ACTIVITY SEQUENCING

Activity sequencing involves identifying and documenting the logical precedence relationships among activities. Activities need to be logically sequenced with proper precedence relationships to support later development of a realistic and achievable schedule. Sequencing can be performed by using project management software or by using manual techniques. Manual and automated techniques can also be used in combination.

6.2.1 Activity Sequencing: Inputs

Described in Section 6.1.

.2 Activity List Attributes Described in Section 6.1.

.3 Project Scope Statement

Product characteristics often affect activity sequencing, such as the physical layout of a plant to be constructed, or subsystem interfaces on a software project. While these effects are often apparent in the activity list, the product scope description should generally be reviewed to ensure accuracy (Section 4.2).

.4 Milestone List

Described in Section 6.1.

6.2.2 Activity Sequencing: Tools and Techniques

PDM is a method of constructing a project schedule network diagram that uses boxes or rectangles, referred to as nodes, to represent activities, and connects them with arrows that show the dependencies. Figure 6-5 shows a simple schedule network logic diagram drawn using PDM. This technique is also called activity-on-node (AON), and is the method used by most project management software packages.

PDM includes four types of dependencies or precedence relationships:

• Finish-to-Start - the initiation of the work of the successor depends upon the completion of the work of the predecessor.

• Finish-to-Finish - the completion of the work of the successor depends upon the completion of the work of the predecessor.

• Start-to-Start - the initiation of the work of the successor depends upon the initiation of the work of the predecessor.

• Start-to-Finish - the completion of the successor is dependent upon the initiation of the predecessor.

In PDM, finish-to-start is the most commonly used type of precedence relationship.

Start-to-finish relationships are rarely used. Using to-start, finish-to-finish, or start-to-finish relationships can produce unexpected results if these types of relationships have not been consistently implemented.

.2 Arrow Diagramming Method (ADM)

ADM is a method of constructing a project schedule network diagram that uses arrows to represent activities, and connects them at nodes to show their dependencies. Figure 6-6 shows a simple network logic diagram drawn using ADM. This technique is also called activity-on-arrow (AOA) and, although less prevalent than PDM, is still used in teaching schedule network theory and in some application areas, such as forensic delay analysis.

ADM uses only finish-to-start dependencies and can require the use of “dummy”

activities to define all logical relationships correctly.

.3 Schedule Network Templates

Standardized schedule network templates can be used to expedite the preparation of schedule network diagrams of project activities. They can include an entire project or only a portion of it. Portions of a project schedule network are often referred to as a subnetwork or a fragment network. Subnetwork templates are especially useful when a project includes several identical or nearly identical features, such as floors on a high-rise office building, clinical trials on a pharmaceutical research project, coding program modules on a software project, or the start-up phase of a development project.

.4 Dependency Determination

Three types of dependencies are used to define the sequence among the activities.

• Mandatory dependencies. The project management team determines which dependencies are mandatory during the process of establishing the sequence of activities. Mandatory dependencies are those that are inherent in the nature of the work being done. Mandatory dependencies often involve physical limitations, such as on a construction project, where it is impossible to erect the superstructure until after the foundation has been built; or on an electronics project, where a prototype must be built before it can be tested. Mandatory dependencies are also sometimes referred to as hard logic.

• Discretionary dependencies. The project management team determines which dependencies are discretionary during the process of establishing the sequence of activities. Discretionary dependencies should be used with care and fully

documented, since they can create arbitrary float values and can limit later scheduling options. Discretionary dependencies are sometimes referred to as preferred logic, preferential logic, or soft logic. Discretionary dependencies are usually established based on knowledge of:

• Best practices within a particular application area

• Some unusual aspect of the project where a specific sequence is desired, even though there are other acceptable sequences

• Preferred activity sequences based upon previous experience on a successful project performing the same type of work.

• External dependencies. The project management team identifies external dependencies during the process of establishing the sequence of activities.

External dependencies are those that involve a relationship between project activities and non-project activities. For example, the testing activity in a software project can be dependent on delivery of hardware from an external source, or environmental hearings may need to be held before site preparation can begin on a construction project. This input can be based on historical information (Section 4.1) from previous projects of a similar nature or from seller contracts or

proposals (Section 12.4).

6.2.3 Activity Sequencing: Outputs

Project schedule network diagrams are schematic displays of the project’s activities and the logical relationships referred to as dependencies, among them. Figures 6-5 and 6-6 illustrate two different approaches to drawing a project network diagram. A project schedule network diagram can be produced manually or by using project management software. The network diagram can include full project details, or have one or more summary activities. A summary narrative accompanies the diagram that describes the basic approach used to sequence the activities. Any unusual activity sequences within the network are fully described.

.2 Activity List (Updates)

In much the same manner that the activity definition process can generate updates to the WBS, preparation of project schedule network diagrams might reveal instances where an activity must be divided, or otherwise redefined, to diagram the correct logical

relationships, which results in a revision to the activity list.

.3 Project Management Plan and Project Scope Statement (Updates)

Updates to the Project Management Plan (Section 4.3) and Project Scope Statement (Section 4.2) are developed depending upon the nature of the changes and impact they can have on other plans. Requested changes (additions, modification, revisions) to the project management plan and its subsidiary plans are processed through integrated change control (Section 4.6).