DataTable is an API only (i.e. virtual class with no slots) for accessing objects with a rectangular shape like DataFrame or RangedData objects. It mimics the API for standard data.frame objects.
A FilterMatrix object is a matrix meant for storing the logical output of a set of FilterRules, where each rule corresponds to a column. The FilterRules are stored within the FilterMatrix object, for the sake of provenance. In general, a FilterMatrix behaves like an ordinary matrix.
A FilterRules object is a collection of filter rules, which can be either expression or function objects. Rules can be disabled/enabled individually, facilitating experimenting with different combinations of filters.
The Hits class is a container for representing a set of hits between a set of left nodes and a set of right nodes. Note that only the hits are stored in the object. No information about the left or right nodes is stored, except their number.