1 B. SW Project planning & scheduling Recap from previous slide: It is important to decide on who is responsible for each activity. See Yeates & Cadle (OHT 8.8) for a Linear Responsibility Chart. Such a chart could be used, for example, in section “2.4 Project Responsibilities” of the “software development plan”. Note the different kins of roles and their degree of “responsibility”

2 B. SW Project planning & scheduling Establishing precedence relationships between activities. Each work package description should identify the inputs and outputs from its constituent activities. At this stage, we are concerned with “real” precedence relationships rather than those that might arise because of, say, lack of workers. A table such as illustrated in Yeates & Cadle (OHT 8.9) is helpful – this kind of information can be easily inputted into Microsoft Project. We can see that the immediate predecessors of A, B, C, D and E are, respectively, D & C, A, D, None and C (check!)

3 B. SW Project planning & scheduling The basic tool for depicting activities and their inter-relationships is a project network model. Two kinds of commonly in use activity-on- arrow and activity-on-node. The basic rules for “activity-on-node” networks are (e.g. Yeates & Cadle (OHT 8.13) –Only one start or end node (No dangles!) –A node normally has duration (except maybe “start” and/or “end”) –Might choose initially not to put in duration – just the precedence –Links normally have no duration – just represent relationships –Time moves from left to right (if at all possible) – can have arrows –No loops allowed –May wish to represent lagged activities (e.g. two parallel activities one starting 2 days after the other).

4 B. SW Project planning & scheduling The basic rules for “activity-on-arrow” networks are (e.g. Yeates & Cadle (OHT 8.10) [node=event, link=activity] –Only one start or end node (No dangles!) –A link (arrow) normally has duration (except maybe “start” and/or “end”). (Dummy activities have zero duration – see below) –Might choose initially not to put in duration – just the precedence –Nodes have no duration – represent points in time –Time moves from left to right (if at all possible) – can have arrows –Nodes are numbered sequentially – no precise rules –No loops allowed –Dummay activities (dotted arrows) have zero duration. Used for example to show that preceding activities must all finish before next can start –May wish to represent lagged activities (e.g. two parallel activities one starting 2 days after the other). Not as neat as for “activity-on-node.

5 B. SW Project planning & scheduling The Critical Path is the sequence of activities in a network which are such that if any one of them is delayed then the whole project is delayed. To identify the critical path we must add in the time dimension. This means that we must come up with estimated durations for all activities. See Yeates & Cadle (OHT 8.11) for an example of an activity-on-arrow network with durations included and the critical path in bold. Normally a tool such as Microsoft Project will calculate the critical path but it is important to understand the principles involved …

6 B. SW Project planning & scheduling In general, the Critical Path Method is concerned with (a) planning such that the project is completed as soon as possible and (b) calculating the actual critical path. The method requires that one works out 4 times associated with each activity (see Yeates & Cadle (OHT 8.12) ). The times are worked out in a forward pass (from start to finish) followed by a backward pass (from finish to start). These times can be displayed in the network diagram (see Yeates & Cadle (OHT 8.13) ). Activity Total float = Activity LST – Activity EST (see Yeates & Cadle (OHT 8.15) ). Any activity with a float of zero is critical and it can be shown that there will always be at least one path joining these critical activities – the Critical Path.