Page 160 - DCAP304_DCAP515_SOFTWARE_PROJECT_MANAGEMENT

Software Project Management

Notes Start-to-start: The start-to-start (SS) dependency is displayed with an arrow emanating from
the left edge of the predecessor (A) and leading to the left edge of the successor (B). It says that
activity B may begin once activity A has begun. It means both the activity A and B could start at
the same time. For example, we could alter the data collection and data entry dependency: As
soon as we begin collecting data (activity A), we may begin entering data (activity B).
Start-to-finish: The start-to-finish (SF) dependency is displayed with an arrow emanating from
the left edge of activity A to the right edge of activity B. It is little more complex than the FS and
SS dependencies. Here activity B cannot be finished sooner than activity A has started. For
example, suppose you have built a new information system. You don’t want to eliminate the
legacy system until the new system is operable. When the new system starts to work (activity A)
the old system can be discontinued (activity B). SF dependencies can be used for just-in-time
scheduling between two tasks, but they rarely occur in practice.
Finish-to-finish: The finish-to-finish (FF) dependency is displayed with an arrow emanating
from the right edge of activity A to the right edge of activity B. It states that activity B cannot
finish sooner than activity A. For example, let’s refer back to our data collection and entry
example. Data entry (activity B) cannot finish until data collection (activity A) has finished.

Notes To preserve the connectedness property of the network diagram, the SS dependency
on the front end of two activities should have an accompanying FF dependency on the
back end.

8.2.2 Constraints

The type of dependency that describes the relationship between activities is determined as the
result of constraints that exist between those activities. Each type of constraint can generate any
one of the four dependency relationships. There are four types of constraints:
 Technical constraints
 Management constraints

 Interproject constraints
 Date constraints

Technical Constraints

Technical dependencies between activities arise when one activity (the successor) requires output
from another (the predecessor) before work can begin on it. In the simplest case, the predecessor
must be completed before the successor can begin.

Management Constraints

A second type of dependency arises as the result of a management-imposed constraint. For
example, suppose the product manager on a software development project is aware that a
competitor is soon to introduce a new product with similar features to theirs. Rather than
following the concurrent design-build strategy, the product manager wants to ensure that the
design of the new software will yield a product that can compete with the competitor’s new
product. He or she expects design changes in response to the competitor’s new product and,
rather than risk wasting the programmers’ time, imposes the FS dependency between the design
and build activities.

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