The family of problems of a machine model on parallel machines has the constraint fields machine environment, number of machines, number of jobs, processing times, machine sets, release dates, deadlines, precedence constraints with time lags, communication delays, a server, forbidden times and the input encoding, and the completion-time objectives.

A problem $\alpha \mid \beta \mid \gamma$ of the three-field notation is one specification of this family: $\alpha$ is the machine environment and count, $\beta$ lists the values of the constraint fields, and $\gamma$ is the objective. The entry $\mathrm{pmtn}$ of $\beta$ selects the preemptive machine model, and the entry restarts the model with restarts; the concept on one family for parallel machines joins the three models into a single family with an interruption field. For example $1 \mid\mid \sum C_j$, $1 \mid r_j \mid \sum C_j$, $P \mid p_j = 1, \mathrm{chains} \mid C_{\max}$ and $R \mid r_j, \mathrm{prec} \mid \sum w_j T_j$ are the specifications below.

Theorem. In every machine model, a specification that is field by field a special case of another describes a special case of the other's problem, and a specification that reduces to another describes a problem whose decision version reduces to that of the other. The same holds for reductions through flow time in every machine model in which jobs start no later than they complete. In particular $1 \mid\mid \sum C_j$ is a special case of $R \mid r_j, \mathrm{prec} \mid \sum w_j T_j$.