Originally posted by: BEA123

I would like to create a model that pulls its data from Access, but I cannot execute the following constraint:

forall (p in period)

 workers[p]-workers[p-1]==hire[p]-fire[p];

where period is the string used to reference the access data base.  I guess my real question is it even possible to create a constraint that references the previous string value, e.g. workers in NOV - workers in OCT, or is there another way to connect to access without using strings that will allow me to execute the above constraint?

I think what you are looking for is this (also see the reference documentation about sets):

{string} period = { "JAN", "FEB", "MAR" };
dvar int workers[period];
dvar int hire[period];
dvar int fire[period];
 
minimize 0;
subject to {
  forall (p in period : p != first(period))
    workers[p]-workers[prev(period, p)]==hire[p]-fire[p];
}

Note that there is a Forum dedicated to OPL. You may be better off asking your question there.