DEPENDENCIES IN PROJECTS

Flow of Activities and Dependencies in Project Management

Determining the schedule of activities that comprise the project is a key element of project management. After gathering all the information, the project’s master schedule is developed. The project’s master schedule is a summary level schedule that encompasses the entire project scope that includes major events and provides a view of the entire project. As the project activities continue, the planning continues to include more details as additional information becomes available. Major revisions may be necessary in response to events both inside and outside the project that change critical dates on the schedule.

Types of Schedules

  1. Conceptual Schedule

When the scope of the project is being determined, a simple schedule that shows the major tasks and approximate start and end dates is developed to allow senior management to make decisions about the scope of the project. Detail is not required at this stage because entire tasks might be dropped from the scope, or the whole project might not be approved.

  1. Master Schedule

If the project is chosen, a master schedule is created. It has major events and dates such as the starting date and the completion date. The master schedule is often part of a contract. Changes to the master schedule must be approved using a documented change process with approval by the project sponsor and client.

  1. Detailed Schedule

To execute the master schedule, the major activities are broken down into smaller activities and resources are assigned to those activities. The most detailed versions or portions of the schedule may be developed a few weeks prior to the execution of those activities and are called two-week plans. Portions of the master schedule that affect particular vendors might be sent to them so that they can provide detailed activities that they would perform.

DEPENDENCIES

No project activity or task exists in isolation. Each task relies on the output of another activity in some way and contributes to the end result of the project. The relationship between two tasks is defined as the dependency between them. A project dependency is the logical, constraint based on preferential relationship between two activities or tasks such that the completion or the initiation of one is reliant on the completion or initiation of the other.

Eg

In painting a wall, the application of the paint is one activity, preparation of the wall is another.  The paint cannot be applied unless the surface has been brushed with the primer. If the primer is not available for 3 days, the painting completion will be delayed by 3 days because painting cannot commence.

Some Dependency Related Terms:

Activity Sequencing

Determining the schedule of a project begins by examining each activity in the WBS to determine its relationship to the other activities.

Project Logic

The project logic is the development of the activity sequence or determining the order in which the activities will be completed. The process  involves identifying the predecessors—activities that come before—and successors—the activities that come after.

ConstraintDependencies and constraints have a cause and effect relationship. In its simplest form a constraint is a restriction within the boundaries of which the task has to be completed or executed. A constraint may be driven by lack of resources like money and man-power or shortage of available time and even lack of expertise. Sometimes constraints can give rise to dependencies.

Eg

If there are four cakes to be creamed and only one baker is skilled enough to do it, then the creaming of one cake is automatically dependent on the completion of creaming of another. A dependency might be the reason behind a constraint

Eg

In a tailoring shop the actual sewing can’t proceed unless the measurements are taken first. This is a bona fide logical dependency. If the measurement takes 20 minutes and the seamstress only has two hours to complete the dress, then under the circumstances, she will get just 100 minutes to meet the deadline.

Classic project management defines three constraints of – cost –time –scope. This is  considered as the three sides of a triad. The area of the triangle is the quality of the deliverables. Any changes introduced to the constraints alter the triangle’s area and thus the overall quality of the project. The project manager keeps track of all the constraints and dependencies and re-allocates resources in a way that ensures final project quality.

Lag and Lead Times

Most activities in a network diagram have a finish-start relationship. If a certain amount of time must go by before a successor activity can begin, the required delay is called lag time.

Eg

Lag time is required between the end of pouring concrete and the beginning of construction. Similarly, you must allow lag time for payment checks to be processed by the banking system before you can spend the money. i e. required time between activities is lag time. In some cases, the successor activity can overlap the end of its predecessor activity and begin before the predecessor is finished. This is called lead time.

Lead is therefore the duration of time by which a successor activity can be advanced or accelerated with respect to the predecessor task, especially if some schedule compression techniques need to be applied.

If activity B is scheduled to start when activity A completes, which is in 10 days, and if B is started just 5 days after A, then under the circumstances, B has a lead of 5 whole days. This can be done only when the dependency between A and B is discretionary.

Critical Path and Float

Critical Path

The critical path is the path through the network that results in the latest completion date of the project. A  Critical Path is the longest unbroken chain of sequential activities or dependent tasks such that altering the duration of completion of the tasks in any way directly impacts the deadline of the project, leading to possible violations.

While making a cake, baking and decoration of the sponge are part of the Critical Path chain. Any delays in these tasks will delay the presentation of the cake at the guest table.

Float

Float, sometimes called slack, is the amount of time an activity, network path, or project can be delayed from the early start without changing the completion date of the project.

Total Float

Total float is the difference between the finish date of the last activity on the critical path and the project completion date. Any delay in an activity on the critical path would reduce the amount of total float available on the project. A project can also have negative float, which means the calculated completion date of the last activity is later than the targeted completion date established at the beginning of the project.

Calculating Early Start Dates and Late Start Dates

Early Start Dates

Starting dates can be assigned to each activity by doing a forward pass proceeding from left to right in the network diagram beginning with the project start date. The dates derived by this method are the early start (ES) dates. The early start date for an activity is the earliest date the activity can begin. The estimate considers durations and resource availability calendars. To calculate early start dates, begin with the project start date and assign that date as the start date of activities that have no predecessor activities. Follow these steps to calculate the early start dates of subsequent activities, assuming finish-start relationships:

  • Add the predecessor activity’s duration to its start date.
  • Add the lag time or subtract the lead time.
  • Refer to the resource calendar (or calendars) that applies to the people and equipment necessary for the activity, and add the number of off-days that the activity would span on those calendars.
  • Assign the calculated date as the early start date of the successor activity.

Late Start Dates

The next step is to work through the network diagram from right to left beginning with the mandated completion date, which is a milestone that is set in the project plan. Subtract the duration of each activity in each path to determine the latest date the activity could begin and still meet the project completion date. Resource calendars must be considered in the backward pass as well as the forward pass.

To calculate late start dates, begin with the project completion milestone and assign that date as the finish date of its predecessor activities. Follow these steps to calculate the late start dates of predecessor activities, assuming finish-start relationships:

  • Subtract the predecessor activity’s duration from its late finish date.
  • Subtract the lag time or add the lead time to the late finish date.
  • Refer to the resource calendar (or calendars) that applies to the people and equipment necessary for the activity, and subtract the number of off days that the activity would span on those calendars.
  • Assign the calculated date as the late start date of the predecessor activity.

The difference between the early start date and the late start date for activities on the critical path is usually the same as the total float, unless the activities are affected by the resource calendars differently in the forward and backward pass.

Eg

If a piece of key equipment is only available for a few days, activities that depend on it have the same start and finish dates in the forward and backward passes.

Free Float

If activities that are not on the critical path have a difference between their early start date and their late start date, those activities can be delayed without affecting the project completion date. The float on those activities is called free float.

To calculate total project float, begin at the start date and add the duration of each activity in each possible path through the network diagram, including nonworking days from the resource calendars, to determine the early project end date. The longest path through the network is the critical path. The difference between the early end date and the required completion date of the project is the total project float, and the start date of each activity is the early start date. To calculate the late start dates, begin with the required project completion date and work backward, subtracting the duration of each activity through each possible pathway.

Accelerating the Schedule

The project manager must know how to accelerate a schedule to compensate for unanticipated events that delay critical activities or to accommodate changes in the project completion date. Compressing or crashing the schedule are terms used to describe the various techniques used to shorten the project schedule. Project managers utilize several techniques to keep projects on schedule.

Contingency Resources

One method of accelerating the schedule is to add activities to the critical path that are empty or that are optional. If the project is behind schedule, the time can be made up by dropping these activities. This extra time that is built into the schedule is called contingency time, buffer, or reserve time.

CLASSIFICATION OF DEPENDENCIES

  1. Based on the Nature of the Dependency

External Dependencies

In the project, sometime we may have to depend on the activity beyond our work. These are generally known as prerequisites for the project, but still they are dependencies for activities in the project.

To perform any installation, we may be dependent on the hardware and software procurement, which may be procured from an external party.

Mandatory dependencies- As the name suggests, these dependencies are mandatory and must be fulfilled at any cost. For example until one downloads the software, one cannot install the software on the server.

Internal dependencies- These dependencies usually are within the project manager’s and the project team’s control and hence the name internal dependencies.

In the project, sometime we may have to depend on the activity beyond our work. These are generally known as prerequisites for the project, but still they are dependencies for activities in the project.

Generally to perform any installation, you may be dependent on the hardware and software procurement, which may be procured from an external party

Causal or Logical dependencies- are those dependencies that can’t be avoided, They are fundamental requirements and intrinsic to the nature of the project and the nature of the tasks involved.

The stomach can’t digest food unless food is eaten first. This is a causal or logical dependency. Without completion of one step, the next can’t be initiated in any way.

Resource based dependencies- are driven by constraints, if there are only a limited number of skilled professionals available to work on a project, there is often no need to proceed sequentially simply because there aren’t enough man power to complete everything simultaneously. Where resource based constraints are, thus dependencies are present, and generally there is no causal dependency – that is all the activities can be tackled together if the needed facilitators are present.

Preferential dependencies / Discretionary dependencies

These dependencies are not really the barriers; they are a matter of preference. Meaning that they are good to fulfill as a matter of preference and are guided by best practice or convenience.  E.g. watering the wall or the floor after construction work has been completed, or soaking the foundation of the roof for at least 5 to 7 days before laying the tiles. They are generally introduced in projects to focus on quality of deliverables.

  1. FS, SF, FF & SS Dependencies

In all dependencies in project management, there are two letters denoted in the short form. For example FS, FF, SS, SF. The first letter always tells about the predecessor activity. And the second letter always tells about the successor activity. Meaning that in FS (Finish-to-start) dependency, the Successor activity cannot start until the predecessor finish the activity.

When talking about the predecessor activity and successor activity, always the predecessor activity is independent. Meaning that there is no constraint on the predecessor. The constraint of dependency is always on the successor activity.

Finish-to-Start (FS) – Successor activity cannot start until the predecessor activity finishes the first task needs to be completed before the second task can start. is the simplest one among the dependencies in project management. This is the most frequently used dependency when sorting the order of activities in the project.  For example, a new software installation has to start before the old installation can be stop. In a waterfall model, the development activity (successor) cannot start until the design finish (predecessor activity).

Finish-to-Finish (FF) – Successor activity cannot finish until the predecessor activity finish. I.e. the second task can’t be completed until the first task has been done. For example, wires can’t be fitted into the wall until they’ve been inspected. The broadcasting activity cannot finish until the tournament finishes.

Start-to-Start (SS) – Successor activity cannot start until the predecessor activity start. The following task can’t commence until the first task has started. For example, a concrete floor can’t start to be levelled until the concrete has poured  into the designated space. The sales team can’t start selling the product until the basic product road map documentation starts.

Start-to-Finish (SF) – Successor activity cannot finish until the predecessor activity start. The first task has to start before the second task can be completed. This is the rarest among the other dependencies in project management.  And hence it is very difficult to visualize. It is a logical relationship in which a successor cannot finish until the predecessor activity has started.

The successor activity B cannot finish until the start of the predecessor activity A.

How to Effectively Tackle Dependencies in Project Management:

  • The project manager Brainstorms all possible project dependencies and associated constraints keeping in mind the triple constraints model. If there are many dependencies and constraints, the Critical Path has to be identified as well.
  • He engages with stakeholders to ensure that they understand what the most important dependencies and constraints are.
  • He brainstorms risks and challenges associated with these dependencies and constraints and adds them to the change and risk management documents.

Dependencies are inevitable in project management. When planning to schedule project activities, the project manager must figure out the relationship between the activities in order to determine the order of their execution.

Setting out the project’s dependencies is crucial to its overall success. A project manager needs to:

  • Lay out the sequences of tasks within the project plan.
  • Calculate the tasks’ critical paths, i.e. how long each one is going to take.
  • Identify the necessary resources to complete the tasks.
  • Identify potential scheduling issues.
  • Monitor and manage tasks as part of the overall project plan.
  • Identify actions or any opportunities to accelerate the project’s task schedule.

Example

In a construction project, the plastering can’t start until the wall has been built, and the necessary pipes and wiring have been fitted. The wall can’t be decorated until the plastering has been done, including around the pipes and wiring.

Some dependencies are external, rather than internal. In the example above, the construction company building may rely on third-party suppliers for building materials. Before they can even start building, they’ll also need licenses and planning permission.

Dependencies are shown between the activities using the activity on node (AON) or precedence diagramming method (PDM), or arrow diagramming method which is limited to showing only finish to start (FS) dependencies

Importance of Dependencies

Dependencies are often shown as Gantt charts, which can help:

  1. Track the time a project is taking to complete.
  2. Decide and allocate resources.
  3. Order the tasks.
  4. Aid the management of dependencies between tasks.

Managing dependencies helps to work and manage tasks in their best possible order to ensure a project is completed on time or ahead of time.

Resource Leveling

The schedule of activities is constrained by the availability of resources. If you apply the resource calendar to each activity to be sure the people and equipment are available on those dates, you can still miss an important constraint. If there are several activities that use a particular person’s time on the same days, that person could end up with too many activities scheduled for the same days and very little on other days. If key people are overloaded, the activities to which they are assigned might not be completed on time. Managing the schedule of activities to ensure that enough resources are available to complete each task by distributing the work load is called resource leveling. Activities to which that person is assigned and that have free float can be delayed to reduce work overload of key people.

Reassigning Resources

Activities that are not on the critical path that have free float can be delayed without delaying the end date of the project if they start by the late start date. Project managers can divert some resources from activities with free float to activities on the critical path without delaying the completion of the project.

Changing Scope

The unit cost of work to be performed on a project is calculated at the beginning of the project based on the execution strategy of the project to meet the project completion date. If the project completion date is moved up, then the unit cost of work will likely increase. Conversely, a project team may be able to save money by extending the project end date. With more time, the project team may be able to schedule activities in such a way to reduce their costs.

Eg

An activity requiring overtime to be paid can now pay the labor at normal rates, saving the overtime premium. Changing elements of the master schedule means a change in scope. Scope changes often affect costs and require agreement by the parties who signed the original scope documents.

Additional Resources

Another option is to allocate funds that can be used to add resources if necessary. Available resources can be increased by adding overtime to existing resource calendars or by hiring additional contract workers or renting additional equipment.

NOTE

Progress can be measured by:

  1. determining the percentage of resources expended.
  2. completion of activities by scheduled dates.
  3. milestones achieved.
  4. fraction of activities accomplished.
  5. Standards used to measure progress, particularly when partial payment to contractors is concerned, should be specified in contract documents.
  • Resource leveling is essential to reallocate people and equipment to remove periods of overuse or underuse.
  • Unplanned delays and costs can be anticipated by including contingency time and budget amounts where needed to keep the schedule on time.
  • Resource allocation and resource calendars should be examined to determine if a resource is overcommitted.
  • Free float can be used to delay noncritical activities that use the same resource to allocate its time more evenly.
  • If it is necessary to accelerate the schedule, activities that are not on the critical path can be delayed using their free float and their resources can be moved to activities on the critical path to complete them sooner.
  • Contingency resources can be committed to speeding up the activities.
  • If necessary, the scope can be changed to bring in additional resources or lower the quality.

A PERT chart – the Program Evaluation and Review Technique – is useful for analysing tasks involved in a project. It lays out the minimum time needed to complete the project, showing a hierarchical breakdown of the project requirements.

(Visited 108 times, 1 visits today)
Share this:

Written by