Custom Rule Engine in WPF - MVVM

using System.Collections.Generic;

namespace CustomRulesMVVM.Models
{
    class CustomRule:IRule
    {
        #region Members
        private const string COUNTRY = "COUNTRY";
        private const string CITY = "CITY";
        private const string STATE = "STATE"; 
        Country country;
        City city;
        State state;
        #endregion

        #region Properties
        public bool IsSelected { get; set; }
        public string SelectedItem { get; set; }        
        public string CodeLHS { get; set; }
        public string  Operator { get; set; }
        public string  ValueRHS { get; set; }
        public int Source { get; set; }
        public string RuleJoinOperator { get; set; }
        public int? RuleSeqNum { get; set; }       
        public string RuleDescription { get; set; }
        #endregion

        #region Public methods
        /// <summary>
        /// This function evluates each custom rule by calling method in RuleHelper
        /// </summary>
        /// <param name="collection"></param>
        /// <returns></returns>
        public bool Eval(Dictionary<string, object> collection)
        {
            if (collection.ContainsKey(COUNTRY))
                country = (Country)collection[COUNTRY];
            if (collection.ContainsKey(CITY))
                city = (City)collection[CITY];
            if (collection.ContainsKey(STATE))
                state = (State)collection[STATE];            

            switch (this.Source)
            {
                case 1 :
                    this.IsSelected = RuleHelper.EvaluatePropertyValue(this,country);
                    break;
                case 2:
                    this.IsSelected = RuleHelper.EvaluatePropertyValue(this, city);
                    break;
                case 3:
                    this.IsSelected = RuleHelper.EvaluatePropertyValue(this, state);
                    break;
                default:
                    this.IsSelected = false;
                    break;
            }
            return this.IsSelected;
        }
        #endregion
    }
}