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A C B D E context (all superstates) substate 1 3 2 4 GDS = {A, B, C, D} A Goal Dependency Set Primer Robert Wray Soar 24 10 Jun 2004 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 1 5 A C B D E context (all superstates) substate Why a Primer? Why now? 1 3 2 4 5 GDS = {A, B, C, D} Covered in 1996/1997/1998/2001 Soar workshops Soar community changed a lot since GDS 1st conceived No Soar-specific documentation other than Soar 8 release notes Frustrated users (draft) Soar GDS documentation now available Motivation for Goal Dependency Set (GDS) What the GDS does Constraints on agent design Memory management Operator elaborations Reentrancy Kernel level view Introduces other new (Soar 8) mechanisms 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 2 Terminology I(nstantiation)-support Justification-based truth maintenance system Assertion persists only as long as it justified I-support: Production instantiation provides justification Applies to State elaborations Operator proposals (Soar 8) Operator elaborations (Soar 8, o-support-mode 4) Preference productions 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 3 A A i-supported WME Terminology O(perator)-support 1 o-supported WME 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 4 dependency (LHSRHS) A Operator applications remain in memory regardless of As justification/instantiation New preferences are required to change an O-supported WME (e.g., reject) Applies to State elaborations Operator proposals (Soar 8) Preference productions retracted WME context (all superstates) substate 1 A context (all superstates) substate As 1 A A i-supported WME Motivation for GDS 1 o-supported WME Problem space/state interactions with persistence context (all superstates) substate 1 As A Previous assertions can become inconsistent with newer information context (all superstates) substate Learn a rule that has conditions that can never be simultaneously satisfied 1 As Non-contemporaneous constraints in chunks A B context (all superstates) substate 1 As Both problems require lots of low-level knowledge design, possibly incomplete 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 5 dependency (LHSRHS) # A&B are mutually exclusive sp {non-contemporaneous*chunk (state <s> ^attribute A ^attribute B) (<s> ^result 3) A Symbol level “quirks” in Soar 7 retracted WME A 2 B 3 context (all superstates) substate As 1 2 3 GDS Solution GDS ensures persistent WMEs within a substate are sensitive to superstate context(s) State, not individual element justification GDS := “I-support for states” Justification is updated dynamically as new persistent WMEs are asserted GDS misnomers States, not “goals” GDS is the data structure, not the process Process: Dynamic Hierarchical Justification 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 6 A A i-supported WME GDS Solution A 1 o-supported WME dependency (LHSRHS) GDS is NIL until/unless o-supported elements have been asserted in the local state C B retracted WME context (all superstates) substate 1 A C B GDS = { } GDS uses an algorithm comparable to chunking’s backtrace to establish dependencies for persistent WME D context (all superstates) substate 1 3 2 A C B GDS = {A, D} D E context (all superstates) substate GDS is updated dynamically as new persistent assertions are created in the substate 1 3 2 4 A C B substate 1 3 2 GDS = {A, B, C, D} 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 7 E context (all superstates) GDS = {A, B, C, D} Not every new persistent WME requires a backtrace D 4 5 A A i-supported WME GDS Solution Soar monitors WME changes for WMEs that appear in a state’s GDS… A 1 o-supported WME C B retracted WME dependency (LHSRHS) D context (all superstates) substate 1 3 2 GDS = {A, B, C, D} When a GDS WME is retracted, Soar immediately removes the impasse state (retraction of the GDS state) 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 8 5 4 A B C D context (all superstates) no substate Alternative Solution GDS assumes it is cheaper to regenerate dependent assertions than to compute which WME changes should be associated with which persistent WMEs. A C B D context (all superstates) substate 1 3 2 4 A S-support retracted only dependent o-supported WMEs, rather than the entire state 5 C B D context (all superstates) substate 1 3 2 4 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 9 5 S-support was potentially expensive and led to a number of technical problems Impact of the GDS on agent design Where to store o-supported assertions Depends on reason persistence was used Operator elaborations Operator elaborations now receive I-support O-support-mode 4 (Soar 8.5.1) I-support ensures no effect on GDS Reentrant problem spaces Any substate problem space can be interrupted at any time 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 10 Where to assert o-supported WMEs Soar 21 Recurrent questions Why shouldn’t I just put all o-supported WMEs in the top state? Shouldn’t everything have global persistence? When should I return something to the top state? When should something have global persistence? Answer: Reason for creating o-supported structures will tell you where they should be asserted 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 11 Soar 21 Categories of Persistence Different reasons for using an operator to assert a WME: Non-monotonic reasoning Hypothetical reasoning Remembering Avoiding expensive computations (see Soar 21 for specific examples of each) 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 12 Soar 21 Guidelines If your o-supported WME is being created for: It should be located in: Non-monotonic R. Hypothetical R. Local state - Want changes in context/situation to be communicated to the local state Remembering Avoiding Recalculation Top state - Want to be able to remember these things independent of any justification Some combination of first group with second group Top state Replacing an old value to be remembered (e.g., current-desired-speed) with a new one requires global persistence Conclusions: • For most plan execution applications, all o-supported WMEs should be asserted in the top state • Inconvenient when o-support provided but not needed 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 13 Augmenting the GDS Solution Soar 7 has other persistent WMEs context support (persistent operator selections) Eliminated in Soar 8/operator selections are Isupported “elaboration persistence” (interaction between isupport and o-support) Soar 8 decision cycle “Waterfall” (parallelism limited to prod firings w/i a goal) O U TP U T SELECT INP UT ELABORATE & COMPARE Soar Agent PERSISTENT ELABORATION PERSISTENT STEP INPUT PHASE ELABORATION ELABORATION Soar 8 Decision Cycle P AP LY 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 14 OUTPUT PHASE DECISION PHASE A C B D E context (all superstates) substate Conclusions 1 3 2 4 5 GDS = {A, B, C, D} GDS + Encourages reentrancy in design/simple, compact operator reps. (more “Soar”-like implementations) + Provides a complete, architectural (reusable) solution to hierarchical inconsistencies + Makes it much easier to use chunking in dynamic domains - Breaks locality assumptions for most o-supported WMEs - Not well documented/understood by Soar community at-large - Not well implemented (“gradware”) - Management of top-state WMEs not well codified/explored For Soar systems focused on plan execution in dynamic domains, most o-supported elements should be stored in the top state. GDS seems to provide little utility and lots of frustration for nonlearning systems (run-time flag?) Function of documentation/understanding or a fundamental flaw? 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 15 A C B D E context (all superstates) substate Additional Information 1 3 2 4 5 GDS = {A, B, C, D} GDS Primer http://www.speakeasy.org/~wrayre/soar/gds-primer.pdf Thanks to Brian Magerko, Bob Mariner, Andy Nuxoll, and Glenn Taylor for suggestions/comments on current draft More feedback needed/appreciated Papers describing motivations for Soar 8 & solution specifics Wray, R.E. and J.E. Laird, An architectural approach to consistency in hierarchical execution. Journal of Artificial Intelligence Research, 2003. 19: p. 355-398. Wray, R.E. and R.M. Jones. Resolving Contentions between Initial and Learned Knowledge. in Proceedings of the 2001 International Conference on Artificial Intelligence. 2001. Las Vegas, NV. Wray, R.E. and J.E. Laird. Maintaining consistency in hierarchical reasoning. in Fifteenth National Conference on Artificial Intelligence. 1998. Madison, Wisconsin. Wray, R., Ensuring Consistency in Hierarchical Architectures, PhD Thesis in Computer Science & Engineering. 1998, University of Michigan: Ann Arbor. Wray, R.E., J.E. Laird, and R.M. Jones. Compilation of Non-Contemporaneous Constraints. in Proceedings of the Thirteenth National Conference on Artificial Intelligence. 1996. Portland, Oregon: AAAI Press. 2004 Soar Technology, Inc. 10 Jun 2004 Robert Wray Slide 16