Abstract:
A server services client requests in an improved manner by a utilizing a combination of sending an id of the last article that has been previously sent to the client, load balancing servers to provide efficient servicing of clients and providing redundant servers so that a failure of any one server does not result in the termination of server services to clients.

Description:
COPYRIGHT NOTIFICATION 
     Portions of this patent application contain materials that are subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document, or the patent disclosure, as it appears in the Patent and Trademark Office. 
     FIELD OF THE INVENTION 
     This invention generally relates to improvements in computer systems, and more specifically, to improved servicing of client requests on a network. 
     BACKGROUND OF THE INVENTION 
     An internet is a group of networks and individual computers communicating via a common protocol. The Internet is a world-wide “network of networks” that use the TCP/IP (Transmission Control Protocol/Internet Protocol) protocol suite for communications. TCP/IP is a set of protocols and programs used to interconnect computer networks and to route traffic among different types of computers. These protocols describe allowable data formats, error handling, message passing, and communication standards. Computer systems that use TCP/IP speak a common language, regardless of hardware or operating system differences. 
     Part of the popularity of the TCP/IP protocol suite is due to its ability to be implemented on top of a variety of communications channels and lower-level protocols such as T1 and X.25, Ethernet, and RS-232-controlled serial lines. Most sites use Ethernet connections at local area networks to connect hosts and client systems, and then connect that network via a T1 line to a regional network (i.e., a regional TCP/IP backbone) that connects to other organizational networks and backbones. Sites customarily have one connection to the Internet, but large sites often have two or more connections. Modem speeds are increasing as new communications standards are being approved, thus versions of TCP/IP that operate over the switched telephone network are becoming more popular. Many sites and individuals use PPP (Point-to-Point Protocol) and SLIP (Serial Line IP), to connect networks and workstations to other networks using the switched telephone network. 
     Many large networks conform to these protocols, including the Internet. Thousands of computers at universities, government agencies, and corporations are connected to a network that follows the TCP/IP protocols. Any machine on the Internet can communicate with any other. Machines on the Internet are referred to as hosts or nodes and are defined by their Internet (or IP) address. 
     The Internet was created initially to help foster communication among government-sponsored researchers. Throughout the 1980&#39;s, the Internet grew steadily to include educational institutions, government agencies, commercial organizations, and international organizations. In the 1990&#39;s, the Internet has undergone phenomenal growth, with connections increasing faster than any other network ever created (including the telephone network). Many millions of users are now connected to the Internet, with roughly half being business users. The Internet is being used as the basis for the National Information Infrastructure (NII). 
     Many organizations are in the process of connecting to the Internet to take advantage of Internet services and resources. Businesses and agencies are now using the Internet or considering Internet access for a variety of purposes, including exchanging e-mail, distributing agency information to the public, and conducting research. Many organizations are connecting their existing internal local area networks to the Internet so that local area network workstations can have direct access to Internet services. 
     Internet connectivity can offer enormous advantages, however security needs to be a major consideration when planning an Internet connection. There are significant security risks associated with the Internet that often are not obvious to new (and existing) users. In particular, intruder activity, as well as vulnerabilities that could assist intruder activity, are widespread. Intruder activity is difficult to predict and at times can be difficult to discover and correct. Many organizations already have lost productive time and money in dealing with intruder activity; some organizations have had their reputations suffer as a result of intruder activity at their sites being publicized. 
     A firewall system is one technique that has proven highly effective for improving the overall level of site security. A firewall system is a collection of systems and routers logically placed at a site&#39;s central connection to a network. A firewall system can be a router, a personal computer, a host, or a collection of hosts, set up specifically to shield a site or intranet from protocols and services that can be abused from hosts outside the intranet. A firewall system is usually located at a higher-level gateway, such as a site&#39;s connection to the Internet; however, firewall systems can be located at lower-level gateways to provide protection for some smaller collection of hosts or intranets. A firewall forces all network connections to pass through the gateway, where they can be examined and evaluated, and provides other services such as advanced authentication measures to replace simple passwords. The firewall may then restrict access to or from selected systems, or block certain services, or provide other security features. The main purpose of a firewall system is to control access to or from a protected network (i.e., a site). It implements a network access policy by forcing connections to pass through the firewall, where they can be examined and evaluated. 
     The general reasoning behind firewall usage is that, without a firewall, an intranet&#39;s systems expose themselves to inherently insecure services and to probes and attacks from hosts elsewhere on the network. A firewall provides numerous advantages to sites by helping to increase protection from vulnerable services, controlled access to site systems, concentrated security, enhanced privacy, logging and statistics on network use, and misuse policy enforcement. In a firewall-less environment, network security relies totally on host security and all hosts must, in a sense, cooperate to achieve a uniformly high level of security. The larger the intranet, the less manageable it is to maintain all hosts at the same level of security. As mistakes and lapses in security become more common, break-ins occur, not as the result of complex attacks, but because of simple errors in configuration and inadequate passwords. 
     A firewall provides the means for implementing and enforcing a network access policy. In effect, a firewall provides access control to users and services. Thus, a network access policy can be enforced by a firewall. One problem is that Intranets that have a significant number of clients deployed often overwhelm the throughput capacity of the firewall. 
     A proxy server in general is a process that provides a cache of items available on other servers which are presumably slower or more expensive to access. 
     More specifically, a caching proxy server is used for a World-Wide Web server which accepts uniform resource locators (URLs) with a particular prefix. When it receives a request for such a URL, it strips off the prefix and looks for the resulting URL in its local cache. If found, it returns the document immediately, otherwise it fetches it from the remote server on the Internet, saves a copy in the cache and returns it to the requester. The cache will usually have an expiry algorithm which flushes documents according to their age, size, and access history. Caching proxy servers are often implemented to alleviate the problem of firewalls or proxy gateway servers that are overwhelmed by requests. 
     In comparison, a proxy gateway server is a computer and associated software which will pass on a request for a URL from a Internet browser to an outside server and return the results. This provides clients on Intranets a trusted agent that can access the Internet on their behalf. The proxy gateway is transparent to the client. A proxy gateway is a server that simply forwards requests from clients or other proxies on to another server or proxy. The second server or proxy sees the original proxy as just another HTTP client. When the proxy receives a response to the forwarded request, it simply returns it to the client. An Internet gateway proxy services HTTP requests by translating them into protocols other than HTTP. The reply sent from the remote server to the gateway is likewise translated into HTTP before being forwarded to the user agent. 
     In HTTP messaging, proxies use the header of the request to indicate the intermediate steps between the user agent and the server (on requests) and between the origin server and the client (on responses). The header is intended to trace transport problems and to avoid request loops. 
     Furthermore, agents can be implemented on clients or servers which are connected to the Internet. In the client-server model, an agent is the part of the system that performs information preparation and exchange on behalf of a client or server. Especially in the phrase “intelligent agent,” it implies an automatic process which can communicate with other agents to perform some collective task on behalf of one or more humans. The term agent is used to describe an automatic computer process that performs an action, such as information preparation or exchange, with no human intervention involved. Examples of Internet agents are brokers, wanderers, spiders, worms and viruses. Agents can facilitate work and coordinate tasks among machines and other agents. 
     Data is transmitted across the Internet in packets. A packet is a logical grouping of information that includes a header, control information, and a body that usually contains user data. A message may be segmented into a number of packets. When sent from one user to another via the Internet, individual packets may go by different routes and the packets are reassembled into the original message before reaching the destination. This contrasts with circuit switching in which the two users are actually connected by an end-to-end circuit, telephone network. Packet is the common name for a layer  3  PDU (Physical Data Unit: A unit of information at any given level of the 7-layer OSI protocol stack. Layer  3  PDUs are often called packets while layer  3  PDUs are often called frames) IP datagrams are often called packets. 
     Packets can be intercepted at any point within a packet-based network unless special security measures are in place. Capturing packets in this manner is known as network “snooping,” “packet sniffing,” and “promiscuous monitoring.” Sniffers are either hardware or software devices that can intercept and capture electronic messages not addressed to it, but rather addressed to another address on a network. Sniffers are a network monitoring tool that can capture data packets and decode them to show protocol data. 
     Sniffers typically have the capability of capturing every packet on a network and of decoding all seven layers of the OSI protocol model; the physical layer, the datalink layer, the network layer, the transport layer, the session layer, the presentation layer, the application layer. Capture frame selection can be based on several different filters such as protocol content at lower levels, node addresses, destination class, and pattern matching. 
     Network sniffers typically display network traffic information and performance statistics in real time, and in user-selectable formats. Numeric station addresses are translated to symbolic names or manufacturer ID names. Network activities measured include buffer use, frames accepted, and Kbytes accepted. Counters for activities specific to particular networks may be implemented. Network activity is expressed as frames/second, Kbytes/ second, or percentage of network bandwidth utilization. Data collection by a sniffer may be output to printer or stored to disk in either print-file or spread-sheet format. 
     In addition to the problem of firewalls overwhelmed by requests, distribution of internal communication via an organization&#39;s Intranet is often cumbersome and inconvenient to the users of client computers and the administrators of the Intranets. 
     The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World-Wide Web since 1990. An HTTP client submits requests to an HTTP server. The server responds by returning a response code and any appropriate data indicated by the original request. HTTP allows an open-ended set of methods that indicate the purpose of a request. A method indicates the operation that the client requests the server to perform. HTTP builds on the discipline of reference provided by the Uniform Resource Identifier (URI), as a location (URL) or name (URN), for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by Internet mail as defined by the Multipurpose Internet Mail Extensions (MIME). HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems, including those supported by the SMTP, NNTP, FTP, Gopher, and WAIS protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications. 
     While the set of HTTP methods is open-ended, the HTTP methods GET and HEAD must be supported by all servers that are HTTP-compliant. All other methods are optional. The GET method retrieves information identified by the Request-URI. 
     The Request-URI is a Uniform Resource Identifier and identifies the resource upon which to apply the request. 
     
       
         Request-URI=“*”|absolute URI|abs_path 
       
     
     The three options for Request-URI are dependent on the nature of the request. 
     (1) The asterisk “*” means that the request does not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily apply to a resource. One example would be 
     
       
         OPTIONS*HTTP/1.1 
       
     
     (2) The absolute URI form is required when the request is being made to a proxy. The proxy is requested to forward the request or service it from a valid cache, and return the response. Note that the proxy may forward the request on to another proxy or directly to the server specified by the absolute URI. In order to avoid request loops, a proxy must be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example Request would be: 
     
       
         GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1 
       
     
     All HTTP-compliant servers must accept the absolute URI form in requests, even though HTTP-compliant clients will only generate them in requests to proxies. 
     (3) The absolute path (“abs_path”) of the URI must be transmitted where a resource on an origin server or gateway is identified. 
     The semantics of the GET method change to a “conditional GET” if the request message includes an If-Modified-Since, If-Unmodified-Since, If-Match, If-None-Match, or If-Range header field as described by IETF publication at http://ds.internic.net/rfc/rfc2068.txt. A conditional GET method requests that data be transferred only under the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already held by the client. 
     The above method of specifying GETs is problematic in the complexity of the variations of the GET method. 
     SUMMARY OF THE INVENTION 
     The foregoing problems of servicing client requests in an improved manner by a server is facilitated utilizing a combination of sending an identifier (id) of the last article that has been previously sent to the client, load balancing servers to provide efficient servicing of clients and providing redundant servers so that a failure of any one server does not result in the termination of server services to clients. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of the invention may be better understood by referring to the following description, in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a typical hardware configuration of a computer in accordance with the subject invention; 
     FIG. 2 illustrates the topology of an intranet containing a caching proxy server and firewall connected to the Internet in accordance with a preferred embodiment; 
     FIGS. 3A and 3B represent tables which show which GET requests of each category id are processed by the six caching proxy agents in accordance with a preferred embodiment; 
     FIG. 4 illustrates the flow-of-control and sequence of events between the client, the caching proxy server and the destination server in regards to a “proxy_GET” request in accordance with a preferred embodiment; 
     FIG. 5A illustrates formats of HTTP GET requests by a client to a caching proxy server or a destination computer in accordance with a preferred embodiment; 
     FIG. 5B illustrates the flow-control and sequence of events between the client, the caching proxy server and the destination server in regards to a GET request by the client in accordance with a preferred embodiment; 
     FIGS. 6A and 6B illustrate the flow-of-control of the Proxy cache agent on the caching proxy server in accordance with a preferred embodiment; 
     FIG. 7 illustrates the format of the 0.dc file in accordance with a preferred embodiment; 
     FIG. 8 illustrates the format of the corp.dat file in accordance with a preferred embodiment; 
     FIG. 9 illustrates the flow-of-control of the retrieval of data Adstats data in accordance with a preferred embodiment; 
     FIG. 10 illustrates the flow-of-control of establishing communication between a client and the Content Server in accordance with a preferred embodiment; 
     FIGS. 11A and 11B illustrate the flow-of-control of the retrieval of data by a client from the content server in accordance with a preferred embodiment; 
     FIGS. 12 and 13 are system diagrams of the network environment in accordance with a preferred embodiment; 
     FIG. 14 is a system diagram of the network routing environment in accordance with a preferred embodiment; 
     FIG. 15 is a system flow diagram of the network transmissions in accordance with a preferred embodiment; 
     FIG. 16 is a system flow diagram of the network Data Center Capacity Planning and Equipment Requirement in accordance with a preferred embodiment; 
     FIG. 17 is a spreadsheet illustrating various sources of information in accordance with a preferred embodiment; 
     FIG. 18 is a flow diagram of the local cache logic in accordance with a preferred embodiment; 
     FIG. 19 shows how cache manager and server client work together in accordance with a preferred embodiment; 
     FIG. 20 is a flow chart setting forth the cache logic simplified by adopting the scheduled cache data refreshing methods in accordance with a preferred embodiment; and 
     FIG. 21 is a flowchart of the proposed URI cache scheme in accordance with a preferred embodiment. 
    
    
     DETAILED DESCRIPTION 
     A representative hardware environment is depicted in FIG. 1, whch illustrates a typical hardware configuration of a computer  100  in accordance with the subject invention. The computer  100  is controlled by a central processing unit  102  (which may be a conventional microprocessor) and a number of other units, all interconnected via a system bus  108 , are provided to accomplish specific tasks. Although a particular computer may only have some of the units illustrated in FIG. 1, or may have additional components not shown, most server computers will include at least the units shown. 
     Specifically, computer  100  shown in FIG. 1 includes a random access memory (RAM)  106  for temporary storage of information, a read only memory (ROM)  104  for permanent storage of the computer&#39;s configuration and basic operating commands, and an input/output (I/O) adapter  110  for connecting peripheral or network devices, such as a disk unit  113  and printer  114 , to the bus  108 , via cables  115  or peripheral bus  112 , respectively. A user interface adapter  116  is also provided for connecting input devices, such as a keyboard  120 , and other known interface devices, including mice, speakers, and microphones to the bus  108 . Visual output is provided by a display adapter  118  which connects the bus  108  to a display device  122 , such as a video monitor. The computer has resident thereon and is controlled and coordinated by operating system software such as the SUN Solaris, Windows NT, or JavaOS operating system. 
     FIG. 2 illustrates the topology of an intranet containing a caching proxy server and firewall connected to the Internet in accordance with a preferred embodiment. Client computers, typically PC-based workstations or UNIX-based workstations  200  communicate to a caching proxy server  210  having a cache of data  220  which communicates to a firewall  230  via a local area network or intranet  240 . The intranet  240  communicates to the Internet  250 , which communicates to a destination computer  260  having a database  270 . 
     When a caching proxy server  210  having a cache  220  is installed into the intranet  240  and is in operation, a plurality of agents will operate on the caching proxy server  210 , a corporate agent, an adstats agent, a proxycache agent, a passthrough agent, and an administration agent. All HTTP GET requests from client computers  200  are served by assigned agents on the caching proxy server  210 . 
     When a caching proxy server  210  having a cache  220  is installed into the intranet  240  and is in operation, this event is received and stored by the destination computer  260 . To begin operation of the caching proxy server  210 , a “proxy_GET” request is sent to the destination computer  260  having a database  270 . 
     The destination computer  260  transmits a table to the caching proxy server  210  that identifies which caching proxy server agent will serve a GET request. The distinction is based on the category id of the GET request. 
     FIGS. 3A and 3B represent tables which identify which GET requests of each category id are processed by the six caching proxy agents in accordance with a preferred embodiment. When a GET request is received by the caching proxy server, the category id of the request is examined to determine which agent on the caching proxy server should serve the request. This operation is different than the function of a sniffer because a sniffer examines the protocol content at lower levels, node addresses, destination class. The caching proxy server is examining a different element of the packet, the category id. The caching proxy server is also different from a sniffer in that the caching proxy server intercepts the request and uses the category id to determine which process should server the request, while a sniffer never intercepts the requests. 
     The Private Corporate Agent  300  serves requests of the Content Server, which private internal communication facility. The AdStats Agent  310  serves requests to pass advertisement statistical information to a destination computer. The PassThrough Agent  320  serves requests that are to be passed through to a destination computer. The Redirection Agent  330  serves all “proxy_GET” requests to redirect subsequent client request to another caching proxy server. The Administration Agent  340  serves all system administrative functions, such as deleting the caching proxy server cache. The ProxyCache Agent  350  serves requests to retrieve specific information from the caching proxy server. 
     An illustrative embodiment of the invention in a network computing environment is one in which a “Redirection” software agent on a caching proxy server fulfills “proxy_GET” requests from a client by transmitting a list of proxy server(s) within the Intranet of the client that will serve the client, a “Proxycache” agent that will fulfill HTTP GET client requests by either retrieving cached data or passing the request to a “Passthrough” agent that will pass the client request through to the destination server, an “Administration” agent that will process administrative requests from clients, and a “Corporate” agent that will store and distribute internal organization information. 
     FIG. 4 illustrates the flow-of-control and sequence of events between the client, the caching proxy server and the destination server in regards to a “proxy_GET” request when no caching proxy server is actively serving as a caching proxy server to the client in accordance with a preferred embodiment. The polling loop of events begins  400  on the client computer whereby if the amount of time that has lapsed since the last proxy_GET was transmitted by the client to the destination computer is not greater than one day, and if the amount of time that has lapsed since the last proxy_GET was transmitted by the client to the destination computer is not greater than the value set in NEXT-UPDATE  410 , then loop  410  is reiterated, otherwise the client transmits a proxy_GET to the destination computer  420 . 
     The destination computer receives the proxy_GET transmission from the client  430 . If the destination computer has received instruction to redirect client to caching proxy server  440 , then the destination computer transmits to client 1) a list of TCP/IP addresses that the caching proxy server will serve for client requests, 2) the NEXT_UPDATE value, and 3) a flag indicating whether a private content channel within the intranet is to be enabled by the client  450 , the transmission is received by the client  453  and the client saves the list of TCP/IP addresses that the caching proxy server will serve for client requests to file 0.dc  456 . Otherwise, the destination computer transmits to client 1) HTTP 204 indicating that and 2) NEXT_UPDATE value  460  and the client receives the transmission from the destination computer  470  and, if a file named “0.dc” exists on the client computer  480 , the client erases file 0.dc to indicate no redirection to a caching proxy server is in effect  490 . Then the sequence of events returns to the beginning of the loop  400 . 
     When an active caching proxy server receives a proxy_GET request from a client 
     FIG. 5A illustrates formats of HTTP GET requests by a client to a caching proxy server or a destination computer in accordance with a preferred embodiment. 
     FIG. 5B illustrates the flow-control and sequence of events between the client, the caching proxy server and the destination server in regards to a GET request by the client in accordance with a preferred embodiment. The client transmits a GET request from the computer at the IP address selected from the 0.dc file  5 B 00 . If the caching proxy server determines that the IP address is for a machine other than the caching proxy server  5 B 10 , the caching proxy server passthrough agent transmits the request to the destination computer  5 B 20  and the client computer regains flow-of-control  5 B 00 . If the caching proxy server determines that the category ID of the request indicates the proxycache agent  5 B 30 , the caching proxy server retrieves the requested data from the cache and transmits the data to the client  5 B 40  and the client regains flow-of-control  5 B 00 . If the caching proxy server determines that the category ID of the request indicates the adstats agent  5 B 50 , the caching proxy server manages the request data in accordance with  5 B 60  and the client regains flow-of-control  5 B 00 . If the caching proxy server determines that the category ID of the request indicates the corporate agent  5 B 50 , the caching proxy server manages the request data in accordance with  5 B 60  and the client regains flow-of-control  5 B 00 . Otherwise, the caching proxy server passthrough agent transmits the request to the destination computer  5 B 20  and the client computer regains flow-of-control  5 B 00 . 
     FIGS. 6A and 6B illustrate the flow-of-control of the Proxycache agent on the caching proxy server in accordance with a preferred embodiment. The primary purpose of this flow-of-control is to refresh the cache at designated intervals. Flow-of-control begins with a URI passed to the proxycache agent  600 . The URI is parsed through use a PCNHTTP class object  605  and, if “Cache Folder” is in &lt;Category ID&gt;\&lt;Search Argument&gt;  610 , then a cache is instantiated and NEXT_UPDATE is set to numeric 0  615 . If NEXT_UPDATE is not past the elapsed time  620  indicating that the cache not need be refreshed, the flow-of-control is exited with a successful status  625 . 
     Read and write operations are blocked from the cache  630 . The largest last id (the latest file) in the cache is identified  635  and a GET request is transmitted to the destination server in the following format: /FIDO-1/NumItm-&lt;number of items requested by client&gt;/&lt;Category ID&gt;-&lt;largest last id caching proxy server currently has&gt;/&lt;Search Argument&gt;  640 . The response from the destination computer is received  645 . 
     If the return code from the response is numeric decimal  200   650 , then NEXT_UPDATE is set to the first header value  655  and 0 or more files are received from the destination computer and segmented and stored in memory in the current cache directory with a name equal to the “Last ID” associated with the file  660 . 
     If the return code from the response is numeric decimal 204  665 , NEXT_UPDATE is set to a value equivalent and representative of one hour  670 , otherwise, and error flag is set indicating that the destination server did not respond to the request appropriately  675 . 
     Read and write operations to the caches are unblocked  680 , the last “NumItms” files in the &lt;Category ID&gt;\&lt;Search Argument&gt; in cache with last_id&gt;requested_last_id are transmitted  685 , and the flow-of-control is exited with a successful status  690 . 
     FIG. 7 illustrates the format of the 0.dc file in accordance with a preferred embodiment. A 0.dc file resides on each client computer that communicates with a caching proxy server. The data in the file is transmitted to the client from the destination computer or the redirection agent of an active caching proxy server in response to a proxy_GET request (category 66560) from the client. This file is used to identify the IP address of the caching proxy server to the client. The first entry is the name of the destination computer that transmitted the data in the 0.dc file to the client  700 . The second entry is a flag indicating whether or not the private content channel is enabled  710 , numeric 0 indicates no and numeric 1 indicates yes. The originator of the 0.dc file is identified at  720 . The usage mode of how the following list of caching server IP addresses is to be used is indicated at  730 , numeric 1 indicates that an IP address is to be selected randomly from the list by the client so that the capacity load on the caching proxy servers from the clients will be more even balanced, and numeric 0 indicates sequential selection from the list. An interative list of at least one caching proxy server address(es) follows  740 . This address is used by the client computer instead of the IP address of the destination computer for HTTP GET requests so that cached data on the caching proxy server can be used to satisfy data requests, relieving the firewall of the burden of passing on the request to the destination computer and returning the data from the destination computer to the client. 
     FIG. 8 illustrates the format of the corp.dat file in accordance with a preferred embodiment. A private corporate channel configuration file, named corp.dat, must reside in the directory, %PCN_HOME%\corp to enable the private channel. The name of the channel, channel_name, is displayed on the channel button in the PointCast Viewer in character string format  900 . SS_LOGO, the filename of the logo of the GIF or JPEG file that is to be displayed in the SmartScreen to replace the commercial that normally plays  910 . This line, AD_LOGO and the SS_FILE line are used by the client to determine whether it needs to fetch the files specified. If the files specified by these three lines are already present on the client, it will not attempt to fetch them again. Thus, if an administrator changes one of these files, the administrator will have to change the name of the file to signal the client to fetch it again. 
     AD_LOGO is the character string name of the logo of the GIF or JPEG file that is to be displayed in place of the commercial while the user is in the corporate channel of the PointCast Viewer  920 . SS_FILE is the character string name of the SmartScreen file selected by the MIS administrator from the list of template SmartScreens provided with the Content Server  930 . This SmartScreen will be played by the client when it is time to play a SmartScreen for the corporate channel. FLASH_FILE is the character string name of the file that contains a list of messages that scroll across the ticker tape, alongside the stock quotes and sports scores  940 . 
     GROUP is the character string name that appears on the Nth “tab” of the group directory window  950 . Following the GROUP line are the description lines for all the documents in this group. All document lines that describe the same document must NOT be separated by other command lines, although blank and comment lines are allowed. DOC_SUBJECT=subjectN_M is a character string subject of the Mth document in the Nth group, as displayed in the group directory window  960 . This is also the text that appears in a title sprout when the SmartScreen for this channel comes up. DOC_ID=DocIDN_M is the character string identifier (URL) used to load the source article  970 . This must follow its corresponding DOC_SUBJECT line. In general, DocIDN_M takes the format of an URL as defined by W3C. DOC_SUMMARY=sumN_M is the character string HTML document that will appear as a summary sprout when the SmartScreen for this channel is intialized  980 . This field usually consists of the first few paragraphs of the article, although an administrator can specify whatever he or she would like to appear as the summary sprout if the first few paragraphs are not appropriate. This must follow its corresponding DOC_ID line. DOC_SUMMARY_END denotes the end of the HTML document above  990 . 
     The entire GROUP section  950 - 990  can be substituted with a single line with the following format: GROUP_FILE=location where location specifies a file which contains a GROUP section. location can either be a URL if the file exists on a remote Web server, or a full-qualified pathname if the file exists on the same machine as the the Content Server. When a client requests a corp.dat file, the Content Server will parse the file and substitute any GROUP_FILE statements with the contents of the file identified by location before returning the corp.dat file to the client. If the Content Server is unable to locate the file in question, the entire line is ignored and a corp.dat file is generated without that particular group. A warning is signaled. 
     FIGS. 9A and 9B illustrate the flow-of-control of the retrieval of AdStats data in accordance with a preferred embodiment. 
     AdStats data is statistical data on advertisements viewed by the user on the client computer. However, any other type of statistical information on usage of the client computer or content could also be involved. 
     To upload the AdStats data from the client to the caching proxy server, the client compresses and transmits AdStat data to the caching proxy server  10 A 00 . The caching proxy server receives AdStat data and AdStat agent stores the data on  10 A 10 . If the caching proxy server AdStat agent successfully received and stored the AdStat data  10 A 20  the caching proxy server transmits successful status to client  10 A 30  and when the client receives successful status, the client erases AdStat data  10 A 40  and the flow-of-control ends  10 A 50 . If the caching proxy server AdStat agent did not successfully receive and store the AdStat data  10 A 20  the caching proxy server transmits unsuccessful status to the client  10 A 60 , the client divides AdStat data into segments half the size of the last attempted unsuccessful transmission, but not less than 140 bytes  10 A 70  and the flow-of-control continues at the beginning to attempt another transmission  10 A 00 . 
     To upload the AdStats data from the caching proxy server to the destination computer, the caching proxy server compresses and transmits AdStat data to the destination computer  10 B 00 . The destination computer receives AdStat data and AdStat agent stores the data  10 B 10 . If the destination computer AdStat agent successfully received and stored the AdStat data  10 B 20  the destination computer transmits successful status to caching proxy server  10 B 30  and when the caching proxy server receives successful status the caching proxy server erases AdStat data  10 B 40  and the flow-of-control ends  10 B 50 . If the destination computer AdStat agent did not successfully receive and store the AdStat data  10 B 20  the destination computer transmits unsuccessful status to the caching proxy server  10 B 60 , the caching proxy server divides AdStat data into segments half the size of the last attempted unsuccessful transmission, but not less than 140 bytes  10 B 70  and the flow-of-control continues at the beginning to attempt another transmission  10 B 00 . 
     FIG. 10 illustrates the flow-of-control on a client in establishing communication between the client and the Content Server in accordance with a preferred embodiment. The Content Server enables an organization to implement an internal electronic communication infrastructure. 
     If file 0.dc does not exist  1100 , indicating that no Content Server for the client exists, then flow-of-control terminates  1110 . Otherwise, the channel ID of the private channel is retrieved and appended to the list of mandatory channels in the initialization file  1120  and the private channel DLL is instantiated  1130 . If either file corp.dat does not exist or file 0.dc indicates that the private channel should not be enabled  1140 , then flow-of-control terminates  1150 . Otherwise, the private channel is activated  1160  and the Channel Viewer displays the private channel to indicate to the user that the private channel is active  1170  and then flow-of-control terminates  1180 . 
     FIGS. 11A and 11B illustrate the flow-of-control of the retrieval of data by a client from the Content Server in accordance with a preferred embodiment. In order to perform a HTTP GET request, the client transmits a request to the content server to transmit the corp.dat and flash.dat files to the client. 
     The flow-of-control of a HTTP GET begins on the client. If the NEXT-UPDATE value has expired,  12 A 00 , indicating that the client needs a new copy of the corp.dat file, the client transmits a request to the Content Server to transmit the corp.dat and flash.dat files to the client  12 A 10 . When the Content Server receives the request,  12 A 20 , if the CorpDirectory parameter in the registry on the Content Server present,  12 A 30 , indicating that the CorpDirectory is active, the Content Server will read the corp.dat file from the disk location specified by CorpDirectory parameter in the registry on the Content Server,  12 A 40 , otherwise the Content Server will read the corp.dat file from disk at subdirectory C:/vserver  12 A 50 . 
     Then, if the CorporateRemoteLevel registry parameter on the Content Server equals numeric 1,  12 A 60 , all lines in the corp.dat file that are name=value pairs with a name of GROUP_FILE are resolved by replacing the lines with the contents of the file identified by the value portion of the GROUP_FILE specification,  12 A 70 , and then the corp.dat file is stored in the directory identified in the CorporateScatch-Directory  12 A 80 . 
     More specifically, the CorporateScratchDirectory actually contains two subdirectories, /0 and /1 referred to as cache #0 and cache #1. The Content Server always begins by serving requests for the resolved corp.dat from cache #1. As soon as the corp.dat file in the CorpDirectory is changed, or a fixed time specification of minutes have elapsed, another corp.dat and its associated files are built in cache #0. 
     While the other corp.dat file is being built in cache #0, the resolved corp.dat file in cache #1 is transmitted to clients. When cache #0 is complete, the Content Server compares the contents of the two caches. If the files have the same contents, the Content Server continues to serve clients from cache #1. If the corp.dat file contents in cache #0 and cache #0 are different, the Content Server switches all new clients to cache #0 and starts the process over by building a new corp.dat file in cache #1. Then the Content Server transmits the corp.data file to the client  12 A 90 . The client receives and stores the corp.dat file transmitted by the Content Server  12 B 00 . 
     If the files specified by the AD_LOGO, SS_LOGO and SS_FILE entries in the corp.dat file do not exist on the client  12 B 10 , the client will transmit GET requests to the Content Server for the non-existent files  12 B 20 , if the CorpDirectory parameter in the registry on the Content Server present,  12 B 30 , indicating that the CorpDirectory is active, the Content Server will retrieve the request file(s) from the disk location specified by the CorpDirectory parameter in the registry on the Content Server and transmit the file to the requesting client,  12 B 40 , otherwise the Content Server will retrieve the requested file(s) from disk at subdirectory C:/vserver and transmit the file(s) to the requesting client  12 B 50 . 
     The client then will display through a browser the titles of documents specified in the corp.dat file  12 B 60 . When the user selects one of the documents  12 B 70 , the client transmits a request for the document to the computer addressed by the URL specified for the document in the corp.dat file on the client  12 B 80 , and the client receives and displays the requested document  12 B 90 . The flow-of-control for the retrieval of documents for the Content Server ends. 
     The documents that the Content Server serves to the clients may be in any format, such as ASCII text, MIME, Microsoft Word, Rich Text Format, compressed ZIP, graphics GIF or HTML. In the preferred embodiment the Content Server serves HTML files for use with a browser on the client computer. 
     System clients provide an intuitive user interface with automatic content delivery to your desktop. To fulfill our commitment to providing an enjoyable user experience, we have many challenges. The Data Center needs to always be available for content updates, able to deliver content fast, and able to scale up capacity quickly without interruption to service. The architecture of the System Network is composed of an Internet security system, a robust network infrastructure, a Request Processing Module, and a Content Processing Module. 
     Internet security system acts as an Internet firewall which permits only authorized accesses to The System Network-like Web, FTP, and client update accesses. FIG. 12 is a system diagram of the network environment in accordance with a preferred embodiment. The network topology is composed of 2 FDDI rings and 10/100 Switched Ethernet segments. FDDI rings deliver high-performance and high-availability to critical components of the network-like Internet routers, database servers, and 10/100 switching hubs which connect Servers. FIGS. 13 and 14 are a system diagram of the network routing environment in accordance with a preferred embodiment. 
     Request Processing Module is composed of Routers and Servers running Microsoft WindowsNT operation system. Routers provide the load-balancing functionality by redirecting PCN Clients to available Servers. Servers process client requests and transmit requested contents back to clients. If requested contents aren&#39;t in Server&#39;s local cache, it will obtain them from data servers. 
     FIG. 15 is a system flow diagram of the network transmissions in accordance with a preferred embodiment. A content Processing Module is composed of a variety of Feed 
     Handling Servers running Microsoft WindowsNT. Many custom applications were developed to handle incoming feeds in a variety of ways—like via Satellite, FTP, Web, and Email. There are two components to the feed handling process. First, store incoming raw contents and convert them to HTML format. Second, insert new contents to all production databases. 
     FIG. 16 is a system flow diagram of the network Data Center Capacity Planning and Equipment Requirement in accordance with a preferred embodiment. The System Data Center architecture uses industry standard computers and networking equipment. The equipment is very scaleable. Nevertheless, we need to identify the capacity of the Data Center that we intend to support, based on active clients. An accurate count of active clients would be the total distinct clients update from the Data Center on a monthly basis. The following spreadsheet provides an estimated equipment list for different sizes of Data Center by daily active users. Daily active users are usually sixty percent of monthly active users. FIG. 17 is a spreadsheet illustrating various sources of information in accordance with a preferred embodiment. 
     Data Center Implementation Strategy 
     In order to successfully implement a Data Center, we need to locate and/or prepare a facility, order necessary equipment, install and configure equipment, and run acceptance tests. Data Center has a unique facility requirement; it requires dedicated air conditioner to control temperature and humidity and power backup system. Power backup system includes UPS for power protection and power generator to keep equipment running during power outage. 
     1. Facility Preparation—A typical Data Center facility requires a raised floor for ventilation and cabling. Dedicated air conditioner is needed to maintain temperature around 60 degree F. and humidity around 30. All equipment should connect to UPS which then connect to utility power with power generator bypass switch. It is common to install a UPS on the bottom of each machine cabinet. Network cables should be laid under the raised floor to each equipment cabinet with proper labels. 
     2. Equipment Purchase—Many of the network equipment and data servers require long lead time to order—sometimes up to 1 month. Therefore, it is important to order them early. This is especially true for Internet connection. Depending on bandwidth requirements, it can take up to 60-90 days to implement a DS3 circuit in the United States. Company may also need to register company domain name and IP subnet addresses. 
     3. Installation and Configuration—Data Center requires a functional network before other equipment can be efficiently installed and configured. It is also important to test Internet connectivity and configure network security before proceeding to other tasks. Database servers are next in the priority list. They are required to test feed servers and Servers. Monitoring tools should also be installed to monitor network, database, and server utilization. 
     4. Acceptance Test—This involves testing client updates and performing load simulation tests. After content updates are successful, we still need to fine-tune the Data Center setup. The Data Center&#39;s ability to handle high-load efficiently involves balancing the database server load, as well as balancing the network load. The real acceptance test is usually perform after the Data Center goes production. We need to assure that Servers are processing acceptable number of request per second with low retransmission rate and database servers are correctly loaded.                           
     Post-Installation Management 
     The challenges begin after a Data Center goes production. 
     Common Issues: 
     1. Internet Service Providers (ISP) instability—Internet backbone is getting more and more congested which means frequent short instability or outages. Having redundant routing protocol in place allows automatic Internet rerouting. This prevents complete outage of a Data Center. Instability is difficult to prevent. Usually, the connection gets very slow with many retransmissions but is reachable. Correcting these type of problems require manual intervention-like manually modify routing. That&#39;s the reason for having Internet connections from more than one ISP. 
     2. Server Version Upgrade Process—We frequently introduce new versions of Router, Server, and Feed Server for bug fixes, new features support, and efficiency improvement. Having a good migration strategy prevents unexpected problems. We typically pass through QA and Production Test Network, before slowly phase-in to production network. 
     3. System and Network Management—It is important to maintain a healthy network and perform growth projections. We are currently using in-house built tools, as well as commercial tools. HP Openview is our primary network management platform which provides realtime network analysis and alerts on error conditions. There are 3rd party integrated tools for indepth network troubleshooting and analysis-like RMON, Router Manager, etc. An in-house tool, called Inspector, provides realtime Server utilization graph with color-coded Router, Server, Database Server, and Feed Server load conditions. Database servers are managed by Platinum&#39;s DBvision and DBserver. 
     4. Content Processing—Content providers frequently introduce new features or format changes, sometimes without notice, that require ongoing maintenance on feed handling applications. 
     5. Version Control Process—Advertisement and SmartScreen frequently require updates via version control process, as well as migration of new client versions. This is a very complicated process which involves mapping brand and version of the client and determines who should get what. This involves a lot of database table mapping and QA efforts. 
     6. Backup and Maintenance—All database servers should perform a hot backup on a daily basis and a cold backup on a weekly basis. Backing up management servers is also important. We don&#39;t recommend Server backup because they are identical and easy to rebuild. It is a good practice to store a complete set of backup tapes offsite on a monthly basis. To increase disk access efficiency and assure a virus free environment, disk defragmentation and virus scan are recommended to be performed on a weekly basis. 
     7. Transaction Logging and Advertisement statistics Processing—Do we need to log transactions? It provides lots of details of client behavior. How to store and upload advertisement statistics? It is needed to show advertisers. 
     Database Manager monitors and manages a PointServer&#39;s connections to its content databases. 
     Database Manager is one of the core server threads and is started up as a “normal” priority thread of the Service during server startup. 
     Database Manager has to be started up before Application Manager so that it can help in setting up Agent pools and is shutdown after the Application Manager has been successfully terminated during a normal shutdown. IA failure to start the Database Manger triggers the Server shutdown. 
     Database Manager maintains an in-memory structure to track status of all the databases currently being accessed by the various modules on the server. It uses this information to trigger failovers and failbacks appropriately. 
     Architecture 
     There are three modules in the Server which need access to the databases: 
     1. Service Agents to read the content and save the registration and upload information 
     2. Cache Manager to pre-fetch and refresh static Caches on the PointServers. 
     3. Transaction Manager to write the transaction log. 
     Each Service Agent requiring access to the databases creates and maintains a sharable database connections pool. This pool is established at the Server startup. The number of connections in the pool, primary database and secondary database can be specified by the Registry entries. A Database Manager thread provides means and resources to the Service Agents to manage their database pools. 
     The Database Manager helps in managing this pool in the following ways: 
     Database Manager checks periodically if all the pools are active—it triggers a repair if it sees dead or hung connection 
     Database Manager manages Database Failovers. Any thread (Client thread, Transaction Manager or Cache Manager) that experiences difficulty in accessing database posts a failover message to the Database Manager. The database Manager checks to see if it is a ‘failover’ condition and it triggers failover for all the connection pools currently under its management. 
     Inspector can post a message to Database Manager for failback. The Database Manager triggers failback of all connection pools to their Primary Databases on receiving this message. 
     Implementation 
     DBPoolCheckPoint 
     Provides a timer based call back to the ServiceAgents to do housekeeping on their DBPool. 
     Database Manager creates a worker thread and calls a pre-defined function::OnDBPoolTimer(intTimerId) for every Agent loaded on the Server. 
     This function can be customized by every Service Agent. In general it does following: 
     Check all DB Pools created by the Agent for list of locked connections. Any connection hanging for longer than the SESSION_TIMEOUT period is closed, deleted and re-created. This is done to re-claim the connections that were lost due to client session timing out. 
     Check all DB Pools for the total available connections. Available connections are the sum of free connections and the locked connections. They should be equal to the number specified in registry for this agent. If not, create connections to replenish the pool. 
     Make sure that all the free connections are still alive by ‘ping’ing the server and re-establish them if needed. 
     DBPool Failover 
     When a data server fails, Database Manger creates worker threads and re-establishes all the connection in the pools to the backup Data Server. 
     The ‘failure’ is triggered when an error is returned from the database operation. The thread which experiences the error could be a Cache Manager, a Transaction Manager or a Client Process. The ‘triggering thread’ posts a ‘FAILOVER’ message to the Database Manager. 
     The Database Manager checks the status of Database. The database could be in one of the following states: 
     1. On Line 
     2. Failing Over 
     If the status is OnLine, the Database Manger sets the status to ‘Failing Over’ and creates worker threads to run failover methods defined by the Transaction Manager, the Cache Manager and the Service Agents. 
     After Failover of all the pools is completed, the status of the Database is set to ‘On Line’ again. 
     If the status was already set to ‘Failing Over’ when a ‘FAILOVER’ message is received, the Database Manager discards it. 
     DBPoolFailback 
     When the Primary data server comes back on-line the Database Manager invokes another function in the Transaction Manager, Cache Manager and Service Agents to move the DBPool back to the Primary Data Server. Failback notification is provided from Inspector&#39;s Control Panel. 
     This documents describes the design specifications for Server URI cache. It covers the design goals, design considerations and subsequent decisions made. Many implementation guidelines are also suggested. This document doesn&#39;t cover the functional spec for the design. The ultimate goal for local cache is to reduce the number of trips to dataserver by using the data items already fetched to boost the server performance. To accomplish this, a local URI cache scheme is needed designed with the specific way Fido client fetches Server data. 
     Key Assumptions 
     The design of URI caching scheme is based on the following assumptions. Some are closely related to how Fido and the Server work. These will be key factors deciding how cache schemes are implemented. 
     Fido client always fetches the latest articles regardless of what category is involved. 
     There is an maximum number of articles each Fido request can get. This number is fixed depending on the category and searched items. 
     The articles fetched always start from the latest one consecutively back to whatever number is specified. For iS example, 5 means the latest 5 articles. 
     A single request of 500 stock quotes from datacenter every 5 minutes will have negligible overhead on Server. 
     Datacenter has the capability to determine which set of data to cache when needed. 
     The life span of each cached item is known to the cache. 
     Disk space in the server will be assumed of less concern when there are trade-offs between space and time. 
     Design 
     Based on the above requirements, this session describes key design decisions and detailed descriptions on how URI caches functions. 
     Key Design Considerations 
     To satisfy the above described requirements with the listed assumptions, several key design issues need to be addressed. A very primitive cache operation is used as a reference to illustrate salient features of different design choices. Major design considerations will be needed to reduce synchronization cost and number of trips to the datacenter. 
     Generic Cache Operations 
     FIG. 18 is a flow diagram of the local cache logic in accordance with a preferred embodiment. There are three possible results when query the local cache, either hit, miss, or another client is already on its way to datacenter for the desired data items. Serialization is needed for both cache query and update (shaded blocks), because query might require an update on wailing client list, and cache update include deletion and addition to the cache storage and corresponding table. Since usage information will be used only as a heuristic guide to determine how cache should be updated (primarily what to delete), serialization is not needed. 
     With a cache update algorithm (e.g. LRU) in place, a very generic cache mechanism can be implemented. The overhead in serialization and cache management might be too expensive for the resulting cache performance, especially when it is not known how good the resulting hit ratio can be. 
     Use of Cache Manager 
     With the help of a cache manager thread for updating and managing cache, server client won&#39;t need to update cache after fetching data items. In addition, most changes regarding cache scheme can be done through cache manager, hence a clean interface between server client and cache is possible with increased flexibility. FIG. 19 show how a cache manager and server client work together in accordance with a preferred embodiment. Note that server client cache query will be serialized when cache manager updates the cache. The cache manager is associated with cache tables and a list of memory mapped files that implement the local cache storage. The granularity of synchronization is determined directly by the design of tables. The more the tables, the finer the synchronization granularity will be and the less the serialization bottlenecks with a cost of more synchronization resources. 
     Refreshing Cached Data 
     If the set of cached data changes much slower than the data itself, major cost of cache management will be the constant need to keep the cached set fresh. Number of trips to the datacenter and the subsequent management of caching the fetched data are to primary factors contributing to the cost. Variations on when and how these updates are done could have different effects on the caching performance. Taking advantage of the specific way Server data is fetched and relieving the consistency constraint between cached data and its corresponding part in the datacenter, some cost saving measures are possible. 
     With the knowledge of data item life span, two methods are possible to simplify cache management by refreshing cached data at every preset time interval. The basic idea is to update cache in one batch instead of many individual trips to the datacenter. Scheduled updating and database pull are two of the alternate methods for facilitating this processing. 
     Scheduled Update 
     At every scheduled time interval, the cache manager will fetch a fresh set of cached data items from datacenter, hence keep all the cached item in the database fresh all the time. This only applies when the selection of cached data set is stable relative to scheduled time interval. If the time interval is T, the age of cached data using the scheme is guaranteed to be no older than 2T. 
     Database Pull Update 
     This requires datacenter to send notification to cache manager whenever the data in the database has changed. Cache manager would respond by fetching a fresh set of data, hence guarantees the synchronization of database and cache to some acceptable degree. It is suitable when the selected set of cached data doesn&#39;t change often and the frequency of database update is low so the notification message won&#39;t clog the network. If the database is updated every interval T, this approach guarantees the age of cached items no older than T. FIG. 20 is a flow chart setting forth the cache logic simplified by adopting the scheduled cache data refreshing methods in accordance with a preferred embodiment. Note that the data fetched by the client is not passed over to the cache manager for it is assumed that cache miss occurs rarely. 
     Reducing Serialization by Extra Cache Copy 
     When the server client is not responsible for updating the cache, synchronization cost can be greatly reduced if extra space is traded and some latency between the cached data and datacenter base is allowed. The cache manager makes a new copy of cached data during updating while making the old one available for reading at the same time. It switches to the new copy when done and subsequent cache query will reference the new one instead. No server client needs to wait for cache update using this scheme. Some server clients might get the old data at the time cache is updated. However, this interval can be negligible for Server application. Using this method to the above displayed flow, the need to both cache query and update synchronization won&#39;t be needed. 
     Selection of Cached Data 
     The set of data cached for each category can be determined by a priori usage knowledge or on the fly usage information. Any items fetched should be cached whenever possible. However, there are constraints on storage size and performance penalty under multi-threaded environment. Some Server categories can take advantage of the fact that only the latest articles are fetched and there is a limitation on maximum number of articles allowed. Such knowledge makes implementation of cache easier. 
     On the fly usage information will be updated on each cache query and referenced when the set of cached items need to be changed. This information will be used primarily to determine which cache items to purge when there is a need to do so as new cache items are added. Examples of usage information can be as simple as to support “least recent used” or “least frequently used” cache purging scheme. URI cache manager design would allow the flexibility of using different methods in selecting the set of data to cache for different categories. Adding a new fetched item to cache incurs serialization penalty that other client threads would be locked out from accessing the cache before the update is complete. Although this cost can be justified if overall it is less than the time spent for trips to database, it should still be minimized as much as possible. This is possible when the cached set is quite stable relative to the life cycle of cached data and the scheduled update can be adopted. Under this condition, a separate cache table can be used to record new changes without interrupting current cache accessing. The new items will be cached in next time cache is updated. 
     Cache Hit/Miss Decision 
     Cache query will be based primarily on the lastID and search items of the incoming request. It could also uses the time stamp information to validate the cached data. When request comes with search items, all should be in the cache to be considered as hit. The sever client is responsible to package an URL from either or both the returned data items by cache query and datacenter fetch. This happens when search items are involved or when, for example, five out ten latest articles are to be returned rather than all ten. 
     Proposed URI Cache Schemes 
     Based on the above described design considerations, one cache manager is proposed to handle the local URI cache. It will maintain separate cache tables for different categories to reduce potential synchronization issues among different categories hence increase the flexibility to extend the design when needed. Under the current Server, there are 27 different categories. Based on the way Server data is fetched, different schemes are needed to implement the URI cache for different categories, depending on the life cycle of category data and the certainty on which set of data to fetch. 
     The following table lists the existing Server data category, how files are fetched, how often data are updated, and allowed delay between cache and database. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Maximum 
                 Update 
                   
               
               
                   
                 Fetched 
                 Num. of Files 
                 Frequen 
                 Delay 
               
               
                   
                 Files 
                 Fetched 
                 cy 
                 Allowed 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Business News 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 Business Summary 
                 Latest 
                 1 
                 hourly 
                 1 hour 
               
               
                 Industry News 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 Entertainment News 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 Entertainment Variety 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 News 
               
               
                 Entertainment Variety 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 Business 
               
               
                 Entertainment News 
                 Latest 
                 1 
                 hourly 
                 1 hour 
               
               
                 Summary 
               
               
                 Entertainment 
                 Latest 
                 1 
                 low 
                 1 hour 
               
               
                 Horoscopes 
               
               
                 Entertainment Lottery 
                 Latest 
                 1 
                 twice/day 
                 1 hour 
               
               
                 Finance Historical 
                 Selected 
                 1 (per 
                 daily 
                 1 hour 
               
               
                   
                 Latest 
                 selection) 
               
               
                 Finance Current 
                 Selected 
                 1 (per 
                 per 15 
                 5 min. 
               
               
                   
                 Latest 
                 selection) 
                 min. 
               
               
                 Finance Articles 
                 Selected 
                 10 (per 
                 low 
                 1 hour 
               
               
                   
                 Latest 
                 selection) 
               
               
                 Hot Site 
                 ? 
                 ? 
                 ? 
                 ? 
               
               
                 National News 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 National News 
                 Latest 
                 1 
                 hourly 
                 1 hour 
               
               
                 Summary 
               
               
                 Washington News 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 Washington News 
                 Latest 
                 1 
                 hourly 
                 1 hour 
               
               
                 Summary 
               
               
                 International News 
                 Latest 
                 10 
                 low 
                 1 hour 
               
               
                 International News 
                 Latest 
                 1 
                 hourly 
                 1 hour 
               
               
                 Summary 
               
               
                 Sports News 
                 Latest 
                 10 (per 
                 low 
                 1 hour 
               
               
                   
                   
                 selection) 
               
               
                 Sports News Summary 
                 Latest 
                 1 
                 hourly 
                 1 hour 
               
               
                 Version Software 
                 All 
                 All 
                 very low 
                 1 hour 
               
               
                   
                 Latest 
               
               
                 Version AdPool 
                 All 
                 All 
                 very low 
                 1 hour 
               
               
                   
                 Latest 
               
               
                 Version Screen Saver 
                 All 
                 All 
                 very low 
                 1 hour 
               
               
                   
                 Latest 
               
               
                 Weather Maps 
                 All 
                 All 
                 twice/day 
                 1 hour 
               
               
                   
                 Latest 
               
               
                 Weather Cities 
                 All 
                 1 
                 twice/day 
                 1 hour 
               
               
                   
                 Latest 
               
               
                 Web Configuration 
                 ? 
                 ? 
                 ? 
                 ? 
               
               
                   
               
             
          
         
       
     
     With the assumption that all category data comes with explicit next update information and the above listed characteristics, the following schemes are proposed for a simple implementation of URI local cache using the scheduled fetching refreshing methods with extra copy of cached data. Memory mapped files will be used for cache storage. FIG. 21 is a flowchart of the proposed URI cache scheme in accordance with a preferred embodiment. 
     Note that server client cache query has an extra return called “none” which applies when the requesting client has already the most up to date information (i.e. latest articles) and there is no need to return anymore. Cache manager will use the next update information of the cached items to schedule fresh fetch of cache data for itself. Hence the updating message are basically timer message activated by the cache manager besides special notification messages from datacenter. 
     URI Cache Based on Scheduled Fetching with Fixed Cache Set For categories where the tolerance of data consistency is high (e.g. 1 hour difference) and the set of data to cache is fixed, scheduled update URI cache scheme is applicable. 
     Cache query is based on lastID using the cache table for the corresponding category. It will return all articles with more recent lastID. Cache query should result in either hit or none. Hit will return the list of articles the requesting client needs to be updated. Otherwise, it none would return without sending anything. Miss will happen when cache manager determines the cached data is corrupted and turn the itself off. 
     Cache manager is responsible to refresh the cache at scheduled interval according to the next update information embed in the cached items. 
     Protective mechanism using timeout and next update information would be used to protect any failure during scheduled fetch. When this occurs, the cache manager would retry the fetch while keep using the old cache data or turn off the cache for that particular category temporarily 
     Datacenter would be able to send notification message to the cache manager to change the selection of cached data, for example the number of latest articles to cache for a particular category. 
     URI Cache Based on Scheduled Fetch with Stable Cache Set Assuming the set of data to be cached doesn&#39;t change that often, a similar scheme to the previous one can be applied to all categories supporting selection, namely Finance Current, Finance Historical, Finance Articles, and Sports News. The main difference is the additional responsibility of cache manager to schedule an update on a new set of cached data. Some implications for this scheme are: 
     Cache query returns hit/miss by whether all selected items are in the cache. Only when all items are found will be a hit, otherwise it would be a miss. For example, AAPL, INTC, and IBM are selected, but only AAPL and INTC are cached, query will results in miss. Miss will still return found cached items back. It is up to the server client to package them, if any, along with fetched items together. 
     Cache manager has two schedules, one for updating a fresh set of cache data and the other for selecting a new set of cached data. Cache data refreshing schedule is known. While when the set of cached data needs to change requires some tuning, or notification message from datacenter. 
     Usage information will be updated whenever fetches occurs. Since this usage statistics will be used only as a reference for cache manager to update a new cache selection, it needs not to be thread safe. 
     The size of cached data is predetermined in terms of number of data items. An initial selection of cached data is necessary. For example, stock quotes (Finance Current) will cache 500 hot stocks initially selected by known usage pattern. 
     Number of items covered in usage information table should be larger than that of cached data so change of the cached data set is possible. 
     Whether the cost of scheduled fetching by the cache manager is justifiable depends on the real hit ratio. Parameter to adjust include the cache size, selection criteria, selection set update frequency etc. 
     Two copy of caches will be used for cache manager to circumvent serialization problem. 
     When there is miss for cache query, trips to datacenter are needed. The newly fetched data won&#39;t be added back to cache by design. It is assumed that the serialization cost thus incurred is not worth the saving in further hit for the fetched item. Whether this assumption is correct remains to be seen. 
     Implementation Criteria 
     The following criteria should be followed for implementing URI local cache: 
     URI local cache interface with server should be done at the object level. Unplugging local URI cache should be done simply by not [p the cache object. 
     The implementation priority should follow the following order: 
     1. Fixed set based scheme: least complicated yet with the best guaranteed payoff. 
     2. Stable set based scheme: payoff unknown with the extra effort of implementing cache selection scheme, strong dependency of how accurate the “stable set” assumption holds. 
     3. General scheme: most complicated and most costly in terms of multi-thread serialization, extra tuning effort needed to see how effective URI local cache could achieve. 
     URI cache codes should be inherited from generic cache design with different scheme left as implementation details. 
     The proposed URI cache design depends on the availability of next update information from cached data. If this data won&#39;t be available during development, an alternative scheme of preset fixed time interval cache refreshing scheme will be adopted. 
     Rose/Solo will be the tools used to document the design at the object design/analysis level. 
     While the invention is described in terms of preferred embodiments in a specific system environment, those skilled in the art will recognize that the invention can be practiced, with modification, in other and different hardware and software environments within the spirit and scope of the appended claims.