A Formal System for Slot Grammar

The purpose of this document is to describe a syntax rule formalism, SGF, for Slot Grammar (SG), along with enough system information so that the reader should be able to write the syntax rules for a Slot Grammar for a specific natural language. The syntax of SGF itself is Cambridge Polish (Lisp-like). SGF follows the central theme of Slot Grammar -- that analysis (or parsing) consists of slot-filling. A typical rule of SGF deals with filling a slot S, where the proposed filler (or modifier) phrase M and the higher phrase H (the "owner" of the slot S) have been tentatively chosen by the parsing algorithm. The main function of such a slot-filling rule is simply to decide whether M can indeed fill S in H. But the rule can do other things, such as setting features in H or M, "raising" slots from M into H, or affecting a numerical parse score for H with its new modifier. The SGF formalism makes it easy to "explore" the phrases M and H, examining features or other ingredients in any subphrases within these phrases, or even querying alternative parses for existing word spans. There is a rich and flexible set of operators for examining the components of parse trees. The SGF rules are in a sense object-oriented , because in any part of a rule there is always an implicit phrase (node) in focus -- the phrase being examined by that part of the rule. Selection operators need not mention the current phrase in focus because it is implicit, so they can be more succinct. There are convenient operators for shifting the focus, like going down to a modifier, which can proceed non-deterministically, depending on conditions placed on the modfier.