TRALE-EXTENSION:The Chart Display

Trale includes code to produce output for a Chart Display developed at the DFKI in Saarbrücken. The chart display has the following functionality:

• All passive edges that are produced during a parse are displayed.
• Several subsets of edges might be displayed:
  • All edges that contributed to solutions.
  • All edges that start/end at a certain position.
  • All edges that were licenced by a certain rule.
  • All dominated edges of a certain edge.
  • All edges that dominate a certain edge.
• A list of rules in the grammar is displayed and they can be inspected.
• The rules can be applied interactively to edges in the chart and unification failures are displayed (not fully implemented yet).
• You can generate from an edge (not fully tested).
• If your grammar has an MRS semantics you can display MRSses.

TRALE-EXTENSION:Installation and Customization

To get the Tcl/TK code please contact Stephan Busemann (Stephan.Busemann@dfki.de (mailto:Stephan.Busemann@dfki.de)). The TCL/TK code has to be installed in the trale directory under chart_display/TCL. Tcl/TK has to be installed and wish has to be in your search path.

Specify the following in your theory.pl

:- load_cd.              % loads the code for the chart display

root_symbol(@root).      % symbol for input that does not end with punctuation
imp_symbol(@imp).        % symbol for input that ends with '!'
decl_symbol(@decl).      % symbol for input that ends with '.'
que_symbol(@que).        % symbol for input that ends with '?'

cont_path([synsem,loc,cont]). % the path to the semantic content

:- chart_display.        % switches the chart display on (default)
:- nochart_display.      % switches the chart display off

:- english.              % the commands in the Chartdisplay are English (default)
:- german.               % the commands in the Chartdisplay are German

:- tcl_warnings.         % output of warnings in a TCL window (default)
:- notcl_warnings.       % output of warnings to console

:- mrs.                  % output of MRS for a parsed string
:- nomrs.                % no output (default)

:- fs.                   % switches feature structure output on (default)
:- nofs.                 % switches feature structure output off

The macros that are given as arguments to root_symbol, imp_symbol, decl_symbol, and que_symbol have to be specified in your grammar.

You may customize the chart display yourself or use one of the dot.chartdisplay files supplied in trale_home(chart_display). They should be moved to ~/.chartdisplay.

If you put the following line in your .emacs, the prompt of the command go will be recognized by SICStus Prolog and you can type Ctrl-C Ctrl-P to get to the previous input and parse it (or call it) again.

(setq sicstus-prompt-regexp ">>> *\\|| [ ?][- ] *")

If your coursor is in the line of a priviously parsed utterance, you may simply hit return and the sentence is parsed again.

TRALE-EXTENSION:Working with the Chart Display

Typing go. brings you to an interactive mode. You can type in a sentence and you will get parsing results displayed either with grisu or to stdout depending on whether you use grisu (strongly recommended). If not open the chart display will pop up (after a parse) and the chart will be displayed. The left mouse button gives you actions you can apply to the edge you point to and the right mouse button gives you actions you can perform on the whole chart. The rule names at the left hand side are also clickable. Empty elements are not clickable yet.

While in the interactive mode, you can execute simple commands directly, provided the command does not correspond to a lexical item in your grammar. For instance reloading of a grammar can be done in the interactive mode by typing c.. However, if your grammar contains the letter c as a lexical object, it will be parsed rather than executed.

fs and nofs only affect the feature structure output for sentences parsed in the interactive mode. Parses initiated with rec directly are not affected by this switch.

TRALE-EXTENSION:Debugging

You can use the chart display for debugging rule applications: First select a rule by clicking at the rule and choosing the menu item `Select rule'. Then select an edge from the chart. All goals that are at the first position of the rule (specified with goal> in the rule) will be executed. Then the selected edge will be unified with the first daughter of the rule. If the unification succeeds and the blocked constraints that are attached to the rule and to the edge are satisfied, the next goals specified in the rule will be executed. If this succeeds it is checked whether there are further daughters. If this is not the case we have a passive edge which is shown to the user. If there are further daughters an active edge is stored. This active edge can be displayed by clicking somewhere in the display and pressing the right mouse button. In the following other passive edges from the chart can be combined with the active edge. If the combination succeeds, the rule and the successfully combined daughters are marked green. Otherwise the edge that could not be combined is marked red. In case of a failure another passive edge can be tested against the active edge.

If you select another rule, the active edge is deleted.

The debugging of constraints that fire due to instantiations during a unification is difficult. To enable the debugging of single constraints a flag is set if the char tdisplay is used for debugging. For instance if you want to check whether a certain constraint fires, you may include debug information in the constraint. In the following example the flag chart_debug/1 is tested and if its value is on, a debug message is printed.

undelayed_accusative([El|T1]) if
  prolog((chart_debug(on) ->
          write(user_error,'Trying to assign accusative.'),
          nl(user_error)
         ;true
         )),
  assign_acc(El),
  accusative(T1).

Instead of printing a message you can also call the debugger or do other things. Since this constrinat may be called during the lexicon compilation as well it would be very difficult to debug without the flag, since you would enter debug modus thousand times before you loaded the grammar completely.

TRALE-EXTENSION:Generation

Chart edges can be used as input for generation. You have to specify the path in your feature structures that yields the semantic information. (SYNSEMLOCCONT is the predefined path.) The semantic contribution of a selected chart edge will be taken as input for generation and all generation results will be displayed.