This FAQ explains how to do interactive unification. To learn about when to use interactive unification, see this FAQ. If you've tried interactive unification, and you're not getting the result you expect, look here. In the chart, click on each of the daughter edges, and select "feature structure" to get the feature structures for the edges. (Interactive unification can also be used to debug a unary rule. Here I'm going to talk about binary rules.)

• In the LKB top menu, choose View > Grammar Rule and pick the rule you think should have applied. This will give you a feature structure for the rule.

• In the feature structure for the rule, scroll down until you find the HEAD-DTR feature (it may be easier to shrink the values for SYNSEM, ARGS, and C-CONT on the way).

• Click on the type that is the value of HEAD-DTR (probably sign, but possibly something more specific), and choose "select" out of the pop-up menu.

• In the feature structure for the edge that should be the head daughter, click on the highest type (e.g., common-noun-lex or head-comp-phrase) and in the pop-up menu choose "unify".

• If the unification failed already, there will be a message in the LKB window telling you the first point at which the two feature structures didn't unify (there may be more).

• The rules tend to be fairly non-specific, so this first unification usually works. If it does, you'll get a new window called "unification result" which is exactly the information from the rule with the information of the head daughter unified in.

• In the unification result feature structure, scroll down (or shrink down) to the NON-HEAD-DTR feature. Click on the value of that feature and choose "select".

• In the feature structure for the edge that should be the non-head daughter, click on the highest type (e.g., det-lex or head-spec-phrase) and choose "unify".

• Go look at the LKB top window for a message indicating the first point at which the two feature structures didn't unify (there may be more). This information should be useful for debugging.

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