Auxiliary Resources

The CPM Procedure

Auxiliary Resources

Sometimes, the use of a certain resource may require simultaneous use of other resources. For example, the use of a crane necessitates the use of a crane operator. In other words, if an activity needs the resource, CRANE, it will also need a corresponding resource, CRANEOP. Such requirements can be easily modeled by adding both CRANE and CRANEOP to the list of resources required by the activity.

However, when alternate resources are used, the problem becomes more complex. For example, suppose an activity requires a CRANE and there are two possible cranes that can be used, CRANE1 and CRANE2. You can specify CRANE1 and CRANE2 as the alternate resources for CRANE. Each of the two cranes has a specific operator, CRANEOP1 and CRANEOP2, respectively. Specifying CRANEOP1 and CRANEOP2 separately as alternates for CRANEOP will not necessarily guarantee that CRANEOP1 (or CRANEOP2) is used as the alternate for CRANEOP in conjunction with the use of the corresponding CRANE1 (or CRANE2).

You can model such a situation by the use of Auxiliary resource specification: specify CRANEOP1 and CRANEOP2 as auxiliary resources for CRANE1 and CRANE2, respectively. Auxiliary resources are specified via the Resource data set, using observations identified by the keyword AUXRES for the value of the OBSTYPE variable. For an observation of this type, the RESID variable specifies the name of the primary resource. (This is similar to the specification of ALTRATE and ALTPRTY.)

Once auxiliary resources are specified in the Resource data set, it is sufficient to specify only the primary resource requirements in the Activity data set. In this situation, for example, it is sufficient to require a CRANE for the activity in the Activity data set.

In the Resource data set, add a new observation type, `AUXRES', which will specify the auxiliary resources that are needed for each primary resource. For an observation of this type, the RESID variable specifies the name of the primary resource. The value for each auxiliary resource indicates the rate at which it is required whenever the primary resource is used. You will also need to specify CRANE1 and CRANE2 as the alternate resources for CRANE in the Resource data set.

When scheduling the activity, PROC CPM will schedule CRANE1 (or CRANE2) as the alternate only if both CRANE1 and CRANEOP1 (or CRANE2 and CRANEOP2) are available.

For instance, the above example will have the following Resource data set:

  OBSTYPE   RESID   PER     CRANE CRANE1 CRANE2 CRANEOP1 CRANEOP2 
 
  AUXRES    CRANE1   .        .     .      .        1       . 
  AUXRES    CRANE2   .        .     .      .        .       1 
  ALTRATE   CRANE    .        .     1      1        .       . 
  RESLEVEL    .     10DEC99   .     1      1        1       1

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