In order to complete a rule, all the rules' daughters should be found in the chart as edges. Looking for a matching edge for a daughter is accomplished by attempting unifications (matches) with edges stored in the chart, resulting in many failed unifications.
This section introduces a general indexing method that will be used as the backbone of all indexing methods introduced in this thesis. Without entering into details pertaining to a specific grammar formalisms, the mechanism for indexing a chart parser is presented. The general method outlined here can be applied to any chart-based parser.