4.8 Trace formats

4.8.1 Generator trace

4.8.2 Recognizer trace

Figure 4.16 Level 1 generator trace

Figure 4.17 Level 2 generator trace

Figure 4.18 Level 3 generator trace

Figure 4.19 Level 1 recognizer trace

Figure 4.20 Level 2 recognizer trace

Figure 4.21 Level 3 recognizer trace

This section explains how to read the output of the generator and recognizer traces. Traces are produced by the set tracing command described in section 4.5.6.1. The amount of detail shown in the trace display is set by the tracing level. The level argument to the set tracing command can range from 0 to 3, where 0 is no tracing at all and 3 is the most detailed level of tracing.

4.8.1 Generator trace

There are three levels of tracing differing in the amount of detail they display: Level 1 gives the least amount of detail, level 2 (the default) gives a moderate amount of detail, and level 3 gives the most detail. Figure 4.16 is a level 1 generator trace of the lexical form `fox+s (taken from the English example). The only difference from no tracing at all is that the RESULT line is displayed. This line differs from the normal result that is returned because it prints all NULL symbols in the output surface form.

Figure 4.16 Level 1 generator trace

Figure 4.17 is from a level 2 generator trace for the form `fox+s. To limit the size of the trace, the Gemination rules (14 and 15) were turned off. Line numbers and column numbers are printed here for reference in the description that follows. Each description refers to an element beginning at the line and column indicated.

Figure 4.17 Level 2 generator trace

• Line 1: Input line. Lexical form input to the generator function.

• Line 19: RESULT line. Surface form produced by the generator function. At the point where the input lexical form is empty and each automaton is in a final state, the trace shows that the generator has recorded a result. The generator continues looking for additional results (lines 21 and following).

• Column 1: Level number (all lines except 1, 19, and 42). This represents the level of recursion. Level 0 represents the initial invocation of the generator. Notice that the number coincides with the number of characters in the result string so far.

• Column 1: Backtracking indicator (lines 10, 11, 13). The symbol - indicates that the generator is blocked at that level. The symbol < indicates that the generator is backtracking (that is, returning to a lower level to try another path).

• Column 2: Input pair (lines 2-9, 12, 14-16). This is the lexical:surface pair (from the set of feasible pairs) that is currently being considered by the generator (for example, f:f on line 4). The rest of the line shows the results of stepping the automata with the pair as input. The results are indicated by either a new state configuration (for example, line 5) or a BLOCKED BY RULE message (for example, line 10).

• Lines 10, 13: BLOCKED BY RULE message. Indicates that a feasible pair input to the function that steps the automata caused a rule to fail. Gives the number and name of the rule (from the header line of the state table) that failed.

• Columns 3-17: State configuration (lines 2-9, 11-12, 14-17). These are the current states of each of the rules. The leftmost number is the state of rule 1, the second is rule 2, and so on.

• Column 18: Result (lines 4-9, 11-12, 14-17). This is the current value of the result string.

• Lines 21-41: The generator continues to backtrack, looking for other possible paths to a result, until finding no other path it returns to its initial state.

There is one other tracing message not exemplified in the above display. This is the END OF INPUT message. It indicates that the end of the input form has been reached but the generator function has failed on the rule specified because it was not in a final state. For example,

END OF INPUT, FAILED RULE 4: Palatalization

Figure 4.18 Level 3 generator trace

Figure 4.18 is part of a level 3 trace for the same form. The level 3 trace differs from the level 2 trace in how it displays rule failures that block the generator. Compare line 10 in the level 2 trace with lines 10 and 11 of the level 3 trace. The level 3 trace explicitly shows what state the automata are in after stepping them. In line 10 of the level 3 trace we can see that the proposed input pair puts rule 3 in state 0, which means that it fails. Notice that the rest of the state array is filled with question marks. This is because if one rule fails the whole configuration fails, so the rest of the rules are not even tried. (This shows that even though conceptually the automata operate in parallel they must still be stepped one at a time).

4.8.2 Recognizer trace

There are three levels of tracing differing in the amount of detail they display: level 1 gives the least amount of detail, level 2 (the default) gives a moderate amount of detail, and level 3 gives the most detail.

Figure 4.19 Level 1 recognizer trace

Figure 4.19 is a level 1 recognizer trace of the surface form foxes (taken from the English example). Like the level 1 generator trace, the level 1 recognizer trace displays the RESULT line but does not show the feasible pairs as they are tried or the states of the rules. However, it does display a record of how the recognizer moves through the lexicon, either with an ENTERING} or a BACKING UP message.

Figure 4.20 is from a level 2 recognizer trace of the form foxes. To limit the size of the trace, the Gemination rules (14 and 15) were turned off. Line numbers and column numbers are printed here for reference in the description that follows. Each description refers to an element beginning at the line and column indicated.

Figure 4.20 Level 2 recognizer trace

• Line 1: Input line. Surface form input to the recognizer function.

• Line 30: RESULT line. At the point where there are no lexicons in the continuation class of an entry, the input surface form is empty, and each automaton is in a final state, the trace shows that the recognizer has recorded a result. The recognizer continues looking for additional results (lines 32 and following).

• Column 1: Level number (lines 2, 6-11, 13-19, 21-23, 27-28). This represents the level of recursion. Level 0 represents the initial invocation of the recognizer. Notice that the number coincides with the number of characters in the result string so far.

• Column 1: Backtracking indicator (lines 8, 15, 18, 22-23). The symbol - indicates that the recognizer is blocked at that level. The symbol < indicates that the recognizer is backtracking (that is, returning to a lower level to try another path).

• Column 2: Input pair (lines 2, 6-7, 9-11, and so on). This is the lexical:surface pair (from the set of feasible pairs) that is currently being considered by the recognizer (for example, f:f on line 9). The results of stepping the automata with the pair as input are indicated by either a new state configuration (for example, line 10) or a BLOCKED BY RULE message (for example, line 15).

• Lines 3, 5, 12, 20, 25: ENTERING LEXICON message. This is the name of the sublexicon that the recognizer is about to search.

• Lines 4, 24, 26: ACCEPTING NULL ENTRY message. message} Indicates that a null lexical entry (that is, an entry whose lexical item is the NULL symbol) has been accepted.

• Line 22: BLOCKED IN LEXICON message. Indicates that no lexical entry could be found in the current lexicon that continues with the input pair under consideration. The remaining part of the input form is displayed on the line (in line 22 it happens that nothing is left of the input form).

• Lines 108, 110: BACKING UP message. Indicates that there were no further sublexicons left in the continuation class, so the recognizer must back up to the previous lexicon branch.

• Lines 8, 15, 18: BLOCKED BY RULE message. Indicates that a feasible pair input to the function that steps the automata caused a rule to fail. Gives the number and name of the rule (from the header line of the state table) that failed.

• Columns 3-17: State configuration (lines 2, 6-7, 9-11, and so on). These are the current states of each of the rules. The leftmost number is the state of rule 1, the second is rule 2, and so on.

• Column 18: Result (lines 6-7 and so on). This is the current value of the result string.

• Lines 108-111: The recognizer continues to backtrack, looking for other possible paths to a result, until finding no other path it returns to its initial state.

The END OF INPUT message may also occur in a recognizer trace. See section 4.8.1 on the generator trace for an explanation of it.

Figure 4.21 Level 3 recognizer trace

Figure 4.21 is part of a level 3 trace for the same form. Like level 3 of the generator trace, level 3 of the recognizer trace explicitly shows the state array when a rule fails. Compare line 8 of the level 2 trace with lines 18 and 19 of the level 3 trace. In addition, the level 3 recognizer trace shows pairs that are weeded out by the lexicon even before they are tried with the rules. Compare lines 3-4 of the level 2 trace with lines 3-10 of the level 3 trace. In lines 4-9 the level 3 trace shows explicitly several pairs that are tried but immediately fail. Since the recognizer is at the beginning of the input form, the only possible feasible pairs to try are those whose surface character is 0 (the NULL symbol) or f (the first character of the input form foxes). Rather than trying each of these pairs with the rules, the recognizer first looks to see if the lexical character of each pair matches any lexical character available in the sublexicon it is currently searching. In each case the match fails, indicated by the message LEXICAL CHARACTER NOT MATCHED. After trying all the pairs, the lexicon accepts the null entry and enters a new sublexicon. This exhaustive process takes place at each point in the recognition process where the recognizer is trying a new pair.