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In most Windows programs there are three types of screen windows used: application windows, document windows, and dialog boxes. An application window is the first window opened in a Windows program, and it usually contains the main menu as the entry point to the rest of the program. All other windows in the program are document windows or dialog boxes.
Along with these three screen window types, there are two user interface design conventions that are used in Windows programs: the Single Document Interface (SDI), and the Multiple Document Interface (MDI).
An SDI program usually only contains linear logic that allows the user to take only one execution path (thread) at a time; it does not open separate execution threads which the user may move between. This is the same type of program logic used in most DOS programs. An SDI program would not contain a Clarion APPLICATION structure as its application window. The Clarion WINDOW structure (without an MDI attribute) is used to define an SDI program's application window, and the subsequent document windows or dialog boxes opened on top of it.
An MDI program allows the user to choose multiple execution paths (threads) and change from one to another at any time. This is a very common Windows program user interface. It is used by applications as a way of organizing and grouping windows which present several execution paths for the user to take.
A Clarion APPLICATION structure defines the MDI application window. The MDI application window acts as a parent for all the MDI child windows (document windows and dialog boxes), in that the child windows are clipped to its frame and automatically moved when the application frame is moved. They can also be concealed en masse by minimizing the parent. There may be only one APPLICATION open at any time in a Clarion Windows program.
Document windows and dialog boxes are very similar in that they are both defined as Clarion WINDOW structures. They differ in the conventional context in which they are commonly used and the conventions regarding appearance and attributes. In many cases, the difference is not distinguishable and does not matter. The generic term for both document windows and dialog boxes is “window” and that is the term used throughout this text.
Document windows usually display data. By convention they are movable and resizable. They usually have a title, a system menu, and maximize button. For example, in the Windows environment, the “Main” program group window that appears when you DOUBLE-CLICK on the “Main” icon in the Program Manager's desktop, is a document window.
Dialog boxes usually request information from the user or alert the user to some condition, usually prior to performing some action requested by the user. They may or may not be movable, and so, may or may not have a system menu and title. By convention, they are not resizable, although they can have a maximize button which gives the dialog two alternate sizes. A dialog box may be system modal (the user must respond before doing anything else in Windows), application modal (the user must respond before doing anything in the application), or modeless. For example, in the Clarion environment, the window that appears from the File menu's Open selection is an application modal dialog box that requests the name of the file to open.