The Chart Display

The chart display lists the edges as blocks arranged over the input string. Since many parsers such as the ones in TRALE and QType proceed by trying to establish edges according to phrase-structure rules, the chart is a very helpful component for understanding which structure the parser is currently working on.

Navigation

Chart edges are tightly coupled with the corresponding parsing steps, allowing the user to jump to the relevant position in the control flow tree by selecting a chart edge. This coupling of steps and the chart also works the other way around: whenever the user selects a step in the control flow tree or in the trace-like message console, the chart display highlights the edge that this step contributed to.

Highlighting

The highlighting can be configured to also include the descendants and/or the ancestors of the selected edge, providing an intuitive visualization of the edges that contributed to the current edge, or the uses of the current edge in establishing larger constituents.

Failed Edges (Experimental)

In addition to the display of all edges that could be established (in green), the chart display allows the user to selectively display all the failed edges (in red) for some phrase-structure rule. The step IDs associated with the failed edges will carry a user directly to the step where the corresponding rule failed, providing direct and detailed access to the reasons why some edge could not be established. A problem of this approach is that backtracking often makes it impossible to identify a single step whose failure is responsible for the failure of a superordinate goal. Therefore, while trying to construct an edge, we usually encounter many substeps which fail, but do not necessarily prevent the edge from being established. Conversely, if a predicate fails, it usually fails multiple times (once in every branch of the search tree), leading to a confusing proliferation of failed edges on the chart. Using a few simple heuristics for distinguishing relevant and spurious failures, this problem can be somewhat alleviated, but the conceptual difficulty remains.