A dataset is a sequential array of factoids (ground atoms). See example below.
[p(a,b), p(b,c), p(c,d), q(b), r(c)]
EpilogJS datasets can be either indexed or unindexed. An indexed dataset is one that is also an index. (See index.) In EpilogJS, datasets are "full" indexed by default (see fullindex). The user can alter this default by changing the value of the variables dataindexing. An unindexed dataset is one that does not have an index. As a result, lookup, update, and inference procedures must search the entire dataset rather than relying on an index to economize on this work.