Software project management (intro) Scheduling Network

Network Planning Model: PERT vs CPM PERT Do A Do C Do B Do D CPM Do A Do B Do C Do D

Constructing CPM Network A network project may have only one start node A network project may have only one end node A link has duration Nodes has no duration 34 code Program test Data take-on install

Constructing CPM Network (2) Time moves from left to right Nodes are numbered sequentially A network may not contain loops 24 code Program test Data take-on install 3 correct diagnose A loop represents an impossible sequence

Constructing CPM Network (3) A network may not contain dangles It would suggest there are two completion points for the project It would suggest there are two completion points for the project 24 code Program test install 3 Write manual Precedents are the immediate preceding activities

Constructing CPM Network (4) Dummy Activities Shown as dotted lines Shown as dotted lines Have a zero duration Have a zero duration Use no resources Use no resources 13 Specify hardware 23a Design data structures 4 Place order 5 Code software

Example – Case ActivityDuration(Weeks)Precedents A – Hardware selection 6 B – Software design 4 C – Install hardware 3A D – Code & test software 4B E – File take on 3B F – Write user manual 10 G – User training 3 E, F H – Install & test system 2 C, D

Example – CPM Network Convention Event number slack Latest date Earliest date A = 6 F = 10 B = 4 C = 3 D = 4 H = 2 E = 3 G = 3

Example – CPM Network (2) Forward pass A = 6 F = 10 B = 4 C = 3 D = 4 H = 2 E = 3 G = 3 Event number slack Latest date Earliest date

Example – CPM Network (3) Backward pass A = 6 F = 10 B = 4 C = 3 D = 4 H = 2 E = 3 G = 3 Event number slack Latest date Earliest date

Critical path Any delay on critical path will delay the project Critical path at least one path through the network joining the critical events (any event with a slack of zero) at least one path through the network joining the critical events (any event with a slack of zero) The longest path through the network The longest path through the network

Critical path – Previous example A = 6 F = 10 B = 4 C = 3 D = 4 H = 2 E = 3 G = 3 Event number slack Latest date Earliest date

Activity Float The difference between ES and LS (or between EF and LF) of an activity It shows how long the activity’s start and completion may be delayed without affecting the end date of the project

Activity Float – Previous Example A = 6 F = 10 B = 4 C = 3 D = 4 H = 2 E = 3 G = 3 TF = LS – ES = LF – EF Total float of A = (2 – 0) = (8 – 6) = 2 B = (3 – 0) = (7 – 4) = 3 C = (8 – 6) = (11 – 9) = 2 D = (7 – 4) = (11 – 8) = 3 E = (7 – 4) = (10 – 7) = 3 F = (0 – 0) = (10 – 10) = 0 G = (10 – 10) = (13 – 13) = 0 H = (11 – 9) = (13 – 11) = 2 Event number slack Latest date Earliest date

Precedence Network Notation ID (Identification Duration ES (Earliest Start) EF (Earliest Finish) LS (Latest Start) LF (Latest Finish)

Example ActivityDescription Preceding Activity Activity Time A System Analysis None5 B Database design A15 C Interface Design A10 D Architectural Design A5 E Data connection B, C 15 FPrototype B, C, D 10 GRevisionF170 HDelivery E, G 35

Network (PERT) ADr: 5 ES: 0EF: 5 LS: 0LF: 5 BDr:15 ES: 5EF: 20 LS: 5LF: 20 CDr: 10 ES: 5EF: 15 LS: 15LF: 20 DDr: 5 ES: 5EF: 10 LS: 15LF: 20 FDr: 10 ES: 20EF: 30 LS: 20LF: 30 GDr: 170 ES = 30EF: 200 LS = 30LF: 200 HDr:35 ES: 200EF: 235 LS: 200LF: 235 EDr: 15 ES: 20EF: 35 LS: 185LF: 200

Gantt Chart

Critical Path The longest activity path(s) through the network. Can be distinguished by identifying the collection of activities that all have the same minimum slack. Indication: the fastest finish = the latest finish (its slack time = 0)

Float/Slack Total slack: the amount of time an activity can be delayed and yet not delay the project Even though it may delay the subsequent/next activities SL = LS – ES SL = LS – ES SL = LF – EF SL = LF – EF

Slack (2) Free slack: The difference between the EF of an activity and the ES of the activity that follows it. The difference between the EF of an activity and the ES of the activity that follows it. Only activities that occur at the end of a chain of activities (usually where there is a merge activity) can have free slack. Only activities that occur at the end of a chain of activities (usually where there is a merge activity) can have free slack. An activity with free slack can be delayed without delaying the ES of activities following it. An activity with free slack can be delayed without delaying the ES of activities following it.

Example 2 ADur = 4 ES = 0EF = 4 LS = 0LF = 4 BDur = 5 ES = 0EF = 5 LS = 5LF = 10 CDur = 5 ES = 4EF = 9 LS = 11LF = 16 DDur = 8 ES = 4EF = 12 LS = 4LF = 12 EDur = 2 ES = 5EF = 7 LS = 10LF = 12 FDur = 3 ES = 9EF = 12 LS = 16LF = 19 GDur = 7 ES = 12EF = 19 LS = 12LF = 19 HDur = 4 ES = 5EF = 9 LS = 15LF = 19 IDur = 0 ES = 19EF = 19 LS = 19LF = 19

Total Slack Total Slack from the previous figure: B: slack 5 = 10 – 5 B: slack 5 = 10 – 5 C: slack 7 = 16 – 9 C: slack 7 = 16 – 9 E: slack 5 = 12 – 7 E: slack 5 = 12 – 7 F: slack 7 = 19 – 12 F: slack 7 = 19 – 12 H: slack 10 = 19 – 9 H: slack 10 = 19 – 9 Free Slack from the previous figure: E: 5 E: 5 F: 7 F: 7 H: 10 H: 10