KnowledgeBase.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / DataEntity / System / Data / Common / Utils / Boolean / KnowledgeBase.cs / 1305376 / KnowledgeBase.cs
                        

                        
                            //---------------------------------------------------------------------- 
// 
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// 
// @owner [....]
// @backupOwner [....] 
//--------------------------------------------------------------------- 

using System; 
using System.Collections.Generic;
using System.Text;
using System.Globalization;
using System.Collections.ObjectModel; 
using System.Diagnostics;
 
namespace System.Data.Common.Utils.Boolean 
{
    ///  
    /// Data structure supporting storage of facts and proof (resolution) of queries given
    /// those facts.
    ///
    /// For instance, we may know the following facts: 
    ///
    ///     A --> B 
    ///     A 
    ///
    /// Given these facts, the knowledge base can prove the query: 
    ///
    ///     B
    ///
    /// through resolution. 
    /// 
    /// Type of leaf term identifiers in fact expressions. 
    internal class KnowledgeBase 
    {
        private readonly List> _facts; 
        private Vertex _knowledge;
        private readonly ConversionContext _context;

        ///  
        /// Initialize a new knowledge base.
        ///  
        internal KnowledgeBase() 
        {
            _facts = new List>(); 
            _knowledge = Vertex.One; // we know '1', but nothing else at present
            _context = IdentifierService.Instance.CreateConversionContext();
        }
 
        /// 
        /// Adds all facts from another knowledge base 
        ///  
        /// The other knowledge base
        internal void AddKnowledgeBase(KnowledgeBase kb) 
        {
            foreach (BoolExpr fact in kb._facts)
            {
                AddFact(fact); 
            }
        } 
 
        /// 
        /// Adds the given fact to this KB. 
        /// 
        /// Simple fact.
        internal virtual void AddFact(BoolExpr fact)
        { 
            _facts.Add(fact);
            Converter converter = new Converter(fact, _context); 
            Vertex factVertex = converter.Vertex; 
            _knowledge = _context.Solver.And(_knowledge, factVertex);
        } 

        /// 
        /// Adds the given implication to this KB, where implication is of the form:
        /// 
        ///     condition --> implies
        ///  
        /// Condition 
        /// Entailed expression
        internal void AddImplication(BoolExpr condition, BoolExpr implies) 
        {
            AddFact(new Implication(condition, implies));
        }
 
        /// 
        /// Adds an equivalence to this KB, of the form: 
        /// 
        ///     left iff. right
        ///  
        /// Left operand
        /// Right operand
        internal void AddEquivalence(BoolExpr left, BoolExpr right)
        { 
            AddFact(new Equivalence(left, right));
        } 
 
        public override string ToString()
        { 
            StringBuilder builder = new StringBuilder();
            builder.AppendLine("Facts:");
            foreach (BoolExpr fact in _facts)
            { 
                builder.Append("\t").AppendLine(fact.ToString());
            } 
            return builder.ToString(); 
        }
 
        // Private class improving debugging output for implication facts
        // (fact appears as A --> B rather than !A + B)
        private class Implication : OrExpr
        { 
            BoolExpr _condition;
            BoolExpr _implies; 
 
            // (condition --> implies) iff. (!condition OR implies)
            internal Implication(BoolExpr condition, BoolExpr implies) 
                : base(condition.MakeNegated(), implies)
            {
                _condition = condition;
                _implies = implies; 
            }
 
            public override string ToString() 
            {
                return StringUtil.FormatInvariant("{0} --> {1}", _condition, _implies); 
            }
        }

        // Private class improving debugging output for equivalence facts 
        // (fact appears as A <--> B rather than (!A + B) . (A + !B))
        private class Equivalence : AndExpr 
        { 
            BoolExpr _left;
            BoolExpr _right; 

            // (left iff. right) iff. (left --> right AND right --> left)
            internal Equivalence(BoolExpr left, BoolExpr right)
                : base(new Implication(left, right), new Implication(right, left)) 
            {
                _left = left; 
                _right = right; 
            }
 
            public override string ToString()
            {
                return StringUtil.FormatInvariant("{0} <--> {1}", _left, _right);
            } 
        }
    } 
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.

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