Diagnosis via Model Based Reasoning

Transcription

1 Diagnosis via Model Based Reasoning 1 Introduction: Artificial Intelligence and Model Based Diagnosis 1.1 Diagnosis via model based reasoning 1.2 The diagnosis Task: different approaches

2 Davies example Expert Systems: Where Are We? And Where Do We Go From Here? Randall Davies. The AI Magazine, Spring Problem: Field service. Can I help you? Yeah. My machine doesn t work! What seem to be wrong? Well, when I sit at the console terminal and load the system, everything s just fine. The hardware powers up, the operating system loads, and it s clear that the operating system is running. From the console terminal everything is just fine. But he user terminals don't work. They re turn on and they look OK, but when you type something, absolutely nothing happens. So what s wrong Valladolid 2009 Diagnosis via model based reasoning 2

3 Davies example Console Terminal Computer OK BAD BAD BAD Users Terminals BAD BAD BAD Valladolid 2009 Diagnosis via model based reasoning 3

4 To start with... To reason about the system we need to know Structure Components behaviour Valladolid 2009 Diagnosis via model based reasoning 4

5 System configuration Console Terminal CPU MEM MEM Bus #1 Bus #2 INT Disc Users Terminals Valladolid 2009 Diagnosis via model based reasoning 5

6 Exoneration Console Terminal CPU MEM MEM Bus #1 INT Disc Bus #2 Users Terminals Some components probably work properly because they do what they are expected to do: we can load the operating systems from disc ant it respond to the console terminal inputs Valladolid 2009 Diagnosis via model based reasoning 6

7 Incrimination Console Terminal CPU MEM MEM Bus #1 INT Disc Bus #2 Users Terminals Some components are suspicious, because if all of them work properly, something must be observed at users terminals Valladolid 2009 Diagnosis via model based reasoning 7

8 Which components remain suspicious? Console Terminal CPU MEM MEM Bus #1 INT Disc Bus #2 Users Terminals Since Console Terminal, CPU, MEM, MEM, Bus #1, DISC, and DISC have been exonerated, the only suspicious elements are INT, Bus #2, Terminals and Users Terminals Valladolid 2009 Diagnosis via model based reasoning 8

9 Model expansion Eliminate unlikely faults Console Terminal CPU MEM MEM Bus #1 INT Disc Bus #2... Users Terminals Users Terminals Users Terminals Representational change: part-of hierarchy It is very unlikely that all terminals fail identically. The failure must be located in a common area preceding terminals Valladolid 2009 Diagnosis via model based reasoning 9

10 Focus of suspicion INT Bus #2 T There are diagnostics programs to test this hardware! Valladolid 2009 Diagnosis via model based reasoning 10

11 Run diagnostics DIAGNOSTICS RESULTS TEST 6 EXPECTED AAAA 3333 F0F0 FFFF RECEIVED AAA F0F0 FFFD TEST 7 EXPECTED RECEIVED D TEST 8 EXPECTED 0A0A 0312 RECEIVED 0A Valladolid 2009 Diagnosis via model based reasoning 11

12 Understand Diagnostics We need to know 1. the intend of the test that encountered the error 2. the behaviour of the device responsible for the error In our example 1. send bit patterns back and forth from CPU and bus terminator 2. consider bus terminator as three registers Hypothesis ( that reasonably explain data ) bit#1 is dropped somewhere on the path from CPU to bus terminator Valladolid 2009 Diagnosis via model based reasoning 12

13 Where to probe? Test bit#1 path from INT to TERMINATOR another representation change (more detail) INT B7 C12 AF2 XCVR DATA 1 Signal reaches bus interface 3 bit#1 looses between bus#1 (pin B7) and bus#2 (pin C12) 2 bit#1 do not reach bus terminal new focus of suspicious B7, INT, C12 Valladolid 2009 Diagnosis via model based reasoning 13

14 Up to now... 2 changes of representation part-of hierarchy subsystem Tests diagnostics Probe Focus of suspicious (B7, INT, C12) Focus of attention (Bit#1 through INT) Another representation change... Valladolid 2009 Diagnosis via model based reasoning 14

15 Expand E4 B7 Gate Array XM EN 6 C12 assume wires OK gates arrays have a long time to failure EN, XM must be OK (diagnostics) check pin 6 of chip E4 Valladolid 2009 Diagnosis via model based reasoning 15

16 Reject assumptions E4 B7 Gate Array XM EN 6 C12 the signal is OK at pin 6! reject assumption: wires may be wrong shift representation: physical structure between pin 6 and C12 Valladolid 2009 Diagnosis via model based reasoning 16

17 Physical structure CHIP E4 pin 6 C12 Testing with a ohmmeter at both sides of the wire probes it is good! Valladolid 2009 Diagnosis via model based reasoning 17

18 A Contradiction? E4 6 EN C12 B7 Gate Array XM 6 The problem can not be explained with the electrical model More physical mechanical- detail is needed Valladolid 2009 Diagnosis via model based reasoning 18

19 Diagnosis Diagnosis: bent connector Valladolid 2009 Diagnosis via model based reasoning 19

20 Issues Diagnosis based on structure and function Utility of causal models Need for multiple, specialized representations Physical Electrical Abstract functional Strong focussing effect Structure -at several levels- Empirical associations experience, knowledge- Valladolid 2009 Diagnosis via model based reasoning 20