THE SCHEMA SYSTEM EMBODIES A KNOWLEDGE-BASED APPROACH TO SCENE INTERPRE- TATION. LOW-LEVEL ROUTINES ARE APPLIED TO EXTRACT IMAGE DESCRIPTORS CALLED TOKENS, AND THESE TOKENS ARE FURTHER ORGANIZED BY INTERMEDIATE-LEVEL ROUT- INES INTO MORE ABSTRACT STRUCTURES THAT CAN BE ASSOCIATED WITH OBJECT INST- ANCES. THE THOUSANDS OF TOKENS THAT ARE EXTRACTED FROM AN IMAGE CAN BE GROUPED IN A COMBINATORIALLY EXPLOSIVE MANNER. THEREFORE, KNOWLEDGE IN THE SCHEMA SYSTEM IS NOT LIMITED TO THE DESCRIPTIONS OF OBJECTS; IT INCLUDES INFORMATION ABOUT HOW EACH OBJECT CAN BE RECOGNIZED. OBJECT SCHEMAS CONTROL THE INVOCATION AND EXECUTION OF THE LOW-LEVEL AND INTERMEDIATE-LEVEL ROUT- INES WITH THE GOAL OF FORMING HYPOTHESES ABOUT OBJECTS IN THE SCENE. THE SYSTEM DESCRIBED PRODUCES IMAGE INTERPRETATIONS BASED ON TWO-DIMENSIONAL REASONING, ALTHOUGH NOTHING IN THE SYSTEM ORGANIZATION AND CONTROL STRATEG- IES PRECLUDE THE INCLUSION OF THREE-DIMENSIONAL INFORMATION. THE SCHEMA FRAMEWORK EXPLOITS COARSE-GRAINED PARALLELISM IN A COOPERA- TIVE INTERPRETATION PROCESS. SCHEMA INSTANCES RUN CONCURRENTLY, AND AN OB- JECT SCHEMA OFTEN HAS AVAILABLE A VARIETY OF STRATEGIES FOR IDENTIFICATION, EACH ONE INVOKING KNOWLEDGE SOURCES TO GATHER SUPPORT FOR THE PRESENCE OF A HYPOTHESIZED OBJECT. INTER-SCHEMA COMMUNICATION IS CARRIED OUT ASYNCHRON- OUSLY THROUGH A GLOBAL BLACKBOARD. IN THIS WAY SCHEMA INSTANCES COOPERATE TO IDENTIFY AND LOCATE THE SIGNIFICANT OBJECTS PRESENT IN THE SCENE.