The two step method

The activity on arrow technique of networking was designed to provide a more thorough understanding of project logic. However, the drawings sometimes were extremely complicated and detailed. Recognizing this, project analysts conceived what is known now as Precedence networking. Precedence was developed to simplify the network. The proponents of Precedence felt that there was too much confusion in the presentation of the arrow, bubble, dummy, restraint technique. When the precedence diagraming method of networking was presented to a computer programmer, the programmer saw that the relationships between activities could be a useful tool in generating more accurate schedule information, thus the “start to start” and “finish to finish” concept was brought about. The programmer added values to the relationships and presented these values as lead or lag times. This concept has both good and bad points, but the one outstanding point (whether good or bad) is the interpretation of the information presented. To the programmer, the interpretation was simple. He said (in the case of start to start) that an activity can start after its predecessor has started. If a lag value of five days were used, the activity could start five days after its predecessor has started. To the programmer, the finish to finish has a similar interpretation. However, to the person in the field, the interpretation took on different proportions. To that person, an activity could not start until five days after its predecessor has been completed. Thus the arrow technique was blended, by interpretation, with Precedence. Precedence became accepted as another, somewhat sophisticated, form of network diagramming.

Some analysts in project networking found Precedence to be a solution to the problem of reducing the quantity of activities in a network. Many others could not or would not agree that this benefits more than offsets the rather simple appearance presented by arrow diagramming. Most analysts would agree that, when the network exceeded the space allowed for its presentation, it was difficult, if not impossible, to follow. They will also agree that when the network diagram can no longer be clearly read and understood, its effectiveness is seriously limited. To the person in the field, the opinion concerning complicated network diagrams was usually “after we’ve planned the project a bar chart would do a better job.” I must confess he or she may be 100% correct.

Realizing that some compromise must be made, I concluded that a combination of both Precedence and activity on arrow might help to simplify the network diagrams. More importantly, I know that whatever the presentation, it must be simple, easily read and understood. The resulting interpretation of this combination must, if at all possible, be singular. Therefore, I offer as fulfillment of the above specification what I call the “Two Step Method.”

The Two Step Method is based on the following premises:

All activities have a start and a finish.

The finish of an activity always follows (comes after) the start.

All networks are read from left to right, top to bottom.

The finish of an activity always appears on the diagram in line and on the same line as its start.

To demonstrate this concept I will begin with a simple network of five activities.

Activity “A”

Activity “B”

Activity “C”

Activity “D”

Activity “E”

The logic is represented in the following manner:

In this demonstration, I purposefully reversed the order of listing to further emphasize how the two step method helps to solve a problem inherent in all forms of networking, i.e. the order is not always numeric or alphabetic.

At first glance the two step method indicates more detail and unnecessary information. However, most projects are not quite this simple; therefore I will make the network fit situations that often exist when a project is being planned or in progress. Consider the logic I now propose and observe the difference in the three networking techniques demonstrated.

“D” can start after “E” has started.

“D” must be completed before “C” can be completed.

The start of “B” depends on the start of “C” and the finish of “E”.

“A” can start after “B” has finished.

The finish of “C” depends on the finish of “A”.

Without further diagramming, the Two Step Method presents the logic in clear, concise terms. Left to right, top to bottom. Note that no arrow points are necessary. While it is possible to overcome the reverse arrow shown in the arrow diagram, it is not possible with Precedence. The arrow diagram would obviously need considerable rearrangement and additional dummies to accomplish the “left to right” feature.

The ease in which the Two Step Method can be applied to logic situations is best demonstrated by using the precedence procedure of listing activities and predecessors. In alphabetical order this would be:

Precedessor Activity
Finish of B to start of A
Start of C and finish of E to start of B
Finish of A and finish of D to finish of C
Start of E to start of D
None E

In the activity column of this list, the activity start and finish is implied.

The Two Step Method of diagramming can now be accomplished with little difficulty by applying the following 4 rules:

1. The network format is always presented as a series of parallel columns and lines.

2. Starting with the first activity in the list (A), it is determined whether or not there are any predecessors. (It is seen that A is preceeded by the finish of B.) If there are no predecessors, this activity starts the network. If there is a predecessor, move then to the predecessor. (In the example, it would be B.) This process is repeated until no predecessors are found for the first activity in the list. (In the example it would be E.)

3. A start activity is always assigned the first two available successive spaces in the network (reading left to right). In the event that there are more than one start activity in a network, the start is always placed in the same column as the start of the last previous activity listed. (Note: The latter half of this rule may seem arbitrary but it is a helpful means of spreading the start activities throughout the network. Otherwise they would build up on the left.)

4. The finish of an activity is never placed on the diagram until all of its predecessors have been. This is to maintain the left to right continuity.

Realizing that personal innovations and adaptations can be applied to the Two Step Method, I offer the following suggestions:

Use dates instead of durations. Durations, including lead or lag, have little use when dates are available.

Do not try to fill all the spaces with an activity, start or finish (Single blank spaces will occur.)

Develop a routine and stick to it.

Since I first started to use the Two Step Method, I have found it can be computerized for digital reports and it can also be time scaled with ease. These two additional bonuses have contributed greatly to reducing of time required to produce and update project networks.

This material has been reproduced with the permission of the copyright owner. Unauthorized reproduction of this material is strictly prohibited. For permission to reproduce this material, please contact PMI.



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