規則引擎由推理引擎發展而來，是一種嵌入在應用程序中的組件，實現了將業務決策從應用程序代碼中分離出來，並使用預定義的語義模塊編寫業務決策。接受數據輸入，解釋業務規則，並根據業務規則做出業務決策。應用背景： 企業級管理者對企業IT系統的開發有著如下的要求：
1. 為提高效率，管理流程必須自動化，即使現代商業規則異常復雜。
2. 市場要求業務規則經常變化，IT系統必須依據業務規則的變化快速、低成本的更新。
3. 為了快速、低成本的更新，業務人員應能直接管理IT系統中的規則，不需要程序開發人員參與。
下面介紹一個開源的引擎（NXBRE Rule-engine）實現動態折扣價格計算：
折扣邏輯配置使用XML（擴展名.xbre）為文件，後期修改XML打折策略，在程序代碼無需修改的情況，實現柔性折扣策略的目的。
折扣規則文件：discount.xbre
1 <?xml version="1.0" encoding="UTF-8"?> 2 <xBusinessRules xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="xBusinessRules.xsd"> 3 <!-- 全局變量--> 4 <Integer id="10i" value="10"/> 5 <Integer id="40i" value="40"/> 6 <ObjectLookup id="QuantityOrdered" objectId="CurrentOrder" member="Quantity"/> 7 <Logic> 8 <If> 9 <And> 10 <GreaterThanEqualTo leftId="ClientRating" rightId="ClientRatingThreshold"> 11 <!-- CurrentOrder為訂單對象--> 12 <ObjectLookup id="ClientRating" objectId="CurrentOrder" member="ClientRating"/> 13 <String id="ClientRatingThreshold" value="C"/> 14 </GreaterThanEqualTo> 15 </And> 16 <Do> 17 <!-- 對於評分高的客戶指定的折扣策略 Discount rules for high rate customers --> 18 <Logic> 19 <If> 20 <And> 21 <GreaterThan leftId="QuantityOrdered" rightId="40i"/> 22 </And> 23 <Do> 24 <!-- AppliedDiscount為應用的折扣--> 25 <Evaluate id="AppliedDiscount"> 26 <!-- Percent為折扣比例--> 27 <Parameter name="Percent" value=".7"/> 28 </Evaluate> 29 </Do> 30 </If> 31 <ElseIf> 32 <And> 33 <GreaterThan leftId="QuantityOrdered" rightId="10i"/> 34 </And> 35 <Do> 36 <Evaluate id="AppliedDiscount"> 37 <Parameter name="Percent" value=".8"/> 38 </Evaluate> 39 </Do> 40 </ElseIf> 41 <Else> 42 <Evaluate id="AppliedDiscount"> 43 <Parameter name="Percent" value=".9"/> 44 </Evaluate> 45 </Else> 46 </Logic> 47 </Do> 48 </If> 49 <Else> 50 <!-- 對於評分低的客戶指定的折扣策略 Discount rules for low rate customers --> 51 <Logic> 52 <If> 53 <And> 54 <GreaterThan leftId="QuantityOrdered" rightId="40i"/> 55 </And> 56 <Do> 57 <Evaluate id="AppliedDiscount"> 58 <Parameter name="Percent" value=".9"/> 59 </Evaluate> 60 </Do> 61 </If> 62 <Else> 63 <Evaluate id="AppliedDiscount"> 64 <Parameter name="Percent" value="1"/> 65 </Evaluate> 66 </Else> 67 </Logic> 68 </Else> 69 </Logic> 70 </xBusinessRules>
所有的業務邏輯都在discount.xbre 中定義，下面我們定義一個窗體來解析折扣邏輯並顯示計算的結果：
1 using System;
2 using System.Collections.Generic;
3 using System.ComponentModel;
4 using System.Data;
5 using System.Drawing;
6 using System.Linq;
7 using System.Text;
8 using System.Threading.Tasks;
9 using System.Windows.Forms;
10 using System.Collections;
11 using NxBRE.FlowEngine;
12 using NxBRE.FlowEngine.IO;
13 using BREFactory = NxBRE.FlowEngine.Factories.BREFactory;
14 using Reflection = NxBRE.Util.Reflection;
15 namespace WinApp
16 {
17 public partial class frmDiscountRBE : Form
18 {
19 public frmDiscountRBE()
20 {
21 InitializeComponent();
22
23 }
24
25 /// <summary>
26 /// 規則xml文件名稱
27 /// </summary>
28 public const string FLOW_RULES_FILENAME = "discount.xbre";
29 public const string ORDER = "CurrentOrder";
30 public const string APPLIED_DISCOUNT = "AppliedDiscount";
31 public const string PERCENT = "Percent";
32 /**/
33 /// <summary>
34 /// 定單
35 /// </summary>
36 struct Order
37 {
38 public Int32 Quantity;
39 public Double TotalCost;
40 public string ClientRating;
41 public Order(int _q, double _t, string _c)
42 {
43 this.Quantity = _q;
44 this.TotalCost = _t;
45 this.ClientRating = _c;
46 }
47 }
48 /**/
49 /// <summary>
50 /// 計算結果
51 /// </summary>
52 /// <param name="aBRC">規則引摯上下文</param>
53 /// <param name="aMap"></param>
54 /// <param name="aStep"></param>
55 /// <returns>結果</returns>
56 static object AppliedDiscount(IBRERuleContext aBRC, IDictionary aMap, object aStep)
57 {
58 Order _order = (Order)aBRC.GetObject(ORDER);
59 double _d = Convert.ToDouble(Reflection.CastValue(aMap[PERCENT], typeof(double)));
60 return _order.TotalCost * _d;
61 }
62 private void btnDiscount_Click(object sender, EventArgs e)
63 {
64 try
65 {
66 //載入規則
67 IRulesDriver rulesDriver = new XBusinessRulesFileDriver(FLOW_RULES_FILENAME);
68 //工廠
69 BREFactory breFactory = new BREFactory();
70 //引摯實例
71 IFlowEngine bre = breFactory.NewBRE(rulesDriver);
72 //委托實例
73 ExecuteRuleDelegate executeRuleDelegate = new ExecuteRuleDelegate(AppliedDiscount);
74 bre.RuleContext.SetFactory(APPLIED_DISCOUNT, new BRERuleFactory(executeRuleDelegate));
75 //設置規則引摯環境變量
76 //Order order = new Order(5, 25, "A");
77 Order order = new Order(Int32.Parse(this.txtQuantity.Text), Double.Parse(this.txtTotalCost.Text), this.txtClientRating.Text);
78 bre.RuleContext.SetObject(ORDER, order);
79 //執行
80 bre.Process();
81 //得到執行結果
82 double result = (double)bre.RuleContext.GetResult(APPLIED_DISCOUNT).Result;
83
84 this.txtPayCost.Text = result.ToString();
85 this.txtPayCost.ReadOnly = true;
86 //Console.Out.WriteLine("\nOrder: Calculated discounted total={0} (expected: {1})\n",
87 // result, 25);
88 //Console.ReadLine();
89 }
90 catch (Exception ex)
91 {
92 MessageBox.Show(ex.Message);
93 }
94 }
95
96 private void frmDiscountRBE_Load(object sender, EventArgs e)
97 {
98
99 }
100
101 }
102 }
運行程序，界面如下：
數量>40，折扣0.7
數量大於10且小於40，折扣0.8
