Commonsense Reasoning About Task Instructions
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Commonsense Reasoning about Task Instructions Rakesh Gupta Ken Hennacy Honda Research Institute USA, Inc. University of Maryland 800 California Street, Suite 300 Institute for Advanced Computer Studies Mountain View, CA 94041 College Park, MD 20742 [email protected] [email protected] Abstract to handle the various difficulties associated with change and scalability (Minker 1991). We have developed an approach for commonsense reason- ing using knowledge collected from volunteers over the web. As an alternative to formal methods that guarantee solu- This knowledge is collected in natural language, and includes tions, implementational approaches place more emphasis on information such as task instructions, locations of objects in adaptation and knowledge acquisition. Studies involving hu- homes, causes and effects, and uses of objects in the home. man interactions and natural language, for example, have This knowledge stored in tables in a relational database is shown promise in developing agents that can learn and rea- filtered using statistical methods and rule-based inference. son about human-centric information (W. L. Johnson 2004). Missing details within natural language task instructions are According to Rasmussen et al (1983), human behavior in fa- reasoned to determine the steps to be executed in the task. miliar environments doesn’t require extensive decision mak- These missing details are handled by meta-rules which work ing. It is controlled by a set of rules or steps which have across the knowledge categories and interact with the appro- priate tables to extract the right information. Our reasoning proven successful previously. The sequence of steps may approach is illustrated for common household tasks. have been derived empirically in the past or communicated from another person’s know-how as instructions. A variety of knowledge sources and knowledge represen- Introduction tations have been proposed for such approaches. Knowledge Since the work of McCarthy (McCarthy 1959), common- bases such as CYC (Guha et al. 1990) have been manu- sense reasoning has been widely investigated with formal ally developed. Their rule base utilizes domain heuristics treatment of logic. Formal representations involve a vari- and is manually designed. OpenMind projects (Stork 1999; ety of operator definitions, depending upon the type of logic 2000) have been developed to capture information provided (e.g. epistemic, modal). Operator evaluations can be embed- by the public in natural-language form. Applications such ded within inference rules to generate facts that drive further as a hypermedia authoring agent have been developed with evaluations. However most real-world problems, require de- OpenMind knowledge (Lieberman & Liu 2002). feasible reasoning, e.g. non-monotonicity (Zernik 1988). Implementation of logic takes many different forms, as Formal representations for commonsense require many reflected in the base languages and systems that have been axioms to represent even the most basic household tasks. developed over the years. Traditional logic programming From an implementation standpoint, a knowledgebase com- languages such as Prolog (Colmerauer 1990) favor the use prised of a collection of such axioms will hold little advan- of backward chaining for applications that involve, for ex- tage over other forms of programming unless the axioms are ample, planning or theorem proving. CLIPS (Giarratono & broadly applicable among tasks. This is difficult to achieve Riley 1998) is optimized for production systems (forward and contradictions arise as the knowledgebase is scaled to chaining). A situational calculus within GOLOG (Levesque larger sizes. Tracking which axioms to use for a given prob- et al. 1997) or fluent calculus within FLUX (Thielscher lem statement then becomes difficult. 2002) facilitate planning in dynamic environments. Sys- On top of this difficulty, a dynamic world represented tems built upon semantic networks such as SNEPS (Shapiro within knowledgebases introduces conflicting information & Rapaport 1987) provide a suite of powerful search tech- over time that may need to be retracted. One method for niques on semi-structured knowledge to support belief revi- maintaining psuedo-monotonicity in the face of a dynamic sion with natural language text. Finally, modules such as world relies upon the tagging of all information with a times- memory chunking in SOAR (Rosenbloom & Laird 1990) tamp (Elgot-Drapkin & Perlis 1990). Such schemes can be provide a method to implement reflective introspection. used to identify conflicts however they typically do not per- Considerations for choosing an appropriate reasoning form well for real-time applications. Various maintenance paradigm include the knowledge acquisition method, scal- rules for nonmonotonicity have been explored over the years ability, knowledge representation, and known uncertainties Copyright c 2005, American Association for Artificial Intelli- that the system might encounter. In this paper, it is assumed gence (www.aaai.org). All rights reserved. that a user requests the robot to carry out a household task such as making coffee or washing clothes. For this kind <change the filter in the coffeemaker> of knowledge we bind task instructions (e.g. change fil- <add ground coffee onto the filter> ter) from the user to explicit action-object-state assignments <pour water into coffeemaker top> via class rules and meta-rules. Such assignments can then <turn on the coffeemaker>. be executed by the robot hardware to accomplish the task. OpenMind Indoor Common Sense (OMICS) data (Gupta & Other relational tables we have used from OMICS include Kochenderfer 2004) is used as a source for the task instruc- Locations, Uses,andCauses.TheLocations activity asso- tions. The various categories of collected data are discussed ciates objects with the rooms where they are typically found. in the section on Knowledge Capture. For example, the user might be prompted with, ‘A room where you generally find a dinner table is the .’ The We then discuss how class rules process distributed Uses activity associates objects with their uses. For exam- knowledge using symbolic techniques. Statistical methods ple, the user might be prompted with the form, ‘A hanger is are used to filter out variations in word choice and sentence used to .’ structure. However in this paper, it will be assumed that ei- ther a single user’s instructions are being used, or a com- The Causes activity captures causality. An example of the posite set of available choices are available. We use the Causes data is ‘When the tap is on, the sink becomes full.’ processed OpenMind knowledge with manually designed These are stored as pairs of object properties, the first being meta-rules to fill in missing information for household tasks. the cause and the second being the effect. These class and meta-rules are illustrated with the task of In general, natural language phrases are parsed and stored making coffee. The system implementation is described in in appropriately tagged fields in a SQL database with dif- the following section on the integration of knowledge, mem- ferent tables mapping to different relations. The OMICS ory and rules. This is followed by Conclusions and Future knowledge base is also the source for the grammars, object Work. states and action descriptions. Such knowledge representa- Our long-term goal is to implement this approach in tion is relatively self-contained, and can be augmented with robots that interact with humans to help them perform com- natural language statements by interactions with humans. mon household tasks. Task steps may be communicated ex- plicitly to a robot. However typical instructions will rely Processing Distributed Knowledge with Class upon implied understanding and provide sketchy details. Rules The robot will need to use commonsense principles to seek the details in real time to perform these tasks. Our approach towards reasoning is implementation-based with constraints expressed in SQL queries and pattern recog- nition implemented with regular expressions. Raw text task Knowledge Capture instructions captured in OMICS must be processed using a Research on distributed knowledge capture methods is Penn Treebank parser (Klein & Manning 2001). Interpre- growing in popularity due to concepts such as the Seman- tation of parses is performed via class-rules, i.e. rules spe- tic Web. There is vast amount of internet information avail- cific to grammatical constructs and knowledge content (such able, however contextual analysis of natural language state- as action references). The class rules work effectively as ments still represents a holy grail for AI research. To ad- filters— requiring specific, unique relationships to be stated dress this challenge, OpenMind projects worldwide collect in order for logic to construct facts for processing. knowledge in a structured format with contextual informa- Our discussion of class rules is illustrated with common- tion. The goal of the OpenMind Indoor Common Sense sense reasoning as it applies to the coffee-making task. To (OMICS) 1 project is to develop a relational database of in- begin with, the database is queried whenever a request for door home and office knowledge from volunteers (netizens) a task is identified. Other causes, such as observances of over the web. The database table entries are created from change-of-state variables tied to certain behaviors of the responses to fill-in-the-blank prompts generated by seed ta- robot could also have initiated