Date, we have a situation
where the "trigger" event for Task 101 is in its own future. Since you can
never know for sure when you are at 10 days sooner than the start of Task
100 until after it has happened, Task 101 can never be started. The software
let's you plan it even though it can't be executed. Suggest sticking with FS
Links and positive lag.

 

[Jan De Messemaeker]

Hi Trevor and all,

I LOVE this explanation as much as I DISLIKE negative lag.

 

[davegb]

I hate to split hairs, but I think that's not quite what it means, without
qualification, and the exact meaning can be important.
It means, that:
if we are scheduling forwards iaw with good Critical Path Method (you would
have to like pain to do anything else)
and if there are no date constraints to consider on either Task (Task
Properties, Constraint Type and Date)
and if both Tasks use the same Calendar and there are no other Calendar
considerations (eg Resource Calendars, Working Time)
and bearing in mind that we are talking about working days rather than edays
and if there is no progress recorded in Actuals along with Tasks having been
re-scheduled and perhaps split, depending on calculation options,
and if there are no other Predecessor Links with other Tasks
and if there is no Resource Leveling involved

.. and we may as well throw in Task Type and effort driven as a
consideration except that it would seem to be the only thing that doesn't
have to be kept in mind here because it can only affect duration which also
doesn't come into this case.

Then Task 101 will be scheduled to start as soon as possible (Day 1), but NO
SOONER than 10 days before Task 100 starts, because, according to what you
have put into your model, it can't (due to something immutable like the law
of gravity). So it means don't expect to be able to do it sooner than this
(and if it is on the critical path make sure you do it no later).

When you actually come to do it the condition may not be so strict after all
and you can do it sooner, and choose to or not, or other events not modeled
may prevent it from happening that soon anyway.

However, after all this arduous thinking, unless start of Task 100 is a
fixed Date (like the opening ceremony of the olympic games or a solar
eclipse) in which case Task 101 is also a fixed Date, we have a situation
where the "trigger" event for Task 101 is in its own future. Since you can
never know for sure when you are at 10 days sooner than the start of Task
100 until after it has happened, Task 101 can never be started. The software
let's you plan it even though it can't be executed. Suggest sticking with FS
Links and positive lag.

Thanks, Trevor, for giving the most confusing answer to a relatively
simple question I've ever seen posted on this NG!

 

[Trevor Rabey]

My pleasure.
However, I don't think it is confusing, just complete.

 

[davegb]

My pleasure.
However, I don't think it is confusing, just complete.

Funny about that. When I write something, I seldom find it confusing,
or I wouldn't have written it that way! My experience is, that if
someone experienced finds my explanations confusing, I've left a
beginner way behind me.

 

[Steve House [Project MVP]]

FWIW, I don't think it was all that confusing. If we say task X's start is
determined by some sequence of preceeding events and task Y must be timed
based on Task X so that it starts 10 days before the date X actually starts,
that presumes we can KNOW with certainty what task X's actual start date
will be. But since everything in a project schedule is only an educated
guess until we actually do it, we can never know with certainty when we are
at the "10 days before X will start" point in time unless we hire a very
reliable psychic. With the possible exceptions of Nostradamus and Casandra,
reliable psychics have been notoriously absent from the scene for most of
recorded history and finding one to add to our project team would be hard to
do on short notice. Thus since we cannot know with any degree of certainty
when task X will start, we should not base our decisions on when to schedule
Task Y on the mere hope that X will actually start on some particular date.

I view links as being permissive controls mandated by the process logic. A
task may not be started (or declared to be ended) until something grants it
permission to do so. The SS link says the act of X's starting grants
permission for task Y to start. But while they may be anticipated, a
permission can't actually be granted before the granting event occurs. Even
the conventional FS links work that way and in a project plan where X and Y
are linked FS, the start of Y should be always interpreted as "task Y will
be released to start on this date IF task X ends on that date." But you
can't know for certain what date that will be until X has ended.

Basic epistimology <grin>.

 

[davegb]

FWIW, I don't think it was all that confusing. If we say task X's start is
determined by some sequence of preceeding events and task Y must be timed
based on Task X so that it starts 10 days before the date X actually starts,
that presumes we can KNOW with certainty what task X's actual start date
will be. But since everything in a project schedule is only an educated
guess until we actually do it, we can never know with certainty when we are
at the "10 days before X will start" point in time unless we hire a very
reliable psychic. With the possible exceptions of Nostradamus and Casandra,
reliable psychics have been notoriously absent from the scene for most of
recorded history and finding one to add to our project team would be hard to
do on short notice. Thus since we cannot know with any degree of certainty
when task X will start, we should not base our decisions on when to schedule
Task Y on the mere hope that X will actually start on some particular date.

I view links as being permissive controls mandated by the process logic. A
task may not be started (or declared to be ended) until something grants it
permission to do so. The SS link says the act of X's starting grants
permission for task Y to start. But while they may be anticipated, a
permission can't actually be granted before the granting event occurs. Even
the conventional FS links work that way and in a project plan where X and Y
are linked FS, the start of Y should be always interpreted as "task Y will
be released to start on this date IF task X ends on that date." But you
can't know for certain what date that will be until X has ended.

Basic epistimology <grin>.

I don't recall saying I didn't understand what he said, only that I
felt it was consfusing. To be even more honest, I thought it was more
of a "look how smart I am, I know all these things" post than a real
effort to help the OP with a problem. It was like if a 10 yr old asked
me how an internal combustion engine works and I gave him a one hour
explanation starting with the Carnot cycle and finishing with an
explanation of how electronic fuel injection works.
Any of the regular contributors here know that there are probably a
minimun of 50 variations to any change you make in Project. But listing
all 50 to a less experienced user only confuses, in my opinion. Others,
of course, can reply in as much detail as they think neccessary.

 

[Trevor Rabey]

Protest!

C'mon Dave, you read too much into my motives ("look at me, Im a smarty
pants").
I saw the simple answer and just thought it needed some qualifications.
When I started the reply, I only meant to make a couple of points but the
list got longer as I wrote it.
It is interesting how much that little link really says and what it really
means.
CPM/MSP is like that.
Sure, I know a few things about CPM and MSP, all learned the hard way, but
it still surprises me every day and is never boring.
Also, it bites if I drop my guard.
50 is an exageration.
We've heard nothing back from Diane. Maybe she did find it helpful.

 

[John Sitka]

So what did help the original poster?
Filling her schedule with logic that only applies or makes sense with fixed date constraints.
Way to go newsgroup. As a reward everybody is invited to my cottage for a snipe hunt,
davegb gets first baggings. Rick can recite him snipe hunters manual.

 

[davegb]

Protest!

C'mon Dave, you read too much into my motives ("look at me, Im a smarty
pants").
I saw the simple answer and just thought it needed some qualifications.
When I started the reply, I only meant to make a couple of points but the
list got longer as I wrote it.
It is interesting how much that little link really says and what it really
means.
CPM/MSP is like that.
Sure, I know a few things about CPM and MSP, all learned the hard way, but
it still surprises me every day and is never boring.
Also, it bites if I drop my guard.
50 is an exageration.
We've heard nothing back from Diane. Maybe she did find it helpful.

I don't know your motives, Trevor, it was just a comment on the
helpfullness of that kind of reply. I've thought about giving one like
that many times, may have even done so many years ago. But now I try to
keep it as simple as I can, knowing that most posters here don't begin
to understand the intricasies of Project (excepting most of the
regulars). I was trying to point out that I don't think going into all
that detail is constructive in helping someone new to solve a problem.
Just my NSHO (not so humble opinion).
If I gave offense, I apologize.
I hope she found someone's response helpful. Hard to tell when they
don't reply at all, but I understand why she might not after the
replies we gave her.

 

[davegb]

So what did help the original poster?
Filling her schedule with logic that only applies or makes sense with fixed date constraints.
Way to go newsgroup. As a reward everybody is invited to my cottage for a snipe hunt,
davegb gets first baggings. Rick can recite him snipe hunters manual.

And your contribution accomplishes what in helping the OP?