Which architecture should be followed while developing WCF Service application?

I am developing window phone 7 application. I am using XML files for storing & retrieving data for the window phone 7 application. In my application I have created the class libraries for my current window phone 7 application. I have the 'CoreClassLayer' , 'DataAccessLayer' & 'BusinessLayer' labraries for my current application. In the CoreObjectLayer class library I am using the following code for one class as follows (for e.g Category class)

public class Category
    {
        public int ID { get; set; }
        public String Name { get; set; }
        public int TransactionType_ID { get; set; }

        public Category()
        {
        }

        public Category(int ID, String Name, int TransactionType_ID)
        {
            this.ID = ID;
            this.Name = Name;
            this.TransactionType_ID = TransactionType_ID;
        }

        public Category(XElement xElement)
        {
            ID = Convert.ToInt32(xElement.Element("ID").Value.ToString());
            Name = xElement.Element("Name").Value;
            TransactionType_ID = Convert.ToInt32(xElement.Element("TransactionType_ID").Value.ToString());
        }

        public XElement Information
        {
            get
            {
                return new XElement("Category",
                        new XElement("ID", ID),
                        new XElement("Name", Name),
                        new XElement("TransactionType_ID", TransactionType_ID));
            }
        }
    }

In the DataAccessLayer I am using the following code for one class ( for e.g. CategoryList class)

public class CategoryList : List<Category>
    {
        public void GetCategoryObjects(params int [] TransactionType_ID)
        {
            int TransactionType_ID_Val = TransactionType_ID.Count();
            XDocument doc = null;
            XMLFileManager XMLDocObj = new XMLFileManager();
            doc = XMLDocObj.LoadXMLFile("Categories.xml");

            if (TransactionType_ID_Val == 0)
         开发者_开发知识库   {
                var vAllCategories = from s in doc.Descendants("Category")                                 
                                     select new Category(s);
                this.Clear();
                AddRange(vAllCategories);
            }
            else
            {
                var vCategories = from s in doc.Descendants("Category")
                                  .Where(x => x.Element("TransactionType_ID").Value == TransactionType_ID[0].ToString())
                                  select new Category(s);
                this.Clear();
                AddRange(vCategories);
            }
        }

In my BusinessLayer I am using the following code for one class (for e.g. CategoryManager class)

public CategoryList GetCategories(params int [] TransactionType_ID)
            {
                CategoryList m_dbList = new CategoryList();
                m_dbList.GetCategoryObjects(TransactionType_ID);
                return m_dbList;
            }

   public List<String> LoadCategories(params int [] TransactionType_ID)
           {
              CategoryManager CategoryManagerObj = new CategoryManager();
              CategoryList CategoryListObj = new CategoryList();
              List<String> CategoryNames = new List<string>();
              CategoryListObj = CategoryManagerObj.GetCategories(TransactionType_ID);
            foreach (Category vCategory in CategoryListObj)
            {
              CategoryNames.Add(vCategory.Name);
            }

            return CategoryNames;
          }

Now I am using the business layer to create the user interface layer of my mobile application. Now I want to put all above three layers - CoreLayer, DataAccessLayer & BusinessLayer logic into the WCF Web Service. I want to expose the method LoadCategories() from my WCF Service. Similarly to the above case I want to expose different methods from the WCF Service. So what architecture should I follow ? Should I add the 'WCF Service Library' in my current WCF Service application for CoreObjectlayer as well as 'WCF Service Library' for DataAccessLayer to the WCF Service Application & my current WCF Service Application will act as a business layer ?. Is this right way to go ? Or should I continue with my current WCF Service Application without any 'WCF Service Library' & single method LoadCategories() contain the logic included in all three layers ? Or Is there any other way ? Can you provide me any solution or link through which I can resolve the above issue ? If I am doing anything wrong then please guide me.

Without arguing the merits of the dozens of architectures you could use here- keep it simply and expose as little as you need.

If you simply need to return a set of data objects (Server.GetListOfPeanutButters()), then expose just "LoadCategories()"- you should really be thinking, "What do I really have to make public on my backend to get this to work" and everything else should, generally, not be exposed via the service.

Start there and evolve as needed- that'd be my advice.