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‎.gitignore

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npm-debug.log*
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node_modules

‎app.js

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const readline = require('readline-sync');
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const kb = require('./kb-plants.js');
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const verbose = false;
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const forwardChain = function(assertions) {
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// Select the first rule.
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let ruleIndex = 0;
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let rule = kb[ruleIndex];
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// While there are more rules.
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while (ruleIndex < kb.length) {
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// If all premises in the rule are in assertions
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const allPremisesExist = rule.premises.every(premise =>
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assertions.some(assertion => assertion.attribute === premise.attribute && assertion.value === premise.value)
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);
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// If all premises from the rule are in the assertions but not the conclusion.
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if (allPremisesExist && !assertions.some(assertion => assertion.attribute === rule.conclusion.attribute && assertion.value === rule.conclusion.value)) {
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// Add the conclusion to assertions.
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assertions.push(rule.conclusion);
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// Go back to the first rule, since the new assertion might exist as a premise in another rule.
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// This can be optimized by sorting rules based on if A's conclusion is a premise in B's, then place A before B.
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ruleIndex = 0;
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}
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else {
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// Select the next rule.
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rule = kb[++ruleIndex];
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}
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}
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return assertions;
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};
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const backChain = function(goal, assertions) {
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// Select the first rule.
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let ruleIndex = 0;
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assertions = assertions || [ goal ];
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// If there is an assertion with goal as its attribute.
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verbose && console.log(`Current goal: ${JSON.stringify(goal)}`);
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verbose && console.log(`Current assertions: ${JSON.stringify(assertions)}`);
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let assertion = assertions.filter(assertion => assertion.attribute === goal.attribute && assertion.value);
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assertion = assertion.length ? assertion[0] : null;
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verbose && console.log(`Found assertion: ${JSON.stringify(assertion)}`);
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if (!assertion) {
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// Go back to the first rule.
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ruleIndex = 0;
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while (!assertion && ruleIndex < kb.length) {
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const rule = kb[ruleIndex];
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if (rule.conclusion.attribute === goal.attribute) {
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let premiseIndex = 0;
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let allPremisesTrue = false;
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let premise = rule.premises[premiseIndex];
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let isPremiseAssertionTrue = true;
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verbose && console.log(`Rule conclusion: ${JSON.stringify(rule.conclusion)}`);
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while (!allPremisesTrue && isPremiseAssertionTrue) {
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const nextGoal = premise;
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verbose && console.log(`Calling backChain for goal ${JSON.stringify(nextGoal)}`);
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trueAssertion = backChain(nextGoal, assertions);
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verbose && console.log(`trueAssertion: ${JSON.stringify(trueAssertion)}`);
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// Add the assertion to the assertion list.
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assertions.push(trueAssertion);
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verbose && console.log(`${JSON.stringify(premise)} === ${JSON.stringify(trueAssertion)}`)
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// Is the trueAssertion equal to the premise?
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isPremiseAssertionTrue = JSON.stringify(premise) === JSON.stringify(trueAssertion);
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if (isPremiseAssertionTrue) {
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verbose && console.log(`${premiseIndex + 1} < ${rule.premises.length}`);
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if (++premiseIndex < rule.premises.length) {
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premise = rule.premises[premiseIndex];
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verbose && console.log(allPremisesTrue);
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verbose && console.log(`Using new premise ${JSON.stringify(premise)}`);
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}
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else {
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verbose && console.log('All premises true!');
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allPremisesTrue = true;
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}
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}
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}
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if (allPremisesTrue) {
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verbose && console.log(`New assertion: ${JSON.stringify(rule.conclusion)}`);
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assertion = rule.conclusion;
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}
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}
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// Select the next rule.
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ruleIndex++;
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}
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if (!assertion) {
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let existingAssertion = assertions.filter(a => a.attribute === goal.attribute);
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existingAssertion = existingAssertion.length ? existingAssertion[0] : null;
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if (existingAssertion) {
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assertion = existingAssertion;
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}
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else {
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// Prompt user for goal.
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const value = readline.question(`What is the value for ${goal.attribute}? `);
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assertion = { attribute: goal.attribute, value }; // Enter new assertion for the type and value specified by the user.
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}
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}
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else {
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const index = assertions.indexOf(a => a.attribute === assertion.attribute && !a.value);
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if (index > -1) {
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verbose && console.log('Updating value!');
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assertions[index].value = assertion.value;
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}
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}
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}
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return assertion;
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};
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//
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// Test forward-chaining.
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// User inputs: stem woody, position upright, one main trunk yes, broad and flat no
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// Output includes: type is tree (because of original inputs), then using type is tree we can now deduce class gymnosperm
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//
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let assertions = [];
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let attribute = 1;
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while (attribute) {
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attribute = readline.question('Enter an attribute? ');
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if (attribute) {
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let value = readline.question('Enter a value? ');
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value && assertions.push({ attribute, value });
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}
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}
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assertions = forwardChain(assertions);
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console.log(assertions);
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//
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// Test backward-chaining.
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// User inputs: class, stem woody, position upright, one main trunk yes, broad and flat yes
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// Output: angiosperm
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//
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let goal = { attribute: readline.question('What attribute type do you want to know? ') };
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assertion = backChain(goal);
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if (assertion.value) {
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console.log(assertion.value);
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}
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else {
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console.log(`You cannot answer enough questions to determine ${goal.attribute}.`);
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}

‎kb-plants.js

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const KB = [
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{
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premises: [
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{ attribute: 'class', value: 'gymnosperm' },
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{ attribute: 'leaf shape', value: 'scalelike' }
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],
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conclusion: { attribute: 'family', value: 'cypress' }
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},
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{
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premises: [
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{ attribute: 'class', value: 'gymnosperm' },
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{ attribute: 'leaf shape', value: 'needlelike' },
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{ attribute: 'pattern', value: 'random' }
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],
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conclusion: { attribute: 'family', value: 'pine' }
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},
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{
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premises: [
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{ attribute: 'class', value: 'gymnosperm' },
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{ attribute: 'leaf shape', value: 'needlelike' },
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{ attribute: 'pattern', value: 'two even lines' },
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{ attribute: 'silvery band', value: 'yes' }
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],
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conclusion: { attribute: 'family', value: 'pine' }
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},
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{
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premises: [
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{ attribute: 'class', value: 'gymnosperm' },
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{ attribute: 'leaf shape', value: 'needlelike' },
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{ attribute: 'pattern', value: 'two even lines' },
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{ attribute: 'silvery band', value: 'no' }
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],
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conclusion: { attribute: 'family', value: 'bald cypress' }
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},
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{
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premises: [
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{ attribute: 'type', value: 'tree' },
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{ attribute: 'broad and flat', value: 'yes' }
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],
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conclusion: { attribute: 'class', value: 'angiosperm' }
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},
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{
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premises: [
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{ attribute: 'type', value: 'tree' },
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{ attribute: 'broad and flat', value: 'no' }
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],
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conclusion: { attribute: 'class', value: 'gymnosperm' }
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},
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{
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premises: [
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{ attribute: 'stem', value: 'green' },
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],
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conclusion: { attribute: 'type', value: 'herb' }
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},
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{
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premises: [
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{ attribute: 'stem', value: 'woody' },
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{ attribute: 'position', value: 'creeping' },
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],
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conclusion: { attribute: 'type', value: 'vine' }
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},
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{
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premises: [
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{ attribute: 'stem', value: 'woody' },
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{ attribute: 'position', value: 'upright' },
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{ attribute: 'one main trunk', value: 'yes' }
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],
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conclusion: { attribute: 'type', value: 'tree' }
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},
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{
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premises: [
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{ attribute: 'stem', value: 'woody' },
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{ attribute: 'position', value: 'upright' },
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{ attribute: 'one main trunk', value: 'no' }
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],
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conclusion: { attribute: 'type', value: 'shrub' }
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},
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];
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module.exports = KB;

‎package.json

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{
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"name": "knowledge-base-test",
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"version": "0.0.1",
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"main": "app.js",
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"dependencies": {
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"readline-sync": "*"
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}
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}

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