- Email: [email protected]
Artificial intelligence
br Laurence L. Left 1. Electrical Engineering Cleopatra provides a natural language interface to circuit-simulation post processing. It allows the user to ask questions such as "What is the maximum voltage at nl after VXI goes high'?" rather than forcing him to extract the information from an often voluminous print-out. {Tariq Samad, Honeywell Inc. and Stephen W. Director of the Department of Electrical and Computer Engineering at Carnegie-Mellon University). PLA-ESS will evaluate a user-designed PLA to determine a design for testability that will meet various user specified characteristics. When no technique will meet the given requirements, the user is provided with information to help him resolve conflicts between requirements and what is feasible. Techniques are evaluated on the basis of such qualities as fault coverage, number of pins, area and gate delays added, application techniques and costs. (M. A. Breuer, Xi-an Zhu, Department of Electrical Engineering-Systems, University of Southern California), The expert system, WEAVER, provides routing of interconnections in VLSI circuits. WEAVER has been tested on several problems where it outperformed various algorithms, MAGIC and hierarchical routing. In some cases, it solved problems that other techniques were unable to do. It considers a variety of routing metrics and is not constrained to use an assigned layer for each direction. The system uses a blackboard based system which has experts which perform a) constraint propagation; b) determination of which nets should be routed closer to a given set based upon minimum wire length; c) analysis of vertical constraint graph information; d) determination of which nets can be routed on the same row or column; e) analysis of the congestion on each row or column; f) application of rules of thumbs; g) determination of which expert should be activated next. (Ross Joobbawi, Trimeter Technologies, Pittsburgh). A general framework for the representation of CAD system has been developed and applied to the task of generating test vector sequences for VLSI. The techniques involve frames and demons. A library of integrated circuits is classified starting with such broad categories as division into memories, operators and registers going down into generic type numbers and finally specific parts. Classification types such as asynchronous versus synchronous are applicable to items at various levels in the hierarchy. (N. Giambiasi et al., University of AIXMarseille III, France). ADAM integrates custom layout tools, an expert system for testable circuit design, natural language,
database, knowledge-based synthesis and custom layout. A subsystem to generate clocking schemes for asynchronous systems has been completed. The system treats various phases of the design process, e.g. laying out a PLA, as operators in a planning process to determine which design procedures to execute. This is in contrast with other integrated systems where the design steps are fixed. Estimates are made of the results and costs of applying various techniques, e.g. time to execute a minimizatuon algorithm or the expected area and speed after the minimization is performed. These are used in deciding what steps to take, e.g. whether it is worth running the minimizer. (J. Granacki, D. Knapp, A. Parker, University of Southern California). K N O B - P L A C E plans the placement ofcomponents on PCB boards where the circuits are bus-oriented circuits such as single board computers. Objects are placed based upon a clustering approach. Clustering is based upon the type of net connecting the elements, the type of elements and the number of pins connected. For example a CPU and Buffer would be kept together as they are part of the same functional unit. The data base is set up by a computer analysis of manually configured systems. The system has been run on five CPU boards, a video-signal controller and a memory board and achieved results comparable to that of manual placement. (G. Odawara, K. lijima and K, Wakabayashi, Department of Precision Engineering, University of Tokyo). D I A L O G checks the adherence of a CMOS circuit to appropriate design rules. This system will decompile the circuit to a higher level circuit to check consistency. The system was originally developed in FORTRAN but has been converted to an AI language, LEXTOC, to allow for flexibility in adding new rules. When machine translated to PASCAL, the system will handle debugging of circuits containing 50000 transistors. (H. J. De Man et al., Katholieke Universiteit Leuven, Belgium). VALID analyses the timing behaviour of digital systems using temporal logic against a set of constraints that specify the desired behaviour. It has analysed a FIFO queue element within 25 seconds on a VAX 11/780. IS. Bapat, Department of Computer Science, Indian Institute of Technology, Bombay and G. Venkatesh, Solid State Electronics Group, Tata Institute of Fundamental Research, Bombay). A hardware test vector is generated using AI tools from a chip-level functional description in VHDL, the VHSIC Hardware Description Language. Each statement of the H D L is examined and faults such as the following are added to the list of possible faults to test for: a) a micro-operation fails to some other operation; b) an assignment statement fails to a no-operation; c) an IF statement behaves as a stuck-at-THEN and stuck-at-ELSE; d) all clauses in case statement become a no-operations. These faults are then converted to a list of basic tests that are then put into an AND-OR tree. Next, the AND-OR tree is traversed to generate a test vector. (D. S. Barclay, J. R. Armstrong, Electrical Engineering Department, Virginia Tech). HAL converts a data flow graph, representing the operations to be performed in a digital circuit, to a data path consisting of operator cells, registers, multiplexors and busses. This is the middle part of a silicon compiler that takes a high level description of the circuit and Artificial Intelligence, 1987, Vol. 2, No. 1
45
,4I News Letter: L. L. Le[l" converts it into instructions for the chip foundry. This system is optimized for use in generating telecommunications software. An explicit timing constraint is also provided and this is used in generating the chip. In the first module to receive the data flow graph, the system identifies a critical path. Then operations are assigned to cycles along the critical path so as to attempt to minimize the concurrency of similar operations. Operations that t, se similar resources are scheduled to occur on different cycles. For example, an addition and a subtraction that could both use the same A L U would be scheduled for different cycles. The middle phase attempts to associate operations to components using a rule-based approach. For example if several operations could use the same ALU, then they all might be assigned to one. The last phase does the final assignment and generation of the data path. (P. G. Paulin, et al., Bell Northern Research, Ontario, Canada). Fujitsu has developed DDL/SX which converts technology-independent functional diagrams to technology-dependent diagrams. For example, there are rules that will use two N A N D gates to perform an AND operation if such is available and AND gates are not and to insert buffers when the fan-out on a pin is too high. The system took 15 seconds to convert a 2000 gate circuit. Hitachi has developed a rule based system that converts conventional logic to IlL circuits. The system was able to achieve 40 to 60 percent gate reduction over direct translation. The system was as efficient in reducing gate count as a designer with ten years experience, taking 250 seconds on a Hitachi M-200H.
2. Other Engineering Carnegie-Mellon is developing an expert system for the design of aluminium alloys in conjunction with Alcoa. Initial emphasis is on aluminium-lithit, m alloys used in aerospace. (J. Hultageeral, ISL, Robotics Inst., C-MU). Expert systems techniques are being applied to the design of the superheater section of a fossil fuel utility boiler. The system allows for the input and use of user preference rules such as 'In the ct, rrent design context, pressure drop is more important than outer wall temperature', (Donald E. Brown, Chelsea C. White, III, Department of Systems Engineering, University of Virginia). Fuzzy sets have been used to represent the performance of components in a structure and determine the possibility of failure. Linguistic terms such as 'good' or 'small' are converted into ft, zzy models for the performance of components, the magnitude of possible sources of failure and the consequences of these events on various components of the structure. (Fabian C. Hadipriono, Hock-Slew Toh, Ohio State University). FRIL is another system based on fuzzy logic for assessing safety of bridges. It has been applied to the assessment of bridges as it is being constructed. SPERIL-I and II will assess the safety of objects after they have been damaged by earthquake or other disaster. P R O L O G has been used in developing an expert system to choose a construction method for a bridge. (Hitoshi Furata, et al., Kyoto University, Japan). Architectural detailing is being assisted by a knowledge based system using design grammars and knowledge engineering. This work is exemplified by a design language to produce the detail of the junction of walls and 46
Art(ficial Intelligence, 1987, Vol. 2, No. 1
roofs following standards to match Australian construction circa 1910. IA. D. Radford. J. S. Gero. Department of Architectural Science, University of Sydney. Australia).
3. Optimization Several people have used rule based systems during multivariate optimization with constraints. Sometimes, in optimization the direction of search should be normal to a particular constraint. However, this may be odds with the goal of maximizing the objective function. This causes zig-zagging with the constraint becoming active and inactive on alternative steps. Papalambros and Li have developed a system to use global information using rules that indicate a specific constraint is active, inactive or dominant in a given region. The technique was exemplified in the design of a speed-reducer and a ridering. In J. S. Arora's system, rt, les will cause the system to temporarily ignore the constraint or to move along it.
4. Representation issues Different levels of abstraction in simulation are modeled using levels of abstraction. The system can be used to represent concurrency between objects such as a concurrent system such as the Dining Philosophers problem. The system can play back a real-time animation of the system at various levels of abstraction. (Pat, l Fishwick, Department of Computer and Information Science, University of Pennsylwmia). Design codes have been represented as expert systems. One of these efforts involved the conversion of the Australian Model Uniform Building code to an expert system. (Michael A. Rosenman, John S. Gero, Department of Architectural Science, University of Sydney, Australia). Ernest Davis at NYU has been developing a system for reasoning qualitatively about the behaviour of simple objects. For example, we should be able to predict that a hook will catch a ring, objects firmly planted on tables will stay still and the direction of motion of objects left in an unstable state. One approach is to look for proofofthe desired shape. For example, an object placed in a funnel must come out on top, come out the bottom or stay forever in the middle. It cannot come out on top since that will require more energy than its ct, rrent potential energy. It can't stay motionless in the middle since the sides of the funnel are too steep. And it can't continue moving indefinitely within the funnel so therefore it must come out the bottom. A proof theory has been developed for hard objects such as opened and closed boxes, rings, buttons. In geometric reasoning, objects are defined using a first order predicate calculus with equality in terms of st,ch concepts as tangency, equality, parallel, etc. For example the concepts of polygon is defined using predicates such as: a) polygon (p,n) (true if p is an n sided polygon); b) vertex-of(v,i,p) (true if point v is the ith vertex of polygon p); c) edge-of(e,p) (true if e is an edge of p). Geometric reasoning is similar to executable specifications and abstract data types for computer programs that deal with geometrical objects. (Jeannette
,4I News Letter: L. L. Lq[]
M. Wing. Department of Computer Science. Carnegie Mellon University and Farhad Arbab, Computer Science Department. University of Southern California).
5. Manufacturing A system that plans the assembly of objects by analysing the structure of the object, applying assembly principles and then using Al planning techniques to generate a sequence of operations was developed at The University of Cincinnati. The workpiece is represented as frames with geometry representation omitted. The system has generated assembly instructions for an assembly unit containing two robot arms, holders, tool stands and feeders for devices exemplified by a power supply. (KaiHsiung Chang, William G. Wee, Department of Electrical and Computer Engineering, University of Cincinnati). AI-based software controls the movement of work-inprocess in DEC's circuit board production plant. The system includes a 75-station transporter, two carousels for work-in-progress-storage and a conveyor to and from an inserter/extractor device. The Al-based software automatically assigns and tracks the work in progress, interfaces to the mover control software and alerts management to problems. This software is general enough to be moved to other DEC plants without major changes. (Mark Wynot, Digital Equipment Corporation). SIPP (Semi-lntelligent Process Planner) develops least-cost plans for the creation of metal parts. The system uses a frame based representation for the problem-solving knowledge with the planning done by using a modified Branch and Bound process. The system treats each surface independently and currently does not recognize when a surface is inaccessible due to other parts of the object. (D. Nau, Computer Science Department, University of Maryland). Northrop has developed an AI system for simulation and evaluation of sheet-metal fabrication, SIMKIT, an extension to KEE for simulation, was used to represent the system as a frame-based structure. Graphics were used to represent cell components, their relationships and statistical measurements of their performance and utilization. This allowed the user to set up and analyse the results of simulations of sheet metal manufacturing setups without doing any programming.
6. Plant Control F A L C O N will detect and identify faults in an adipic acid reactor. It will use explanation generation software to interact with the operator. The operator will press a 'WHY" button and then touch the rectangle that he is interested in. Falcon will recognize areas outside of its domain of expertise and will be aware of actions for which corrections are underway so as to avoid repetitive alerts. The system is scheduled for installation later in 1986. (Joint project of the University of Delaware, DuPont Co and Foxboro Inc.) Electric Power Research Institute has developed an expert system to reconfigure the fuel assemblies inside a nuclear power reactor. This must be done on a periodic basis as the fuel is used up. The goal is to make the shutdown period while this is being down as short as
possible as shutting down a nuclear reactor costs half a million dollars per day. TOAST assists the operator of a large utility in diagnosing failures in the distribution of power. The system uses a rule based discrete-event simulator that predicts what happens to a network after a disturbance. The diagnostic module views the power system as a collection of busses, lines, breakers and relays in isolating a problem [Sarosh N. Talukdar et al., Carnegie-Mellon University).
7. Scheduling FIXER schedules repairs on aircraft for the Royal Air Force. The system takes into account constraints on resources, sequences that tasks must be performed in and actions that must be done together. The same techniques are being used in scheduling a VLSI wafer laboratory. (T. J. Grant, Brunel University, Uxbridge).
8. Diagnosis Comparing the symptoms of earlier failures with that of a new failure are used to assist a production system in diagnosis of the new problem. A large database contains failure symptoms from diagnostic tests of previous failures. This database is clustered and cluster representatives are chosen to assist in its search. When a new failure is presented to the system, the diagnostic system matches the information against the cluster representatives and the maximum distance of a cluster representative to other members of the cluster. This enables the system to find the best match of failure symptoms without looking at all the test cases. The techniques of clustering and matching come from the field of Information Retrieval. (Marguerite T. Denoncourt, Bell Communications Research). An expert system now can diagnose failures in the DSCS-11I satellite altitude control system. This system was developed by having the system deduce diagnosis heuristics from the device model. (Michael J. Pazzani, The Aerospace Corporation, Los Angeles). The Naval Research Center has developed a diagnostic system to assist the technician in determining the tests to use and how to interpret them. The system contains knowledge about modules that are likely to occur in more than one object under test and provides facilities to allow the knowledge engineer to quickly add new devices. It is hoped that much of this information can be acquired by a direct interface with the CAD-CAM database. The system has been tested on analog equipment containing approximately 10 modules. To readers of our journal, we are interested in all newsworthy items connected with the field of Artificial Intelligence in Engineering. American readers should send items of interest to Mr L. Left, Computer Science and Engineering, Southern Methodist University, Dallas, TX 75275, USA. By electronic mail: UUCPnet allegra!convex!smu!leff C S N E T , A R P A N E T leff~smUD CSNET-RELAY. U K and European should write to Dr K. J. MacCallum, Director, Faculty of Engineering, CAD Centre, 131 Rottenrow, Glasgow G 4 0 N G . Artificial Intelli,qence, 1987, Vol. 2, No. I
47
database, knowledge-based synthesis and custom layout. A subsystem to generate clocking schemes for asynchronous systems has been completed. The system treats various phases of the design process, e.g. laying out a PLA, as operators in a planning process to determine which design procedures to execute. This is in contrast with other integrated systems where the design steps are fixed. Estimates are made of the results and costs of applying various techniques, e.g. time to execute a minimizatuon algorithm or the expected area and speed after the minimization is performed. These are used in deciding what steps to take, e.g. whether it is worth running the minimizer. (J. Granacki, D. Knapp, A. Parker, University of Southern California). K N O B - P L A C E plans the placement ofcomponents on PCB boards where the circuits are bus-oriented circuits such as single board computers. Objects are placed based upon a clustering approach. Clustering is based upon the type of net connecting the elements, the type of elements and the number of pins connected. For example a CPU and Buffer would be kept together as they are part of the same functional unit. The data base is set up by a computer analysis of manually configured systems. The system has been run on five CPU boards, a video-signal controller and a memory board and achieved results comparable to that of manual placement. (G. Odawara, K. lijima and K, Wakabayashi, Department of Precision Engineering, University of Tokyo). D I A L O G checks the adherence of a CMOS circuit to appropriate design rules. This system will decompile the circuit to a higher level circuit to check consistency. The system was originally developed in FORTRAN but has been converted to an AI language, LEXTOC, to allow for flexibility in adding new rules. When machine translated to PASCAL, the system will handle debugging of circuits containing 50000 transistors. (H. J. De Man et al., Katholieke Universiteit Leuven, Belgium). VALID analyses the timing behaviour of digital systems using temporal logic against a set of constraints that specify the desired behaviour. It has analysed a FIFO queue element within 25 seconds on a VAX 11/780. IS. Bapat, Department of Computer Science, Indian Institute of Technology, Bombay and G. Venkatesh, Solid State Electronics Group, Tata Institute of Fundamental Research, Bombay). A hardware test vector is generated using AI tools from a chip-level functional description in VHDL, the VHSIC Hardware Description Language. Each statement of the H D L is examined and faults such as the following are added to the list of possible faults to test for: a) a micro-operation fails to some other operation; b) an assignment statement fails to a no-operation; c) an IF statement behaves as a stuck-at-THEN and stuck-at-ELSE; d) all clauses in case statement become a no-operations. These faults are then converted to a list of basic tests that are then put into an AND-OR tree. Next, the AND-OR tree is traversed to generate a test vector. (D. S. Barclay, J. R. Armstrong, Electrical Engineering Department, Virginia Tech). HAL converts a data flow graph, representing the operations to be performed in a digital circuit, to a data path consisting of operator cells, registers, multiplexors and busses. This is the middle part of a silicon compiler that takes a high level description of the circuit and Artificial Intelligence, 1987, Vol. 2, No. 1
45
,4I News Letter: L. L. Le[l" converts it into instructions for the chip foundry. This system is optimized for use in generating telecommunications software. An explicit timing constraint is also provided and this is used in generating the chip. In the first module to receive the data flow graph, the system identifies a critical path. Then operations are assigned to cycles along the critical path so as to attempt to minimize the concurrency of similar operations. Operations that t, se similar resources are scheduled to occur on different cycles. For example, an addition and a subtraction that could both use the same A L U would be scheduled for different cycles. The middle phase attempts to associate operations to components using a rule-based approach. For example if several operations could use the same ALU, then they all might be assigned to one. The last phase does the final assignment and generation of the data path. (P. G. Paulin, et al., Bell Northern Research, Ontario, Canada). Fujitsu has developed DDL/SX which converts technology-independent functional diagrams to technology-dependent diagrams. For example, there are rules that will use two N A N D gates to perform an AND operation if such is available and AND gates are not and to insert buffers when the fan-out on a pin is too high. The system took 15 seconds to convert a 2000 gate circuit. Hitachi has developed a rule based system that converts conventional logic to IlL circuits. The system was able to achieve 40 to 60 percent gate reduction over direct translation. The system was as efficient in reducing gate count as a designer with ten years experience, taking 250 seconds on a Hitachi M-200H.
2. Other Engineering Carnegie-Mellon is developing an expert system for the design of aluminium alloys in conjunction with Alcoa. Initial emphasis is on aluminium-lithit, m alloys used in aerospace. (J. Hultageeral, ISL, Robotics Inst., C-MU). Expert systems techniques are being applied to the design of the superheater section of a fossil fuel utility boiler. The system allows for the input and use of user preference rules such as 'In the ct, rrent design context, pressure drop is more important than outer wall temperature', (Donald E. Brown, Chelsea C. White, III, Department of Systems Engineering, University of Virginia). Fuzzy sets have been used to represent the performance of components in a structure and determine the possibility of failure. Linguistic terms such as 'good' or 'small' are converted into ft, zzy models for the performance of components, the magnitude of possible sources of failure and the consequences of these events on various components of the structure. (Fabian C. Hadipriono, Hock-Slew Toh, Ohio State University). FRIL is another system based on fuzzy logic for assessing safety of bridges. It has been applied to the assessment of bridges as it is being constructed. SPERIL-I and II will assess the safety of objects after they have been damaged by earthquake or other disaster. P R O L O G has been used in developing an expert system to choose a construction method for a bridge. (Hitoshi Furata, et al., Kyoto University, Japan). Architectural detailing is being assisted by a knowledge based system using design grammars and knowledge engineering. This work is exemplified by a design language to produce the detail of the junction of walls and 46
Art(ficial Intelligence, 1987, Vol. 2, No. 1
roofs following standards to match Australian construction circa 1910. IA. D. Radford. J. S. Gero. Department of Architectural Science, University of Sydney. Australia).
3. Optimization Several people have used rule based systems during multivariate optimization with constraints. Sometimes, in optimization the direction of search should be normal to a particular constraint. However, this may be odds with the goal of maximizing the objective function. This causes zig-zagging with the constraint becoming active and inactive on alternative steps. Papalambros and Li have developed a system to use global information using rules that indicate a specific constraint is active, inactive or dominant in a given region. The technique was exemplified in the design of a speed-reducer and a ridering. In J. S. Arora's system, rt, les will cause the system to temporarily ignore the constraint or to move along it.
4. Representation issues Different levels of abstraction in simulation are modeled using levels of abstraction. The system can be used to represent concurrency between objects such as a concurrent system such as the Dining Philosophers problem. The system can play back a real-time animation of the system at various levels of abstraction. (Pat, l Fishwick, Department of Computer and Information Science, University of Pennsylwmia). Design codes have been represented as expert systems. One of these efforts involved the conversion of the Australian Model Uniform Building code to an expert system. (Michael A. Rosenman, John S. Gero, Department of Architectural Science, University of Sydney, Australia). Ernest Davis at NYU has been developing a system for reasoning qualitatively about the behaviour of simple objects. For example, we should be able to predict that a hook will catch a ring, objects firmly planted on tables will stay still and the direction of motion of objects left in an unstable state. One approach is to look for proofofthe desired shape. For example, an object placed in a funnel must come out on top, come out the bottom or stay forever in the middle. It cannot come out on top since that will require more energy than its ct, rrent potential energy. It can't stay motionless in the middle since the sides of the funnel are too steep. And it can't continue moving indefinitely within the funnel so therefore it must come out the bottom. A proof theory has been developed for hard objects such as opened and closed boxes, rings, buttons. In geometric reasoning, objects are defined using a first order predicate calculus with equality in terms of st,ch concepts as tangency, equality, parallel, etc. For example the concepts of polygon is defined using predicates such as: a) polygon (p,n) (true if p is an n sided polygon); b) vertex-of(v,i,p) (true if point v is the ith vertex of polygon p); c) edge-of(e,p) (true if e is an edge of p). Geometric reasoning is similar to executable specifications and abstract data types for computer programs that deal with geometrical objects. (Jeannette
,4I News Letter: L. L. Lq[]
M. Wing. Department of Computer Science. Carnegie Mellon University and Farhad Arbab, Computer Science Department. University of Southern California).
5. Manufacturing A system that plans the assembly of objects by analysing the structure of the object, applying assembly principles and then using Al planning techniques to generate a sequence of operations was developed at The University of Cincinnati. The workpiece is represented as frames with geometry representation omitted. The system has generated assembly instructions for an assembly unit containing two robot arms, holders, tool stands and feeders for devices exemplified by a power supply. (KaiHsiung Chang, William G. Wee, Department of Electrical and Computer Engineering, University of Cincinnati). AI-based software controls the movement of work-inprocess in DEC's circuit board production plant. The system includes a 75-station transporter, two carousels for work-in-progress-storage and a conveyor to and from an inserter/extractor device. The Al-based software automatically assigns and tracks the work in progress, interfaces to the mover control software and alerts management to problems. This software is general enough to be moved to other DEC plants without major changes. (Mark Wynot, Digital Equipment Corporation). SIPP (Semi-lntelligent Process Planner) develops least-cost plans for the creation of metal parts. The system uses a frame based representation for the problem-solving knowledge with the planning done by using a modified Branch and Bound process. The system treats each surface independently and currently does not recognize when a surface is inaccessible due to other parts of the object. (D. Nau, Computer Science Department, University of Maryland). Northrop has developed an AI system for simulation and evaluation of sheet-metal fabrication, SIMKIT, an extension to KEE for simulation, was used to represent the system as a frame-based structure. Graphics were used to represent cell components, their relationships and statistical measurements of their performance and utilization. This allowed the user to set up and analyse the results of simulations of sheet metal manufacturing setups without doing any programming.
6. Plant Control F A L C O N will detect and identify faults in an adipic acid reactor. It will use explanation generation software to interact with the operator. The operator will press a 'WHY" button and then touch the rectangle that he is interested in. Falcon will recognize areas outside of its domain of expertise and will be aware of actions for which corrections are underway so as to avoid repetitive alerts. The system is scheduled for installation later in 1986. (Joint project of the University of Delaware, DuPont Co and Foxboro Inc.) Electric Power Research Institute has developed an expert system to reconfigure the fuel assemblies inside a nuclear power reactor. This must be done on a periodic basis as the fuel is used up. The goal is to make the shutdown period while this is being down as short as
possible as shutting down a nuclear reactor costs half a million dollars per day. TOAST assists the operator of a large utility in diagnosing failures in the distribution of power. The system uses a rule based discrete-event simulator that predicts what happens to a network after a disturbance. The diagnostic module views the power system as a collection of busses, lines, breakers and relays in isolating a problem [Sarosh N. Talukdar et al., Carnegie-Mellon University).
7. Scheduling FIXER schedules repairs on aircraft for the Royal Air Force. The system takes into account constraints on resources, sequences that tasks must be performed in and actions that must be done together. The same techniques are being used in scheduling a VLSI wafer laboratory. (T. J. Grant, Brunel University, Uxbridge).
8. Diagnosis Comparing the symptoms of earlier failures with that of a new failure are used to assist a production system in diagnosis of the new problem. A large database contains failure symptoms from diagnostic tests of previous failures. This database is clustered and cluster representatives are chosen to assist in its search. When a new failure is presented to the system, the diagnostic system matches the information against the cluster representatives and the maximum distance of a cluster representative to other members of the cluster. This enables the system to find the best match of failure symptoms without looking at all the test cases. The techniques of clustering and matching come from the field of Information Retrieval. (Marguerite T. Denoncourt, Bell Communications Research). An expert system now can diagnose failures in the DSCS-11I satellite altitude control system. This system was developed by having the system deduce diagnosis heuristics from the device model. (Michael J. Pazzani, The Aerospace Corporation, Los Angeles). The Naval Research Center has developed a diagnostic system to assist the technician in determining the tests to use and how to interpret them. The system contains knowledge about modules that are likely to occur in more than one object under test and provides facilities to allow the knowledge engineer to quickly add new devices. It is hoped that much of this information can be acquired by a direct interface with the CAD-CAM database. The system has been tested on analog equipment containing approximately 10 modules. To readers of our journal, we are interested in all newsworthy items connected with the field of Artificial Intelligence in Engineering. American readers should send items of interest to Mr L. Left, Computer Science and Engineering, Southern Methodist University, Dallas, TX 75275, USA. By electronic mail: UUCPnet allegra!convex!smu!leff C S N E T , A R P A N E T leff~smUD CSNET-RELAY. U K and European should write to Dr K. J. MacCallum, Director, Faculty of Engineering, CAD Centre, 131 Rottenrow, Glasgow G 4 0 N G . Artificial Intelli,qence, 1987, Vol. 2, No. I
47