Patent Publication Number: US-2004049530-A1

Title: Distributed computer system using a graphical user interface toolkit

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This application claims priority to U.S. Provisional Patent Application Serial No. 60/210,643, filed on Jun. 9, 2000, entitled “Method and System to Support Rich User Interfaces on Light Clients,” and U.S. Provisional Patent Application Serial No. 60/277,498, filed on Mar. 21, 2001, entitled “Thin Client Graphical User Interface Toolkit,” both of which are hereby incorporated by reference in their entirety herein. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] This invention relates to computer systems using distributed user interfaces, and more particularly, to distributed user interfaces using user interface toolkits.  
       [0003] Many approaches have been researched academically and deployed commercially to support a distributed computing paradigm in which the network separates the presentation of the user interface from the application logic. Two approaches are commonly used in both industry and academia: web-based and remote frame-buffer-based. A third approach, distributed user interface toolkits, provides additional advantages, but still has significant drawbacks.  
       [0004] The first approach to distributed computing is one of the most widely deployed approaches to thin-client computing, and uses HyperText Transfer Protocol (HTTP) (See T. Berners-Lee et al., “Hypertext transfer protocol”—HTTP/1.0 RFC1945, 1996) and HyperText Markup Language (HTML) (See T. Berners-Lee et al., “Hypertext markup language”—2.0 RFC1866, 1995 and D. Conolly et al., “The text/html media type,” RFC2854, 2000) for the client with the server, commonly known as the world wide web. The architecture of an application developed using a web-based methodology is depicted in FIG. 1. As illustrated in FIG. 1, a server  10  is in communication with a client  12  over a network. The application logic  14  and the web server  16  reside on the server  10 . A special web application programmer interface  18  (API) is provided to allow the application to communicate with the web server. Typical web API&#39;s are CGI (See “The Common Gateway Interface.” http://hoohoo.ncsa.uiuc.edu/cgi/overview.html), ISAP (See “ISAPI Extensions Overview.” http://msdn.microsoft.com/library/psdk/iisref/isgu9kqf.htm), NSAPI (See NSAPI FAQ. http://developer.netscape.com/support/faqs/champions/nsapi.html), ASP (See “An ASP you can grasp: The ABCs of active server pages.” http://msdn.microsoft.com/workship/server/asp/ASPover.asp.), PEP (See “PHP: Hypertext Preprocessor.” http://www.php.net), or JSP (See “JavaServer Pages: Dynamically Generated Web Content.” http://java.sun.com/products/jsp). HTTP is used to negotiate the transfer of HTML data between the client web browser  20  and the web server  16 . The web browser  20  then renders the HTML  21  onto the client frame buffer  22 , from which visual presentations are generated on the display of the client. The user may interact with the displayed presentation to send data back to the web server via HTML  
       [0005] One severe limitation of a web-based approach using HTTP/HTML is the “pull-only” data transfer methodology, which prevents the application from generating events. For example, when a user executes a search on a web search engine, the engine must ideally complete the search in its entirety within a few seconds of the request because the user is expecting an immediate response. After the initial page has been displayed, the web search engine cannot notify the user that better results have been found. A second problem is that HTTP is stateless, which makes it difficult for programmers to create even a simplistic notion of persistence between page accesses. In addition, the user interaction is also extremely limited, providing only a handful of the most commonly used interactive functions.  
       [0006] Many attempts have been made to address these problems, including sending entire applications over HTTP (e.g., JAVA™ applets. See JAVA™ Applets. http://java.sun.com/applets), designing browser “plug-ins” that interpret their own language to provide a richer user experience (e.g., Macromedia Flash and Shockwave See Macromedia, Inc. http://www.macromedia.com), creating a 3D world in which the user can navigate (e.g., VRML), and providing an application programmer interface (API) for storing persistent session identification data (e.g., cookies. See D. Kristol et al., “HTTP state management mechanism,” RFC2109, 1997). All these approaches to addressing the problems with HTTP/HTML create new problems.  
       [0007] JAVA™ applets raise numerous security concerns because HTTP is used to transport executable code to the client. Although the byte codes transmitted across the network are in compiled form, JAVA™ decompilers are readily available that will allow any user to have access to the source code of the application. In addition, the use of JAVA™ applets typically violates the thin-client principle of not running any application logic on the client. Flash and VRML define richer languages that have been built with user interactivity in mind, but suffer from the problem that mature browsers for anything other tan the Microsoft Windows desktop operating systems are generally not available. HTTP cookies raise numerous security concerns because they permit the server program to write data to the permanent storage device on the client. In addition, HTTP cookies have been the target of severe criticism due to a recent surge in public awareness regarding privacy concerns when using the Internet. These issues make HTTP cookies an unattractive method for programmers to add server-side state to the HTTP protocol.  
       [0008] A second approach to distributed computing involves creating a remote virtual frame buffer on the server, on which the application can draw, and then transporting the resulting raster image to the client. In essence, this approach attempts to bring the server&#39;s desktop to the user and thereby permits a full range of user interactivity. Products such as CITRIX™ METAFRAME™ (See http://www.citrix.com/products/metaframe/), INSIGNIA SOLUTIONS™ NTRIGUE™ (See http://www.insignia.com), SCO TARANTELLA™ (See http://www.tarantella.sco.com), GRAPHON™ RapidX (See http://www.graphon.com) and SYMANTEC™ PCANYWHERE™ (See http://www.symantec.com) are among those that have been providing this type of functionality for many years as an extension to the underlying operating system. A recent explosion in the popularity of this approach occurred when AT&amp;T released their cross-platform VNC system to the public free of charge. (See Q. Li et al., “Integrating Synchronous and Asynchronous Collaboration with VNC,”  IEEE Internet Computing,  4(3):26-33, May-June 2000.) Microsoft has now made this capability a standard part of their Windows 2000 operating system (See http://www.microsoft.com/windows2000/technologies/terminal/default.asp).  
       [0009] The architecture of a remote frame buffer based application is illustrated in FIG. 2 for transmission between a server  24  and client  26 . The application  28  is typically written using a standard user interface toolkit API  30 , such as JAVA™ Foundation Class (hereinafter “JFC”) (See “JAVA™ Foundation Classes: Now and the Future” http://java.sun.com/products/jfc/whitepaper.html), Microsoft Foundation Class (See  Microsoft Visual C++ MFC Library Reference.  Microsoft Press, Redmond, Wash., 1997), Tk (See J. Ousterhout.  Tcl and the Toolkit.  Addison-Wesley, 1994), or MOTIF (See  Modular Toolkit Environment.  IEEE 1295), and renders onto a remote virtual frame buffer  32 . The resulting pixel data  34  is transported across the network using a proprietary protocol, such as ICA (See Citrix Metaframe. http://www.citrix.com/products/metaframe), RFB (See “Microsoft Windows 2000 Terminal Services.” http://www.microsoft.com/windows2000/guide/server/features/terminalsvs.asp), or RDP (See T. Ricardson et al., “Virtual network computing,”  IEEE Internet Computing,  2(1):33-38, January-February 1998) to the client  26 . The client viewer  36  receives the pixels and reconstructs the image, and then copies the image onto the client frame buffer  38  for presentation on the client&#39;s display.  
       [0010] Although the remote frame buffer approach addresses many of the problems with a web-based approach that uses HTTP/HTML, it also introduces a number of other problems. Whereas the web-based approach using HTTP/HTML is capable of operating reasonably well over relatively low-bandwidth modem network links, the remote frame buffer approach demands high-bandwidth connections. This is because the remote frame buffer approach is essentially sending a video stream of computer-generated graphics from the server to the client.  
       [0011] Although the use of advanced lossy video compression algorithms (e.g. MPEG (See ISO/IEC JTC1/SC2/WG11.MPEG.  ISO,  September 1990)) has been proposed (T. Ricardson et al., “Virtual network computing,”  IEEE Internet Computing,  2(1):33-38, January-February 1998), implementation of such techniques may presents several technical difficulties. For example, real-time compression of MPEG streams usually requires special hardware that can only handle one or two streams at a time, thereby eliminating the possibility of using the remote frame buffer approach on a current shared server. In addition, the use of lossy compression techniques introduces unwanted compression artifacts into the display, reducing the system&#39;s usability, particularly when working with text and detailed graphics.  
       [0012] The existence of server-side state and asynchronous event generation by the server permits the remote frame buffer approach to provide a rich level of user interactivity that a web-based approach using HTTP/HTML cannot. However, there is a practical limitation caused by network latency. For example, such problems may arise in connection with the display of a mouse pointer on a typical client “viewer,” i.e., the remote frame buffer analogue of the web browser. Under certain circumstances, the client viewer may display two mouse pointers. One mouse pointer represents where the cursor should be pointing, and is tied to the local mouse. A second mouse pointer, which typically lags behind the first mouse pointer, displays where the mouse position is on the server. When a remote fame buffer system is run on anything other than a high-speed LAN connection (e.g., 100 megabit per second over category 5 cabling), there is always a noticeable difference in position between the client (virtual) and server (real) mouse positions. On a slow modem link (e.g., 56.6 kilobit per second transmission over a standard telephone line), this makes highly interactive user interfaces difficult to control, and, in extreme cases, may even make the system unusable.  
       [0013] A third approach to distributed computing is distributed user interface toolkits, which address the issues that arise when employing web-based HTTP/HTML and remote frame buffer approaches by allowing a server to manipulate user interface toolkit components directly on the client. The server can create, modify, and delete any of the components available in the distributed toolkit as if it were working with a local application. This approach is analogous to an implementation of a remote frame buffer with an extremely efficient, lossless compression algorithm. Instead of sending pixel data rendered on the server across the network, the distributed user interface toolkit sends the semantics necessary to render that pixel data on the client. In addition, since the mouse is handled locally on the client, there is no additional perceived latency beyond that caused by the processing that is necessary to service users requests when the application is running locally.  
       [0014] The current approaches to distributed user interface toolkits have several disadvantages. The X Window System (See R. Scheifler et al., “The X Window System,”  ACM Trans. on Graphics,  5(2):79-109, April 1986), for example, transports low-level drawing commands. If a high-level user interface toolkit is used with X, the high-level user interface toolkit commands (e.g., draw button) are actually translated into low-level commands (e.g., lines and rectangles) before being transmitted across the network. Another disadvantage is that the X Window System stores state on the client computer that is presenting the output to the end user. Consequently, it is very difficult to “share” X Window System sessions between multiple users, and if the X Window System running on the client computer fails, the user session is lost. It is for these reasons that a remote virtual frame buffer system, such as VNC, is often employed to transport an X Window System desktop from a UNIX server to an X Window System viewer running on a UNIX workstation, rather than relying on the built-in networking facilities of X.  
       [0015] There is therefore a need in the art for a distributed user interface that runs the application logic on the server computer but which also allow the server computer to asynchronously generate events and transmit them to the server. There is also a need for a distributed user interface that allows relatively sophisticated graphics without requiring high-bandwidth connections. In addition, there is also a need for a distributed user interface which is easily implemented and does not require the creation of a new protocol of communication.  
       SUMMARY OF THE INVENTION  
       [0016] It is an object of the invention to provide a distributed computer system which is compatible with toolkits of well-known programming languages and implicitly creates a protocol of network communication.  
       [0017] It is another object of the invention to provide a distributed computer system that does not require high-bandwidth to operate and which allows a high degree of user interactivity.  
       [0018] These and other objects of the invention which will become apparent with respect to the disclosure herein, are accomplished by a novel distributed computer system having at least one server and one remote client to execute an application entirely on the server, wherein the application so configured to interact with a user interface toolkit according to an application programming interface. A user interface toolkit is provided, which resides on the remote client and has at least one component configured to perform a function on the remote client. In an exemplary embodiment, JAVA™ Foundation Class is the user interface toolkit which has a plurality of components known as the Swing component class.  
       [0019] A remote-capable user interface toolkit resides on the server. The remote-capable user interface toolkit has at least one remote-capable component which interfaces with the application according to the same application programming interface as the user interface toolkit and which is configured to generate a message to perform the respective function of the corresponding component in the user interface toolkit in response to an invocation by the application. The remote-capable component is otherwise identical to the component.  
       [0020] The protocol of communication between the remote-capable component of the remote-capable user interface toolkit on the server and the component of the user interface toolkit on the client comprises the transmitting of messages by the remote-capable component invoked by the application.  
       [0021] The component in the user interface toolkit may be configured to render a graphical item and the remote-capable component may be configured to generate a command to render a graphical item. Similarly, the server may be configured to communicate the message to the user interface toolkit on the remote client to render a graphical item in response to the invocation by the application. The component of the user interface toolkit on the remote client may be configured to render the graphical item in response to the message.  
       [0022] The component in the user interface toolkit may be configured to install an event handler and the remote-capable component may be configured to generate a command to install an event handler. Similarly, the server may be configured to communicate the message to the user interface toolkit on the remote client to install an event handler, and the component of the user interface toolkit on the remote client may be configured to install the event handler in response to the message.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 is a simplified block diagram of a prior art system.  
     [0024]FIG. 2 is a simplified block diagram of a second prior art system.  
     [0025]FIG. 3 is a simplified block diagram of the system in accordance with the invention.  
     [0026] FIGS.  4 ( a )- 4 ( c ) illustrate prior art user interface toolkit components.  
     [0027]FIG. 5 illustrates a user interface in accordance with the invention.  
     [0028] FIGS.  6 ( a )- 6 ( b ) illustrate an application as rendered on a client buffer in accordance with the invention.  
     [0029]FIG. 7 illustrates another application as rendered on a client buffer in accordance with the invention.  
     [0030]FIG. 8 illustrates a further application as rendered on a client buffer in accordance with the invention.  
     [0031]FIG. 9( a ) illustrates executable code in accordance with the invention.  
     [0032]FIG. 9( b ) illustrates prior art executable code. 
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
     [0033] The architecture of a distributed user interface system  100  in accordance with the invention is illustrated in FIG. 3 and includes a server  102  and a client  104 . The application logic  106  resides on the server  102 . A novel remote-capable user interface toolkit  108  resides on the server  102  and a baseline user interface toolkit  110  resides on the client  104 . As will be described below, the remote-capable user interface toolkit  108  has components which correspond to components in the baseline interface toolkit  110 , but which issue remote messages rather than execute graphical functions. These messages are interpreted by a server JAVA™ virtual machine  112  (“server VM”) that transmits the commands across the network to the client  104 . A client viewer JAVA™ virtual machine  114  (“client viewer”) translates the messages issued by the remote-capable user interface toolkit  108  into function calls of the baseline interface toolkit  110 , which are rendered on the client fame buffer  116 . It is noted that according to another exemplary embodiment, using a programming language other than JAVA™, the system is implemented without a virtual machine.  
     [0034] The distributed user interface system  100  makes use of visual components (often called widgets or controls) that are gathered together in libraries that are usually referred to as user interface toolkits. The exemplary embodiment utilizes JFC as the baseline graphical user interface toolkit  110 . (The JAVA™ language specification, B Joy et al.,  The JAVA Language Specification,  Addison Wesley, 2d Ed., 2000 and http://java.sun.com/docs/books/jls/second_edition/html/j.title.doc.html and JAVA™ virtual machine specification, T. Linde et al.,  The Java Virtual Machine Specification,  Addison Wesley, 2d Ed., 1999 and http://java.sun.com/docs/books/vmspec/2nd-edition/html/VMSpecTOC.doc.html, and “JAVA™ Foundation Classes: Now and the Future” http://java.sun.com/products/jfc/whitepaper.html, have been incorporated by reference in their entirety herein.) JFC has been utilized in the exemplary embodiment because of its ability to create cross-platform compatible graphical user interfaces. However, it is noted that the system and methods described herein are also compatible with any available toolkit.  
     [0035] A user interface toolkit, as understood in the specification and claims, is computer code which provides an application programming interface that (1) renders at least one graphical component related to user interaction in response to an invocation by the application, and (2) generates an event coupled to the graphical component in response to user interaction with that graphical component. These functions are described in greater detail herein. First, a toolkit has the ability to draw a frequently-used, graphical components on a user display as commanded by an application running on the computer. Each graphical component is concerned with an aspect of user interaction, and therefore visually provides the user with one or more selectable options as well as a manner of making a selection. Typical components in a toolkit draw graphical items such as buttons, scrollbars, menus, text fields, and the like. In rendering the graphical component, the toolkit may include commands to display a plurality of shapes, colors, and text. The toolkit is configured to interact with the application according to an application programming interface. For example, the toolkit receives an invocation, or call, from the application to draw graphical components at certain times during the operation of the application. In the exemplary embodiment, JFC has a well-defined application programming interface.  
     [0036] It is noted that a toolkit may comprise a single component, such as a button, or it may generate a plurality of multiple components. JFC, for example, provides many components bundled together in a component set referred to as “Swing.” (See “The Swing Component Galley” http://java.sun.com/products/jfc/tsc/articles/component_gallery/index.html, which is incorporated by reference in its entirety herein.) Exemplary components of Swing include “JButton,” illustrated in FIG. 4( a ), “JCheckbox,” illustrated in FIG. 4( b ), and “JRadioButton,” illustrated in FIG. 4( c ). JButton is a commonly used component that may be selected, i.e., “clicked,” by the user. JCheckbox is an image including a group of items and provides the user with the ability to select or de-select one or more of these items. Similarly, JRadioButton is an image including a group of buttons. In contrast with JCheckbox, JRadioButton allows only one button at a time to be selected. (According to convention, selecting a new button in JRadioButton will simultaneously select the new button and de-select a previously selected button.)  
     [0037] A second, related feature of a toolkit is the ability to generate an event based on a user response, if any, to the component rendered on the user display. The toolkit is thus able to provide a link between (1) the syntax of the user interaction (e.g., typing a character or pressing a mouse button), and (2) the semantics necessary to carry out the function commanded by that user interaction (e.g., closing a text window.) The toolkit includes an event handler that “listens” (i.e., waits), for a specific user interaction to occur, and then generates an event when that interaction occurs. (Each event may be represented by an object that gives information about the event and identifies the event source.). For example, a button (e.g., JButton), may be configured to wait for the user to click the button (i.e., press a mouse key while positioned over the button). When the user clicks the button, the toolkit generates an event. In this case, the result may be that a toolkit text window is automatically closed when the event listener detects an event triggered by the button component.  
     [0038] It is further noted that the procedures described herein are applicable to a user interface toolkit which “renders” an item to the user which may be graphical audio, tactile, olfactory or other sensory modality, that may be coupled with the generation of an event in the nature of a user interface.  
     [0039] The toolkit, as described above, interacts with the application according to an application programming interface. In addition to receiving commands to draw graphical items, the toolkit generates events, which are usually associated with components. These events are then conveyed to the application according to the application programming interface, which enables the application to take some action based on the events generated by the user. JFC, as implemented in the exemplary embodiment, interacts with the application according to a well-defined application programming interface from the standpoint of conveying events to the application.  
     [0040] The user interface toolkit provides an abstraction layer for drawing the graphical items and generating events, by using the low-level drawing and interaction routines made available to programmers by the graphics subsystem that is usually bundled with the operating system. This abstraction allows programmers to quickly create commonly used visual components, such as buttons, scrollbars, menus, and text fields. End users also benefit, since most of the applications they run on a particular operating system will have roughly the same “look and feel” because the applications are all built out of components from the same user interface toolkit.  
     [0041] The typical implementation of a user interface toolkit, such as JFC, is on a system in which the application logic execution and the user interface presentation occur on a single computer. The tight binding of the user interface toolkit to the underlying graphics subsystem allows this type of implementation. However, the use of the toolkit when creating distributed applications in which the application logic execution and user interface presentation occur on different computers may present significant challenges.  
     [0042] With continued reference to FIG. 3, the distributed user interface system  100  is configured to work with any toolkit, as described above, which interfaces with application logic  106  and has the capability to draw graphical components and generate or respond to events. The system  100  includes a remote-capable interface toolkit  108 , which resides on the server  102 . As described above, JFC was used as the baseline user interface toolkit  100  implemented on the client  104 , and “Remote JAVA™ Foundation Classes” (RJFC) was created as a remote-capable version of JFC. JFC was selected as a baseline interface toolkit  108  for the exemplary embodiment because of its familiarity to programmers and richness in functionality. JFC API is extremely complex, and includes over 600 individual source files, each providing between 10 to 100 methods for the programmer to use.  
     [0043] The remote-capable version of the toolkit  108  is a toolkit which appears to the application logic  106  as a local toolkit for drawing graphical components and generating events. However, when invoked by the application logic  106 , the remote-capable user interface toolkit issues a remote process invocation, such as JAVA™ RMI, for drawing the graphics or generating events on the remote client  104 . More particularly, RJFC has one or more components that are substantially identical to components in the corresponding baseline toolkit  110 , JFC. Thus, there is a one-to-one correspondence between JFC components and RJFC components. A significant difference between these components, however, is that a JFC component, when invoked, locally performs a particular function (e.g., it draws a button on the local VM or it generates an event, as described above). In contrast, the corresponding RJFC component is configured to send a message to perform that same function, i.e., drawing a graphical item or generate an event, which is transmitted to the remote client  104 . Alternatively, if the RJFC component is an event handler, it is configured to receive a remote signal concerning the occurrence of an event. Thus, the application programming interface of the RJFC  108  tracks the design pattern and functionality of the application programming interface of the standard JFC  110  as closely as possible, with the exception that the presentation displays on a remote client  104  or the event is generated at the remote client  104 , rather than on a local frame buffer.  
     [0044] RJFC components are generated automatically from the JFC source code by a “code generator” application. Since the source code to JFC is readily available, a code generator reads the JFC source and produces a RJFC component for each JFC component. In the exemplary embodiment, a modified version of JAVA™ Doclet has been used to read the JFC source code in the JAVA™ programming language and to produce RJFC code (also in the JAVA™ programming language) for each respective JFC component. The Doclet is a publicly available tool that was designed to read in source code and automatically generate documentation. In accordance with the invention, the Doclet has been modified to generate source code in the JAVA™ programming language rather than documentation.  
     [0045] The procedure of using a code generator provides a great degree of automation and flexibility because the components of the remote-capable toolkit  108  do not have to be separately and individually programmed. In addition, the remote-capable toolkit components do not have to be rewritten if the underlying toolkit is modified. This approach may be used to generate different versions of the remote-capable toolkit system for various implementations and releases of the JAVA™ SDK, making it possible to handle a broad range of supported JAVA™ VM&#39;s.  
     [0046] Another advantage of creating the remote-capable toolkit by use of a code generator is that the application programming interface of the remote-capable user interface toolkit  108  is implicitly identical to the application programming interface of the baseline interface toolkit  110  which resides on the client  104 . Consequently, manipulation of the RJFC components (e.g., changing the text of a label) and association of event handlers by the application logic  106  is syntactically identical to the JFC API. Although each RJFC component has an actual associated JFC component that resides in the client viewer&#39;s memory space, the application logic  106  which resides on the server  102  interacts with the remote client  104  by making calls on the RJFC components on the server  102  alone. Since the actual JFC components that are used to create the display on the client frame buffer are hidden from the application logic  106 , the application logic  106  is not modified to operate in the distributed environment. Since RJFC components track the JFC API and follow the Sun JAVA™ Beans standard (See G. Voss “JAVA™ Beans” http://developer.java.sun.com/developer/onlineTraining/Beans/Beans1/simpledefinition.html), they may also be easily used in graphical user interface builders such as SUN FORTE™ for JAVA™ (See http://www.sun.com/forte/ffj), BORLAND™ JBUILDER™ (See http://www.borland.com/jbuilder) and WEBGAIN™ VISUALCAFE™ (See http://www.webgain.com/products/visual_cafe).  
     [0047] The procedure for distributed processing through a server and a remote client proceeds as follows. The application logic  106  is executed entirely in the server  102 . The application logic  106  is configured by the programmer to interact with the user interface toolkit according to an application programming interface. A user interface toolkit, as defined above, comprises one or more components that perform several functions: the component may render a graphical item when invoked by an application, and may generate an event in response to a user interaction with that graphical item. In the exemplary embodiment, the baseline user interface toolkit  110  may be JFC, and the components may be the Swing component set.  
     [0048] An early stage in the procedure may be to provide the user interface toolkit  110  on the remote client  104  such that the component is configured to perform the function on the remote client  104 . In the exemplary embodiment, the JFC components are provided on the remote client and are able to render the graphical items on the client frame buffer  116  and generate events at the remote client VM  114 .  
     [0049] A subsequent stage may be to provide a remote-capable user interface toolkit  108  on the server  102 . The remote-capable user interface toolkit  108  is provided by creating at least one remote-capable component which is configured to interact with the application logic  106  according to the same application programming interface as the baseline user interface toolkit  110  and which is configured to generate a remote message to the component on the remote client  104  to perform the respective function on the remote client  104 . According the exemplary embodiment, the remote-capable user interface toolkit  108  is referred to as RJFC wherein each component of RJFC is syntactically identical to each component in JFC, with the except that the portion of the code in the remote-capable component has been substituted with a portion of code that generates a remote message to the JFC component to perform the same function.  
     [0050] A next stage in the procedure may be to invoke the remote-capable user interface toolkit  108  by the application logic  106  according to the application programming interface to perform a function. At a subsequent stage, the remote-capable user interface toolkit  108  generates a remote message to perform the function invoked by the application logic  106 . Since there is a one-to-one correspondence between the JFC component and the RJFC component, a protocol of communication between the RJFC component and the JFC component is implicitly defined. This protocol of communication comprises the transferring of massages to perform JFC functions, and such messages are issued in the manner in which the JFC toolkit would normally perform functions on a single computer. Therefore, there is no need to specifically create a protocol of communication.  
     [0051] The message may be communicated between the remote-capable user interface toolkit on the server and the user interface toolkit on the remote client in a subsequent step. In the exemplary embodiment, this communication between the server  102  and the client  104  uses remote method invocation (RMI) (See S. McPherson, “JAVA™ Servlets and Serialization with RMI,” http://developer.java.sun.com/developer/technicalArticles/RMI/rmi/.  
     [0052] A later stage may be to perform the function on the remote client by the component of the user interface toolkit in response to the message. Thus, when an RJFC component is instantiated, modified, or deleted on the server  102  by the application logic  106 , the RJFC toolkit  108  transparently informs the client viewer  114  of the event that has occurred. The client viewer  114  reacts to the message by performing the exact same action on the client viewer  114  that would have occurred on the server  102  if the JFC API were used.  
     [0053] For example, the standard JFC component JButton serves as the basis for the RJFC component RJButton. (Whereas JButton renders a button, RJButton sends a message to remotely render a button.) If the server  102  requests that a new RJButton be created, the RJFC toolkit  108  would generate a message which the server VM  112  transmits to the client viewer  114 . The client viewer  114  receives the message and then creates a JButton using the standard JFC API  110 , thus causing the actual button to be rendered on the client frame buffer  116 . Similarly, when the server  102  installs an event handler into a RJFC component, the server  102  communicates with the client viewer  114 , using RMI, to install a proxy JFC event handler into the associated JFC component that is being displayed on the client frame buffer  116 .  
     [0054] One key performance optimization in the RJFC Protocol is the use of a component-generating object, referred to in the exemplary embodiment as “RJFCFactory,” that resides in the client viewer&#39;s memory space. RJFCFactory is a piece of code that defines what components the application logic  106  can cause to appear on the client  104 . This code for RJFCFactory is automatically generated by the code generator, described above. The code generator reads the JFC source code and creating a remote-capable method for each baseline JFC method. RJFCFactory performs two actions: (1) it creates JFC components in the client viewer&#39;s memory space and (2) transmits to the server  102  a reference to RJFCFactory. (In the exemplary embodiment implemented in the JAVA™ programming language, RJFCFactory extends UnicastRemoteObject and implements an interface that extends Remote.) When a client viewer  114  connects to a server  102 , the client viewer  114  passes the reference to the RJFCFactory during a display registration method implemented on the server  102 . Once the server  102  has received the reference to RJFCFactory, the server  102  can do the following: (1) transmit commands to RJFCFactory to create JFC components that reside in the client viewer&#39;s memory space and (2) receive a remote reference to the associated RJFC wrapper object from the client  104 . This procedure eliminates the need to create a serialized object in the server&#39;s memory space, subsequently send the serialized object to the client  104 , and then send a remote reference to the wrapper object back to the server  102 . Test measurements show that a RMI call as described above consumes approximately five Ethernet packets whereas sending a serialized JButton consumes more than ten times that number.  
     [0055] The protocol for the remote-capable user interface toolkit  108  in accordance with the invention accomplishes event handling using a similar methodology. The following protocol may be followed to allow the client  104  to transmit client-generated events to the server  102 : If an event handler is installed into a RJFC component on the server  102 , the server  102  may transmit a simple message to the client viewer  114 , using RMI, that tells the client viewer  114  to install a proxy event handler in the associated JFC component. The proxy event handler on the client  104  makes a call to the server  102  whenever a new event is generated on the client side. The actual semantics of the event handler, as defined by the application logic  106 , is executed on the server  102  when the server  102  receives the RMI call from the client  104 . Similarly, the following protocol may be followed for transmitting server-generated events to the client  104 : The server  102  retains the reference to the RJFC component returned by the RJFCFactory after the display initialization is completed. When the server  102  generates events, it transmits a command to the client  104  with a remote reference to the RJFC component. This protocol enables the server  102  to asynchronously generate events at will, i.e., without requests from the user at the remote client.  
     [0056] An exemplary RJFC viewer  200 , as illustrated in FIG. 5, provides a context in which the application logic  106  which resides on the server  102  can manipulate the client frame buffer  116 . The viewer is an application, which may be hand-coded, that uses the baseline interface toolkit  110 , e.g., JFC, and emulates the functionality found in a typical thin-client system. The user of the system invokes the client viewer  114 , at which point a JFrame window  202  is created with a form  204  that allows the user to connect to a server  102 . Once a connection is established, a second JFrame window  206  is created for the server  102  to manipulate remotely. The server  102  may also request that additional windows be created by asking for dialogue boxes using the RJFC API. FIGS.  6 - 8  illustrate several small applications being run in the client viewer  114 . FIGS.  6 ( a )- 6 ( b ) illustrate a “notepad” application  210  being run on the client viewer  114  as rendered by the JFC toolkit  110  in response to commands from the RJFC toolkit  108  residing on the server  102  as described herein. The notepad application  210  implements several of the JFC Swing components, such as JButton  212 , JScrollPane  214 , JPopUpMenu  216 , and JOptionPane  218 .  
     [0057] Similarly, FIG. 7 illustrates a simple web browser application  230  which conducts searches for web pages in response to user requests, as is well known in the art. As described above, the invention provides the capability to transmit server-generated events to the client  104 : In the exemplary embodiment, RJFCFactory object resides on the client  104 , and it sends an RJFCFactory reference to the server  102  during the display initialization. The server  102  retains this reference to the RJFC component. When the server  102  generates events, it transmits a command to the client  104  with a remote reference to the RJFC component. This protocol enables the server  102  to asynchronously generate events at will, i.e., without requests from the user at the remote client. As illustrated in FIG. 7, the application may be a web browser. The protocol according to the invention provides a substantial benefit over the HTTP/HTML web browser applications. For example, when the user requests a web search, the server sends commands to the client to display initial results of the search. (This is similar to the HTTP/HTML system.) However, in accordance with the invention, the server  102  may continue to search for additional results. When these newer results are found, the server  102  generates an event, and is able to transmit an RJFC command to the client with a RJFCFactory reference to the appropriate JFC component on the client  104  to display the results on the client frame buffer  114 . This process may proceed asynchronously to update the search results without any further inputs from the user.  
     [0058]FIG. 8 illustrates a simple spreadsheet application  240 , each of which is rendered on the client buffer  116  in response to commands generated by the RJFC toolkit  118  in accordance with the invention.  
     EXAMPLE  
     [0059] An example of code for creating a simple “notepad” application written using the RJFC API is shown in FIG. 9( a ), and a baseline, i.e., non-network-aware version of the code in JFC API is shown in FIG. 9( b ). The code generator was configured such that the resulting RJFC API has a one-to-one correspondence to JFC components. In the exemplary embodiment, a capital “R” (indicative of the remote-capable functionality) is prepended to the name of the toolkit component being referenced. The significant difference between the non-network-aware JFC application of FIG. 9( b ) and the remote-capable RJFC application of FIG. 9( a ) is that the JFC code calls “new” to instantiate a component, whereas the RJFC code makes a remote method invocation to an RJFCFactory object (as described above) which resides in the client viewer&#39;s memory space.  
     [0060] The distributed user interface in accordance with the invention was compared with the web-based thin-client approach using HTTP/HTML as illustrated in FIG. 1 and the remote frame buffer approach as illustrated in FIG. 2, above. The implementation of HTTP/HTML consumes very little bandwidth because HTML represents a presentation&#39;s semantics at an extremely high level. While this causes a relatively small amount of information to be transported, this approach suffers from the problem that HTTP was not designed for implementing remote applications, but rather for sharing static data.  
     [0061] In contrast, the remote frame buffer approach operates on the premise that compatibility with existing applications is paramount at the expense of network bandwidth. This is because many of the remote frame buffer implementations were designed for corporate or lab network environments whose administrators are trying to move users away from desktop computers to a thin-client subsystem with a lower total cost of ownership.  
     [0062] The RJFC distributed user interface toolkit in accordance with the invention combines the benefits of both approaches without their performance and usability issues by transmitting the high-level semantics of a display using a standard toolkit API. The network bandwidth consumed by RJFC is closer to that of the web-based approach using HTTP/HTML than that of the remote frame buffer approach, while permitting rich user interaction without artificially introduced latency. TABLE 1 is a comparison of the bandwidth consumed by RemoteJFC and the AT&amp;T VNC remote frame buffer system. TABLE 1 shows the number of Ethernet packets transmitted over the network by VNC and by the distributed user interface system  100  using the remote-capable user interface toolkit  108  when simple operations were performed in a notepad application similar to that illustrated in FIG. 9( a ). In the VNC system, a large number of packets transmitted were due to movement of the mouse by the user. The amount of mouse movement by a novice user may be significantly greater than the movement of a more experienced user. Since the amount of user experience may affect the comparison, both VNC novice and VNC expert data is included in TABLE 1. (Since a web-based method using HTTP/HTML would not be able to provide the same level of user interactivity, this approach was omitted from TABLE 1. It is noted, however, that the Client Connection cost of a web-based “notepad” application is approximately 10 packets.)  
                           TABLE 1                       Operation   RJFC   VNC Expert   VNC Novice                                                Client Connection   620   450   450       Load File   85   860   2600       Popup About Dialog   24   70   1500       Close About Dialog   32   85   630       Maximize Window   8   690   1000       Scroll to Bottom of Page   0   420   1700                  
 
     [0063] Thin-client systems need some kind of software browser or viewer that must reside in permanent storage on the client computer. Because the web-based approach and the novel remote-capable user interface toolkit approach both transmit high-level information across the network, the size of the client software package is therefore larger than that of the VNC viewer.  
     [0064] The size of a typical web browser download is about 25 megabytes, as compared to the VNC viewer which can be about 110 kilobytes. The client viewer  114  lies somewhere in between: the RJFC library adds 2.5 megabytes to the underlying JAVA™ runtime environment, which can vary in size from 30 to 15 megabytes. In addition, the VNC viewer memory image when attached to an 800×600 desktop consumes 1.5 megabytes of RAM, whereas both the web browser and client viewer  114  require approximately ten times that amount. This also results in faster startup times for the VNC viewer than a web browser or the client viewer  114 .  
     [0065] Overall, the remote frame buffer approach is much “thinner” than the web-based and RemoteJFC approaches and is capable of running on less powerful hardware, but requires much more network bandwidth to operate effectively.  
     [0066] An appendix which sets forth the computer code for the significant code routines is appended hereto and incorporated by reference in its entirety herein. In particular, Doclet is the main routine for the code generator program, as described above. Doclet is only executed once to create the RJFC library. The Viewer routine resides on the client. It is the vehicle through which the RJFC application displays its output. NotepadServer is a demo RJFC application. It resides on the server, and has the control logic that can generate the graphics shown in FIGS.  5 - 9 , above. RJFCServer is a routine that executes on the server, and allows a client viewer to register a display with the server and hence allow the server to control the display. RJFCFactory is a routine that defines what elements the application can cause to appear on the client. This code is automatically generated by the code generator by reading the Swing source code and creating a RJFC method for each Swing method. This code executes on the client and passes references back to the server.  
     [0067] It will be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.