To separate the two main tasks of the system, gathering pages and interacting with the user, these two phases are run as two independent programs. One program, the engine, gathers and organizes pages; the actors involved are the ferrets, filters, advisors, mapmaker, and the database. The other program, the interface, manages the user interface and gathers information about the user's preferences and activities; the actors involved include the user interface and the generalizer.

The database is the only connection between the two programs. The engine produces it and the interface accesses it. The interface uses the pages in the database to prepare the window for the user and the generalizer adjusts the data in the database in response to user activity.

To begin a session, the user starts up a KSApplet. Its init() method connects to the database through an RMI socket then creates an InterfaceWindow, passing it a reference to the database. The InterfaceWindow constructs the display window. When the user ends a session by closing the KSApplet, the applet's stop() method calls the InterfaceWindow's savePreferences() method to store the user's preferences.

The InterfaceWindow constructor looks for the last user preferences page, and if found, it starts the window with the user's preferences set in the last session. Once the InterfaceWindow is created, it creates three of the components of the display. One of these components, the CloseUp, is then responsible for creating and containing the fourth display component, the Overview.

The four components of the display

Overview	reduced view of the entire space of pages
CloseUp	enlarged view of the active portion of the space of pages
CollapsibleToolBar	tool bar to allow user feedback
StatusBar	place for the system to show URLs of pages

The database stores a Document for each page gathered. A Document is an object containing a reference to the page, a list of the page's attributes (number of images, size of page, modification date, and so on), and a list of other pages whose content is similar to the page's content.

The InterfaceWindow invokes the database's getAllPages() method, which returns a vector of Documents currently stored in the database. This vector is passed to a Plotter, a class that translates the information into a displayable two-dimensional IconSet.

The IconSet is a vector of Icons representing the pages in the vector of Documents. Each Icon object contains a location, size, and color for a specific page in the space of pages.

The Plotter algorithm is going to take experimentation. It must be predictable from session to session so that it places icons consistently. It won't always place an Icon correctly, however, so the interface must let the user move the Icon. This movement is very important information and is passed to the generalizer, which updates the database to reflect this change. On the next session with the user the Icon will appear at its new location.

The Plotter calculates the distance between two pages based on a similarity value. This value is contained in the page's Document objects given by the database. Due to the complexity of the Plotter's task we have discussed several algorithms. The algorithms we chose to develop are explained after all of the user interface is explained so that you will have a better understanding of the problems involved.

CloseUp and Overview

The CloseUp is created in the InterfaceWindow's constructor. The IconSet is passed as an argument to the CloseUp's constructor, along with a reference to the InterfaceWindow and an initial zoom level, which the user has indicated as a preference. The zoom level is used to determine how close up to display the icons.

The CloseUp needs a reference to the InterfaceWindow to notify the Generalizer of user activity by invoking methods in the InterfaceWindow. The Generalizer updates the database in response to user activity so that the system can better serve the user. The Generalizer registers with the InterfaceWindow, which implements the UserInterface.

The CloseUp contains two components to provide views of the space of pages: the CloseUpViewport and the Overview, which contains an OverviewViewport. Both viewports use the IconSet to determine what Icons to display for the user.

The CloseUpViewport displays detailed versions of the Icons near the user's current location (the pages the user is currently viewing). The OverviewViewport displays a simplified version of all the Icons in the space of pages; depending on the zoom level it can give the user a complete view of the space of pages. The CloseUp passes the IconSet to the Overview as an argument to the Overview's constructor, who in turn passes it to the OverviewViewport's constructor.

The CloseUpViewport can take up the full dimensions of the window to display its Icons. There are two other components that are displayed above the CloseUpViewport though they may both be resized to give a full view of the CloseUpViewport, at the user's discretion. One of these components is the Overview, which is displayed in the lower left corner of the CloseUp, and the other is the CollapsibleToolBar, a separate component of the InterfaceWindow.

The user can resize the Overview by clicking on the edge of the Overview and dragging the mouse. The user can also collapse the tool bar into a single button.

User Activities in the Overview and CloseUp

The Overview and Closeup both need to know about user activity that effects the viewports, zoom value, or user's location. To communicate this information to each other, they both implement OverviewListener and the CloseUpListener, respectively. They also both then register as a listener with their counterpart.

Some user activities possible in the CloseUpViewport are: moving Icons to new locations, deleting Icons, scrolling the viewport, and displaying previews of pages. To move an Icon, the user clicks on it and drags it to a new location in the viewport. To delete an Icon, the user clicks on the kill button included in the CollapsibleToolBar, which puts the mouse curser in "kill mode", then clicks on the offending Icon. The user can move through the space of pages by placing the mouse at one of the viewport's edges, causing the viewport to scroll in that direction.

The CloseUp notifies its listeners, currently only the Overview, of these activities. The Overview then updates its viewport to remain synchronized with the CloseUp's viewport.

When the user pauses the mouse cursor over an Icon in the CloseUpViewport, the viewport displays a PagePreview of the Icon's respective page. This PagePreview is a simplified page showing the top portion of the "real" page. This lets the user view the page's title (if it has one) and the first portion of the page.

Clicking the mouse inside the PagePreview causes the Overview to send the page to the user's browser for viewing. Moving the mouse off the PagePreview causes the PagePreview to be removed from the viewport.

All of these actions have an associated class that extends UserAction, a very basic class. These UserActions are constructed inside methods of the InterfaceWindow. The CloseUp uses the reference it has to the InterfaceWindow to invoke these methods providing the method with any specific information it needs to construct the corresponding UserAction. After constructing the UserAction, each of these methods then informs the InterfaceWindow's listeners of the activity. Cuurrently, the only listener is the Generalizer, who then uses the information to tailor the database in response to user activities.

The user can change location by clicking the mouse anywhere in the viewport or by dragging the current landmark with the mouse. A landmark, currently shown as a '+' symbol, is a symbol that is drawn above the icons in the OverviewViewport. There can be one or more of these displayed. There will, however, always be at least one that is drawn larger than the rest; it shows where the user is in the space of pages. This particular landmark follows the user's movement.

The user can add a new, fixed landmark with the "add" button in the Overview. When the user clicks on this button the viewport installs a permanent landmark at the user's current location. When the user moves from this location, and the current landmark follows, there is still a permanent landmark left behind. This lets the user easily relocate this position in the space of pages. Users can delete landmarks by clicking the "delete landmark" button, also provided by the Overview, then clicking on the landmark to be removed.

When the user uses the Overview to change current location the Overview must then notify its listeners of the user's new location. Right now that would be the CloseUp, which will update its viewport to reflect the new location.

CollapsibleToolBar

Another component in the InterfaceWindow is a tool bar, a CollapsibleToolBar. Some of the functionality of this tool bar has already been described above. It lets the user give feedback to the system. This feedback may be about the zoom level of viewports, the "correctness" of pages (location or acceptance), and if the system has failed to gather a page that the user wishes to view.

A zoom dial provided in the tool bar lets the user control to what degree the CloseUpViewport and OverviewViewport views are zoomed in or out in regard to all of the space of pages. The user can change the value on the dial by clicking on the needle and dragging it to a new location/value. As the zoom increases, both viewports give a closer look at the icons currently in the viewports.

The user can remove a page from the space of pages using the "kill" button included in the tool bar. When the user clicks on this button then the next icon clicked on in the CloseUpViewport will be destroyed and removed from the list of displayed icons.

The user can import pages that perhaps have not yet been collected by the Ferrets or perhaps weren't accepted by the Filters. A subclass of Dialog called PageImporter is created when the user presses the import button on the toolbar. It lets the user either add a single URL or add all the URLs from a page. The CloseUp is notified to create the PageImporter and then to have the new URLs added. The CloseUp invokes the addURL() method of the InterfaceWindow to notify the Generalizer. The Generalizer then stores this information in the database to flag the Advisors to have the Ferrets gather these pages and force the Filters to accept them.

The CollapsibleToolBar has a collapse/expand button that causes it to roll up like a window shade, letting the user view more of the CloseUpViewport. Once it has been rolled up, the collapse/expand button is the only thing visible. Pressing this button again will return the tool bar to its original state.

StatusBar

The system displays the URL of the page currently being previewed on the StatusBar. The user can't change the URL in the StatusBar, however, although it is selectable with the mouse. This lets the user paste the URL somewhere else, for instance into a browser.