The sequence of activities can be based on multiple dependencies. Some of them are listed below:
Mandatory Dependency (Hard Logic):
A mandatory dependency is a natural flow of work being done (e.g. you must give the command to print before you can print). It may be required by the contract.
Discretionary Dependency (Preferred, Preferential, or Soft Logic):
A project team cannot easily change other types of dependencies. However, they can change the discretionary dependency. A discretionary dependency is determined by the project manager and the project team. Discretionary dependency is quite useful when there is a need to compress the project schedule or fast track the project.
Parties outside the project can also influence the project. External Dependency is based on the needs of a party outside the project (e.g. labor union, regulators, etc)
A lead may be used to indicate that an activity can start before its predecessor activity is completed. For example, editing of a book may start before the write-up is finished.
A lag is inserted by waiting time between activities, such as requiring to wait for completion of the application testing before the final roll-out of an application. Sequence Activities process may also result in the identification of new risks. It may also lead to updates to activity list and activity attributes.