Patent Publication Number: US-7904421-B2

Title: Transparent virtual machine for mobile applications

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 11/405,492 filed Apr. 18, 2006, now U.S. Pat. No. 7,734,583, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to software, devices and methods allowing varied mobile devices to interact with server-side software applications and, more particularly, to a user interface that allows increased user efficiency in the execution of a virtual machine-based application. 
     BACKGROUND 
     Wireless connectivity is a feature of the modern telecommunications environment. An increasing range of people are using a wide variety of wireless data networks to access corporate data applications. 
     However, there are numerous competing mobile devices that can be used to achieve this. Each mobile device has its own operating system and its own display characteristics. Operating systems are not mutually compatible, nor are the display characteristics—some are color, some are black and white, some are text-only, some are pictorial. 
     To allow for applications to be executed on a variety of different mobile devices, often a virtual machine is employed. The virtual machine may be mobile-device-specific so that applications designed to run on the virtual machine need not be. However, in some cases, to execute an application on a virtual machine on a mobile device, a user may be required to open an interface associated with the virtual machine and then select an application to be executed by the virtual machine. 
     An increasing number of mobile device users are people without a technical background or high level of educational achievement. Such people are often intimidated by the need to first open the interface associated with the virtual machine and then select an application to be executed by the virtual machine. 
     Therefore, a mechanism is desired by which an application may be enabled for multiple mobile devices yet still appear, in a user interface for a given mobile device, among those applications specific to the given mobile device. That is, it is desirable that the execution of the application should be accomplished without the need for separately opening an interface to the virtual machine that runs the application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In figures that illustrate, by way of example, embodiments of the present application: 
         FIG. 1  schematically illustrates a mobile device, exemplary of an embodiment of the present application, including virtual machine software, further exemplary of an embodiment of the present application; 
         FIG. 2  further illustrates the organization of an exemplary virtual machine at the mobile device of  FIG. 1 ; 
         FIG. 3  illustrates an operating environment for the device of  FIG. 1  including a middleware server; 
         FIG. 4  illustrates the structure of an example application definition file stored at the middleware server of  FIG. 3  used by the device of  FIG. 1 ; 
         FIG. 5  schematically illustrates the formation of application definition files at the middleware server of  FIG. 3 ; 
         FIG. 6  schematically illustrates the middleware server of  FIG. 3 , exemplary of an embodiment of the present application, including a database, further exemplary of an embodiment of the present application; 
         FIG. 7  is a flow diagram illustrating the exchange of sample messages passed between the mobile device, the middleware server and the backend application server of  FIG. 3 ; 
         FIG. 8  illustrates steps performed at a mobile device under control of the virtual machine of  FIG. 2 ; 
         FIG. 9  illustrates steps performed at a mobile device under control of the virtual machine of  FIG. 2 ; 
         FIG. 10  illustrates steps performed at a mobile device under control of the virtual machine of  FIG. 2 ; 
         FIG. 11  illustrates the format of messages exchanged in the message flow of  FIG. 7 ; 
         FIG. 12  illustrates a presentation of a user interface for a sample application at a mobile device; 
         FIG. 13  illustrates a sample portion of an application definition file defining the user interface illustrated in  FIG. 12 ; 
         FIG. 14  illustrates the format of a message formed in accordance with the sample portion of the application definition file of  FIG. 13 ; 
         FIG. 15A  illustrates a sample portion of an application definition file defining a local storage at a mobile device; 
         FIG. 15B  schematically illustrates local storage in accordance with  FIG. 15A ; 
         FIG. 15C  illustrates how locally stored data is updated by a sample message in accordance with the sample portion of an application file definition of  FIG. 15A ; 
         FIG. 16  illustrates steps of an exemplary method of executing an application at a virtual machine; and 
         FIG. 17  illustrates steps of an exemplary method of responding, at a mobile device operating system, to the selection of an icon associated with an application definition file for executing on a virtual machine. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with the present application, data from a server-side application executing at a computing device is presented by a client-side application executing at a remote wireless (mobile) device. The mobile device is provided with an application definition file that contains: definitions for a user interface format for the client-side application at the mobile device; a format of network messages for exchange of data generated by the client-side application; and a format for storing data related to the client-side application at the mobile device. Using the definitions, the mobile device may receive data from the server-side application and present a client-side interface for the server-side application. Preferably, the application definition file is an XML file. Similarly, server-side application-specific network messages provided to the device are also formed using XML. In the preferred embodiment, the data from the server-side application is presented at the mobile device by a virtual machine, where the server-side application is based on the application definition file. 
     The inclusion of metadata within the application definition file allows the virtual machine to create an application descriptor file that may be registered with the mobile device operating system so that an icon associated with the application description file may be displayed in the main ribbon. Execution of the client-side application defined by the application definition file may then be initiated when the user selects the icon that is associated with the application definition file. Thus, an improvement is realized over the situation wherein execution of the application defined by the application definition file requires a selection of the runtime environment for the application and then the selection of the application. 
     In accordance with an aspect of the present application, a method of presenting a user interface screen using a virtual machine. The method includes receiving an application definition file, registering the application definition file with an operating system that is executing the virtual machine to cause the operating system to present a reference to the application definition file, receiving an indication of selection of the reference to the application definition file, responsive to the receiving the indication, interpreting the application definition file to create an application and executing the application on the virtual machine. Further aspects of the present application include a computing device adapted to carry out this method. 
     Other aspects and features of the present application will become apparent to those of ordinary skill in the art, upon review of the following description of specific embodiments of the application in conjunction with the accompanying figures. 
       FIG. 1  illustrates elements of a mobile device  10 , exemplary of an embodiment of the present application, in communication with a wireless network  22 . The mobile device  10  may be any conventional mobile device, modified to function in manners exemplary of the present application. As such, elements of the mobile device  10  include a processor  12 , a network interface  14 , a storage memory  16  and a user interface  18  typically including a keypad and/or touch-screen. The network interface  14  enables the device  10  to transmit and receive data over the wireless network  22 . The mobile device  10  may be, for example, be a WinCE-based device, a PalmOS device, a WAP enabled mobile telephone, or the like. The storage memory  16  of the device  10  stores operating system software  20  providing a mobile operating system such as the PalmOS or WinCE. The operating system software  20  typically includes graphical user interface software and network interface software having suitable application programming interfaces (APIs) for use by other applications executing at the device  10 . 
     The storage memory  16  at the device  10  further stores virtual machine software  29 , exemplary of an embodiment of the present application. The virtual machine software  29 , when executed by the mobile device  10 , enables the device  10  to present an interface, for a server-side application provided by a middleware server, as described below. Specifically, a virtual machine  24  (see  FIG. 2 ), which exists through an execution of the virtual machine software  29  on the processor  12 , interprets a text application definition file defining: a user interface  18  controlling application functionality and the display format (including display flow) at the device  10  for a particular server-side application; the format of data to be exchanged over the wireless network  22  for the particular server-side application; and the format of data to be stored locally at the device  10  for the particular server-side application. The virtual machine  24  uses the operating system software  20  and associated APIs to interact with the device  10 , in accordance with the received application definition file. In this way, the device  10  may present interfaces for a variety of server-side applications, executed at a variety of servers. Moreover, multiple wireless devices may use a common server-side application, as each wireless device executes a similar virtual machine that interprets an application definition file to present a user interface and program flow specifically adapted for the device. 
     As such, and as will become apparent, the exemplary virtual machine software is specifically adapted to work with the particular mobile device  10 . Thus, if the device  10  is a PalmOS or WinCE device, the virtual machine  24  that results from executing the exemplary virtual machine software  29  is, correspondingly, a PalmOS virtual machine or a WinCE virtual machine. As further illustrated in  FIG. 1 , the virtual machine  24  is capable of accessing the local storage  26  at the device  10 . 
     Other applications, libraries and software may also be present within the memory  16  or the local storage  26  and are not specifically illustrated. For example, the device  10  may store and execute personal information management (PIM) software, including calendar and contact management applications. Similarly, the device  10  could store and execute software allowing the device  10  to perform a number of functions. Software could, for example, interact with the hardware at the device  10  to allow the device  10  to act as a multimedia player; allowing the device  10  to print; allowing the device  10  to interact with other incorporated hardware not specifically illustrated, including, but not limited to, a Bluetooth interface; a Global Positioning Satellite (GPS) Receiver; and the like. The memory  16  may also store software components in the form of object classes that may be used to extend the functionality of the virtual machine  24 . As will become apparent, these external software components in the form of object classes allow the virtual machine  24  to become extensible. The object classes may, for example, allow the virtual machine  24  to access additional hardware or software local to the device  10 . 
     As detailed below, an exemplary application definition file may be formed using a markup language, such as the known eXtensible Markup Language (XML) or a variant thereof. In accordance with an embodiment of the present application, defined XML entities are understood by the virtual machine  24 . Defined XML entities are detailed in Appendix “A” (FIGS. 16A-16JJ) of US Patent Application Publication 2003/0060896 A9. The defined XML entities are interpreted by the virtual machine  24  and may be used as building blocks to present an interface, at the mobile device  10 , to server-side applications, as detailed herein. 
     Specifically, as illustrated in  FIG. 2 , the virtual machine software  29  includes: conventional XML parser software; event handler software; screen generation engine software; and object classes. The virtual machine software  29 , when executed leads to the virtual machine  24 , which includes: an XML parser  61 ; an event handler  65 ; a screen generation engine  67 ; and instances of the object classes  69 . The object classes correspond to XML entities supported by the virtual machine software  29  and possibly other XML entities contained within an application definition file. Supported XML entities are detailed in Appendix “A” of previously-referenced US Patent Application Publication 2003/0060896 A9. A person of ordinary skill will readily appreciate that those XML entities identified in Appendix “A” are exemplary only and may be extended or shortened as desired. 
     The XML parser  61  may be formed in accordance with the Document Object Model, or DOM, available at www.w3.org/DOM/, the contents of which are hereby incorporated by reference. The XML parser  61  enables the virtual machine  24  to read an application description file. Using the XML parser  61 , the virtual machine  24  may form a binary representation of the application definition file for storage at the mobile device  10 , thereby eliminating the need to parse text each time an application is used. The XML parser  61  may convert each XML tag contained in the application definition file, and its associated data, to tokens, for later processing. As will become apparent, this may avoid the need to repeatedly parse the text of an application description file. 
     The screen generation engine  67  orchestrates the display of initial and subsequent screens at the mobile device  10  in accordance with an application description file  28 , as detailed below. 
     The event handler  65  allows the virtual machine  24  to react to certain external events. Example events include user interaction with presented screens or display elements, incoming messages received from a wireless network, or the like. 
     The object classes define objects that allow the mobile device  10  to process each of the supported XML entities. Each of the object classes includes attributes, which are used to store parameters defined by the XML file and functions allowing the XML entity to be processed at the mobile device, as detailed in Appendix “A” of previously-referenced US Patent Application Publication 2003/0060896 A9, for each supported XML entity. So, as should be apparent, supported XML entities are extensible. The virtual machine software  29  may be expanded to support XML entities not detailed in Appendix “A”. Corresponding object classes could be added to the virtual machine software  29 . 
     As detailed below, upon invocation of a particular application at the mobile device  10 , the virtual machine  24  presents an initial screen on the user interface  18  based on the contents of the application definition file  28 . Screen elements are created by the screen generation engine  67  by creating instances  69  of corresponding object classes for defined elements. The object class instances  69  are created using attributes contained in the application definition file  28 . Thereafter, the event handler  65  of the virtual machine  24  reacts to events for the application. Again, the event handler  65  consults the contents of the application definition file  28  for the application in order to properly react to events. Events may be reacted to by creating instances of associated “action” objects from the object classes. 
     Similarly, the object classes of the virtual machine software  29  further include object classes corresponding to data tables and network transactions defined in the Table Definition and Package Definition sections of Appendix “A” of previously-referenced US Patent Application Publication 2003/0060896 A9. At run time, instances  69  of object classes corresponding to these classes are created and populated with parameters contained within the application definition file  28 , as required. 
     Using this general description, persons of ordinary skill in the art will be able to form the virtual machine software  29  for any particular device. Typically, the virtual machine software  29  may be formed using conventional object oriented programming techniques and existing device libraries and APIs, so as to function as detailed herein. As will be appreciated, the particular format of the screen generation engine  67  and the object class instances  69  will vary depending on the type of virtual machine software, the device operating system and the APIs available at the device. Once formed, a machine executable version of the virtual machine software  29  may be loaded and stored at the mobile device  10 , using conventional techniques. The machine executable version of the virtual machine software can be embedded in ROM, loaded into RAM over a network or loaded into RAM from a computer readable medium. Although, in the preferred embodiment the virtual machine software is formed using object oriented structures, persons of ordinary skill will readily appreciate that other approaches could be used to form suitable virtual machine software. For example, the object classes forming part of the virtual machine software  29  could be replaced by equivalent functions, data structures or subroutines formed using a conventional (i.e., non-object oriented) programming environment. Operation of the virtual machine  24 , while consulting an application definition file containing various XML definitions, is further detailed below. 
       FIG. 3  illustrates the operating environment for the first example mobile device  10 . Further example mobile devices, including a second example mobile device  30 , a third example mobile device  32  and a fourth example mobile device  34  are also illustrated in  FIG. 3 . These further example mobile devices  30 ,  32  and  34  are similar to the first example mobile device  10  and also store and execute virtual machine software exemplary of an embodiment of the present application. 
     Virtual machines, like the virtual machine  24  executed at the first example mobile device  10 , execute on each of the further example mobile devices  30 ,  32 ,  34 , and communicate with a middleware server  44  by way of a first example wireless network  36 , a second example wireless network  38 , a first example network gateway  40  and a second example network gateway  42 . The example gateways  40 ,  42  are generally available as a service for those people wishing to have data access to wireless networks. An example network gateway is available from Broadbeam Corporation, of Cranbury, N.J., in association with the trademark SystemsGo!™. The wireless networks  36 ,  38  are further connected to one or more computer data networks, such as the Internet and/or private data networks by way of the example gateways  40 ,  42 . As will be appreciated, the application may work with many types of wireless networks. The middleware server  44  is, in turn, in communication with a data network that is in communication with the example wireless networks  36 ,  38 . The communication protocol used for such communication may be TCP/IP over an HTTP transport. As could be appreciated, other network protocols such as X.25 or SNA could equally be used for this purpose. 
     The mobile devices  10 ,  30 ,  32 ,  34  communicate with the middleware server  44  in two ways. First, the virtual machine at each device may query the middleware server  44  for a list of applications of which a user of an associated mobile device  10 ,  30 ,  32 ,  34  can make use. If a user decides to use a particular application, the corresponding mobile device  10 ,  30 ,  32 ,  34  can download a text description, in the form of an application definition file, for the particular application from the middleware server  44  over its wireless interface. As noted, the text description is preferably formatted using XML. Second, the virtual machine at each device may send, receive, present and locally store data related to the execution of applications, or its own internal operations. The format of exchanged data for each application is defined by an associated application description file. Again, the exchanged data is preferably formatted using XML in accordance with the application description file. 
     The middleware server  44 , in turn, stores text application description files for those applications that have been enabled to work with the various mobile devices  10 ,  30 ,  32 ,  34  in a pre-defined format understood by the corresponding virtual machines. Software providing the functions of the middleware server  44  in the exemplary embodiment is written in Delphi and uses an SQL Server database. 
     As noted, text files defining application definitions and data may be formatted in XML. For example, XML version 1.0, detailed in the XML version 1.0 specification second edition, dated Oct. 6, 2000 and available at the Internet address www.w3.org/TR/2000/REC-xml-20001006, the contents of which are hereby incorporated herein by reference, may be used. However, as will be appreciated by those of ordinary skill in the art, the functionality of storing XML description files is not dependent on the use of any given programming language or database system. 
     Each application definition file is formatted according to defined rules and uses pre-determined XML markup tags, known to both the virtual machine executed at the mobile device and the complementary server software executed at the middleware server  44 . Tags define XML entities, which are used as building blocks to present an interface to an application at a mobile device. Knowledge of these rules, and an understanding of how each tag and section of text should be interpreted, allows the virtual machine executed at the mobile device to process an XML application definition file and thereafter provide an interface to an application executed at an application server, as described below. The virtual machine effectively acts as an interpreter for a given application definition file. 
       FIG. 4  illustrates an example format for an XML application definition file  28 . As illustrated, the example application definition file  28  for a given mobile device and server-side application includes three components: a user interface definition section  48 , specific to the user interface for the mobile device  10 , that defines the format of screen or screens for the application and how the user interacts with the screens; a network transactions definition section  50  that defines the format of data to be exchanged with the application; and a local data definition section  52  that defines the format of data to be stored locally on the mobile device by the application. 
     Defined XML markup tags correspond to XML entities supported at a mobile device and are used to create an application definition file  28 . The defined tags may broadly be classified into three categories, corresponding to the three sections  48 ,  50  and  52  of an application definition file  28 . 
     Example XML tags and their corresponding significance are detailed in Appendix “A” of previously-referenced US Patent Application Publication 2003/0060896 A9. As noted above, the virtual machine software  29  at the mobile device  10  includes object classes corresponding to each of the XML tags. At run time, instances of the objects are created as required. 
     Broadly, the following example XML tags may be used to define the user interface: 
     &lt;SCREEN&gt;—this tag defines a screen such that a SCREEN tag pair contains the definitions of the screen elements (buttons, radio buttons and the like) and the events associated with the screen and the screen control elements; 
     &lt;BTN&gt;—this tag defines a button and attributes associated with the button; 
     &lt;LIST&gt;—this tag defines a list box; 
     &lt;CHOICEBOX&gt;—this tag defines a choice item, which allows selection of a value from predefined list; 
     &lt;MENU&gt;—the application developer will use this tag to define a menu for a given screen; 
     &lt;EDITBOX&gt;—this tag defines an edit box; 
     &lt;TEXT ITEM&gt;—this tag describes a text label that is to be displayed; 
     &lt;CHECKBOX&gt;—this tag describes a checkbox; 
     &lt;HELP&gt;—this tag defines a help topic that is used by another element on the screen; 
     &lt;IMAGE&gt;—this tag describes an image that appears on those displays that support images; 
     &lt;ICON&gt;—this tag describes an icon; 
     &lt;EVENT&gt;—this tag defines an event to be processed by the virtual machine  24  (events can be defined against the application as a whole, individual screens or individual items on a given screen; sample events include: receipt of data over the wireless interface; and an edit of text in an edit box); and 
     &lt;ACTION&gt;—this tag defines a particular action that might be associated with an event handler (sample actions include: navigating to a new window; and displaying a message box.). 
     The second category of example XML tags may be used in the network transaction section  50  of the application definition file  28 . These may include the following example XML tags: 
     &lt;TABLEUPDATE&gt;—using this tag, the application developer can define an update that is performed to a table in the device-based local storage  26  (attributes of this tag allow the update to be performed against multiple rows in a given table at once); and 
     &lt;PACKAGEFIELD&gt;—this tag defines a field in an XML package that passes over the wireless interface. 
     The third category of XML tags are those used to define a logical database that may be stored in local storage  26  at the mobile device  10 . The tags available that may be used in this section are: 
     &lt;TABLE&gt;—this tag, along with its attributes, defines a table (contained within a pair of &lt;TABLE&gt;tags are definitions of the fields contained in that table; the attributes of a table control such standard relational database functions as the primary key for the table); and 
     &lt;FIELD&gt;—this tag defines a field and its attributes (attributes of a field are those found in a standard relational database system, such as the data type, whether the field relates to a field in a different table, the need to index the field and so on). 
     The virtual machine  24  may, from time to time, need to perform certain administrative functions on behalf of a user. In order to do this, one of the object classes is associated with a repertoire of tags to communicate needs to the middleware server  44 . Such tags differ from the previous three groupings in that they do not form part of an application definition file, but are solely used for administrative communications between the virtual machine  24  and the middleware server  44 . XML packages using these tags are composed and sent due to user interactions with configuration screens of the virtual machine  24 . The tags used for this include: 
     &lt;REG&gt;—this tag allows the application to register and deregister a user for use with the middleware server  44 ; 
     &lt;FINDAPPS&gt;—by using this tag, users can interrogate the middleware server  44  for a list of available applications; 
     &lt;APPREG&gt;—using this tag, a mobile device can register (or deregister) for an application and have the application definition file downloaded automatically (or remove the application definition file from the device-based local storage  26 ); and 
     &lt;SETACTIVE&gt;—using this tag, the user is allowed to identify the device that the user is currently using as the active device (if the user&#39;s preferred device is malfunctioning, or out of power or coverage, the user may need a mechanism to tell the middleware server  44  to attempt delivery to a different device). 
       FIG. 5  illustrates the organization of application definition files at the middleware server  44  and how the middleware server  44  may generate an application definition file  28  ( FIG. 4 ) for a given one of the example mobile devices  10 ,  30 ,  32 ,  34 . In the illustration of  FIG. 5 , only the first example mobile device  10  and the second example mobile device  30  are considered. Typically, since network transactions and local data are the same across devices, the only portion of the application definition file that varies for different devices is the user interface definition section  48 . 
     As such, the middleware server  44  stores a master definition file  58  for a given server-side application. This master definition file  58  contains: an example user interface definition section  48 - 10  for the first example mobile device  10  of  FIG. 1 ; an example user interface definition section  48 - 30  for the mobile device  30  of  FIG. 3 ; a user interface definition section  48 -N for an Nth mobile device; a description of the network transactions that are possible in the network transactions definition section  50 ; and a definition of the data to be stored locally on the mobile device in the local data definition sections  52 . Preferably, the network transactions definition section  50  and the local data definition sections  52  will be the same for all example mobile devices  10 ,  30 , . . . , N. 
     For the first example mobile device  10 , the middleware server  44  composes the application definition file  28  by determining the device type and adding the user interface definition section  48 - 10  for the first example mobile device  10  to the definition sections  50 ,  52  for the network transactions and the device local data. For the second example mobile device  30 , the middleware server  44  composes the application definition file by adding the user interface definition section  48 - 30  for the second example mobile device  30  to the definition sections  50 ,  52  for the network transactions and the device local data. 
     The master definition file  58  for a given application is likely to be created away from the middleware server  44  and loaded onto the middleware server  44  by administrative staff charged with the operation of the middleware server  44 . Master definition files could be created either by use of a simple text editor or by a graphical file generation tool. Such a tool might generate part or all of the file, using knowledge of the XML formatting rules, based on the user&#39;s interaction with screen painters, graphical data definition tools and the like. 
       FIG. 6  illustrates the organization of middleware server  44  and associated master definition files. The middleware server  44  may be any conventional application server modified to function in manners exemplary of the present application. As such, the middleware server  44  includes a processor  60 , a network interface  66 , a storage memory  64  and a server database  46 . The middleware server  44  may, for example, be a Windows NT server, a Sun Solaris server, or the like. Correspondingly, the storage memory  64  of the middleware server  44  stores a server operating system  62  such as Windows NT or Solaris. 
     The network interface hardware  66  enables the middleware server  44  to transmit and receive data over a data network  63 . Transmissions are used to communicate with both the virtual machine  24  of the first example mobile device  10 , via the wireless networks  36 ,  38  and the wireless gateways  40 ,  42 , and a backend application server  70 , which may be considered representative of one or more application servers. The backend application server  70  may be considered both the end recipient of data received by the middleware server  44  from the mobile devices and the generator of data that is to be sent by the middleware server  44  to the mobile devices. 
     The storage memory  64  at the middleware server  44  further stores middleware server software  68 , exemplary of an embodiment of an aspect of the present application. The middleware server software  68 , when executed by the processor  60  of the middleware server  44 , enables the middleware server  44  to compose and understand XML packages that are sent by and received by the middleware server  44 . These XML packages may be exchanged between the middleware server  44  and the first example mobile device  10  or between the middleware server  44  and the backend application server  70 . 
     As mentioned above, communication between the backend application server  70  and the middleware server  44  may use HTTP running on top of a standard TCP/IP stack. An HTTP connection between a running application at the backend application server  70  and the middleware server  44  may be established in response to receipt of an XML package from a mobile device. The server-side application executed at the backend application server  70  provides output to the middleware server  44  over this connection. The server-side application output may be formatted, by the server-side application, into appropriate XML packages understood by the virtual machine  24  at the first example mobile device  10 . 
     That is, a given server-side application (or an interface portion of the server-side application) formats server-side application output into an XML package in a manner consistent with a format defined in the application definition file for the given server-side application. Alternatively, an interface component, separate from the server-side application, could easily be formed with an understanding of the format for output for the given server-side application. That is, with a knowledge of the format of data provided by and expected by the given server-side application at the backend application server  70 , an interface component could be produced using techniques readily understood by those of ordinary skill. The interface component could translate the output of the given server-side application to an XML package, as expected by the middleware server  44 . Similarly, the interface portion may translate an XML package received, via the middleware server  44 , from the mobile device  10  into a format understood by the given server-side application. 
     The particular identity of the mobile device on which the interface to the server-side application is to be presented may be specified by a suitable identifier, contained in a header prefixed to the server-side application output XML package. This header may be used by the middleware server  44  to determine the appropriate mobile device to which to forward the XML package. Alternatively, the identity of the connection between the backend application server  70  and the middleware server  44  could be used to determine, at the middleware server  44 , the appropriate mobile device to which to forward the XML package. 
       FIG. 7  illustrates a flow diagram detailing data flow (application data or application definition files  28 ) between the mobile device  10  and the middleware server  44 , in manners exemplary of an embodiment of the present application. 
     For data requested from the middleware server  44 , the device  10 , under software control by the virtual machine software, transmits requests to the middleware server  44  (see also  FIG. 3 ), which requests pass over the first wireless network  36  to the first network gateway  40 . The first network gateway  40  passes the request to the middleware server  44 . The processor  60  of the middleware server  44  responds by executing a database query on the server database  46 . The response to the query is an indication of the applications that are available to the user and the mobile device  10 . Data representative of the indication is passed, by the middleware server  44 , to the first network gateway  40 . The first network gateway  40  forwards the data representative of the indication to the mobile device  10  over the first wireless network  36 . 
       FIG. 7 , when considered with  FIG. 3 , illustrates a sequence of communications, between the virtual machine  24  at the device  10  and the middleware server  44 , that may occur when the user of the mobile device  10  wishes interact with a server-side application. Initially, the virtual machine  24  interrogates the middleware server  44  to determine the applications that are available for the first example mobile device  10 . This interrogation may be initiated by the user instructing the virtual machine  24  at the first example device  10  to interrogate the middleware server  44 . Responsive to these instructions, the virtual machine  24  composes an XML package requesting the list of applications. The wireless interface hardware  14  (see  FIG. 1 ) of the mobile device  10  transmits the XML package to the middleware server  44  (data flow  72 ). The XML message may be composed to contain a &lt;FINDAPPS&gt; tag, signifying, to the middleware server  44 , a desire for a list of available applications. In response, the middleware server  44  makes a query to the server database  46 . The server database  46 , responsive to this query, returns a list of applications that are available to the user and to the first example mobile device  10 . The list is typically based, at least in part, on the type of mobile device making the request, the identity of the user of the mobile device and the applications known to the middleware server  44 . The middleware server  44  converts the list into an XML list package and transmits the XML list package, including a list of available applications, to the mobile device  10  (data flow  74 ). Again, a suitable XML tag identifies the XML list package as containing a list of available applications. 
     In response to being presented with the list of available applications, a user at the first example device  10  may choose to register for an available server-side application in the list. When the user chooses to register for an application, the virtual machine  24  at the device  10  composes a registration request XML package containing a registration request for the selected application. The wireless interface hardware  14  transmits the registration request XML package to the middleware server  44  (data flow  76 ). The registration request XML package may contain a &lt;REG&gt; tag. The name of the application is specified in the registration request XML package. The middleware server  44 , in response to receiving the registration request XML package, queries the server database  46  for a user interface definition associated with the specified application and the first example mobile device  10 . Thereafter, the middleware server  44  creates the application definition file, as detailed with reference to  FIG. 5 . Then, the middleware server  44  composes an XML package including the composed application definition file and transmits the XML package to the mobile device  10  (data flow  78 ). 
     The user is then able to use the functionality defined by the application definition file to send and receive data. 
     After receiving the XML package including the application definition file, the XML parser  61  of the virtual machine  24  may parse the XML text of the application definition file to form a tokenized version of the application definition file. That is, each XML tag of the application definition file may be converted to a defined token for compact storage and to minimize repeated parsing of the XML text file. The tokenized version of the application definition file may then be stored for immediate or later use by the device  10 . 
     Thereafter, upon invocation of an interface to the particular application for which the device  10  has registered, the screen generation engine  67  of the virtual machine  24  locates the definition of an initial screen for the particular application. The initial screen may be identified within the application definition file for the particular application as corresponding to a &lt;SCREEN&gt; tag with an associated attribute of First screen=“yes”. 
     Exemplary steps performed by the virtual machine  24  in processing the initial screen (and any screen) are illustrated in  FIG. 8 . As illustrated, the screen generation engine  67  generates an instance of an object class, defining a screen by parsing the section of the application definition file corresponding to the &lt;SCREEN&gt; tag in step S 802 . Supported screen elements may be buttons, edit boxes, menus, list boxes and choice items, as identified in sections 5.3, 5.4 and 5.5 of Appendix “A” of previously-referenced US Patent Application Publication 2003/0060896 A9. Other screen elements, such as images and checkboxes, as detailed in Appendix “A”, may also be supported. However, for clarity of illustration, the processing of the other screen elements by the screen generation engine  67  is not detailed. Each supported tag under the SCREEN definition section, in turn, causes creation of instances  69  of object classes within the virtual machine  24 . Typically, instances of objects corresponding to the tags, used for creation of a screen, result in presentation of data at the mobile device  10 . As well, the creation of such instances may give rise to events (e.g., user interaction) and actions to be processed at the device  10 . 
     Each element definition causes the virtual machine  24  to use the operating system of the mobile device  10  to create a corresponding display element of a graphical user interface, as more particularly illustrated in  FIG. 9 . Specifically, for each element, the associated XML definition is read in step S 806 , S 816 , S 826 , S 836 , and S 846 , and a corresponding instance of a screen object defined as part of the virtual machine software is created by the virtual machine  24  in steps S 808 , S 818 , S 828 , S 838  and S 848 , in accordance with steps S 902  and onward illustrated in  FIG. 9 . Each interface object instance is created in step S 902 . Each instance takes, as attributes, values defined by the XML text associated with the element. A method of the object is further called in step S 904  and causes a corresponding device operating system object to be created. Those attributes defined in the XML text file, and stored within the virtual machine object instance, are applied to the corresponding instance of a display object created using the device operating system in steps S 908 S-S 914 . These steps are repeated for all attributes of the virtual machine object instance. For any element allowing user interaction, giving rise to an operating system event, the event handler  65  of the virtual machine  24  is registered to process operating system events, as detailed below. 
     Additionally, for each event (as identified by an &lt;EVENT&gt; tag) and action (as identified by an &lt;ACTION&gt; tag) associated with each XML element, the virtual machine  24  creates an instance of a corresponding event object and action object forming part of the virtual machine software. The virtual machine  24  further maintains a list identifying each instance of each event object and each action object, and an associated identifier of an event in steps S 916  to S 928 . 
     Steps S 902 -S 930  are repeated for each element of the screen in steps S 808 , S 818 , S 828 , S 838  and S 848  as illustrated in  FIG. 8 . All elements between the &lt;SCREEN&gt; definition tags are so processed. After the entire screen has been so created in memory, the screen is displayed in step S 854 , using conventional techniques. 
     As will be appreciated, objects are specific to the type of device executing the virtual machine software. Functions initiated as a result of the XML description may require event handling. This event handling is processed by the event handler  65  of the virtual machine  24  in accordance with the application definition file  28 . Similarly, receipt of data from a mobile network will give rise to events. The event handler  65 , associated with a particular application presented at the device, similarly processes incoming messages for that particular application. In response to the events, the virtual machine  24  creates instances of software objects and calls functions of those object instances, as required by the definitions contained within the XML definitions contained within the application definition file  28 , giving rise to the event. 
     As noted, the virtual machine software  29  includes object classes, allowing the virtual machine  24  to create an object class instance corresponding to an &lt;EVENT&gt; tag. The event object classes include methods specific to the mobile device that allow the device to process each of the defined XML descriptions contained within the application definition file and also allow the device to process program/event flow resulting from the processing of each XML description. 
     Events may be handled by the virtual machine  24  as illustrated in  FIG. 10 . Specifically, as the event handler  65  has been registered with the operating system for created objects, upon occurrence of an event, steps S 1002  and onward are performed in response to the operating system detecting an event. 
     An identifier of the event is passed to the event handler  65  in step S 1002 . In steps S 1004 -S 1008 , this identifier is compared to the known list of events, created as a result of steps S 916 -S 930 . For an identified event, actions associated with that event are processed in steps S 1008 -S 1014 . That is, the virtual machine  24  performs the action defined in the &lt;ACTION&gt; tag associated with the &lt;EVENT&gt; tag corresponding to the event giving rise to processing by the event handler  65 . The &lt;ACTION&gt; may cause creation of a new screen, as defined by a screen tag, a network transmission, a local storage, or the like. 
     New screens, in turn, are created by invocation of the screen generation engine  67 , as detailed in  FIGS. 8 and 9 . In this manner, the navigation through the screens of the application is accomplished according to the definition embodied in the application definition file. 
     Similarly, when the user wishes to communicate with the middleware server  44 , or store data locally, the event handler  65  creates instances  69  of corresponding object classes of the virtual machine software  29  and calls methods of the instances to transmit the data, or store the data locally, using the local device operating system. The format of the data stored locally is defined by the local data definition section  52 ; the format of XML packages transmitted or received is defined in the network transaction package definition section  50 . 
     For example, data that is to be sent to the wireless network is assembled into XML packages using methods of an instance of an XML builder object. Methods defined as part of the XML builder object allow creation of a full XML package before passing the completed XML package to an instance of a message server object. The message server object instance uses the device&#39;s network APIs to transmit the completed XML package across the wireless network. 
     XML packages received from the data network  63  ( FIG. 6 ) give rise to events processed by the event handler  65 . Processing of the receipt of XML packages is not specifically illustrated in  FIG. 9 . However, the receipt of a XML package triggers a “data” event recognized by the device operating system  20  (see  FIG. 1 ). This data event is passed to the virtual machine  24  and the event handler  65  inspects the received XML package. As long as the data received is a valid XML data package as contained within the application definition file, the virtual machine  24  inspects the list of recognized XML entities. 
     So, for example, a user could trigger the transmission of a login request (data flow  80 ,  FIG. 7 ) by interacting with an initial login screen, defined in the application definition file for the application. The login request (data flow  80 ) would be passed by the middleware server  44  to the backend application server  70 . The backend application server  70 , according to the logic embedded within its application, would return a login response (data flow  82 ), which the middleware server  44  would pass to the virtual machine  24 . Other applications, running on the same or other application servers might involve different interactions, the nature of such interactions being solely dependent on the functionality and logic embedded within the backend application server  70  and remaining independent of the middleware server  44 . 
       FIG. 11  illustrates example XML messages passed as part of the message flows illustrated in  FIG. 7 . For each message, the header portion, i.e., the portion enveloped by the &lt;HEAD&gt;&lt;/HEAD&gt; tag pair, is considered to contain a timestamp and an identifier of the sending device. 
     A first example message  72  is representative of a message sent by the mobile device  10  to request the list of applications that the middleware server  44  has available to that user on that device. The first example message  72  specifies a type for the mobile device  10  using text contained by the &lt;PLATFORM&gt;&lt;/PLATFORM&gt; tag pair. A second example message  74  is representative of a message sent, to the mobile device  10  by the middleware server  44 , in response to the first example message  72 . The second example message  74  contains a set of &lt;APP&gt;&lt;/APP&gt; tag pairs, each tag pair enveloping an identity of a single application that is available to the user at the device  10 . A third example message  76  is representative of a message sent from the mobile device  10  to the middleware server  44  to request registration for a single server-side application. The tags specify information about the user and the mobile device  10 . A fourth example message  78  is representative of a message sent, to the mobile device  10  by the middleware server  44 , in response to the third example (registration request) message  76 . The &lt;VALUE&gt;&lt;/VALUE&gt; tag pair envelope a code indicating success or failure. In the fourth example message  78  shown, a success is indicated by “CONFIRM” and is followed by an interface description for the application, enveloped by the &lt;INTERFACE&gt;&lt;/INTERFACE&gt; tag pair. This interface description may then be stored locally within the storage memory  16  of the mobile device  10 . 
     As noted, when a user starts an interlace to an application, an application definition file for which has been downloaded in the manner described above, the virtual machine  24  reads the interface description section of the application definition file. The virtual machine  24  identifies the screen that should be displayed on startup and displays the elements of the screen as detailed in relation to  FIGS. 9 and 10 . The user may then use the functionality defined by the application definition file to send XML packages to, and receive XML packages from, the associated backend application server via the middleware server  44 . 
     For the purposes of illustration,  FIGS. 12 and 13  illustrate the presentation of a user interface for a sample screen on a Windows CE Portable Digital Assistant. As illustrated in  FIG. 13 , a first XML portion  92  of the application definition file  28  is an interface description for a screen with the name “NewMsg”. This interface description may be contained within the user interlace definition section  48  of the application definition file  28  associated with the server-side application. The screen is defined to have a single button identified by a &lt;BTN&gt; tag, which is identified as item D in  FIG. 13 , with attributes NAME=“OK”, CAPTION=“Send”, INDEX=“0”, X=“0”, Y=“15”, HT=“18” and WT=“50”. This button gives rise to a single event (identified by the &lt;EVENTS&gt; tag) that has two associated actions: one defined by the &lt;ACTION&gt; tag with attribute TYPE=“SAVE”; and one defined by the &lt;ACTION&gt; tag with attribute TYPE=“ARML”. The latter action results in the generation of an XML package (defined by the &lt;PKG&gt; tag with attribute TYPE=“ME”), which has a data format as defined enveloped by the &lt;PKG&gt;&lt;/PKG&gt; tag pair. The package is defined to begin with a &lt;MAIL&gt; TAG with attributes MSGID, FROM and SUBJECT. Additionally, the interface description for the screen includes definitions for three edit boxes, as enveloped by the &lt;EDITBOXES&gt;&lt;/EDITBOXES&gt; tag pair. The definitions for the three edit boxes are identified in  FIG. 13  as lines of XML code labeled A, B and C. 
     Upon invocation of the interface to the server-side application at the mobile device  10 , the screen generation engine  67  of the virtual machine  24  processes the interface definition for the screen, as detailed with reference to  FIGS. 8 and 9 . That is, for XML tag D, the screen generation engine  67  creates a button object instance in accordance with steps S 804 -S 812 . Similarly for XML tag pairs A, B and C within the application definition file  28 , the virtual machine  24  creates instances of edit box objects (i.e., steps S 834 -S 842 , see  FIGS. 8 and 9 ). The data contained within the object instances reflects the attributes of the relevant button and edit box tags, contained in the application definition file  28  associated with the server-side application. 
     The resulting screen presented by the user interface  18  of the mobile device  10  is illustrated in  FIG. 12 . The user interface  18  depicts a screen called “NewMsg”, which uses interface items that provide a user with an ability to compose and send data. The screen illustrated in  FIG. 12  has an edit box named “To”  84  corresponding to XML tag pair A in  FIG. 13 , an edit box named “Subject”  86  corresponding to XML tag pair B in  FIG. 13  and an edit box named “Body”  88  corresponding to XML tag pair C in  FIG. 13 . The screen illustrated in  FIG. 12  also incorporates a button named “OK”  90  corresponding to XML tag D in  FIG. 13 . 
     Call-backs associated with the OK button  90  cause graphical user interface application software, as part of the operating system at the mobile device  10 , to return control to the event handler  65  of the virtual machine  24 . Thus, as the user interacts with the user interface  18 , the user may input data within the presented screen using the mobile device API. Once data is to be exchanged with the middleware server  44 , the user may press the OK button  90  and, by doing so, invoke an event, which is initially handled by the operating system of the mobile device  10 . However, during the creation of the OK button  90 , in steps S 804 -S 810 , any call-back associated with the button was registered to be handled by the event handler  65  of the virtual machine  24 . Upon completion, the virtual machine  24  receives data corresponding to the user&#39;s interaction with the user interface  18  and packages this data into an XML package using corresponding objects. The XML package is populated according to the rules within the application definition file  28 . 
     The event handler  65 , in turn, processes the event caused by user interaction with the OK button  90  in accordance with the &lt;EVENT&gt; tag and corresponding &lt;ACTION&gt; tag associated with the &lt;BTN&gt; tag, referenced as XML tag D, associated with the OK button  90 . The events, and associated actions, are listed as data items associated with the relevant user interface item within the application definition file  28 . The &lt;ACTION&gt; tag causes the virtual machine  24  to create an instance of an object that forms an XML package for transmission to the middleware server  44  in accordance with the format defined within the &lt;ACTION&gt;&lt;/ACTION&gt; tag pair. That is, a “template” (defined beginning with the &lt;PKG&gt; tag with attribute TYPE=“ME”) for the XML package to be sent is defined within the &lt;EVENT&gt;&lt;/EVENT&gt; tag pair for a given user interface item. This template specifies the format of the XML package to be sent and may include certain variable fields. The variable fields in the formatted XML package take on contents that vary according to the values received in data entry fields on the current and previous screens. The definition of the template specifies which data entry field should be interrogated to populate a given variable field within the XML package that is to be sent. 
     According to the template, some of the variable fields of the XML package are filled dynamically from data inserted by the user into edit boxes presented on the display of the mobile device  10 . The template includes placeholders delimited by square brackets, i.e., “[“and”]”. These placeholders reference a data source from which data for filling the corresponding section of the template should be obtained. A suitable data source might be a user interface field on the current screen, a user interface field on a previous screen or a table in a device-based logical database. The virtual machine  24 , after reading the data source name, searches for the field corresponding to the referenced data source and replaces the placeholder with data contained within the named field. For example, the SUBJECT attribute of the &lt;MAIL&gt; tag in the first XML portion  92  references [NewMsg.Subject]. As such, content for the SUBJECT attribute may be read from the edit box (field) named “Subject” on the screen named “NewMsg”. This process is repeated for each such placeholder, until the virtual machine  24 , reading through the template, has replaced all placeholders in the template with content to form an XML package. 
     An exemplary XML package  94 , containing data obtained as a result of input provided to the fields of the “NewMsg” screen, is illustrated in  FIG. 14 . The exemplary XML package  94  may have been created responsive to user interaction with the “NewMsg” screen, which user interaction may be considered to have been culminated by interaction with the OK button  90  (see  FIG. 12 ) corresponding to XML tag D in the first XML portion  92 . In this case, the user has entered: the text “steven@nextair.com” into the edit box named “To”  84 ; the text “Hello Back” into the edit box named “Subject”  86 ; and the text “I am responding to your message” into the edit box named “Body”  88 . 
     The virtual machine  24 , using the template, inspects these three edit boxes and places the text contained within each edit box in the appropriate position in the template. For example, the placeholder [NewMsg.Subject] is replaced by “Hello Back”. The virtual machine  24  creates the exemplary XML package  94  by invoking functionality embedded within an XML builder software object to populate the variable fields of the template contained in the first XML portion  92 . Once the exemplary XML package  94  has been assembled in this fashion, a relevant method of the message server object is invoked to transmit the exemplary XML package  94  across the network. 
     When an XML package is received, the event handler  65  of the virtual machine  24  is notified. In response, the virtual machine  24  instructs the XML parser  61  to build a list of name value pairs contained within the received XML package. Thereafter, methods within an object class for processing incoming XML packages are invoked that allow the virtual machine  24  to inspect the XML package to determine a server-side application to associate with the XML package and select a corresponding application definition file. The methods within the object class for processing incoming XML packages also allow the virtual machine  24  to inspect the application definition file to identify the fields in the device-based logical database and the user interface screens that may need to be updated with new data received in the XML package. In the case wherein the user interface screens are updated, such updating may be accomplished according to the procedures normal to the particular device. 
     Handling of incoming XML packages is defined in the application definition file  28 . That is, for each of the possible XML packages that can be received, the application description file  28  includes definitions of device-based logical database tables and screen items that should be updated, as well as which section of the package updates which device-based logical database table or screen item. After an XML package has been received, the event handler  65  uses rules based on the application description file  28  to identify which device-based logical database tables or screen items need to be updated. 
       FIGS. 15A-15C  illustrate how the format of the logical database in the local storage  26  on the device  10 , and the XML packages that update the logical database, are defined in the application definition file  28 . A second XML portion  96  of the application definition file  28 , illustrated in  FIG. 15A , forms part of the local data definition section  52  (see  FIG. 4 ). The second XML portion  96  defines an example format for a portion of the logical database related to the e-mail application interface described with reference to  FIGS. 12 and 13 . 
     Two example tables are defined in the second XML portion  96  of  FIG. 15A  for formatting the logical database for the e-mail application. A first XML item E of the second XML portion  96  corresponds to a first table, labeled “SENTITEMS” in  FIG. 15B . A second XML item F of the second XML portion  96  corresponds to a second table, labeled “RECIPIENTS” in  FIG. 15B . The first table stores details of sent e-mail messages and has four fields. The second table stores recipients of sent e-mail messages and has three fields. 
       FIGS. 15A and 15B  illustrate the use of the local storage  26  to store data related to XML packages that are sent and received. Specifically, the first table, defined by the first XML item E in  FIG. 15A , may store the e-mail message contained in the exemplary XML package  94 , shown in  FIG. 14 . Accordingly, the application definition file  28  for the e-mail application may be required to contain, along with the first XML portion  92  and the second XML portion  96 , a third XML portion  102 , illustrated in  FIG. 15C . The third XML portion  102  defines how the data packages, composed according to the template included in the first XML portion  92  (see  FIG. 13 ), lead to updates of the tables defined by the second XML portion  96 . 
     The third XML portion  102  includes a first section  104  and a second section  106 . The first section  104  defines how fields of a received XML package may be used to update the first table of  FIG. 15B . An example line  108  defines how the “MSGID” field of the received XML package may be used to update a field named “LNGMESSAGEID” in the first table of  FIG. 15B . Similarly, the second section  106  defines how the fields of the received XML package may be used to update fields of the second table of  FIG. 15B . 
     The third XML portion  102  is contained by an &lt;AXDATAPACKET&gt;&lt;/AXDATAPACKET&gt; tag pair. Attributes of the &lt;AXDATAPACKET&gt; tag provide rules that indicate to the virtual machine  24  whether data contained within an XML package of a given XML package type should be used to update tables in the device-based logical database. These rules may be applied whenever an XML package of the given XML package type is sent or received. 
     As can be seen from the preceding description and example, such an approach has significant advantages over traditional methods of deploying applications onto mobile devices. First, the definition of an application&#39;s functionality is separated from the details associated with implementing such functionality, thereby allowing the implementers of a mobile application to concentrate on the functionality and ignore implementation details. Second, application definition files can be downloaded wirelessly, wherever the device happens to be at the time at which the functionality is required. This greatly improves the usefulness of the mobile device, by removing reliance on returning the device to a cradle and running a complex installation program. Third, the use of application definition files allows flexible definitions for numerous applications. Server-side applications may be easily ported to a number of device types. 
     As stated above, by describing a mobile application by way of an application definition file, a given mobile application is allowed to be developed independent of the platform on which the given mobile application will be executed. In the case of each type of platform, the mobile application is executed on a platform-specific virtual machine according to interpretation of an application definition file. In contrast, each type of platform is expected to have native mobile device applications, i.e., applications that have been coded specifically for the relevant platform. Java Platform, Micro Edition or Java ME, falls between these two types of applications. On one hand, a Java ME application arrives at a mobile communication device as an executable in the manner that a native mobile device application arrives. On the other hand, a Java ME application is executed by a virtual machine in a manner similar to the execution of a mobile application described by an application definition file. A mobile application described by an application definition file differs from a Java ME application in that there is a requirement to interpret the application definition file to produce the mobile application rather than simply running the executable Java ME application. 
     One aspect that native mobile device applications and Java ME applications have in common is metadata that allows the mobile device, upon receipt of the executable application, to provide values to variables of an application descriptor file. The application descriptor file may be used by the operating system of the mobile device to add an icon to a main screen (a main “ribbon”) of icons that are presented to the user of the mobile device to allow the selection of an application to execute. The variables of the application descriptor file are known to include such metadata as an icon to display on the main screen and a Universal Resource Identifier pointing to the executable mobile application. An exemplary structure for an application descriptor file follows: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 ApplicationDescriptor begin 
               
               
                   
                    Long moduleHandle; 
               
               
                   
                    Bitmap applicationIcon; 
               
               
                   
                    Int ribbonPosition; 
               
               
                   
                    String startupParameters 
               
               
                   
                 ApplicationDescriptor end 
               
               
                   
                   
               
            
           
         
       
     
     “moduleHandle” identifies the file that is to be executed. 
     “applicationIcon” is the icon to be displayed at the main application ribbon. 
     “ribbonPosition” is the position where the application icon will be displayed on the ribbon. 
     “startupParameters” are the parameters that should be passed to the application when this application descriptor is selected. 
     As originally planned, launching a mobile application described by an application definition file, of the type discussed above, required the selection of a virtual machine icon on the main screen first, thereby launching the virtual machine, and, second, the selection of the mobile application that is to be launched from a list of mobile applications. This two-step mobile application launching method is inconsistent with the manner in which native mobile device applications, and Java ME applications, are typically launched, i.e., by the selection of a representative icon in the main screen. Unfortunately, if it does not occur to a user of a mobile device on which such application-definition-file-described mobile applications are loaded, to launch the virtual machine, the user may not become aware that the application-definition-file-described mobile applications are available. 
     In overview, by specifying the appropriate metadata (e.g., an image and an application location), an application definition file may provide the virtual machine with all the information necessary to create an application descriptor file. The application descriptor file may then be used by the operating system of the mobile device when preparing and displaying the main ribbon. A user may then select an icon on the main ribbon to launch an application-definition-file-described mobile application in the same manner that native mobile device applications and Java ME applications are launched. 
     The metadata for use in providing values to variables of the application descriptor file may, when the application definition file is encoded in XML, be specified as attributes of the root element of the application definition file. For example: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 &lt;application uri=“/KamenMoney” name=“KamenMoney” 
               
               
                   
                 entry=“script_Start” vendor=“Kamen Co.” version=“1.1.75” 
               
               
                   
                 size=“6.16.11.5186” icon=“exampleIcon.png”&gt; 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 (rest of application definition file) 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 &lt;/application&gt; 
               
               
                   
                   
               
            
           
         
       
     
     Based on the above application definition file root element attributes, an exemplary application descriptor file may appear as follows: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 ApplicationDescriptor begin 
               
               
                   
                    Long virtualMachineHandle; 
               
               
                   
                    Bitmap exampleIcon.png; 
               
               
                   
                    Int defaultribbonPosition; 
               
               
                   
                    String KamenMoney; 
               
               
                   
                 ApplicationDescriptor end 
               
               
                   
                   
               
            
           
         
       
     
     In the exemplary application descriptor file, the moduleHandle variable refers to a software handle for the virtual machine  24 , the applicationIcon variable is assigned exampleIcon.png, as a ribbon position is not specified in the attributes of the root element of the application definition file, a default position is used and the name of the application to be executed is specified as a startup parameter. 
     Among the attributes of the root element, the attribute named “icon” is a reference to an image in PNG format. The format of the image is, of course, not limited to PNG and may be specific to a particular implementation. Any standard format for graphic data may be used, i.e., JPG, GIF, SVG, etc. In this particular example, the icon reference is a local reference and a file named “exampleIcon.png” should be downloaded together with the application definition file. In one instance, both the application definition file and the image file can be bundled together in a single archive file. To optimize transmission efficiency, the archive file may be compressed using a known compression scheme, such as PKZIP®. 
     Also among the attributes of the root element, the value of the attribute named “uri” is a Universal Resource Identifier referring to a location on the mobile device at which the application definition file may be located by the virtual machine  24 . Furthermore, among the attributes of the root element, the value of the attribute named “name” provides a textual name for the application defined by the application definition file. 
     In operation, in view of  FIG. 16 , the mobile device  10 , or more particularly the virtual machine  24 , receives an application archive (step S 1602 ) including an application definition file and an image file. The virtual machine  24  then extracts (step S 1604 ) the application definition file and the image file from the application archive. Based on the metadata in the application definition file, the virtual machine  24  creates an application descriptor file (step S 1606 ) and registers the application descriptor file (step S 1608 ) with the operating system of the mobile device  10 . 
     In creating the application descriptor file, the virtual machine  24  may, based on the value of the “icon” attribute of the root element of the application definition file, specify in the application descriptor file an image file to be associated with the application definition file in the main ribbon. Furthermore, the virtual machine  24  may, based on the value of the “name” attribute of the root element of the application definition file, specify in the application descriptor file a name to be associated with the image taken from the image file and displayed in the main ribbon. Additionally, the virtual machine  24  may, based on the value of the “uri” attribute of the root element of the application definition file, specify in the application descriptor file a location for the application definition file to be associated with the image taken from the image file and displayed in the main ribbon. 
     Operation of the device operating system software  20  after the registration of a new application descriptor file is illustrated in  FIG. 17 . Upon receiving an instruction (step S 1702 ) to present the main ribbon, the device operating system software  20  displays a main ribbon (step S 1704 ) that includes a given icon based on the image file referred to in the application descriptor file. 
     When a user has focused attention on, but not yet selected, the given icon, the device operating system software  20  may, elsewhere on the screen, identify the application associated with the given icon by the text provided by the name attribute of the root element and then recorded in the application description file. 
     The device operating system software  20  then receives an indication (step S 1706 ) that an icon on the main ribbon has been selected. Where the selected icon is the icon associated with the application definition file, the device operating system software  20  indicates the selection (step S 1708 ) to the virtual machine  24 . 
     Responsive to receiving (step S 1610 , see  FIG. 16 ), from the device operating system software  20 , the indication that the icon associated with the application definition file has been selected, the virtual machine  24  interprets the application definition file to create an application (step S 1612 ). As discussed above, upon receipt of the application definition file, the virtual machine  24  may, using the XML parser  61 , form a binary representation of the application definition file for storage at the mobile device  10 , thereby eliminating the need to parse the text of the application definition file each time an application is used. 
     Creation of the application (step S 1612 ) may, for instance, proceed as described above with reference to  FIG. 8 . In particular, the steps of  FIG. 9  are undertaken to create a user interface item for each of steps S 808 , S 818 , S 828 , S 838  and S 848 , if necessary. The virtual machine  24  then executes (step S 1614 ) the newly created application. As described above, where the application is a client-side interface to a server-side application, creation (step S 1612 ) and execution (step S 1614 ) may be intermingled in that creation involves developing an interface in memory and then presenting the interface on the display of the device, as described with reference to  FIGS. 8 and 9  and that execution involves recognizing events and executing actions associated with the recognized events, as described with reference to  FIG. 10 . 
     The creation of an application description file that is facilitated by the inclusion of metadata within a given application definition file allows the inclusion of a new icon on the main ribbon of a mobile device. The new icon is associated with the given application definition file, which describes a mobile application that is to be executed as a process that is an extension of an executing virtual machine. Advantageously, the new icon appearing in the main ribbon allows a user to initiate the execution of the associated application without taking the typical first step of opening a virtual machine interface. As such, initiating execution of the application is, to the user, no different than initiating the execution of an application native to the mobile device and, accordingly, the virtual machine for executing the mobile application is transparent to the user. 
     Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.