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CASE-STUDY: PERT TASK DEPENDENCY

Updated on November 2, 2011

A project is set of activities geared towards a specific purpose. These activities can be explained by a graph or a flow chart. For a graphic presentation, there are mainly two formats: Arrows and Boxes. The later is known as AON (Activity-On-Node) which contain many additional features like Floats and Task-Dependency.

Floats have already been covered in a previous hub. Here I would explain Task-Dependency.

 

WHAT IS A TASK DEPENDENCY

Task Dependency is a linkage of a particular task with others called Predecessors. It is a logical relationship. An activity can start only after a certain activity is completed. Two activities may start together or finish together. End of an activity may depend on the start of another activity. If you are good in counting, you might have already noticed that there are four types of linkages between any two activities. This is summarized below:

  • · Finish-to-Start
  • · Start to Start
  • · Finish to Finish
  • · Start-to-Finish

FINISH-to-START (FS)

Building rooms is dependent on acquiring land. Construction cannot begin before land transfer is complete. This is a default dependency. If there are two tasks, “Dig Foundation” and “Pour Concrete”, there is no way of pouring concrete unless excavation work is finished.

START-to-START (SS)

The dependent task can only begin after the one, it depends upon, starts. For SS relationship, the two activities must be linked but one of them started earlier and the other to follow. In other words, these activities must start one after another with a small time-lag. The purpose would not be served if one starts and the other doesn’t pickup or starts with a long time lag.

Supposing there are two tasks: (i) plastering and (ii) painting of thirty rooms. Now it is not necessary to first plaster each and every room and then start painting them. It would much better to ascertain, how long it takes the plaster to dry up. If it takes only one day, the painting can commence next day side by side. Please note that the two activities are linked. If only plastering is done and left for long, it would again require scraping, sanding and filling before a paint can be applied.

FINISH-to-FINISH (FF)

A task cannot be completed until another task is complete. Here again, time lag must not be large else it would look like FS relationship.

Supposing, we have an assignment to recruit as many as drivers we can find. At the same time, we must match an equal number of conductors. Two teams may start interviews but team concerned with drivers must finish its job before other team can complete its job. Obviously, first team would announce the number of drivers they have found suitable for the job. Same number of conductors can now be hired.

START-to-FINISH (SF)

A dependent task cannot be completed unless another task it depends upon has started.

Once again, this implies ‘freshness’. We cannot mix paint and leave it to rot. We wait a signal from the user about the exact time it is needed and would finish mixing a little before. This is reverse of FS where we can purchase the land and start building even after 5 years.

We cannot reverse it like looking for a plot of land when our building design has already finalized. We cannot even design a building as it  would depend on plot dimensions, road accesses, streets, sub-soil conditions, neighbor-hood structures, wind and sunshine directions.

In FS relationship, mixture of paint depends upon start of painting. Painting can be done any time. It is not that paint-mix is ready and now painting must start. Who order for the paint mix? It should have been done only when needed.

Given below are examples for practical experience in task dependency:

FINISH-to-START

  • Machine cannot be installed unless machine-foundation is complete
  • Trial runs cannot be started unless machine is fully installed.

START-to-Start

  • Baking 10 cakes is obvious to decorating which starts after first cake is finished.
  • 50 resumes can be studied and interview can be started after first.

FINISH-to-FINISH

  • Planning for the construction phase can begin before final design approval but it cannot be finished until design is finally approved.
  • Salesmen require back-up staff. Hiring of salesmen and back-up staff can be started at the same time but hiring of salesmen must be completed first in order to ascertain how many support staff would be required.

START-to-FINISH

  • In heart operation, heart is stopped and OXYGENATOR is started. It is only switched off, when heart starts functioning.
  • When electricity is coming through generator, it must be switched off first before turning to main supply.

 

This concludes a series of four hubs relating to networking in project management as given below:

  1. CASE STUDY: Using CPM or PERT in time planning and Control
  2. CASE STUDY: PERT / CPM – Calculating Floats
  3. CASE STUDY: Probability in PERT
  4. CASE STUDY: PERT – Task Dependency

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    • profile image

      sheraz khan 8 years ago

      respected sir,

      article is good and easy to understand.thank you for sending this article.

    • Fahad_Khan profile image

      Fahad_Khan 8 years ago from Karachi

      Very informative and easy-to-understand article. Thanks a lot to Sir for helping us in every possible way regarding Project Management.

      Regards,

      Muhammad Fahad Khan

    • hafeezrm profile image
      Author

      hafeezrm 8 years ago from Pakistan

      Thanks Fahad & Sheraz Khan for your comments.

    • profile image

      sanar rao 8 years ago

      Respected Sir,

      Article is very informative and very simple to understand. thanks a lot sir for such corporation.

    • shahnawaz sheikh profile image

      shahnawaz sheikh 8 years ago from karachi

      AN INTRESTING ARTICLE SIR,

      ESPECIALLY THE PART THAT I REALLY LIKED IN THIS CASE IS THAT AON WHICH IS ONLY CONCERNED WITH FINISH TO START . TASK DEPENDENCY ACTULLY SHOWS THE IMPORTANCE OF A TASK IN A MANNER THAT WHICH TASKS ARE TO BE DONE TOGETHER IN ORDER TO COMPLETE THE POJECT ON TIME WITH LESS COST

      AGAIN THANK YOU FOR THE ARTICLE

    • profile image

      ANAS USMANI 8 years ago

      THIS REALLY IS A MASTERPIECE AND A WONFDERFUL TUTORIAL FOR ME. I HOPE THIS WILL TAKE MY KNOWLEDGE TO A GREATER LEVEL.KEEP UP THE GOOD WORK...

      ANAS USMANI

    • profile image

      Kiran Mehtab 8 years ago

      The article is very informative and easy to understand, thanx a lot for sharing with us :)

    • profile image

      Adeel Aleem 4B 8 years ago

      Nicely done.. this would certainly augment my knowledge..

    • hafeezrm profile image
      Author

      hafeezrm 8 years ago from Pakistan

      Thanks all for your comments.

    • profile image

      Munesh Kumar 8 years ago

      Thank you for such a nice examples it really helps me 2 understand the topic...

    • profile image

      Khan Naseer 8 years ago

      A dry topic made interesting. The writer really has sound knowledge and good experience in choosing the words.

    • Emran Ali profile image

      Emran Ali 8 years ago from karachi

      It is surely an informative article to understand about Task dependency .SS,FF, SF,FS tells how multiple tasks are related with each other .

      I have two questions, i would be glad to have your answers

      AOA or AON , which is mostly used by Project Managers ?

      AON certainly classify logical relations with each other as we go through detailed procedure with 9 defined boxes e.g. ES , EF,LS,LF,ID, Floats . Perhaps Activity on arrow shows task dependency between activities.

      In the Above article project is completed in 12 days , ID no.1 , activity number 4 requires 1 day . How did you reverse this one day gap ? i mean one day gap is convered from the back instead of going forward from activity 3 .

      Task Dependency clears an idea how multiple tasks are inter related with each other . Although it does create ambiguity to understand how and why the connection is build with certain activity

      Last but not least, thank you so much for providing a platform which let us comprehend through articles in an extremely informative manner.

    • profile image

      Adnan Ahmed 7 years ago

      THANX SIR

      now i got the complete them of this article ...i'm more clear and easily understandable.....thand again sir for sharing depth of subject

    • profile image

      Madiha Zulfiqar 7 years ago

      Aoa sir, the case study is very informative and beautifully explains task dependency concept. thank you for the extra effort taken which serves as a great source for students to clarify concepts.

      Regards,

      Madiha Zulfiqar

    • asif jamal profile image

      ASIF JAMAL 7 years ago from Islamabad

      articleis very informative and simple to understand

    • profile image

      hira sami 7 years ago

      sir u have expalined task dependency in a very simple way thanks for explaining us in such an easy way

      regards

      HIRA SAMI

    • profile image

      Khadijah 7 years ago

      Aoa Sir, the informatiion provided here has further helped in understanding the various concepts esp the exmaples which are very easily understandable

      Thank you

      Khadijah

    • Bilal Shahmeer profile image

      Bilal Shahmeer 6 years ago

      the quality of this article is this that it is self explanatory

    • profile image

      kamranqamar 6 years ago

      very critically defined. thnx

    • asadayub profile image

      asadayub 6 years ago

      Respected Sir, the article is very informative. Thank you so much for sharing.

    • profile image

      yasir aziz tanoli 6 years ago

      really very interesting and informative

      each and every point is clearly defined one can understand easily

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