Adds the given Entry (completed constituent) to the chart and
tries to add or extend arcs (possibly adding new entries to the
agenda for completed arcs).
The basic data structure for a chart parser, constisting of a set of
entries (completed constituents) and a set of active arcs (representing
partially-completed constituents corresponding to grammar rules).
From BottomUpChartParser:
If the constituent of the given Entry matches the next Constituent
of the given Arc, then create and return a new Arc extending the given
one, otherwise return null.
If the constituent of the given Entry matches the next Constituent
of the given Arc, then create and return a new Arc extending the given
one, otherwise return null.
A GrammarRule consists of a left-hand side (a single Constituent, the
``product'' or ``mother'' of the rule), and a right-hand side (a list of
Constituents, the ``preconditions'' or ``daughters'' of the rule).
Retrieve the List of GrammarRules whose first rhs constituent
unifies with the given AugmentedConstituent (and which have the
unifying subsitution applied).
An HeadFeaturedGrammar is one whose rules are HeadFeaturedGrammarRules (ie,
whose rules have constituents that are HeadFeaturedConstituents, ie.,
they can be marked as head constituents).