All of the situations considered earlier can be interpreted in terms of resource-constrained project scheduling. To do so, we introduce the concept of an Operation as some process having a certain duration and consuming certain resources. Each two operations may be either dependent or independent in the sense that the calendar time of one of them either affects or does not affect that of another. Each machine may be considered as a non-accumulated indivisible resource which restricts the possibility of performing two or more operations of job processing simultaneously.