Example 2.12: Activity Time Constraints

The CPM Procedure

Example 2.12: Activity Time Constraints

Often, in addition to a project start date or a project finish date, there may be other time constraints imposed selectively on the activities in the project. The ALIGNDATE and ALIGNTYPE statements enable you to add various types of time constraints on the activities. In this example, the data set WIDGET12 displayed in Output 2.12.1 contains two variables, adate and atype, which enable you to specify these restrictions. For example, the activity `Drawings' has an `feq' (Finish Equals) constraint, requiring it to finish by the 16th of December. The activity `Test Market' has a mandatory start date imposed on it.

Output 2.12.1: Activity Data Set WIDGET12

Activity Time Constraints

Activity data set

Obs	task	days	succ1	succ2	succ3	adate	atype
1	Approve Plan	5	Drawings	Anal. Market	Write Specs	.
2	Drawings	10	Prototype			16DEC91	feq
3	Anal. Market	5	Mkt. Strat.			.
4	Write Specs	5	Prototype			16DEC91	sge
5	Prototype	15	Materials	Facility		.
6	Mkt. Strat.	10	Test Market	Marketing		.
7	Materials	10	Init. Prod.			.
8	Facility	10	Init. Prod.			.
9	Init. Prod.	10	Test Market	Marketing	Evaluate	.
10	Evaluate	10	Changes			28FEB92	fle
11	Test Market	15	Changes			17FEB92	ms
12	Changes	5	Production			.
13	Production	0				.
14	Marketing	0				.

The following statements are needed to schedule the project subject to these restrictions. The option XFERVARS in the PROC CPM statement causes CPM to transfer all variables that were used in the analysis to the Schedule data set. Output 2.12.2 shows the resulting schedule.

   proc cpm data=widget12 date='2dec91'd
        xfervars interval=weekday;
      activity task;
      successor succ1 succ2 succ3;
      duration days;
      aligndate adate;
      aligntype atype;
      run;

   options ls=90;
   title 'Activity Time Constraints';
   title2 'Aligned Schedule';
   proc print;
      id task;
      var adate atype e_: l_: t_float f_float;
      run;

Output 2.12.2: Aligned Schedule

Activity Time Constraints

Aligned Schedule

task	adate	atype	E_START	E_FINISH	L_START	L_FINISH	T_FLOAT	F_FLOAT
Approve Plan	.		02DEC91	06DEC91	26NOV91	02DEC91	-4	-4
Drawings	16DEC91	feq	09DEC91	20DEC91	03DEC91	16DEC91	-4	-4
Anal. Market	.		09DEC91	13DEC91	27JAN92	31JAN92	35	0
Write Specs	16DEC91	sge	16DEC91	20DEC91	23DEC91	27DEC91	5	0
Prototype	.		23DEC91	10JAN92	30DEC91	17JAN92	5	0
Mkt. Strat.	.		16DEC91	27DEC91	03FEB92	14FEB92	35	30
Materials	.		13JAN92	24JAN92	20JAN92	31JAN92	5	0
Facility	.		13JAN92	24JAN92	20JAN92	31JAN92	5	0
Init. Prod.	.		27JAN92	07FEB92	03FEB92	14FEB92	5	0
Evaluate	28FEB92	fle	10FEB92	21FEB92	17FEB92	28FEB92	5	5
Test Market	17FEB92	ms	17FEB92	06MAR92	17FEB92	06MAR92	0	0
Changes	.		09MAR92	13MAR92	09MAR92	13MAR92	0	0
Production	.		16MAR92	16MAR92	16MAR92	16MAR92	0	0
Marketing	.		10FEB92	10FEB92	16MAR92	16MAR92	25	25

Note that the MS and MF constraints are mandatory and override any precedence constraints; thus, both the late start and early start times for the activity `Test Market' coincide with February 17, 1992. However, the other types of constraints are not mandatory; they are superceded by any constraints imposed by the precedence relationships. In other words, neither the early start nor the late start schedule violate precedence constraints. Thus, even though the activity `Drawings' is required to finish on the 16th of December (by the `fle' constraint), the early start schedule causes it to finish on the 20th of December because of its predecessor's schedule. This type of inconsistency is indicated by the presence of negative floats for some of the activities alerting you to the fact that if some of these deadlines are to be met, these activities must start earlier than the early start schedule. Such activities are called supercritical.

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