Patent Publication Number: US-5892935-A

Title: Data pre-fetch for script-based multimedia systems

Description:
&#34;This is a divisional of application(s) Ser. No. 08/268,458 filed on Jun. 30, 1994&#34;, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to multimedia systems, and more particularly to script-based client-server systems with remote storage of the main database. A main object of client-server systems is to provide limited-memory client machines (e.g. personal computers) with access to a voluminous database stored in a central server. The link between the server and the client machines is commonly accomplished by means of a single data line by employing time division multiplexing with the on-line client machines. 
     Generally, with such an arrangement, when a client machine requests server-stored data there results a passage of a significant &#34;click-wait-watch&#34; time period while the server proceeds to transmit the desired data to the client machines&#39;s local memory along a limited-bandwidth (i.e. relatively slow) information channel. With many multimedia applications, this slow response time renders the application significantly less useful (and in some cases unworkable). 
     This problem has been a major obstacle to efficient use of the client-server technique to advanced multimedia applications. 
     It is therefore an object of the instant invention to reduce the latency period for client receipt of requested information in client-server multimedia environments. 
     It is a further object of the instant invention to supply only the currently potentially-needed data to the client machine just in time upon request. 
     It is yet a further object of the instant invention to provide a script-analyzing compiler program that controls the pre-fetching of data in accordance with specific applications&#39; script routines. 
     SUMMARY OF THE INVENTION 
     Applicant has developed a novel architecture for providing quick response time in a script-based multimedia client-server system. The client machines (e.g. PCs) employ a hierarchial multimedia script language which is used to describe a decision tree wherein each of the decision points, i.e. &#34;nodes,&#34; have several other nodes to which they can proceed depending on the user&#39;s input. Once a particular node is chosen, multiple possible ensuing choices are made available to the user. The necessary data for these possible choices is pre-fetched automatically by a runtime processor that determines what data might be needed based on the user&#39;s current script node location as signaled to the runtime processor by the compiler. Just this potentially immediately-useful prefetched data is stored temporarily in a local &#34;run time data requirement&#34; memory (e.g. a special harddisk file). The compiler program is specially designed to analyze the script code to accomplish the suitable pre-fetching, so that a script language application programmer can do the programming as usual, and does not need to make any special pre-fetch requests in the script code. There is no interference with the normal operation of the scripting language. In this manner the click-wait-watch times in the application program are minimized, thus allowing limited machine memory PC users connected to the large memory server to take advantage of advanced multimedia applications that were previously practically realizable only in conjunction with large memory machines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The reader&#39;s understanding of a practical implementation of a preferred embodiment of the instant invention will be enhanced by reference to the following detailed description taken in conjunction with the drawing figures, wherein: 
     FIG. 1 depicts a client-server information exchange system. 
     FIG. 2 shows schematically a layered multimedia script selection tree. 
     FIG. 3 is a block diagram representation of a preferred architecture for implementing the method of the instant invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring now to FIG. 1, therein depicted is a client-server system for providing remote limited-memory client machines 103-105, etc. (which are typically personal computers) with access to the extensive memory and database of a server 100 via communications channel 102. The communication channel can be a coaxial cable, a fibre optics cable, a microwave data link, or other similar link. This simple architecture is useful for some purposes, but in certain applications it is cumbersome, if not useless, due to the relatively long time delays (i.e. &#34;click-wait-watch&#34; time) involved in procuring the server-stored data. 
     In multimedia applications involving a &#34;scripting&#34; language it is desirable and often practically essential to keep all system delays to a minimum. Applications with long delays are simply not highly useful or marketable. 
     The instant invention addresses this problem in a novel way that can be better appreciated by reference to FIG. 2. Therein depicted are various nodes of a scripting selection scheme. When a user selects an option, e.g. Node 1B, additional options become available to that user, e.g. Nodes 2F, 2G, and 2H. Each of these nodes in turn have further multiple options, and so on as shown. 
     Once an initial option is chosen, options for each ensuing layer are inherently contained in the script program. So, within the script program resides the information necessary to determine what immediate future selections are possible once the user has chosen a given node. The instant invention comprises taking advantage of this inherent information in the script program by means of a specialized compiler program that analyses the script program and determines automatically what the potential immediate user options are at any given currently-selected node. This information is used by the runtime processor to immediately pre-fetch any potentially needed data from the server prior to an actual request by the user for particular data. 
     For example, once the user has chosen Node 2H in the script selections, any data required from the server to fulfill the requirements of both Nodes 3J and 3K is automatically prefetched from the server (in response to the commands of the compiler) and locally-stored temporarily for potential near-future use. In this regard, this specialized pre-fetch arrangement is somewhat akin, in principle, to a &#34;just in time&#34; parts delivery system for a manufacturing assembly line for customized products. The object is to have the system work &#34;on the fly&#34; as readily as possible without undue (or impossible) local storage. 
     It should be noted that the technique of the instant invention typically involves more data being transferred from the server to the client in a given time period than would otherwise occur. This is due to the fact that a significant portion of the data for all the potential choices is transmitted even though only a fraction of it will actually be used. Therefore, a practical implementation of the instant invention can sometimes require an increased bandwidth data channel between the server and clients beyond what would otherwise be necessary. Nonetheless, at least from the user&#39;s standpoint, this is an acceptable and desirable tradeoff. 
     A preferred architecture for implementing the technique of the instant invention is depicted in FIG. 3. Therein, server 301 comprising a large remote database memory 303 and a prefetch controller 305 is connected for two-way communication to a limited-memory client machine 302 (one of many such clients) via data channel 307 and data channel client connection 309. Pre-fetch requester 311 receives input from data requirements database 313 corresponding to the potentially-needed &#34;next nodes&#34; of data choices (as described above with reference to FIG. 2). The pre-fetch requester then signals the server&#39;s pre-fetch controller to transmit the potentially-needed parts of next nodes of data immediately. Upon receipt of this data from the server, the prefetch requestor 311 directs the data to be temporarily stored in local disk 323. 
     The multimedia script is compiled by the compiler and generates two things: the compiled script program and the data requirements database (313). At a later time, the compiled script program is executed by a runtime processor (321) which executes the instructions from the compiled script, makes data requests, interacts with the user, and generates the desired output to display device 325. 
     The key to efficient operation of this system is the compiler program contained in compiler 317. This program analyses the script program, at compile time, to determine what data is potentially needed next. This program controls the entire prefetch system. Those who are skilled in the art of drafting such programs will be able to prepare a suitable corresponding compiler program as a simple matter of programming for whatever particular type of client machine is used. The resultant codes will differ, but the basic concept of the invention will be equivalent. 
     The foregoing description refers to a preferred embodiment of Applicant&#39;s invention. The scope of the instant invention is not limited to this embodiment, but rather is defined by the appended claims and equivalents thereof.