DiagnostiCar (1) - Introduction

I'm here today to tell my expirience with logic programming on a graduation project - DiagnostiCar.

The DiagnostiCar core feature was an expert system for giving hints to laypeople about their cars symptoms and their causes and consequences to avoid being deceived by mechanics (an habit of the job). Communication between the system and the users was conceived to happen with multiple choice questions forms and at the end the system gives the possible causes for the observed car characteristics.

This is a video of the DiagnostiCar expert system interface working:



Although there are many other interesting aspects about the DiagnostiCar, let's focus on the shell system. The expert system reasoning system used was abductive reasoning which is a kind of reasoning that tries to find a plausible cause (or a set of them) for a given fact occurrence [1][2]. Find the causes for a given observation is exactly what we need for diagnose car problems (the cause of the observable symptoms).

I choose to use Prolog not only because it's default support to first-order logic (although some logic limitations on negation [3]), but it has a nice support for pattern matching and syntax operator definition (most of the Prolog implementations). From the Prolog implementations I've picked SWI Prolog due to it's multi-thread support (necessary for a system running on a multiple user environment), stability and speed (not as fast as the YAP) [4].

To illustrate the process of development of the expert system we will restrict our diagnosis to the problems consisting of some oil leaks problem. Here are some of the knowledge about car diagnosis I will use as example in the next sections:

• A crank case, hydraulic oil reservoir and brakes fluid reservoir damaged are problems;
• The crank case damaged provokes leak of engine oil;
• The hydraulic reservoir damaged provokes leak of hydraulic system oil;
• The brakes fluid reservoir damaged provokes leak of engine oil; 
• If an oil is leaking it dirts the garage's floor.
• The brakes fluid is green.
• The hydraulic oil is red.
• The engine oil is black or brown.
• If the engine oil is black, then it needs to be changed.

For the next parts, it's good to know the basic about Prolog. A VERY good material about Prolog, it's a the book "Building Expert Systems in Prolog"[5] which guided through the realms of logic programming and the nasty api's documentations. It is also very pratical and full of examples to follow. It's also good see the SWI reference to check some SWI particularities[6].

[1] Abductive Logic Programming
[2] Abducive Reasoning
[3] Prolog Negation as Failure
[4] Prologs Implementation Comparisons
[5] "Building Expert Systems in Prolog"
[6] SWI Manual