将类添加到 WCF 服务库

我有一个类，它定义了需要在两个单独的应用程序之间共享的事务。它们都具有对此库的引用，并且可以将类用作数据类型，但不能调用其任何方法：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization;
using System.ServiceModel;
using System.Text;
using ServerLibrary.MarketService;
namespace ServerLibrary
{
    [ServiceContract]
    public interface IService
    {
        [OperationContract]
        string GetData(int value);
        [OperationContract]
        CompositeType GetDataUsingDataContract(CompositeType composite);
        [OperationContract]
        bool ProcessTransaction(Transaction transaction);
    }
    [DataContract]
    public class CompositeType
    {
        bool boolValue = true;
        string stringValue = "Hello ";
        [DataMember]
        public bool BoolValue
        {
            get { return boolValue; }
            set { boolValue = value; }
        }
        [DataMember]
        public string StringValue
        {
            get { return stringValue; }
            set { stringValue = value; }
        }
    }
    // Transaction class to encapsulate products and checkout data
    [DataContract]
    public class Transaction
    {
        [DataMember]
        public int checkoutID;
        [DataMember]
        public DateTime time;
        [DataMember]
        public List<Product> products;
        [DataMember]
        public double totalPrice;
        [DataMember]
        public bool complete;
        public void Start(int ID)
        {
            checkoutID = ID;
            products = new List<Product>();
            complete = false;
        }
        public void Complete()
        {
            time = DateTime.Now;
            complete = true;
        }
    }
}

我做错了什么？

[更新] 我错过了其余的服务。

谢谢。