Before examining the solution of specific sequencing models, you will find it useful to have an overview of such systems. This section classifies the sequencing problems.

The usual pattern of arrivals into the system may be static or dynamic.

**Static.** If certain number of jobs arrive simultaneously and
no further jobs arrive until the present set of jobs has been processed,
then the problem is said to be static.

** Dynamic. **In this case, jobs arrive after certain interval of
time and arrival of jobs will continue indefinitely in future also.

A sequencing problem may be called single processor or multiple processor problem, according to the number of machines available in the shop. The multiple processor case may be further classified as

- parallel
- series
- hybrid

**Fixed sequence.** In this case, given jobs are processed in a
fixed order. An example of such a case will be where each job is to
be processed first on machine 1, then on machine 2 then on machine 3,
and so on.

**Random Sequence.** In this case, given jobs are processed in a
random order.

**Deterministic.** If the processing time is known with certainty,
it is a deterministic problem.

**Probabilistic.** If only expected processing time is known, then
it is a probabilistic problem.