vtwm

The vtwm virtual window manager interface provides users at the highest level with multiple desktop screens which can be used to organize more windows than typical single screen window managers, similar to the Rooms [57] interface. It provides users an overview window, where the outlines of windows on each desktop screen are depicted. Using the overview window, users can switch the current screen to different desktops and also move the windows between different desktops. The vtwm interface also allows users to transform windows into icons, which can be placed on the desktop. The lowest level of the vtwm presentation hierarchy is the page node. Multiple pages can reside in a window, although only one of them is shown at once. Thus at the second level is the window node. At the third and fourth level are the desktop and overview nodes, respectively.

• Icon node: An icon node has a capacity of 1. Its space requirement is fixed. The representation function simply draws an image depending on the application or the type of data.
• Page node: Page is a singular node, thus its capacity is 1. Its space requirement can be changed dynamically as the user resizes the page. The representation function simply draws the contents of the web page (I).
• Window node: There is no limit regarding the number of pages in a window. However, the accessibility of pages determines the usable capacity of the window node. Its space requirement varies according to user control upon resizing a window. The representation function simply draws the contents of the window.
• Desktop node: Theoretically, arbitrary number of windows can be placed on a desktop. However, due to constraints such as screen space and visibility, the capacity decreases as the size of windows grows. The layout function of a desktop node allows windows to be organized in an overlapping manner on a two-dimensional screen space.
• Overview node: Arbitrary number of desktop screens can be placed in an overview, however it decreases the amount of usable screen space in the current desktop. The screen requirements increase as the number of desktops increase since each occupies a fixed amount of space in the overview. Desktop outlines are typically arranged in the overview window side by side in a tiled manner. The representation function simply draws the outline of windows on each desktop in a reduced scale.

• Page-Window link: The access cost of a page from a window depends on the browser windows history and bookmark techniques. Typically, a linear list is kept for the history and a hierarchical list for the bookmarks. Thus, access costs depends on the technique used. The footprint of a page is the title of the page in text, thus it is rather low.
• Window-Icon link: In order to transform a window into an icon the user needs to select the Iconify operation from the window menu or press the appropriate widget on the window decoration. Typically, the image of an icon depends on the type of the information the window contains such as source code, html document, etc. Designers may also create different images, more representative of the application window. The icon label provides textual information about the contents of the window. The footprint value in these regards is relatively high due to both visual and textual representations.
• Icon-Window link: In order to access the window associated with an icon, the user needs to double-click on the corresponding icon. Since Icon-Window link is a 1:1 link, the footprint argument for Window-Icon link is valid here as well.
• Icon-Desktop link: In order to access an icon from a desktop users bring the mouse pointer onto the desired icon. The footprint of an icon is high due to the visibility of icon on the desktop. Overlapping windows or other icons may decrease the footprint value.
• Window-Desktop link: In order to access a window within a desktop users simply bring the mouse pointer onto the desired window. The footprint of a window is very high due to visibility.
• Desktop-Overview link: The access cost of a desktop from an overview window is very little. Users simply click on the reduced scale image of the desired desktop in order to change the current screen. The footprint of desktops is satisfactory. Although only the outlines of windows on each desktop is shown it suffices for most purposes.

Web Accessibility