SHRDLU (1968) › Understanding Through Action
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SHRDLU grounded language in action within what researchers called a "blocks world." This simplified virtual environment contained blocks, pyramids, and boxes of various colors on a flat surface. A simulated robot arm could pick up, move, and stack the objects in response to instructions. Language processing therefore operated against a world whose state the program could inspect and change.
SHRDLU connected several components that earlier dialogue systems had kept separate. It parsed sentences with formal grammar rules, interpreted commands and questions, and maintained a world state that tracked the positions, properties, and relationships of every object. It could then plan and execute requested actions, answer questions about the current arrangement, and recall earlier actions.
Unlike ELIZA's pattern-matching dialogue, SHRDLU used an explicit model of its world. It updated that model after each action and applied rules to spatial relationships and object properties. Within its simulated setting, the system showed how language could be interpreted against a changing context rather than handled as isolated text patterns.