Discrete seriation is a special case of Shortest Path seriation where the feature values happen for an item (artifact or asemblage) to be integral. The seriation technique can be set in the Seriations table. In discrete seriation features are categorized into classes which are numbered discretely: 0, 1, 2, …, n for each feature. The objective is to order items keeping each class together and to progress gradually from one class to the next in nominal size. See Ranked Data.
The underlying assumption in discrete seriation is that a feature will normally be introduced only once in the evolution of an artifact type - once the feature has appeared and then been absent in artifacts for a period of time it will not reappear, and that the values or measures of the individual features will tend to change slowly and smoothly over time. Most implementations of discrete seriation attempt to order the artifacts temporally so as to minimize the number of times that a distinct feature is introduced into the archaeological record (transitions from absent to present, and present to absent) and so as to minimize the number of reversals from increasing to decreasing, or vice versa, of the individual feature's values.
It is important for the user not to set the Objective function to Min Unimodal Index; use Min Path Length or Min Average Rate of Change instead. Note that a perfectly unimodal path would not necessarily be optimal for discrete seriation as the stages could increase for a while and then decrease. If a unimodal seriation is what you want, there is no need to use Discrete seriation; use Shortest Path seriation with an objective of Min Unimodal Index instead.
Discrete seriation is a special case of the Optimal Path seriation model. Setting the parameter Technique to Discrete in the Seriations table specifies OptiPath's standard implementation of discrete seriation. Data may take on any numerical value (fractions are rounded to the nearest whole number) but blanks are assumed to represent an unknown value and the absence of the feature (class or style) in question. All other numerical values are taken to indicate the presence of the feature and non-numerical values are treated as unknowns. Setting the seriation parameter Technique to Discrete causes OptiPath to automatically set the Feature parameters Data, Ranks, Metric, Normalize, Transition, Earlier, Later, Blanks and Zeroes to specific values.
The following are the default Feature parameter settings for Discrete seriation. To change them you must first select the Custom seriation technique.
| Parameter | Value |
| Data | Ranked |
| Ranks | 0 |
| Metric | Manhattan |
| Normalize | No |
| Transition | 50 |
| Earlier | Absent & Unknown |
| Later | Absent & Unknown |
| Blanks | Absent & Unknown |
| Zeroes | Present & Zero |
These settings result in any numerical entry in the data being interpreted as indicating the presence of a feature (class or style) and any blank data being interpreted as absence of the feature with the value unknown. If you do not want blanks or zeroes to be interpreted in this way, you should reset the seriation parameter Technique to Custom and reset the feature parameters Blanks and Zeroes. To see the effect of your settings, look at processed data in the Values table.
In discrete seriation, careful thought should be put into setting the Feature parameters appropriately - see Setting the Earlier, Later, Blanks, Zeroes and Transition Parameters.