1 //---------------------------------------------------------------------
2 // <copyright file="Sentence.cs" company="Microsoft">
3 // Copyright (c) Microsoft Corporation. All rights reserved.
7 // @backupOwner Microsoft
8 //---------------------------------------------------------------------
11 using System.Collections.Generic;
13 using System.Globalization;
14 using System.Collections.ObjectModel;
15 using System.Diagnostics;
18 namespace System.Data.Common.Utils.Boolean
21 /// Abstract base class for nodes in normal form expressions, e.g. Conjunctive Normal Form
24 /// <typeparam name="T_Identifier">Type of expression leaf term identifiers.</typeparam>
25 internal abstract class NormalFormNode<T_Identifier>
27 private readonly BoolExpr<T_Identifier> _expr;
30 /// Initialize a new normal form node representing the given expression. Caller must
31 /// ensure the expression is logically equivalent to the node.
33 /// <param name="expr">Expression logically equivalent to this node.</param>
34 protected NormalFormNode(BoolExpr<T_Identifier> expr) { _expr = expr.Simplify(); }
37 /// Gets an expression that is logically equivalent to this node.
39 internal BoolExpr<T_Identifier> Expr { get { return _expr; } }
42 /// Utility method for delegation that return the expression corresponding to a given
45 /// <typeparam name="T_NormalFormNode">Type of node</typeparam>
46 /// <param name="node">Node to examine.</param>
47 /// <returns>Equivalent Boolean expression for the given node.</returns>
48 protected static BoolExpr<T_Identifier> ExprSelector<T_NormalFormNode>(T_NormalFormNode node)
49 where T_NormalFormNode : NormalFormNode<T_Identifier>
56 /// Abstract base class for normal form sentences (CNF and DNF)
58 /// <typeparam name="T_Identifier">Type of expression leaf term identifiers.</typeparam>
59 /// <typeparam name="T_Clause">Type of clauses in the sentence.</typeparam>
60 internal abstract class Sentence<T_Identifier, T_Clause> : NormalFormNode<T_Identifier>
61 where T_Clause : Clause<T_Identifier>, IEquatable<T_Clause>
63 private readonly Set<T_Clause> _clauses;
66 /// Initialize a sentence given the appropriate sentence clauses. Produces
67 /// an equivalent expression by composing the clause expressions using
68 /// the given tree type.
70 /// <param name="clauses">Sentence clauses</param>
71 /// <param name="treeType">Tree type for sentence (and generated expression)</param>
72 protected Sentence(Set<T_Clause> clauses, ExprType treeType)
73 : base(ConvertClausesToExpr(clauses, treeType))
75 _clauses = clauses.AsReadOnly();
78 // Produces an expression equivalent to the given clauses by composing the clause
79 // expressions using the given tree type.
80 private static BoolExpr<T_Identifier> ConvertClausesToExpr(Set<T_Clause> clauses, ExprType treeType)
82 bool isAnd = ExprType.And == treeType;
83 Debug.Assert(isAnd || ExprType.Or == treeType);
85 IEnumerable<BoolExpr<T_Identifier>> clauseExpressions =
86 clauses.Select(new Func<T_Clause, BoolExpr<T_Identifier>>(ExprSelector));
90 return new AndExpr<T_Identifier>(clauseExpressions);
94 return new OrExpr<T_Identifier>(clauseExpressions);
98 public override string ToString()
100 StringBuilder builder = new StringBuilder();
101 builder.Append("Sentence{");
102 builder.Append(_clauses);
103 return builder.Append("}").ToString();
108 /// Represents a sentence in disjunctive normal form, e.g.:
110 /// Clause1 + Clause2 . ...
112 /// Where each DNF clause is of the form:
114 /// Literal1 . Literal2 . ...
116 /// Each literal is of the form:
124 /// <typeparam name="T_Identifier">Type of expression leaf term identifiers.</typeparam>
125 internal sealed class DnfSentence<T_Identifier> : Sentence<T_Identifier, DnfClause<T_Identifier>>
127 // Initializes a new DNF sentence given its clauses.
128 internal DnfSentence(Set<DnfClause<T_Identifier>> clauses)
129 : base(clauses, ExprType.Or)
135 /// Represents a sentence in conjunctive normal form, e.g.:
137 /// Clause1 . Clause2 . ...
139 /// Where each DNF clause is of the form:
141 /// Literal1 + Literal2 + ...
143 /// Each literal is of the form:
151 /// <typeparam name="T_Identifier">Type of expression leaf term identifiers.</typeparam>
152 internal sealed class CnfSentence<T_Identifier> : Sentence<T_Identifier, CnfClause<T_Identifier>>
154 // Initializes a new CNF sentence given its clauses.
155 internal CnfSentence(Set<CnfClause<T_Identifier>> clauses)
156 : base(clauses, ExprType.And)