Structural Abstraction for Strong Fault Models Diagnosis (DX 2014 BISFAI 2015) Roni SternMeir KalechOrel Elimelech Ben Gurion University of the Negev, Israel Department of Information Systems Engineering

Outline  Introduction to Diagnosis  Model-Based Diagnosis  Definition & Motivation  Abstraction  Literature Review  Research Goal  Methodology  Evaluation  Results  Conclusions  Future Work 2

Outline  Introduction to Diagnosis  Model-Based Diagnosis  Definition & Motivation  Abstraction  Literature Review  Research Goal  Methodology  Evaluation  Results  Conclusions  Future Work 3

What is a Diagnosis? Identifying the reason for a problem by examining observed symptoms. Determining which part of the system is failing. 4

Examples of Diagnosis Domains 5

Diagnosis Approaches Expert Systems. Case-Based Reasoning. Probabilistic Reasoning. Model-Based Diagnosis. And more… 6

Outline  Introduction to Diagnosis  Model-Based Diagnosis  Definition & Motivation  Abstraction  Literature Review  Research Goal  Methodology  Evaluation  Results  Conclusions  Future Work 7

Model-Based Diagnosis 8 Car System ModelA Real Car [Raymod Reiter. A theory of diagnosis from first principles. 1987]. [Johan de Kleer and Brian C. Williams. Diagnosing multiple faults. 1987].

Model-Based Diagnosis 9 Diagnosis Engine System Model Diagnoses Diagnosis Observations

Abstraction Components

11 32 Components Faulty Abstract Diagnosis What caused this black box to fail?

12 Abstraction Input 1 Input 2 Output Inputs 3 & 4 Input 1 Input 2 Inputs 3 & 4 Output Abstraction

13 Grounding Faulty Input 1 = No Fluids Input 2 = No Fluids Expected Output = No Fluids Observed Output = Fluids Inputs 3 & 4 = No Fluids Pipe 9 is Faulty Grounding

14 Architecture & Terminology Original System Abstract System Diagnosis Engine Abstract Diagnoses Diagnoses for the Original System Find Abstraction  Finds Grounding

What if we can’t ground an abstract component? 15

16 Ungroundable Abstract Diagnosis Input = No Fluids Expected Output = No Fluids Observed Output = Fluids Pipe 2 Mode: Healthy \ Blocked Healthy  No Fluids Blocked  No Fluids Pipe 1 Pipe 2 An abstract component of 2 pipes The grounding process fails Using abstraction here is not easy Can’t explain the observed output Faulty

17 Literature Review [Metodi, Stern, Kalech and Codish. Compiling Model-Based Diagnosis to Boolean Satisfaction. 2012] Past work assumed 2 behavior modes: Healthy \ Faulty Faulty  Any desired behavior Pipe 1 Pipe 2 Abstract diagnoses will always be groundable

18 Literature Review Some have already tried to diagnose systems with multiple fault modes.  Conflict-Directed with Abstraction [Feldman, Provan and van Gemund. 2010]  Compilation-Based with Abstraction [Torta and Torasso. 2013]

Our goal is to find an efficient way to diagnose when grounding can fail 19

Outline  Introduction to Diagnosis  Model-Based Diagnosis  Definition & Motivation  Abstraction  Literature Review  Research Goal  Methodology  Evaluation  Results  Conclusions  Future Work 20

Discard abstract components that may not be groundable Pessimistic Approach More components Harder to diagnose The grounding process is easier

22 Keep all abstract components and take the risk of failing during the grounding process. Less components  easier to diagnose The grounding process is harder 2. Optimistic Approaches

Weak-Optimistic Approach 2.2. Strong- Optimistic Approach Grounding Fail Success Grounding Are there more abstract diagnoses? Fail Success No Yes

24 Approaches Tradeoff

Outline  Introduction to Diagnosis  Model-Based Diagnosis  Definition & Motivation  Abstraction  Literature Review  Research Goal  Methodology  Evaluation  Results  Conclusions  Future Work 25

Evaluation Empirical evaluation. The approaches were implemented in Prolog. External SAT Solver. Modified version of the ISCAS-85 benchmark. 26

Results 27 Three systems: Diagnosis algorithm: SATbD Timeout: 20 seconds System ID|Comps.| Before Abstraction |Comps.| After Abstraction c c c X Axis – The Approaches Y Axis - Success Rate of Solved Instances

Conclusions & Summary 28  General approach for abstraction in strong-fault models.  Evaluation on a modified version of the ISCAS-85 benchmark.  Abstraction speeds up the diagnosis process.  Mostly the (weak) optimistic approach is the best.

Schedule & Future Work 29  Find an efficient method to use abstraction in strong-fault models.  Model the approaches to SAT.  Evaluate the approaches (ISCAS-85 benchmark).  Compare our method to Torta and Torasso. 2013, Feldman et al  Optimize the approaches.  Find an hybrid approach based on systems pre-process.

Questions?