Grammar Engineering Frequently Asked Questions

Some of my relations/qeqs aren't showing up in the MRS for the whole parse. Why not?

If relations or qeqs that are contributed by lexical entries or rules are not showing up in the MRS for the whole parse, it is almost certainly because you have a broken diff-list append somewhere in the structure. The most common way for a diff-list append to break is for one of the arguments to be underspecified as to its length. You should check that the RELS and HCONS lists inside CONT on each lexical entry and the RELS and HCONS lists inside C-CONT (NB: not CONT) of each lexical rule and phrase structure rule are bounded. The easiest way to do this is with the <! !> notation:

• <! !> a diff-list with nothing on it.
• <! top !> a diff-list with one thing on it.
• <! top, top !> a diff-list with two things on it.
• <! top, ... !> a diff-list with at least one thing on it: underconstrained!
• [ LIST.FIRST top ] a diff-list with top as its first thing: underconstrained!

Some of the types defined in matrix.tdl already sufficiently specify the length of the RELS and/or HCONS lists. Here is a sample (as of 20-May-2005, courtesy of Jonathan Pool):

• lexeme-to-word-rule
• no-ccont-lex-rule
• basic-head-subj-phrase
• basic-head-spec-phrase
• basic-head-comp-phrase
• basic-head-opt-comp-phrase
• basic-extracted-comp-phrase
• extracted-adj-phrase
• scopal-mod-phrase
• isect-mod-phrase
• declarative-clause
• basic-bare-np-phrase
• no-hcons-lex-item
• scopal-mod-lex
• basic-determiner-lex
• basic-subord-conjunction-lex
• single-rel-lex-item

In most cases, your rules and lexical types should inherit from one of the above. When they don't, you'll need to be sure to constrain the length of the RELS and HCONS lists.

Related topics

• What's a difference list, and why do we use them?
• The LKB says "Cyclic check found cycle at ...". What does this mean and how do I debug it?

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-- EmilyBender - 18 May 2005, 20 May 2005