how does p6 define which is the driving predecessor?

By modeling resource production as activities occur instead of calendar fixed you can simulate the scheduling requirement for an activity to start after certain number of activities have started or finish or any combination of these pre-requisites.

Go to the following link to se a video of how resource leveling drive the sample job to meet your requirements, and a few others for illustration purposes.

http://www.youtube.com/watch?v=MPvMofKADnE

You shall be able to model such simple scenario within your software.

I can imagine hundreds of modeling needs for these but would like to hear the names of your activities out of curiosity.

Hi Mateo,

Driving Activity - at the Activity Detail click 'Relationship' and then on your screen click the activity you are interested to look at, this will show all the relationship of this particular activity. On the left half of your screen are the predecessors and on the right half of your screen are the successors. Now there is a column there named 'Driving' if you see a check in the box, this means it is the driving activity. 

As for your problem, P6 correctly position your activities as Start to start because that is the way you setup the links, if you do not want them to start at the same time, you can add a 'lag' and define the number of days (the difference between the  two start dates).

Best regards and Hope this helps.

Daniel

Hi Daniel thanks for the quick reply,

The thing is I do have both predecessors set as start to start but I want the activity to begin as soon as the earliest starting of the predecessors begins. For example

I am modeling the construction of three separate, independent offices, first I have to do all civil works and then I have to go into architectural details such as finishings, furbishing, etc. I haven't yet defined in what order they will be constructed or when each office civil works will end. Now, I want the architecture work to start as soon as the civil works for one of the offices is complete (keep in mind I don't know which one will be ready first) so I set the architecture work so that the civil work for all three offices are the predecessors with a Finish to Start relationship. P6 sets the latest predecessor as the driving relationship but I want the driving predecessor to be the earliest occurring.

Now I know this isn't the best example but it ilustrates my question, I want to know how P6 determines which the driving activity is, here is a screenshot of what P6 does.

As you can see it shows which the driving activity is, and it shows it in a checkbox, which I think is pretty mean because it gives you the ilusion you can change it, but you can't.

I appreciate any help

Mateo

Hi Mateo,

The problem that you have encountered if I am correct is you have 2 driving activities, both with a start to start relationship to the successor.  As soon as one of the predecessors commences then the successor will start.  At this point, your logic is broken and should be revised (i.e. the successor is no longer dependent upon both predecessors). 

The system will retain the logical link (unless you physically break it or over ride retaining logic during your reschedule - not good practice, best to revise the logic really) and will show the successor activity with a split bar as although it has commenced, it can not finish until both predecessors have started.

The simple answer is there is no way of modeling what you want without first breaking the logic.

Hope this helps.

Regards

Simon

Is very simple, perhaps I complicated it too much in an effort to demostrate more comtplicated scenarios that can be modeled using the methodology.

Take a look at the following link, a screen capture where you will see how Start of Activity 3 is synchronized to happen at the start of either Activity 1 or 2, whichever occur first.

http://www.youtube.com/watch?v=kMCLNTrHdFw

Yes it can be modeled, and is very easy, you have to think out of the box.

Just add 2 activities (one for each predecessor) and then add a summary activity. I will work.

Rafael's solution I think requires using software other than P6 (please cofirm, Rafael?).

Stefano's solution of using a summary task will get you the start date you want, but you can't give a summary task a duration, so you couldn't get the right finish date.

Simon is correct. -Best practise would be to model using a SS from both predecessors, and add a note to the architecrual activity to remind you to check the links at each update and delete the later one once you know which is which.

Gary,

You are correct I use a workaround that instead of using logic uses resource leveling and resource production based on activity timing. I do it because I see no other option. I still do not like it as I believe it prone to error and not transparent. I believe we need software developers that dare to embed such basic logic needs into the software, brave enough to break away with the limitations of traditional PDM or ancient CPM.

Something more up to the computer of today and not the Commodore 64 or the Ataris of 40 years ago. Well 40 years ago we had a local Atari manufacturing plant, good for playing PacMan.

Best regards,

Rafael

As you will see there are many possible combinations of similar requirements, a few as follows;

For a view in action go to the movie on following link:

http://www.youtube.com/watch?v=VBtl3V1p9HA

Change your successor activity type to Level of effort and its start will determined by the start of the first predecessor; later on when your start date/logic is finalized change it back to a normal task.