Working Note 12 - Department of Computer Science
Contents
1. as follows connects connects Wing Fuselag contains ne ne a N l va N 1 Era Epp F big I EDP sige tight nas powers qoutput a powers A Z RQ Flap Input Flow Rat Flow Rate input Fla forall A 777 aircraft exists LW Wing RW Wing LE EDP RE EDP LF Flap RF Flap F Fuselage such that participant LW A participant RW A participant LE A participant RE A participant LF A participant RF A participant F A side LW left imported from Airplane Structure side LE left imported from Airplane Strucuture amp Side Hydraulic Circuit left side LF left imported from Side Hydraulic Circuit left side RW right imported from Airplane Structure side RE right imported from Airplane Strucuture amp Side Hydraulic Circuit right side RF right imported from Side Hydraulic Circuit right connects LW F imported from Airplane Structure connects RW F imported from Airplane Structure contains LW LE imported from Airplane Structure contains RW RE imported from Airplane Structure powers LE LF imported from Hydraulic Circuit via Side Hydraulic Circuit left forall 01 output LE 01 input LF 01 from Hydraulic Circuit via i Side Hydraulic Circuit left powers RE RF imported from Hydraulic Circuit via Side Hydraulic Circuit right forall 02 output RE 02 input RF 02 from Hydraulic Circuit via 132. KM expression A triple is denoted in KM using the notation triple frame slot val expr Each triple in the final axiom set can be asserted into a KM KB using the standard KM notation frame also has slot val expr Component Airplane Structure Synopsis Name Airplane Structure Summary Basic physical layout of an aircraft Parameters none Imported components none Description W Engine driven SA pumps EDP Fuselage connects Wing side contains left EDP side connects contains L EDP side Wing Side right This component describes some of the physical structure of the aircraft in particular focussing on hydraulic components the engine driven pump Local Participants English The left wing of the airplane The right wing The left engine driven pump EDP The right EDP The fuselage Local Axioms English The left wing is connected to the fuselage The right wing is connected to the fuselage The left wing contains the left EDP The left wing contains the right EDP Component representation semi formal def component name Airplane Structure description Structure of a 777 aircraft participants LW Wing where side LW left RW Wing where side RW right LE EDP where side LE left RE EDP where side RE right F Fuselage axioms connects LW F
3. Side Hydraulic Circuit right size LE big imported from Side Hydraulic Circuit left size RE big imported from Side Hydraulic Circuit right Note that the component Side Hydraulic Circuit and thus Hydraulic Circuit has been imported twice once parameterized with side left and once with side right corresponding to the two different sides of the airplane These axioms may then be subsequently asserted in a standard KM KB for question answering purposes Question answering may of course result in inferencing with these axioms including normal inheritance and classification behaviour 5 Additional Issues and Comments for Discussion 5 1 Components and Inheritance The use of components does not remove the need for normal inheritance type reasoning and an isa hierarchy rather components are an additional mechanism The underlying model here is that there is already an isa hierarchy of concepts and some of those concepts already have axioms ie slots value expressions attached to them The components then make additional assertions to the KB about interactions which exist between set of concepts So when should an axiom be placed on a frame in the initial KB and when should it go ina component The rule is if an axiom describes an intrinsic always true property of an object then it should go directly into the KB If however it describes an object s property based on it playing a role in some conceptual system then it sho
4. for power transfer between a producer and consumer and one for fluid flow Local Participants English e A pump e An actuator Local Axioms English e The pump powers the actuator e The output flow rate of the pump equals the input flow rate to the actuator Component representation semi formal def component name Hydraulic circuit participants P Pump A Actuator axioms povers P A forall 0 output P 0 input A 0 Component representation KM notation def component name Hydraulic circuit participants a Pump a Actuator axioms triple Self participants Pump pouers Self participants Actuator triple Self participants Pump output Self participants Actuator input Component Side Hydraulic Circuit Synopsis Name Side Hydraulic Circuit Summary The side hydraulic circuit of a 777 aircraft Parameters side one of Left Right Imported components Hydraulic Circuit Description ZZ LeftOrRight di Flap EDP side lt side Flap size big This component describes the presence of a hydraulic circuit on an aircraft The imported Hydraulic circuit component provides the generic axioms about hydraulic circuits while this component maps those participants into participants of the airplane and adds purely for demo purposes the axiom that the engine driven pump is big Local Participants En
5. representations when building a KB ie trying to represent every conceivable nuiance about the domain of interest rather he she encodes a number of small coherent modules components which can then be composed together to build a KB It is important to distinguish two separate tasks Specification Specifying how one component is a composition of others This is a task which the knowledge engineer does Composition Building the composition ie merging components together in the way which the knowledge enginer specified This is a task which the computer does automatically using the specifications Each component contributes axioms assertions to a composition A composition is thus a larger set of axioms built subject to the mappings which the user specified Note that there is no longer the notion of a single universal KB Rather each compo nent can be thought of as specifying a mini KB which can be assembled my merging the components it imports If this seems strange and you would prefer to still think in terms of building a single KB then arrange the components such that there is one bottom most component build from all the others which can be thought of as the Target KB to build Note also we re here using a slightly different notion of composition than in the AAAT 97 paper Here composition means simply assembling the axiom set and doesn t include computing ramifications of that assembly the la
6. More on Components Working Note 12 Peter Clark Bruce Porter Boeing Research Department of Computer Sciences PO Box 3707 Seattle WA 98124 University of Texas at Austin TX 78712 peter e clarkQ boeing com porter cs utexas edu Feb 27th 1998 Abstract This working note aims to develop the ideas of our earlier AA AV97 paper Clark and Porter 1997 into a more coherent implementation framework We would like to reach the stage where building and linking components becomes a routine task but this requires a concrete description of what a component data structure looks like and how it would be used This document aims to do this adding in some important specifics to the earlier work 1 Introduction This working note aims to develop the ideas of our earlier AA AI 97 paper Clark and Porter 1997 into a more coherent implementation framework We would like to reach the stage where building and linking components becomes a routine task but this requires a concrete description of what a component data structure looks like and how it would be used This document aims to do this adding in some important specifics to the earlier work 2 Components 2 1 Architecture and Usage The idea of a component is to encapsulate a coherent mini theory which may be in corporated perhaps through several different mappings described later in a knowledge base KB The goal is to save the knowledge engineer trying to build the mother of all
7. The output of the EDP equals the input of the flap 11 Component 777 Aircraft Synopsis Name 777 Aircraft Summary The whole 777 aircraft Parameters none Imported components Airplane Structure Side Hydraulic Circuit Left Side Hydraulic Circuit Right Description This component is purely a composition of three other components It doesn t introduce any new participants or axioms Here we want to compose knowledge about the aircraft s structure and hydraulic circuits to build a composite representation Local Participants English none Local Axioms English none Component representation semi formal def component iname 777 aircraft description The whole 777 aircraft just looking at hydraulics import components Airplane structure Side hydraulic circuit side left Side hydraulic circuit side right Component representation KM notation def component iname 777 aircraft description The whole 777 aircraft just looking at hydraulics import components a airplane structure a side hydraulic circuit with side Left a side hydraulic circuit with side Right 12 4 Composition Building the fourth component here using the algorithm described earlier Figure 3 produces a set of axioms which can be informally sketched and more formally expressed
8. c circuit description A trivial model of a hydraulic circuit participants P Pump A Actuator axioms povers P A output P 0 input A O with the semantics that forall X hydraulic circuit exists P Pump A Actuator such that povers P A and forall O output P 0 lt input A 0 In general however a component will also import other components If a component is imported then the system must e work out which participants in the imported component correspond to participants in the importing component e unify those matching participants and e union the resulting axioms together We call this first step working out the mapping between participants as aligning the participants of the two components There are several ways in which this can be im plemented In the AAAI 97 paper we suggested that the knowledge engineer manually specify the mapping by placing role labels on each participant However in retrospect this seems likely to be painful for components with very large numbers of participants Another alternative which we adopt here though it s by no means the best is to use a unification algorithm to automatically determine which participant in one component will match with which participant in the other component KM already has such a mecha nism built in see the amp amp operator in the KM User Manual Clark and Porter 1996 For example using the amp amp operator KM will unify the parti
9. cipant set pump1 _actuator2 from one component with the participant set from another component _edp3 _wing4 to produce the unified set edp3 _actuator2 _wing4 where _pump1 is a pump actuator2 is an actuator edp3 is an engine driven pump and _wing4 is a wing Here KM is using it s knowledge about the classes of the objects being merged to find compatible matches Note that not all participants in one component need to have a corresponding partici pant in the other thus an imported component may introduce extra participants into the importing component This unification based approach to aligning participants is rather pragmatic and has some open issues to resolve but it s the best we can think of for now One interesting aspect is that there may be more than one way in which two participant sets can be aligned in this case the component can be applied in more than one way corresponding to viewing an object in more than one way In this case some additional mechanism would be needed so that the knowledge engineer can specify which alignment she he intended Figure 1 sketches the imports relationship that might exist between components based on the example described in more detail later Figure 2 shows the composition being computed including aligning the participants from different components together The black dots denote participants explicitly declared in the local component the white dots denote participa
10. connects RW F contains LW LE contains RW RE Component representation KM notation def component name Airplane Structure description Structure of a 777 aircraft participants a Wing with side Left a Wing with side Right a Edp with side Left a Edp with side Right a Fuselage axioms triple allof triple allof triple allof allof triple allof allof Self participants Wing where It side Left connects Self participants Fuselage Self participants Wing where It side Right connects Self participants Fuselage Self participants Wing where It side Left contains Self participants EDP where It side Left Self participants Wing where It side Right contains Self participants EDP where It side Right Component Hydraulic Circuit Synopsis Name Hydraulic Circuit Summary Generic hydraulic circuit Parameters none Imported components none Description Pump Se se Output powers Flow Rate Gow 4 Rec EOI See Actuatorl Pump Actuator Describes the relationship between a pump and an actuator There are axioms here describing the power transfer relationship namely the pump powers the actuator and constraints on the flow rate In a fuller implementation these would more likely be two separate generalized components one
11. exas edu users mfkb manuals userman ps Clark and Porter 1997 Clark P and Porter B 1997 Building concept repre sentations from reusable components In AAAI 97 pages 369 376 CA AAAI http www cs utexas edu users pclark papers aaai97 ps Levy 1993 Levy A Y 1993 Irrelevance reasoning in knowledge based systems Tech report STAN CS 93 1482 also KSL 93 58 Dept CS Stanford Univ CA Chapter 7 Miller et al 1993 Miller G A Beckwith R Fellbaum C Gross D and Miller K 1993 Five Papers on WordNet Prinston Univ NJ http www cogsci princeton edu wn 17
12. glish e An engine driven pump EDP e A flap Local Axioms English e The EDP is big Component representation semi formal def component name side hydraulic circuit description The side hydraulic circuit import components Hydraulic circuit parameters side W LeftOrRight participants E EDP where side E W F Flap where side F W axioms size E big 10 Component representation KM notation def component name side hydraulic circuit description The side hydraulic circuit import components Hydraulic circuit parameters side a Side participants a Edp with side Self side a Flap with side Self side axioms triple Self participants Edp size Big The Composition The composition itself can be informally sketched as _ big size EDP side lt output LeftOrRight powers 2 Flow Rate aaen Pt or described as follows forall S Side Hydraulic Circuit exists E EDP F Flap such that participant E S participant F S size E big local axiom powers E F imported from Hydraulic Circuit forall O output E 0 input F 0 imported from Hydraulic Circuit side E X side S X local parameterized property of E side F X side S X local parameterized property of F Note the two axioms importred and specialized from Hydraulic System stating e The EDP powers the flap e
13. here approximately each page will be represented by one component First we turn to page 1 it provides say a description of the physical layout of the aircraft though biased towards hydraulics many but not all hydraulic elements are shown while other major structural features eg the space for the passengers are not A component is built to represent just the information conveyed on that page the physical parts being the component s participants and the relationships between the parts being the component s axioms The fact that this on its own is a poor description of the whole aircraft does not matter at this stage Now we turn to page 2 in our imaginary exercise It provides say a simple overview of the hydraulic circuits This information is represented as a second component some of its axioms provide additional information about participants in the first component oth ers provide information about new participants not previously mentioned We continue likewise for subsequent pages Finally by building the composition of the components we can merge all this informa tion together to build the KB Hopefully the modularity that this approach provides 16 will be substantially beneficial for maintaining and further developing such a RB Time will tell References Clark and Porter 1996 Clark P and Porter B 1996 KM the knowledge machine Users manual AI Lab Univ Texas at Austin http www cs ut
14. n of the components showing how the participants in each compo nent have been automatically aligned The final assembly of axioms can be compiled asserted into a standard knowledge base PROCEDURE Build Component Component Name returning Participants Axioms 1 Create instances denoting the participants P in the component 2 For each imported component 2a Call Build Component to find it s participants P and axioms A 2b unify sets P and P 2c Add axioms A to the component s local set A 3 Return the final set of participants P and axioms A END PROCEDURE PROCEDURE Build KB Component 1 Call Build Component Component returning Axioms 2 For each Axiom in Axioms assert Axiom into the RB END PROCEDUREA Figure 3 Composition algorithm 3 Example The following pages show four simple examples of components which connect together to build a toy KB of an airplane The last component 777 Aircraft can be thought of as The KB The result of assembling it by importing other components and aligning their participants is also shown Although most of the axioms shown for a component are ground clauses they can be any axiom at all A few non ground ones are included also for illustration purposes The KM representation of the components is rather clunky although semantically correct it will have to do for now Axioms are expressed as frame slot value triples where value may be an arbitrarily complex
15. ns are often posed in context for example In the wing what is the EDP connected to or In a 777 what provides emergency hydraulic power Earlier we suggested that a single KB might be built from some bottom most component in the component library In fact it seems more approprate that a question specific mini KB would be synthesized for each question posed A component can be thought of as axiomizing objects which exist in a particular context so given a particular context stated in a question the system can build that axiomatization by building the axiom set which the component specifies and then reason with it to generate an answer to that question Such an axiomatization augments the base KB of universally true axioms describing intrinsic properties of objects in the world 5 3 Some Issues 5 3 1 Aligning Participants The unification approach to aligning participants may sometimes be ambiguous For example a component describing Service might have two Agents as participants one playing the role of a client and one of a server When importing this component to another also containing two agents there s ambiguity about which agent should match with which In this case it seems that it would be useful to add role tags to participants so that the knowledge engineer can specify the mapping A simple implementation trick to do this without requiring new syntactic extensions is to introduce a role sl
16. nts imported from other components This figure also suggests that the final axiom set may be compiled into a more standard representational form eg a KM RB for question answering The algorithm for building a composition is shown in Figure 3 The final axiom set can then be asserted into a KM KB using KM s also has primitive Td Reiger problem is as follows Consider a component C importing two components C1 and C2 A participant in one imported component C1 may map to a participant in the other imported component C2 without that participant ever being mentioned in the importing component C So do we create extra participants in C for all potentially imported participants 3 Hydraulic System Hydraulic System Side Hydraulic Circuit Left N Side Hydraulic Circuit Right N Airplane Structure a 777 Aircraft Figure 1 Example of imports relationships between components Hydraulic System Hydraulic System 0 e IE ales Axioms about those participants Participants declared locally in the component Side Hydraulic Circuit Left Sa 34 Side Hydraulic Circuit Right r Q 7A o Tamm O Participants imported Airplane Structure from upstream component ved Yo a 777 Aircraft compile the axioms Figure 2 Compositio
17. ot to allow the knowledge engineer to tag participants As the unification algorithm won t allow objects with incompatible slot values to unify this would guide the unification algorithm appropriately For example def component iname Service participants a Agent with role Client a Agent with role Server axioms wd def component name Restaurant Visit import components Service participants a Agent with role Client a Agent with role Server axioms the first Agent is hungry the second Agent works for the restaurant etc In this example when the Service component is imported into the Restaurant Visit component and the participants are unified the agent with role Server in the Restaurant Visit will only unify with the agent with role Server due to these role tags attached to the agents This works but still seems rather a hack one cause of the root problem here 15 is that using unification to aligning participants ignores the axioms in the components in practice those axioms should play a role in deciding the alignment As the method currently stands the system may choose an apparently valid alignment of participants only to later find that the axioms from the imported component contradicts those in the importing component There is no mechanism implemented to recover from this in the current implementation eg by backtracking to try a different alignment 5 3 2 Cl
18. tter is done at run time in re sponse to user questions Then run time question answering is performed by posing questions to this set In our particular implementation we choose to also first load this axiom set into a conventional Knowledge Representation System here KM ie a KM KB is built from the axiom set This extra step can be thought of as compiling the ax iom set for efficient inference Thus note that we are not proposing a new representation language but rather a more reusable way for constructing KBs in existing languages eg KM Algernon 2 2 Anatomy of a Component A component consists of 6 items name A identifier for the component description A string of text describing it participants A set of objects which the component is describing axioms A set of axioms assertions about the participants import components A set of components which this component imports parameters Sometimes it is desirable to parameterize the participants of a component The semantics of a component are informally as follows For all instances of that com ponent there exist instances of the participants such that all the axioms hold A simple example of a component which does not import any other components is the one below This states that a hydraulic circuit consists of a pump and an actuator that the pump powers the actuator and that the pump s output equals the actuator s input def component name Hydrauli
19. uld go in a component These latter properties are those which do not hold for all instances of that object type but only those instances participating in that system For example the axioms that an engine driven pump EDP has weight 2 5kg say and is made of titanium say are ie will be modeled as intrinsic properties of an EDP it is always the case that an EDP s weight is 2 5kg and thus that fact would be placed on the EDP frame in the KB taxonomy However an axiom stating that the EDP is connected to an airplane s engine is here modeled as not universally true for example some EDPs are in store rooms prior to aircraft assembly not connected to anything but only true for EDPs which in are part of the wing assembly in conceptual terms just those EDPs participating in the system of relationships describing the wing assembly s physical structure This latter axiom would thus be placed on a component for say the physical structure of a wing assembly In fact a standard frame in a KB can be thought of a component as consisting of a single participant eg def component name Pump participants P Pump axioms veight P 2 5 material P titanium which is then imported into every other component which mentions a participant of the same type In fact this is functionally equivalent to what inheritance does anyway 14 5 2 Questioning the KB and Question Specific Composition It seems that questio
20. unky Syntax The KM syntax in the KM formulations shown in this paper is very clunky it would be much nicer to move to something more standardized For example I was struck how easy it was to download the 20 000 concept WordNet ontology Miller et al 1993 from the Web which is expressed in Prolog and start doing useful things with it in just a few minutes 5 3 3 Relevance and Consistency In this implementation the composition algorithm builds a component s axiom set in all its detail An advanced topic would be to have some more sophisticated composition algorithm which would allow some of it s imported components to be selectively left out on the basis that they were irrelevant to the question being posed A second advanced topic would be to have perhaps multiple alternative components for describing a particular phenomenon Again an algorithm would determine which component was most suitable for answering the current query and ensure that a compo sition was performed only with components based on non conflicting assumptions This approach has already been demonstrated in compositional modeling of physical systems Levy 1993 6 Methodology for Progress Consider taking some on line documentation that we would like to represent eg the 777 hydraulics manual Rather than trying to build the mother of all KBs to represent everything we can instead follow the conceptual organization which the documentation provides w
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