DNN的数据访问的抽象类在\Components\Providers\Data\DataProvider.vb，包括DNN的所有数据访问方法。其中 Instance()就是 factory自己，并且通过WEB.CONFIG加载相应的程序集。
 

        ' provider constants - eliminates need for Reflection later

        Private Const [ProviderType] As String = "data" ' maps to <sectionGroup> in web.config

        ' create a variable to store the reference to the instantiated object

        Private Shared objProvider As DataProvider

        Public Shared Function Instance() As DataProvider

            ' does the provider reference already exist?

            If objProvider Is Nothing Then

                Dim strCacheKey As String = [ProviderType] & "provider"

                ' use the cache because the reflection used later is expensive

                Dim objType As Type = CType(DataCache.GetCache(strCacheKey), Type)

                If objType Is Nothing Then

                    ' Get the provider configuration based on the type

                    Dim objProviderConfiguration As ProviderConfiguration = ProviderConfiguration.GetProviderConfiguration([ProviderType])

                    ' The assembly should be in \bin or GAC, so we simply need to get an instance of the type

                    Try

                        ' Get the typename of the Core DataProvider from web.config

                        Dim strTypeName As String = CType(objProviderConfiguration.Providers(objProviderConfiguration.DefaultProvider), Provider).Type

                        ' use reflection to get the type of the class that implements the provider

                        objType = Type.GetType(strTypeName, True)

                        ' 把类型插入到缓存

                        DataCache.SetCache(strCacheKey, objType)

                    Catch e As Exception

                        ' Could not load the provider - this is likely due to binary compatibility issues

                    End Try

                End If

                ' 保存引用

                objProvider = CType(Activator.CreateInstance(objType), DataProvider)

            End If

            Return objProvider

        End Function
所有的方法都要求重写，也就是说相关的调用都必须重写这个方法。
 

        ' 链接模块

        Public MustOverride Function GetLinks(ByVal ModuleId As Integer) As IDataReader

        Public MustOverride Function GetLink(ByVal ItemID As Integer, ByVal ModuleId As Integer) As IDataReader

        Public MustOverride Sub DeleteLink(ByVal ItemID As Integer)

        Public MustOverride Sub AddLink(ByVal ModuleId As Integer, ByVal UserName As String, ByVal Title As String, ByVal Url As String, ByVal MobileUrl As String, ByVal ViewOrder As String, ByVal Description As String, ByVal NewWindow As Boolean)

        Public MustOverride Sub UpdateLink(ByVal ItemId As Integer, ByVal UserName As String, ByVal Title As String, ByVal Url As String, ByVal MobileUrl As String, ByVal ViewOrder As String, ByVal Description As String, ByVal NewWindow As Boolean)