This work aims to fill a lacunae in the project-oriented production systems literature
providing a formal analytic description of the rework effects formulae and the
determination of the extended design time due to a certain degree of overlapping in a pair
of activities. It is made through the utilization of concepts of workflow construction
with hidden (semi) Markov models theory and establishing a way to disaggregate activities
into sub-activities, in order to determine the activity parameters used by the project
scheduling techniques. With the aim to make a correlation between the entropy of the state
transitions and the probability of changes, the information theory is also used, and the
concept of impact caused by the probability of changes is provided. Numerical examples are
shown for the purpose to demonstrate the applicability of the concepts developed, and one
example of overlapping of two activities is shown. The original contributions of this work
are shown on the last section.