Hello
I want to know if the only data tier is used to be created as WCF project in .NET solution.
or it can be more than one WCF project in a solution for example business workflow.
Here is an example used in WCF, i showed below the code of an example.

implementing interfaces

 NOTA: puede usar el comando "Cambiar nombre" del menú contextual para cambiar el nombre de clase "MAIRServicio" en el código, en svc y en el archivo de configuración a la vez.
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Imports EntidadesNegocio
'Imports Sistema.Componentes

Public Class MAIRServicio
    Implements IMAIRServicio

    Private Cnx As SqlConnection
    Private Dap As SqlDataAdapter
    Private Cmd As SqlCommand
    Private Tb As DataSet
    Private Function getCadenaConexion() As String
        Dim strCnx As String = ConfigurationManager.ConnectionStrings("MiConexion").ConnectionString

        If strCnx Is String.Empty Then
            Return String.Empty
        Else
            Return strCnx
        End If
    End Function

    'Public Function RUNSql(ByVal Sentencia As String) As Integer
    Public Function RUNSql(ByVal Sentencia As String) As DataSet

        'Private Cnx As SqlConnection
        'Call getCadenaConexion()
        Dap = New SqlDataAdapter(Sentencia, getCadenaConexion())
        Tb = New DataSet
        Dap.Fill(Tb)

        Return Tb
    End Function





#Region "Factura"

    Public Function FacturaPrincipal_ins(ByVal FacturaPrincipalx As Factura) As Integer Implements IMAIRServicio.FacturaPrincipal_ins
        Cnx = New SqlConnection(getCadenaConexion)
        Cmd = New SqlCommand("sp_ins_FacturaPrincipal", Cnx)
        With Cmd
            .CommandType = CommandType.StoredProcedure
            .Parameters.AddWithValue("@NumeroFactura", FacturaPrincipalx.NumeroFactura)
            .Parameters.AddWithValue("@CodigoGuia", FacturaPrincipalx.CodigoGuia)
            .Parameters.AddWithValue("@CodigoCliente", FacturaPrincipalx.CodigoCliente)
            .Parameters.AddWithValue("@Subtotal", FacturaPrincipalx.Subtotal)
            .Parameters.AddWithValue("@Igv", FacturaPrincipalx.Igv)
            .Parameters.AddWithValue("@Total", FacturaPrincipalx.Total)
            .Parameters.Add("@Codigo", SqlDbType.Int).Direction = ParameterDirection.Output
        End With
        Try
            Cnx.Open()
            Cmd.ExecuteNonQuery()
            Cnx.Close()
            Return Cmd.Parameters("@Codigo").Value
        Catch ex As Exception
            Throw New Exception(ex.Message)
        End Try

    End Function

    Public Function FacturaPrincipal_upd(ByVal FacturaPrincipalx As Factura) As Integer Implements IMAIRServicio.FacturaPrincipal_upd


        Cnx = New SqlConnection(getCadenaConexion)


        Dim grabo As Int16
        Cmd = New SqlCommand("sp_upd_FacturaPrincipal", Cnx)
        With Cmd
            .CommandType = CommandType.StoredProcedure
            .Parameters.AddWithValue("@NumeroFactura", FacturaPrincipalx.NumeroFactura)
            .Parameters.AddWithValue("@CodigoGuia", FacturaPrincipalx.CodigoGuia)
            .Parameters.AddWithValue("@CodigoCliente", FacturaPrincipalx.CodigoCliente)
            .Parameters.AddWithValue("@Subtotal", FacturaPrincipalx.Subtotal)
            .Parameters.AddWithValue("@Igv", FacturaPrincipalx.Igv)
            .Parameters.AddWithValue("@Total", FacturaPrincipalx.Total)

        End With
        Try
            Cnx.Open()
            Cmd.ExecuteNonQuery()
            Cnx.Close()
            ' grabo = 1   si grabo, grabo = 0  no grabo 
            grabo = 1
            Return grabo
        Catch ex As Exception
            Throw New Exception(ex.Message)
            grabo = 0
            Return grabo
        End Try

    End Function


    Public Function FacturaPrincipal_del(ByVal FacturaPrincipalx As Factura) As Integer Implements IMAIRServicio.FacturaPrincipal_del

        Cnx = New SqlConnection(getCadenaConexion)

        Dim borrar As Int16
        Cmd = New SqlCommand("sp_del_FacturaPrincipal", Cnx)
        Cmd.CommandType = CommandType.StoredProcedure
        Cmd.Parameters.Add("@CodigoFactura", SqlDbType.Int).Value = FacturaPrincipalx.CodigoFactura
        'Dim n As Int16
        Cnx.Open()
        Try
            borrar = Cmd.ExecuteNonQuery
        Catch ex As Exception
            borrar = 0
        End Try

        Cnx.Close()
        Return borrar
    End Function

    Public Function FacturaPrincipal_Listar() As System.Data.DataSet Implements IMAIRServicio.FacturaPrincipal_Listar
        Dim Dap As New SqlDataAdapter("sp_lis_Factura", Cnx)
        Dim dst As New DataSet
        Dap.Fill(dst, "Facturas")
        Return dst
    End Function
#End Region

#Region "Cliente"
    'Public Sub RUNSql(ByVal Sentencia As String)
    '    Da = New SqlDataAdapter(Sentencia, Cn)
    '    Ds = New DataSet
    '    Da.Fill(Ds)
    'End Sub

    Function Clientes_cargar() As DataSet Implements IMAIRServicio.Clientes_cargar
        Dim sentencia As String
        sentencia = "Select * from Clientes"
        Dim registros As DataSet
        registros = New DataSet
        registros = RUNSql(sentencia)
        'registros.Tables(0).Columns(0).ind 
        Return registros
        'Call RUNSql(sentencia)
        'Return 0
    End Function



    Public Function Cliente_ins(ByVal Clientex As Cliente) As Integer Implements IMAIRServicio.Cliente_ins
        Cnx = New SqlConnection(getCadenaConexion)
        Cmd = New SqlCommand("sp_ins_clientes", Cnx)
        With Cmd
            .CommandType = CommandType.StoredProcedure
            .Parameters.AddWithValue("@NombreCliente", Clientex.NombreCliente)
            .Parameters.AddWithValue("@Direccion", Clientex.Direccion)
            .Parameters.AddWithValue("@Telefono", Clientex.Telefono)
            .Parameters.AddWithValue("@NombreContacto", Clientex.NombreContacto)
            .Parameters.Add("@Codigo", SqlDbType.Int).Direction = ParameterDirection.Output
        End With
        Try
            Cnx.Open()
            Cmd.ExecuteNonQuery()
            Cnx.Close()
            Return Cmd.Parameters("@Codigo").Value
            MsgBox("se supone que todo salio bien")
        Catch ex As Exception
            Throw New Exception(ex.Message)
        End Try
    End Function

#End Region

End Class