5th Edition PMBOK® Guide—Chapter 6: Precedence Diagramming Method, Leads and Lags


1. Introduction

The tools & techniques for the process 6.3 Sequence Activities are given in the following summary chart.

6.3 SEQUENCE ACTIVITES
TOOLS & TECHNIQUES
1. Precedence diagramming method (PDM) Used to construct a schedule model in which activities are represented by nodes and are linked to show the sequence in which they are performed.
2. Dependency determination Dependencies between activities are characterized by various attributes: mandatory vs. discretionary, internal vs. external
3. Leads and lags A lead is the amount of time a successor activity can be advanced with respect to a predecessor activity. A lag is the amount of time a successor activity can be delayed with respect to a predecessor activity.

In the last post, I discussed the technique of dependency determination. In this post, I will discuss the first tool, precedence diagramming method, and the third technique, leads and lags.

I will use a typical PMP exam question involving this tool and technique in order to illustrate their use.

2. Precedence Diagramming Method

Description

Note

FS Successor activity cannot start until predecessor activity has finished. Activities are in series—most common relationship.
FF Successor activity cannot finish until predecessor activity is finished. Activities are in parallel—next most common relationship.
SS Successor activity cannot start until predecessor activity has started. Activities are in parallel—next common relationship.
SF Successor activity cannot finish until predecessor activity has started. Least common relationship

Notice that in each four of these relationships, the first letter refers to the predecessor activity and the second letter refers to the successor relationship.

3. Leads and Lags

Definition

Lead Amount of time whereby a successor activity can be advanced with respect to a predecessor activity.
Lag Amount of time whereby a successor activity can be delayed with respect to a predecessor activity.

To see how leads and lags are represented in the Precedence Diagramming Method, let us take a typical exam question.

4. Exam question example

Activity 1 has a duration of 20 days, Activity 2 of 10 days, Activity 3 of 5 days and Activity 4 of 6 days. What is the minimum total duration between the Milestones A and B?

The relationship between the activities is

Predecessor Successor Relationship
Milestone A Activity 1 FS
Activity 1 Activity 2 FS
Activity 2 Activity 3 FF-2
Activity 3 Activity 4 FS+3
Activity 4 Milestone B FS

Now let’s answer the question.

Step 1. Let’s define milestone A as starting on day 0. A milestone has 0 days duration BY DEFINITION so it finishes on day 0.

Activity Starts Finishes
Milestone A 0 0
Activity 1
Activity 2
Activity 3
Activity 4

Step 2.

Activity 1 starts at 0 and it is given in the question that it has a duration of 20 days, so it finishes on day 20.

Activity Starts Finishes
Milestone A 0 0
Activity 1 0 20
Activity 2
Activity 3
Activity 4

Step 3.

When does activity 2 start? The relationship between activity 1 and activity 2 is given as “FS“, which means that Activity 2 (the successor activity) starts IMMEDIATELY after Activity 1 (the predecessor) is finished, so it starts on day 20 as well. Since it is given to have a duration of 10 days in the question, it finishes on day 20 + 10 = 30.

Activity Starts Finishes
Milestone A 0 0
Activity 1 0 20
Activity 2 20 30
Activity 3
Activity 4

Step 4.

When does Activity 3 start?    The relationship between Activity 2 and activity 3 is given as”FF-2″, so you can’t figure out directly when it starts like you could for Activity 2 which used FS.   However, since you are given the relationship as being “FF-2″, it means you can figure out that Activity 3 finishes 2 days BEFORE Activity 2 finishes.   Since Activity 2 finishes on day 30 (see beginning of paragraph for reference), Activity 3 finishes on day 30 – 2 = 28.   And since Activity 3 is given as having 5 days in duration, it must begin on day 28 – 5= 23.

By the way, the fact that the finish of activity 3 is advanced 2 days with respect to the finish of activity 2 means that this is an example of a lead.

Activity Starts Finishes
Milestone A 0 0
Activity 1 0 20
Activity 2 20 30
Activity 3 23 28
Activity 4

Step 5.

When does Activity 4 begin?   The relationship between Activity 3 and Activity 4 is given as “FS + 3“, meaning that Activity 4 starts 3 days AFTER activity 3 ends.   Since activity 3 ends on day 28, activity 4 begins on day 28 + 3 = 31.   When does activity 4 end?   Since the duration of activity 4 is given in the question as 6 days, the answer is 31 + 6 = 37 days.

Activity Starts Finishes
Milestone A 0 0
Activity 1 0 20
Activity 2 20 30
Activity 3 23 28
Activity 4 31 37

By the way, the fact that the start of activity 4 is delayed 3 days with respect to the finish of activity 3 is an example of a lag.

I hope that this example has not only illustrated the Precedence Diagramming Method, but has also demonstrated an example of how to use a lead and lag in this method.

The next week I am on a trip by car to move from Los Angeles to Chicago, so I will be blogging about other topics than project management for the next week until I get settled in the Chicago area. Thank you for your patience!

5th Edition PMBOK® Guide—Chapter 6: Dependency Determination


1. Introduction

The last post discussed the time management process 6.3 Sequence Activities. The three tools & techniques of that process are listed below.

6.3 SEQUENCE ACTIVITIES
TOOLS & TECHNIQUES
1. Precedence diagramming method (PDM) Used to construct a schedule model in which activities are represented by nodes and are linked to show the sequence in which they are performed.
2. Dependency determination Dependencies between activities are characterized by various attributes: mandatory vs. discretionary, internal vs. external
3. Leads and lags A lead is the amount of time a successor activity can be advanced with respect to a predecessor activity. A lag is the amount of time a successor activity can be delayed with respect to a predecessor activity.

The first one is a tool, the second and third are techniques. Must one activity done before another? If so, must it be complete before another one can be started? To answer questions like these, the second technique of dependency determination is used. This determines the nature of the dependency between any two activities, and is the subject of this post.

2. Types of Dependencies

Category Dependency Explanation
Mandatory vs. Discretionary Mandatory

(hard logic)

Involve

  • physical limitations
  • contractual or legal obligations
Discretionary

(soft logic)

 

Based on knowledge of best practices
External vs.

Internal

External Outside of project team’s control, based on relationship of project activities and activities outside project
Internal Within project team’s control, based on relationship between project activities

The reason for the classification into types of dependencies is that the mandatory and external types of dependencies cannot be changed or changed easily. The discretionary and internal types of dependencies can be changed more readily and therefore those activities that have these types of dependencies will be the ones the project manager should go to first if there is a necessity for crashing or fast-tracking in order to compress the schedule.

The next post will discuss the leads and lags technique, which is the third technique of those used in the process 6.3 Sequence Activities.

5th Edition PMBOK® Guide—Chapter 6: Process 6.3 Sequence Activities


1. Introduction

Once the project activities have been identified in process 6.2 Define Activities, the next planning process 6.3 Sequence Activities identifies and documents the relationships among the project activities.

Which need to be done first? Which ones can be done in parallel? By analyzing this logically, you can create a logical sequence of work which will accomplish the work of the project with the greatest amount of efficiency given the other project constraints.

The following is a summary of the inputs, tools and techniques, and outputs used in the process.

6.3 SEQUENCE ACTIVITIES
INPUTS
1. Schedule Management Plan Identifies the scheduling method and tool to be used.
2. Activity List Includes all scheduled activities on the project. This is an output of process 6.2 Define Activities
3. Activity Attributes Describes the predecessor and successor activities, as well as possible leads and lags, associated with each activity. This is an output of process 6.2 Define Activities.
4. Milestone List Gives specific dates for any milestones. This is an output of process 6.2 Define Activities.
5. Project scope statement The product scope description includes product characteristics which may affect activity sequencing. Project deliverables, constraints, and assumptions may also affect activity sequencing.
6. EEFs
  • Government and industry standards
  • Project Management Information System
  • Scheduling tool
  • Company work authorization systems
7. OPAs
  • Project files
  • Policies, procedures and guidelines, templates used with scheduling methodology
TOOLS & TECHNIQUES
1. Precedence diagramming method (PDM) Used to construct a schedule model in which activities are represented by nodes and are linked to show the sequence in which they are performed.
2. Dependency determination Dependencies between activities are characterized by various attributes: mandatory vs. discretionary, internal vs. external
3. Leads and lags A lead is the amount of time a successor activity can be advanced with respect to a predecessor activity. A lag is the amount of time a successor activity can be delayed with respect to a predecessor activity.
OUTPUTS
1. Project schedule network diagrams A graphical representation of the logical relationships (also known as dependencies) among the project schedule activities.
2. Project documents updates
  • Activity lists
  • Activity attributes
  • Milestone list
  • Risk register

2. Inputs

The scheduling methodology and tools to be used are specified in the Schedule Management Plan (the output of 6.1 Plan Schedule Management). The activity list, activity attributes, and the milestone list which were the outputs of the previous process 6.2 Define Activities are now the inputs to this process. Some of the project constraints and assumptions from the project scope statement may be useful in helping analyze the logical relationships or dependencies between the various activities.

3. Tools & Techniques

The Precedence Diagramming Method is a tool used to represent activities by nodes (or boxes) which are then linked to show the sequence in which they are to be performed. Information from the project constraints and assumptions can help in the analysis of the dependencies among the various activities, as well as the leads and lags required between predecessor and successor activities.

4. Outputs

The Precedence Diagramming Method has an output a project schedule network diagram which will show the sequence in which all the activities are to be performed. If any of the attributes of the activities (particularly dependencies, as well as leads and lags) are altered as a result of the detailed analysis done in this process, those are updated. Activity lists, milestone lists, and risk registers may add details as well.

Before going on to the next process, I will take the next two posts to describe in more detail both the tool (Precedence Diagramming Method) and the techniques (Dependency Determination and Leads and Lags) used in this process.

5th Edition PMBOK® Guide—Chapter 6: Process 6.2 Define Activities


1. Introduction

The define activities process uses the process of decomposition to take the work packages identified in the WBS which are nouns, and to identify the activities which are verbs required in order to complete them.

It is therefore the bridge between the planning involved in scope management, and the planning involved in time or schedule management.

The following contains an overview of the inputs, tools & techniques, and outputs related to this process, as listed in the PMBOK® Guide.

6.2 DEFINE ACTIVITIES
INPUTS
1. Schedule Management Plan A key input from the plan is the prescribed level of detail necessary to do the work which would come from the following elements:

  • Units of Measure
2. Scope Baseline Besides the WBS, you would need the following elements from the project scope statement:

  • Constraints
  • Assumptions
3. EEFs
  • Organizational structures and culture
  • Published commercial information from commercial databases
  • Project Management Information System
4. OPAs
  • Lessons learned from previous projects
  • Standardized processes for creating activity list
  • Templates containing activity list from previous projects
  • Activity-planning policies, procedures, guidelines, including scheduling methodology
TOOLS & TECHNIQUES
1. Decomposition Technique for dividing and subdividing project scope and project deliverables into smaller, more manageable parts.
2. Rolling Wave Planning Also known as progressive elaboration. Work in the near term is planned in detail, whereas work in the future is planned at a higher level.
3. Expert Judgment Project team members and other experts can provide expertise in defining activities.
OUTPUTS
1. Activity List Includes all scheduled activities on the project.
2. Activity Attributes Extends the description of each activity by having multiple components associated with each activity such as:

  • predecessor and successor activities
  • leads and lags
  • resource requirements, and constraints (including imposed deadlines) and assumptions.
3. Milestone List Lists all milestones and identifies them as:

  • mandatory (specified by contract)
  • optional (based on historical information)

2. Inputs

As inputs, the basic parameters regarding units of measure are needed from the schedule management plan. Then the WBS is required, because the define activities process is based on further decomposing the work packages contained in the WBS into activities. The EEFs and OPAs give the background information and tools required to do the process.

3. Tools & Techniques

For tools and techniques, the decomposition process is the main one, and since it is the same technique as used in the scope management process 5.4 Create WBS, the schedule management process 6.2 Define Activities can be profitably done in conjunction with that other process.

The rolling wave technique, also known as progressive elaboration, can be used in several situations.

  • very large projects or projects that are totally new
  • projects where you need to start the work of executing the project before you have all of the planning 100% complete
  • projects where the work to be done in the final stages of the project depends on the work to be done in the initial stages of the project and cannot be planned completely until this work is complete

Those work packages which represent work to be done in the near future are completely broken down into activities, whereas the work to be done at later stages in the project are broken down only to a certain level, called planning packages. These are then progressively elaborated as the time gets closer to their execution.

Expert judgment is always a useful technique when dealing with something as complex as the creation of a project schedule. The expertise comes from those who have done this type of activity planning before, either on other projects or preferably on projects that were similar to the one the organization is doing now.

4. Outputs

The activity lists and activity attributes are parallel to the WBS and WBS dictionary in that the former contains an organized list, and the latter contains the information necessary regarding those items in the list to carry on the following planning processes.

Milestones are important because they are used to coordinate internally on the project and also externally, between the organization and the supplier and/or customer.

The next process in schedule management is 6.3 Sequence Activities, and that is discussed in the next post.

5th Edition PMBOK® Guide—Chapter 6: Schedule Management Plan


1. Introduction

The output of the first planning process in the Time Management Knowledge Area, Process 6.1 Plan Schedule Management is, unsurprisingly, the Schedule Management Plan.

What is surprising is that before the 5th Edition PMBOK® Guide, there was no time management process which covered the creation of this plan. It was considered to be done as part of the Integration Management knowledge area under the Develop Project Management Plan process. But somewhere along the line, those reviewing the PMBOK® Guide must have realized that the Project Management Plan integrates the existing subsidiary plans, all of which are encountered for in separate processes EXCEPT for those involving the three major triple constraints on a project: scope, time, cost.

So in the 5th Edition, they went and added in processes that created management plans in these three areas. It’s not that these plans were never created before, it’s just that now they have processes that are explicitly devoted to creating them.

2. Elements of Schedule Management Plan

The Schedule Management Plan sets up the framework for all of the other time management processes. So let’s look at the elements of the Schedule Management Plan and see what processes they are related to.

Element of Plan Description of Element
1. Organizational procedures links WBS is used as framework in order to provide consistency with estimates. 6.2 Define Activities
2. Project Model Schedule Development Specifies scheduling methodology and scheduling tool to be used. 6.3 Sequence Activities 6.6 Develop Schedule
3. Units of measure For each resource, units are defined. 6.4 Estimate Activity Resources
4. Level of accuracy Acceptable range of accuracy of activity duration estimates. 6.5 Estimate Activity Durations
5. Project schedule model maintenance Process used to update status and record progress. 6.7 Control Schedule
6. Control thresholds Amount of variance in schedule performance allowed before action is taken. 6.7 Control Schedule
7. Rules of performance measurement Earned value measurement (EVM) rules are set. 6.7 Control Schedule
8. Reporting formats Formats, frequency of schedule progress reports. 6.7 Control Schedule
9. Process descriptions Descriptions of each schedule management process. ALL

The idea is that the tools and techniques used in the developing of the schedule are specified, as well as the details regarding the units involved with each of the resources. Also the descriptions of the schedule management processes are included if one wants to work on improving them at some stage of the project. Regarding the estimates, you need to specify their level of accuracy (i.e., + or – 10%).

Finally, once the schedule baseline has been established, then you need to set up rules so that when you are actually doing the project, you can periodically take a measurement of the progress on your project with reference to that baseline. Then if the variance where you actually are and where you are supposed to be at any given point on the project gets to be above a pre-defined threshold, you need to set up what actions you will take in order to make sure the project gets back on track.

These policies, procedures, and guidelines that are followed in all of the other processes are listed up here in the Schedule Management Plan

The next post will deal with the next planning process, that of 6.2 Define Activities.

5th Edition PMBOK® Guide—Chapter 6: Process 6.1 Plan Schedule Management


This post gives an overview of the first of the six planning processes in the Time Management Knowledge Area, with summaries of the inputs, tools & techniques, and output of the process.

1. Inputs

As far as inputs are concerned, the most important ones are the scope baseline, because that represents the work that needs to be done, and the schedule will tell you how much time is required to do it. Other knowledge management plans may provide input as well, some of which are completed after the schedule management plan in the list of planning processes. This shows that the planning process is iterative and may require several passes through in order to integrate the various knowledge area management plans.

The project charter will give the high-level time constraints and the list of critical milestones to be achieved on the project, some of which may actually be tied to project approval requirements (i.e., the project may absolutely have to be done within a certain amount of time).

The main EEF or Enterprise Environmental Factor is probably going to be the project management software used to create the schedule; the main OPA or Organizational Process Asset is probably going to be the historical information on prior similar projects that can be used to help estimate the schedule.

6.1 PLAN SCHEDULE MANAGEMENT
INPUTS
1. Project Management Plan The following elements of the PM Plan are used in the development of the Schedule Management Plan:

  • Scope baseline (= project scope statement, WBS, and WBS dictionary)
  • Cost, risk, and communications management plans
2. Project Charter Summary milestone schedule, project approval requirements (particularly those dealing with time constraints).
3. EEFs
  • Organizational culture and structure
  • Resource availability and skills
  • Commercial information available on resource productivity
  • Project Management Software
  • Organizational work authorization systems
4. OPAs
  • Policies, procedures, guidelines, templates for schedule control
  • Historical information on similar projects
  • Monitoring and reporting tools, schedule control tools
  • Change control procedures
  • Risk control procedures
  • Project closure guidelines
TOOLS & TECHNIQUES
1. Expert judgment Uses historical information from prior similar projects and adapts it appropriately to the current project.
2. Analytical techniques Used to choose strategic options related to estimating and scheduling the project:
3. Meetings Planning meetings are used to develop the schedule management plan.
OUTPUTS
1. Schedule Management Plan Establishes the criteria and the activities for developing, monitoring and controlling the schedule.

2. Tools & Techniques

Expert judgment and meetings should be familiar by now as typical techniques that project managers of creating something as complicated and intricate as a schedule. The analytical techniques that can be used with specific reference to the schedule are such methods as:

  • Schedule compression (fast tracking or crashing)
  • Rolling wave planning
  • Leads and lags
  • Alternatives analysis
  • Reviewing schedule performance

UPDATE:   Based on some comments, I wanted to add that the analytical techniques are not actually used in this process, because the schedule itself has not been developed (that takes place in process 6.2 through 6.6).  What the Schedule Management Plan can do is LIST the options for tools & techniques that can be used later on in those scheduling processes.   Sometimes details can be given in terms of under what conditions they will be used, what scheduling software or other tools to be used in conjunction with those techniques, etc.

3. Output

Finally, the output, as you could probably guess by the title of the process, is the Schedule Management Plan. Let’s take a closer look at the contents of the Schedule Management Plan in the next post to see all that goes into it, and how these contents relate to the other project management processes in the Time Management Knowledge Area.

5th Edition PMBOK® Guide—Chapter 6: Time Management Knowledge Area


After Chapter 5, which discusses Scope Management, the next knowledge area covers one of the other major “triple constraints”, that of time.

There are seven project management processes in the Time Management Knowledge Area. Six of these are in the Planning Process Group and one is the Monitoring & Controlling Process Group.

The first planning process, that of Plan Schedule Management, creates the Schedule Management Plan which is the framework for all of the other processes. (NOTE: In the 4th Edition, this plan was created not as a separate process, but as part of the Develop Project Management Plan process in the Integration Knowledge Area.)

The second through six planning process are done in sequence, but may be done in an iterative fashion in the case that not all of the activities are specified in the first pass through these processes. Once the schedule is produced as the output of the last of these planning processes, Develop Schedule, it becomes the schedule baseline against which progress is measured throughout the rest of the project in the Control Schedule process in the Monitoring & Controlling Process Group.

Process Group Process Number Process
Name
Process Description
Planning 6.1 Plan Schedule Management Establishes the policies, procedures, and documentation for planning, executing, and controlling the project schedule. Provides guidance and direction on how the project schedule will be managed throughout the project.

 

Planning 6.2 Define Activities Identifies and documents the specific actions to be performed to produce the project deliverables. Breaks down work packages into activities that form the basis for the project work.

 

Planning 6.3 Sequence Activities Identifies and documents relationships among the project activities. Defines the logical sequence of work to obtain the greatest efficiency given all project constraints.

 

Planning 6.4 Estimate Activity Resources Estimates the type and quantities of resources required to perform each activity. Identifies type, quantity, and characteristics of these requires which allows for more accurate cost and duration estimates.

 

Planning 6.5 Estimate Activity Durations Estimates the number of work periods needed to complete individual activities with estimated resource. Provides the amount of time each activity will take to complete.

 

 

Planning 6.6 Develop Schedule Analyzes activity sequences, durations, resource requirements, and schedule constraints to create the project schedule with planned dates for completing project activities.

 

Monitoring & Controlling 6.7 Control Schedule Monitors status of project activities to update project progress and manage changes to the schedule baseline in order to achieve the plan. Provides the means to recognize deviation from the plan and to take corrective and preventive actions and thus minimize risk.

The next post will go into more detail regarding the inputs, tools & techniques, and outputs involved in the first process, 6.1 Plan Schedule Management.