# Activity Sequencing

Activity Sequencing involves the accurate identification of constraints/relationships among activities and establishing the order in which the activities will be accomplished. There are several inputs to this step:

• The activity list developed in the Activity Definition step,
• The product description and characteristics,
• Mandatory constraints/dependencies, such as the fact that a prototype must be fabricated before it can be tested,
• Discretionary constraints/dependencies developed by the program management team based on “best practices” or specific sequences desired by management,
• External dependencies, such as availability of test sites, and
• Other constraints and assumptions.

Techniques used for this are

• Precedence Diagramming Method (PDM) (also known as Activity On Node (AON) technique) is that method for documenting an activity sequence, by which each activity is represented as a node and each node is connected to its successors by an arrow. (mathematically expressed: an acyclic directed graph, but not necessarily a tree: Nodes may have more than one father, but no daughter can indirectly become a father of its own father). Because in this case the nodes represents activities with a durance, one can determine the successor or predecessor relation by subtypes
• Finish-to-Start :- the predecessor has to be finished before successor can start
• Finish-to-Finish :- the predecessor has to be finished before successor can be finished
• Start-to-Start :- the predecessor has to be start before successor can be started
• Start-to-Finish :- the predecessor has to be start before successor can be finished
• Arrow Diagramming Method (ADM) (also known as Activity On Arrow (AOA) technique) is that method for documenting an activity sequence, by which each activity is represented as an arrow and the nodes are the states (of deliverables) which have been reached (generated) by the activities. Because of the structure of this method there exist only one kind of relationship (finish-to-start). And dependencies between states – which don’t refer to activities – must be expressed as dummy-activities (no work content, zero durance)
• Schedule Network Templates are often given as domain specific template
• Dependency Determination tries to clear the relationship between activities
• Mandatory dependencies “are inherent in the nature of the work being done”.
• Discretionary dependencies are dependencies evoked by tradition or best practice and so on and are also known as those, which base on “soft logic” or “preferential logic”. (But of course best practice might be inadequate for the concrete single case.)
• External dependencies are dependencies on states or products and so on which must be reached, given etc. but which don’t are generated by the project itself. Therefore: external dependencies often should become part of the risk list