Trust me if you understand this you can master planning not just the Primavera software and I am sure most of us will do. I have just simplified it a bit more.
With the advent of sophisticated softwares, tools , techniques and methodologies, Project Management and computer aided planning is often seen as a complicated discipline, you need to spend time, money, lot of effort, may be pass few exams just in order to show that you too understand this and now can do this.
A lot of it would not be required if the industries don’t look for academic certifications but focus on skills and practical education needed to help production and drive the economy. We can learn this from developing economies where less people go for certifications and more focus on things which help them gain skills to make a living first, the rest can then follow.
Relationship(s) is the backbone of planning.
If we understand how it works between two activities , we can understand how it works between blocks of activities from where the concept of Critical Path Method or PERT and other techniques follow. The word ‘Critical’ is so panicking by definition from dictionary that Project Managers start looking at it like patient fighting for life in hospital rather than finding the cause why did the patient land in hospital first.
I am passing the definition of activity as it needs no explanation, a chunk of work the duration of which can be recognised by human beings and of course by the software tools. It has a Start and a Finish. Those which only have Start with no duration are called Start milestones and those which have only Finish are called Finish milestones. There is a term called ‘lag’ which is the wait period between two activities for the successor to start after predecessor.
There are four types of relationships universally recognised.
There are two more which do exist but are a bit philosophical but practical and I will discuss about them at the end of this post.
A very simple example of this is – the Project is awarded (Activity ‘A’) and the Hiring process starts (Activity ‘B’) so Activity B has a Start to Start (SS) relationship with Activity A. However if the hiring process will start after few days say 20 then Activity B still has the SS relationship with Activity A but with a ‘lag’ of 20 days.
The product is manufactured (Activity ‘A’) and then the Delivery process ( Activity ‘B’) starts. So, the delivery of the product has a Finish to Start (FS) relationship with the manufacturing of the product. However if there is a wait period of say 3 weeks to allow for packing and arranging the delivery then Activity B still has a FS relationship with Activity A with a lag of 3 weeks.
Even experienced planners struggle to understand and explain this type of relationship. I have tried to simplify it with this example. Employee B working in a company has resigned. Management negotiates with him about the handing over process and the notice period and it is decided that as soon as a new employee comes on board and takes over from him, he would be released from the company. Employee A comes on board (starts) and Employee B leaves, so here the employment of Employee A has a Start to Finish (SF) relationship with Employee B because B cannot finish until there is A to take over from him. However if the handing over process will take 1 week to complete then A has a SF relationship with B with a lag of 1 week.
Finish to Finish (FF)
You turn off the electricity (Activity ‘A’) and the light goes off in the room (Activity ‘B’). So, the Provision of Light in the room has a Finish to Finish (FF) relationship with the Provision of Electricity (Activity ‘A’). However if there is battery support for the light for say 1 hour then the Provision of Electricity has a FF relationship with the Provision of Light with a lag of 1 hour.
A note about Lag
Lag can be of three types zero, positive and negative. ‘Zero’ lag simply means activities are directly linked with no wait period. Positive lag is formal wait period before next activity can happen however Negative lag means the succeeding activity can happen before the preceding activity finishes by certain amount of time which is the duration of lag.
All the four types of relationships have been shown here in Primavera P6 with no lag, however if you zoom in the picture, you can understand from the relationship lines how the relationship works.
Two other types of relationships
(1) Never start Never Finish (NN)
Government Administration and Legal relationships always exist whether you recognise them in your program or not and quite often substantially affect projects specially construction projects. Generally we try to show it as ‘Level of Effort’ activities in the program for certain time period but the fact is it is always there and will be there if there is project or not. Another example would be environment.
(2) Quick Start Quick Finish (QQ)
Natural disasters e.g. earthquake or Tsunami (Force Majeure) are often related to majority of stakeholders and it needs no explanation that they do affect the project. Unfortunately, such relationships are recognised only after they have happened and mostly during the claim process or Forensic analysis/Post Project Analysis.
I have given only some of the examples here for the practical understanding of the readers, there are many out there starting from our daily life to conjugal life and death, relationships are everywhere.