[ServiceContract]
public interface IContactService
{
    [OperationContract]
    [WebGet(UriTemplate = "")]
    HttpResponseMessage GetAll();

    [OperationContract]
    [WebGet(UriTemplate = "{id}")]
    HttpResponseMessage Get(string id);

    [OperationContract]
    [WebInvoke(UriTemplate = "", Method = "POST")]
    HttpResponseMessage Insert(Contact contact);

    [OperationContract]
    [WebInvoke(UriTemplate = "", Method = "PUT")]
    HttpResponseMessage Update(Contact contact);

    [OperationContract]
    [WebInvoke(UriTemplate = "{id}", Method = "DELETE")]
    HttpResponseMessage Delete(string id);
}