Frequently Asked Questions

I'm trying to add a new feature, and the LKB doesn't like it. What should I do?

There are two rules about where you can declare new features:

"No possible type ..."

If you're getting the error message "No possible type for features (...) at path (...)" you have probably tried to introduce a feature other than in the outermost feature structure. For example, if you wanted to add a feature CASE appropriate only for nouns, the correct way to do it is on the type noun (subtype of head):

noun := head &
   [ CASE case ].

If instead, you tried to do it on noun-lex:

noun-lex := basic-noun-lex & spr-only-lex-item &
                           [ CASE case ] ].
you would get this error message. (If you also have the correct declaration on noun, the constraint shown here on noun-lex won't cause an error, but it will be redundant.)

[feature defined for two different types]

As stated above, features can only be declared for one type. If two types need the same feature, they need to have a common supertype from which to inherit it. You might hit this error if you happen to try to reuse a feature name already in use in the matrix, or if you try to declare a feature for two types at the same time (e.g., FORM on verb and prep) instead of putting it on a supertype.

NB: You can of course mention features on multiple types, and often need to in order to constrain their values appropriately. They just need to be introduced on a supertype to all types that they are appropriate for. This doesn't mean that e.g., noun-lex needs to inherit from noun in order to constrain a value of CASE. In the example above, CASE remains a feature of noun, which happens to be the value at the end of a path inside noun-lex.

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