Case-Based Circuit Design Support System 

ABSTRACT 

We have developped experimental system to illustrate Case-Based Reason-
ing. In design task, it is very important to store and utilize design cases, for 
the designer is often required to cope with a variety of design objects within a 
limited time. This system supports a user in designing a new degital circuits 
using similar precedential circuits. 

KEY FEATURES 

Structural indexing 

Functional hierarchy trees, that represents functional structures of design 
objects, are created interactively and used as indices for case retrieval. 

Flexible case retrieval mechanism 

Structure Mapping Engine(SME) retrieves the cases whose functional struc-
tures are similar to the design object's. To shorten run-time, cases are re-
trieved parallel. The structures of the design object and cases are mapped 
into each processor in good balance. 

Case modification mechanism 

System verifies detail specs of retrieved cases, modifies them, recovers design 
failures with SME, and combines circuit blocks. 



System Configuration 
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ABSTRACT 

Recently, Case-Based Reasoning (CBR) is paid attention, as a methodology 
for aquiring and utilizing knowledge efficiently. We have developped case-
based circuit design support system to illustrate the effectiveness of CBR. 

In design task, it is very important to store and utilize design cases, for the 
designer is often required to cope with a variety of design objects within a 
limited time. This system supports to design new degital circuits using similar 
precedential circuits. 

APPROACH 

Here, we have focused on how to extract the available similar cases. 
. Structure-Mapping Engine(SME) is a kernel engine of case retrieval. 
. Each case is given the tree-structured representations of its function. 

OVERVIEW OF SYSTEM 

Structural indexing 

. Functional hierarchy tree represents hierarchical relations between pri-
  mary function and secondary functions in a tree form to arrange the 
  functions of the design object systematically. 
. Each node of functinal hierarchy tree is a simple sentence representing a 
  function. (Fig. 1 ) 



Fig.1 Functional hierarchy tree for a digital clock 
      in additional function with sensing temparature 
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. Partial functional hierarchy tree is a partial tree divided according to a 
  series of data flow between functions. (problem division) 
. Partial functional hierarchy tree of given problem is a key in case retrieval. 
. Cases(Circuit blocks) have their own functional hierarchy tree as index. 

Flexible case retrieval mechanism 

1. Case Retrieval with SME 

   . SME can extract structurally similar cases to the given problem, if 
     higher relations in given structures are same between the case and the 
     problem, even if the lower relations and entities are not same. 

   . SME evaluates the simirarity between functional hierarchy trees and 
     retrieves circuits which have most similar functions as a whole even 
     though the details are different. (Fig.2) 





2. Parallel Case Retrieval 

   . Cases are retrieved in parallel by distributing the problem and the 
     cases to each processors in good balance. 
   . Speedup of about 20-fold is attained using 64 processors in the case 
     of 22 partial functional hierarchy trees and 180 cases.(Fig.3) 
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Case modification mechanism 

1. Verifying the retrieved cases 

   System verifies the availability of the retrieved cases by modification rules, 
   if there are some incompatible detail specs. Modification rules deal with 
   changing carry or number of devices, replacing another block, etc. 

2. Failure prediction and recovery 

   Precedential failure situations and recovery informations represented with 
   causal relations are also stored into case base. SME also predicts similar 
   failures and advices the failure recoveries.(Fig.4) 





Fig.4 Failure prediction and recovery with SME 





RESULT 

Through experiments of non-stereotyped circuit, we confirmed the effec-
tiveness of CBR method with SME. We also comfirmed the effectiveness of 
parallel processing for case retrieval task requiring a long run time. 

OUTLINE OF DEMONSTRATION 

We deal with an application problem of telemeter circuits (a performance 
monitor of air-conditioner). 

. For 22 partial functional hierarchy trees for the input problem, available 
  circuits are retrieved from 180 design cases, modified and combined. 
. Design result is a block diagram with 118 functional circuit blocks 
. System shows how similar circuits are retrieved and modified. 
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