When a window is visible on the screen it undergoes various stages such as CreateWindow, ShowWindow, etc. Once the window is displayed on the screen it must now make itself ready to take keyboard and mouse input from the user. Windows maintains a message queue for each windows program currently running under windows. When an input occurs, the OS translates this event into a message that it places into the windows message queue. A program receives messages from the message queue by executing a block of code known as the message loop.  While (GetMessage(&msg, NULL, 0, 0)){            TranslateMessage(&msg);            DispatchMessage(&msg);}  The GetMessage call passes to windows a pointer to the message and these fields of the message are filled by windows.  The TranslateMessage call passes the msg structure back to windows for some keyboard translation. The DispatchMessage call passes the message to windows which sends the message to appropriate windows procedure for processing the message. So this means that windows call the window procedure

COM is an acronym for Component Object Model. COM is a way of building objects that is independent of any programming language.  Every COM object implements an interface named IUnknown. It contains three methods: -         QueryInterface: Returns a pointer to another interface -         AddRef:  Increments the objects reference count -         Release: Decrements the objects reference count. One of the rules of COM says that given a pointer to an interface a client can call any IUnknown method through that pointer as well as any methods that are specific to that interface. Hence all interfaces must support the three IUnknown methods in addition to their own methods.

Object Linking and Embedding (OLE) clipboard is a more capable clipboard than the windows traditional clipboard. To transfer a large image using a legacy clipboard one must allocate enough memory space to copy this image. However using the OLE clipboard you can transfer the bitmap in a more sensible medium like a file on a hard disk.OLE drag and drop is a visual method of transferring data. Unlike having separate commands like cut, copy and paste the OLE drag and drop lets you grab a piece of data with the mouse and drop it in the desired location.So to summarize it there are two broad differences between OLE and legacy clipboard. OLE clipboard is completely COM based and secondly it supports storage medium other than global memory.OLE drag and drop is programmatically very similar to OLE clipboard. The data provider or data source creates a data object that encapsulates the data and makes an IDataObject pointer available. The data consumer or drop target retrieves the IDataObject and uses it to extract data from the data object. The drop source initiates a drag and drop operation by passing an IDataObject pointer to ::DoDragDrop. Any window that is interested inbeing a drop target registers itself with the system by calling ::RegisterDragDrop. If drop occurs in a registered window then the drop target is handed the IDataObject pointer passed to ::DoDragDrop.

The concept of namespaces plays a very crucial role in .net framework. It is a concept parallel to the concept of packages in java. In general, a namespace is a logical grouping of types for the purpose of identification. e.g. let's say in an organization there are three people with name Paul Smith each individual in a different role and responsibilities. To resolve this ambiguity we can define three namespaces based on their roles as Secretary, Manager and Operator and then reference each Paul as Secretary.Paul and Manager.Paul and Operator.Paul. This is the concept of namespace.

Yes I have certainly worked on ADO.Net. ADO.net encompasses two groups of classes: content components and managed provider components. The content components include DataSet class and other supporting classes as DataTable, DataRow, DataColumn and DataRelation. The DataSet class is a lightweight cache of a particular database from the data store.  It allows reading and writing of data and schema in XML. ADO.Net involves disconnected datasets because it is geared towards a distributed architecture. All tables and relations in a DataSet are exposed through the DataSet tables and Relations properties.  E.g. Using System; Using System.Data;  DataSet ds = new DataSet("MyDS"); Ds.Tables.Add ("Order"); Ds.Tables["Order"].Columns.Add("OrderNo" Type.GetType("System.Int32"));  The DataSet tightly integrates with XML using the methods WriteXml, ReadXml, WriteXmlSchema and ReadXmlSchema

Error handling that evolve around the various On Error.. statements are referred to as unstructured error handling. The build in object Err is used in this type of error handling. This object has several properties and methods as listed below: Properties:  Description: a short description of the error HelpContext: context ID for the help topic associated with the error HelpFile: fully qualified file name if any Number: Number associated with the error Source: a string that specifies the object that generated the error. Method: Clear: Clears the set values of all properties of the error object. Raise: Generates a runtime error and sets the properties of the Err object to the values supplied in the method call