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L03 FS: Feature-structures Feature Structures o Feature structures (FS) * FS store information about some entity (typically, linguistic entity such as a word, a phrase, etc.). - Information expressed by means of attribute-value pairs - FS is set of attribute-value pairs * Written in matrix-like notation [ CAT n] [ NUMBER sg] [ PERSON 3] - An attribute is atomic + Ex. CAT, NUMBER, PERSON - Values can be atomic + Ex. n, sg, 3 - A FS with only atomic values, called simple FS - A value can be a FS (in which case the FS is called complex or nested FS) + Ex: Nested feature structure (or complex FS) - Separate CAT and agreement features [ CAT n ] [ AGRMNT [NUMBER sg] ] [ [PERSON 3] ] - Value of feature AGRMNT is a feature structure. o Feature path (AGRMNT NUMBER) o Graph notation for feature structure. CAT /----->------o n / ->o NUMBER \ AGRMNT /---->---o sg \------>-----o \---->---o 3 PERSON - The arc labels are attributes - The node is a value, that is: * Leaf node is an atomic value * Non-leaf node is a FS..........................................NEXT PREVIOUS INDEX