Notation for theoretic scheduling problems

Notation for theoretic scheduling problems

A convenient notation for theoretic scheduling problems was introduced by Ronald Graham, Eugene Lawler, Jan Karel Lenstra and Alexander Rinnooy Kan. It consists of three fields: α, β and γ.

Each field may be a comma separated list of words. The α field describes the machine environment, β the job characteristics, and γ the objective function.


Machine environment

Single stage problems

Each job comes with a given processing time.

there is a single machine
there are m parallel identical machines
there are m parallel machines with different given speeds, length of job i on machine j is the processing time pi divided by speed sj
there are m parallel unrelated machines, there are given processing times pij for job i on machine j

The last two letters might be followed by a the number of machines which is then fixed, here m stands then for a fixed number.

Multi-stage problem

open shop problem
flow shop problem
job shop problem

Job characteristics

The processing time may be equal for all jobs (pi = p, or pij = p) or even of unit length (pi = 1, or pij = 1). This makes a difference because all release times, deadlines are assumed to be integer.

for each job a release time is given before which it cannot be scheduled, default is 0.
for each job a deadline is given after which it cannot be scheduled. If the objective is \sum U_i for example, then this field is implicitly assumed.
the jobs may be preempted and execution resumed later, possibly on a different machine
Each job comes with a number of machines on which it must be scheduled at the same time, default is 1.

Precedence relations might be given for the jobs, in form of a partial order, meaning that if i is a predecessor of i' in that order, i' can start only when i is completed.

an arbitrary precedence relation is given
sp-tree, tree, intree, outtree, chain
specific partial orders

Objective functions

Most objective functions depend on the deadline di and the completion time Ci of job i. We define lateness Li = Cidi, earliness Ei = max{0,diCi}, tardiness Ti = max{0,Cidi}, unit penalty Ui = 0 if C_i\le d_i and Ui = 1 otherwise. The common objective functions are C_\max, L_\max, E_\max, T_\max, \sum C_i, \sum L_i, \sum E_i, \sum T_i or weighted version of these sums, where every job comes with a priority wi.


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