Abstract:
A network address is captured from a source document or signal and is stored in a data structure such as a list for subsequent use. When a network resource at the network address is subsequently visited, the network address is automatically deleted from the list. The list storage and deletion functions are integrated into a World Wide Web browser. If a connection cannot be established using the network address, the connection is retried, and the network address is marked for delection after a pre-determined number of retries. Thereafter, if another connection attempt fails, a user may delete the network address or retain it for another retry after a user-defined time. Identified network addresses are accessed over the network to validate their correctness and a snapshot of the page displayed is stored and related to the network address.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to computer systems, and more particularly relates to managing lists of addresses of resources in a network for subsequent visitation. 
     2. Description of Related Art 
     In real-time broadcast media that present transitory information, such as television, references to other information or media have become commonplace. For example, television advertisers often include contact information such as a business address or telephone number in a television advertisement so that viewers of the advertisement can locate the business after the advertisement has disappeared from the screen. 
     As another example, due in part to the explosive growth of the globally accessible computer network known as the Internet, it has become commonplace for advertisers and other users of broadcast media to include an Internet address in broadcast advertisements. 
     One popular technololgy enjoying wide use with the Internet is known as the World Wide Web. The World Wide Web enables a computer to locate a remote server using a server name in an agreed-upon format that is indexed at a central Domain Name Server (DNS); the computer can then retrieve information using a communication protocol called the Hypertext Transfer Protocol (HTTP). A Uniform Resource Locator (URL) uniquely identifies each page of information stored on the remote server. A URL is a form of network address that identifies the location of information stored in a network. The pages of information are files prepared in the Hypertext Markup Language (HTML). 
     As use of the World Wide Web has soared, advertisers have also begun to include URLs in broadcast advertisements so that users often see URLs while they are watching television or other broadcasts. The URLs typically identify a Web server or pages on a Web server that contain information about the products that are advertised. For example, a URL may be listed in a commercial or it may be shown on the screen as part of a show. Typically this is done in news broadcasts or documentaries, though many entertainment shows also have websites that are listed at some time during the broadcast. 
     URLs also may be encountered when a user is browsing the Web and the user sees a URL or link that is interesting while reviewing a Web document. This can occur at a time when it is inconvenient for the user to immediately review the referenced document or link. However, if the URL or link is not immediately investigated, the user may forget its identity or location later when time is available to investigate it. 
     URLs also may be received in a message to the user, such as an email message from another person who is recommending review of a particular website. Often such URLs are encountered at a time when it is inconvenient for the user to immediately review the website identified by the URL. For example, a user may receive an email message from a friend recommending a “cool site” at a time when the user needs to concentrate on other work. 
     Guided tours were described by Trigg in 1988 as a way to recommend a “next place to go” to a user at any time during the user&#39;s navigation of a hypertext, as disclosed in R. Trigg, “Guided Tours and Tabletops: Tools for communicating in a hypertext environment,” ACM Trans. Office Information Systems 6, 4 (October 1988), pp. 398-414. In Trigg, the author of a hypertext document defines a guided tour of a closed and pre-planned hypertext document or hypertext space. The guided tour is conceptually tied into each specific hypertext node and provided a recommended next place to go from that node as defined by the author. 
     The Problems 
     While the Trigg approach provides a way to store a list of locations in a hypertext document for later review, it has several significant disadvantages. For example, the list of locations is pre-defined by the author of the hypertext. It is desirable to provide a way for a user to define a personal, delayed-intention Web tour on the fly while the user is browsing an unbounded hypertext space. It is also desirable to have such Web tours tied into the user&#39;s behavior so that the locations defined in the tour are independent of any outside author. 
     Another disadvantage of the author-defined guided tour approach is that the list of locations to be toured is not altered as the tour takes place. There is a need for a system that can provide a list of locations to be toured, integrated with a touring mechanism such as a Web browser, so that items in the list are removed from the list when the browser visits that location. Thus, there is a need for a system that provides a way for a list of locations to be automatically pruned as the locations are visited. 
     Further, it is typically difficult for a person exposed to a broadcast or advertisement to make a note of the URL, for later use. The URL generally appears in the broadcast advertisement only for a brief moment, for example, in the form of a spoken series of words in a radio advertisement, or a text string flashed on a television screen at the conclusion of a TV ad. Also, some URLs are quite long and need to be spelled with 100% accuracy to be useful. They include unusual typed characters such as colons, slashes and “˜” characters. These characters and other parts of the URL must be remembered and reproduced correctly, or the URL cannot be used successfully to retrieve a Web page. 
     In addition, even if the person exposed to the advertisement successfully records a URL, for example, by writing it down, it must be manually keyed into a computer system in order to access the associated Web page. Also, not all URLs have any secondary or mnemonic meaning; therefore, if any significant time delay passes between recordation of the URL by the person and use of the URL, the person may forget what advertiser or product the URL is associated with. 
     When an interesting URL is encountered in a Web document, an e-mail, or another source, existing technology does not provide a rapid and convenient way to record the URL for subsequent use. For example, using present browser technology, a user can immediately visit the Website identified by the URL and then copy the URL to a bookmark list. The user is essentially forced to visit the Website even though the user desires to visit it at some future time. 
     Alternatively, the user can copy the URL using conventional editing commands, and then paste it into a text file prepared by the user; however, using this approach there is no convenient way to load the URL into a browser at a future time. 
     For all these reasons, there is a need for methods, apparatus and products that can store a network address from a source text in a list for future reference and use. There is also a need for such methods, apparatus and products that can store such network addresses in an ordered way, and provide an automatic way to retrieve network addresses from the list at a subsequent time. 
     There also is a need for methods, apparatus, and products that enable a person exposed to a network address in a source document to retrieve information referenced in the source document conveniently and without error. 
     SUMMARY OF THE INVENTION 
     The invention provides a method, apparatus, and computer program product for managing a network address by retrieving the network address from a source document or signal and placing it in a list for subsequent use. The list is automatically pruned as a network resource at the network address is visited. 
     In one approach, a method comprises the steps of storing a network address that is selected during a network communication session in a list, and deleting the network address from the list when the network address is visited. In one aspect, a method further comprises the step of testing whether a connection to a network resource identified by the network address is a successful connection. Another aspect is marking the network address as pending unless the connection is a successful connection. 
     In yet another aspect, a method further comprises the steps of attempting a second connection to the network resource when the network address is marked as pending, and deleting the network address from the list unless the second connection is a successful connection. Another feature is identifying the network address from an image selected from a broadcast signal. 
     In another aspect, a method further comprises storing the image as an image file; identifying a text item in the image file; and parsing the text item to identify the network address therein. A feature of this aspect is performing optical character recognition (OCR) on the image file to identify the text item in the image file. Another feature is checking whether the string is a valid Uniform Resource Locator (URL), by connecting to a computer network; requesting information from a location in the computer network that is identified by the string; and testing whether the step of requesting information resulted in a successful retrieval. 
     The invention also encompasses a computer system and a computer software product configured with the foregoing features and aspects. 
     The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, features and advantages of the system of the present invention will be apparent from the following description in which: 
     FIG. 1A illustrates a computer of a type suitable for carrying out the invention. 
     FIG. 1B illustrates a block diagram of the computer of FIG.  1 A. 
     FIG. 1C illustrates an exemplary memory medium containing one or more programs usable with the computer of FIG.  1 A. 
     FIG. 2 is a block diagram of one embodiment of a software architecture apparatus for capturing information from broadcast signals according to the invention. 
     FIG. 3 is a block diagram of a file that is created by one embodiment of the invention. 
     FIG. 4A is a flowchart of a method according to one embodiment of the invention. 
     FIG. 4B is a flowchart of a method of validating URLs as part of one embodiment of the invention. 
     FIG. 4C is a flowchart of a method of writing an information summary file as part of one embodiment of the invention. 
     FIG. 5A is a block diagram of a browser and To-Do List according to one embodiment of the invention. 
     FIG. 5B is an exemplary screen display generated by a browser configured according to one embodiment of the invention. 
     FIG. 6A is a flowchart of a method of adding a network address to a To-Do List and retrieving the network address according to an embodiment of the invention. 
     FIG. 6B is a flowchart of additional steps in the method of FIG.  6 A. 
     FIG. 6C is a flowchart of additional steps in the method of FIG.  6 A. 
     Notations and Nomenclature 
     The detailed descriptions that follow may be presented in terms of program procedures executed on a computer or network of computers. These procedural descriptions and representations are the means used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. 
     A procedure is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. These steps are those requiring physical manipulations of physical quantities. Usually, through not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It proves convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be noted, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. 
     Further, the manipulations performed are often referred to in terms, such as adding or comparing, which are commonly associated with mental operations performed by a human operator. No such capability of a human operator is necessary, or desirable in most cases, in any of the operations described herein that form part of the present invention; the operations are machine operations. Useful machines for performing the operation of the present invention include general-purpose digital computers or similar devices. 
     The present invention also relates to apparatus for performing these operations. This apparatus may be specially constructed for the required purpose or it may comprise a general-purpose computer as selectively activated or reconfigured by a computer program stored in the computer. The procedures presented herein are not inherently related to a particular computer or other apparatus. Various general-purpose machines may be used with programs written in accordance with the teachings herein, or it may prove more convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these machines will appear from the description given. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A method, apparatus and computer program product for retrieving information from a source document is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
     FIG. 1A illustrates a computer of a type suitable for carrying out the invention. Viewed externally in FIG. 1A, a computer system has a central processing unit  100  having disk drives  110 A and  110 B. Disk drive indications  110 A and  110 B are merely symbolic of a number of disk drives that might be accommodated by the computer system. Typically, these would include a floppy disk drive such as  110 A, a hard disk drive (not shown externally) and a CD ROM drive indicated by slot  110 B. The number and type of drives varies, typically, with different computer configurations. The computer has a display  120  upon which information is displayed. A keyboard  130  and a mouse  140  are typically also available as input devices. Preferably, the computer illustrated in FIG. 1A is a SPARC workstation from Sun Microsystems, Inc. 
     FIG. 1B illustrates a block diagram of the internal hardware of the computer of FIG. 1A. A bus  150  serves as the main information highway interconnecting the other components of the computer. CPU  155  is the central processing unit of the system, performing calculations and logic operations required to execute programs. Read only memory ( 160 ) and random access memory ( 165 ) constitute the main memory of the computer. Disk controller  170  interfaces one or more disk drives to the system bus  150 . These disk drives may be floppy disk drives, such as  173 , internal or external hard drives, such as  172 , or CD ROM or DVD (Digital Video Disk) drives such as  171 . A display interface  125  interfaces a display  120  and permits information from the bus to be viewed on the display. A modem bank interface  190  is used if the computer is configured as a proxy or an Internet Service Provider (ISP). The modems of the modem bank  190  are connected to a telephone network  191  in the usual manner. Communications with a network  195  or with other external devices can occur over communications port  185 . 
     In one embodiment, the data network  195  is coupled to a globally accessible computer network such as the Internet  50 . Alternatively, the network  195  is a local area network. For example, using a modem bank  190  and telecommunications software, the computer can call a local Internet Service Provider (ISP) and establish a dial-up connection to the Internet  50 . A remote Web server  62  is connected to the network. The remote server  62  contains source documents, such as pages formatted in the HTML language, or websites referenced in a source document. 
     FIG. 1C illustrates an exemplary memory medium that can be used with drives such as  173  in FIG. 1B or  110 A in FIG.  1 A. Typically, memory media such as a floppy disk, CD ROM, or Digital Video Disk will contain program information for controlling the computer to enable the computer to perform its functions in accordance with the invention. 
     FIG. 1A also illustrates an alternate embodiment of an apparatus for receiving information from source documents according to the invention. In this embodiment, the hardware elements discussed above in connection with FIG. 1A, in combination with a signal processing system  4   a  and a remote control system  4   b , are collectively identified as an information capturing system  2 . The system  2  comprises a signal source  10  coupled to a signal interface  12  that is coupled to the bus  150 . The signal source  10  provides a broadcast signal that contains information to be captured. For example, the signal source can be a television antenna, a cable television cable, a satellite dish, or a radio antenna. The signal interface  12  converts a broadcast signal received from the signal source  10  into a digital form that is usable by the CPU  155 . The internal configuration of the signal interface  12  is dependent on the nature of the signal source  10 . For example, if the signal source  10  is a television antenna, then the signal interface  12  comprises a channel tuner, an amplifier, and a video digitizer. 
     The signal interface  12  may be integrated into a computer system in the form of a single device that has computational capabilities and the ability to receive, store and display an external analog signal such as a video signal. For example, the MacTV device available from Apple Computer, Inc., and the WebTV device developed by WebTV Networks, Inc. and available from Sony, have components that are suitable. Also, the CPU  155  and other hardware elements of FIG. 1B may be remote from the signal interface  12  and connected to it by a cable or by wireless means. 
     As shown in FIG. 2, a World Wide Web browser  3  runs on the system  2 , for example, by residing in the main memory ( 160 ,  165 ) or in the data storage devices  171 ,  172 ,  173  that are described herein. The browser  3  is any program or device that is capable of interpreting documents prepared in HTML and commanding the system  2  to display the document as interpreted. An exemplary browser  3  is the HotJava browser available from Sun Microsystems, Inc. The browser  3  is used to establish a connection using the HTTP protocol to a remote Web server computer  62 . The Web server computer  62  runs a Web server program that uses the HTTP protocol to respond to the browser  3 . The Web server computer  62  has a storage device that stores documents such as HTML format documents or Web pages. 
     A remote signaling system  4   b , comprising for example a remote control  16 , is coupled to the bus  150  through a remote interface  132 . The remote control  16  is preferably coupled to the interface  132  by wireless means, such as an infrared LED at the remote control  16  that signals to an infrared detector at the interface  132 . 
     In an alternative embodiment, a microphone  17  is coupled to a voice recognition processor  19 , which is coupled to the bus  150 . A user speaks into the microphone  17 , and the spoken sounds are digitized by the voice recognition processor  19  and provided to the system  2 . The remote signaling device may comprise any other means that signals the computer to grab a frame from the signal source  10  and identify information in it, such as network address or a URL. 
     The bus  150  is also coupled to a frame grabber  20 . The frame grabber  20  receives an analog broadcast signal, such as a television signal from the signal interface  12 . The frame grabber  20  has a high-speed analog-to-digital converter that makes a digitized copy of a single frame of the television signal. Television signals adhering to the NTSC standard widely used in North America are transmitted at sixty interleaved frames per second; each interleaved frame contains video information to energize one-half of the scan lines of a standard television receiver. In this patent document, the term “frame” refers to the smallest complete image that can be displayed at an instant in time, such as a pair of interleaved NTSC frames. Because a television signal changes rapidly in real time, the process of capturing and saving a single frame is known as “grabbing” a frame off the air. The frame grabber  20  saves the grabbed frame, for example, by writing it to a local memory in the frame grabber  20 . In one embodiment, the grabbed frame is written to an image file  22  that is coupled to program elements of the system  2  shown in FIG.  2 . 
     In an alternate embodiment, a frame storage  21  is coupled to the frame grabber  20  and to the signal interface  12 . The frame storage  21  contains a large, fast local electronic memory that can receive in real time and store a large number of frames. Frames in the frames storage  21  are organized in first-in, first-out manner. The frame storage  21  provides a way to store frames that disappear from the television screen before a user has a chance to signal the system  2  using the remote signaling device to capture information in a frame. The system  2  can retrieve a frame from the frame storage  21  that was displayed earlier in time. For example, the frame storage  21  is configured to store the  150  most recently viewed frames, providing a five-second period (at thirty frames per second) in which the user can react to the video signal and signal the system  2  to capture information from a frame. When the remote signaling device is activated, the frame storage  21  provides its first frame, i.e., the oldest of the  150  frames, to the frame grabber  20 . 
     An optical character recognition (OCR) processor  24  is coupled to the bus  150 . Under control of the OCR program  76  shown in FIG. 2, the OCR processor  24  can scan a digital image file and identify human-readable typographical characters within the image file  22 . When characters are recognized in the image file  22 , the characters are written to a text file  26  that is readable and writable by the CPU  150 . 
     Due to known limitations in the art of OCR processing, it is possible that the OCR processor  24  or OCR program  76  may output several alternative interpretations of data in the image file  22 , in the form of a plurality of text strings. Some known OCR processors pass such alternative text strings to a natural language parser that applies natural language rules to the alternative text strings in an effort to determine the best natural language interpretation of the text strings. In the invention, all the text strings are written to the text file  26 . A parser program  28  runs on the computer system. The parser  28  is configured to read the text file  26 , to identify strings of characters or words in the text file  26  that represent references to other information, and to write the words in a text file such as the URL list  30 . 
     In one embodiment, the parser  28  is configured to identify a network address, such as a URL that represents a reference to a remote World Wide Web server  62 , known as a website. URLs generally are formatted according to the following template: 
     
       
         &lt;protocol id&gt;://{&lt;server&gt;}&lt;second level domain&gt;&lt;top level domain&gt;{&lt;directory&gt;}{&lt;file&gt;} 
       
     
     The &lt;protocol id&gt; identifies the transmission protocol to be used. For example, in the case of the Web it is &lt;http&gt;, and in the case of an anonymous file transfer protocol transaction it is &lt;ftp&gt;. The &lt;server&gt; element is an optional server name such as &lt;www.&gt;. The, &lt;server&gt; element may also identify a directory on a storage device of the Web server  62  that contains HTML documents. The &lt;second level domain&gt; element is the name of the server domain as found in the DNS table, such as &lt;sun&gt;. The &lt;top level domain&gt; element identifies the type of the second level domain, and must be an item selected from a finite set of globally recognized top level domains, such as “com,” “org,” “mil,” “edu,” “gov,” and others. The &lt;directory&gt; element is an optional name of a directory within the &lt;server&gt;, such as &lt;DocumentRoot/&gt;. The &lt;file&gt; element is an optional name of a file, document or image to be retrieved, such as &lt;Index.html&gt;. Thus, a URL serves as one type of a network address to locate a document anywhere in a network. 
     The parser  28  is preferably configured to locate and identify URLs that strictly meet this convention, such as http://www.sun.com/, or canonical Website domain names, such as www.sun.com. Canonical website domain names are commonly used in broadcast signals as shorthand for a URL, because the syntactically correct string prefix &lt;http://&gt; can be inferred from the use of &lt;www&gt; as a server name. Accordingly, the templates available to the parser  28  include templates for all commonly used shorthand URL formats. When a canonical Website domain name is identified, the system  2  converts the canonical Website domain name into a complete, syntactically correct URL. 
     Thus, in one embodiment, the system  2  is used by a user who is watching television on a device that also has computational capabilities and is connected to the Internet. 
     FIG. 2 is a block diagram of a software architecture with which an embodiment of the present invention can be implemented. 
     An operating system (OS)  78  is installed in the central processing unit  100 , such as on the hard drive  172 . In conventional manner, the OS  78  is loaded by the CPU  155  into the main memory when the computer is powered up. The OS  78  controls and supervises the operation of one or more application software programs, and facilitates interaction of the application programs with functions of the operating system  78  and of the computer hardware. The browser  3  is one of the application programs. 
     In one embodiment of the invention, a control program  70  coordinates operation of the hardware and other software elements. In the embodiment that uses voice command to trigger retrieval of information from frames, a voice recognition program  72  runs on top of OS  78  under control of the control program  70 . The voice recognition program  72  controls the voice recognition processor  19  to receive an analog voice signal from the microphone  17 . The voice recognition program  72  writes the analog voice signal, in known manner, to one or more speech files  13 , and carries out conversion of the analog voice signal to digital form. 
     A frame grab program  74 , OCR program  76 , and parser  28  each run under control of the OS  78  and the control program  70 . As described below, the frame grab program  74  writes frames to an image file  22 . The OCR program  76  reads the image file  22  and writes strings of text recognized in the image file  22  to a text file  26 . The parser  28  reads the text file  26 . The parser  28  reads the text file  26  and writes network addresses, such as URLs, that are recognized in the text file to a URL List file  30 . The control program  70  reads and writes website image files  32 . In this embodiment, the source documents from which information is retrieved comprise broadcast signals or broadcast programs. 
     The website image file  32  and image file  22  are saved on the data storage devices  172 ,  173  in a standard graphic image format, such as JPEG or GIF. The text file  26 , URL list  30 , and HTML file  40  are conventional text files. The image file  22 , text file  26 , URL list  30 , and HTML file  40  may be stored in the data storage device  107 . 
     The present invention is related to the use of system  2  to retrieve information from a source document. According to one embodiment, retrieval of information from a source document is performed by system  2  in response to CPU  155  executing sequences of instructions contained in memory  160 ,  165 . Such instructions may be read into the memory from another computer-readable medium, such as data storage devices  171 ,  172 ,  173 . Execution of the sequences of instructions contained in the memory causes CPU  155  to perform the process steps that will be described hereafter. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the present invention. Thus, the present invention is not limited to any specific combination of hardware circuitry and software. 
     In one embodiment, the system  2  is operated when a user is watching a broadcast television program carried from the signal source  10  to the television receiver  14 . The television program is concurrently carried to the bus  150  through the signal interface  12  so that a user can watch television on the television receiver  14  while the system  2  is in operation. During an advertisement or other portion of the broadcast television program, a URL is included in an image that is broadcast. The user wishes to view a website at the remote server  62  that is identified by the URL at some subsequent time. Accordingly, the user activates the remote control  16  to indicate a desire to grab a URL currently displayed on the television screen. 
     In response, under control of the control program  70  the system  2  sends the current video frame to a frame grabber  20  that converts the current video frame into an image file. In one embodiment, system  2  commands the frame grabber  20  to grab the frame currently contained within the broadcast television signal. The frame grabber  20  digitizes a copy of the current frame and writes the frame to the image file  22 . The frame grabber  20  reports to the system  2  that a frame has been successfully grabbed. 
     Using the OCR program  76 , the system  2  then commands the OCR processor  24  to read the grabbed frame from the image file  22  and to identify any text information that is found within the image file  22 . In response, the OCR processor  24  and OCR program  76  read the image file and, using conventional optical character recognition techniques, locate any text information that is in the frame. The OCR program  76  may use a probabilistic algorithm to “guess” at the most likely text information found in the image file  22 . As a result, the OCR program  76  may output more than one set of text information or text string. If text is successfully located, it is passed to the control program  70  and written by the control program  70  in the text file  26 . If the OCR processor  24  locates multiple strings of text, or determines that a particular portion of the image file  22  may be interpreted as several different strings of text, all the alternate representations or text strings are written to the text file  26 . 
     The control program  70  commands the parser  28  to prepare a list of URLs from the text file  26 . The parser  28  reads the text file  26  and examines each text item within the text file  26 . The parser  28  identifies text in the form of a valid URL or in the form of a canonical Web server domain name. Recognized text is reformatted into one or more syntactically valid URLs that are written to a URL list  30 . Parsing can be carried out, for example, by scanning the text file, compiling character strings into word strings, testing the word strings against a vocabulary of valid items or against templates of valid URL semantics, and building in memory a list of valid items. As an example, a word string can be tested against the URL template described above. Another way to carry out the parsing step is to scan the text file for a valid top level domain identifier, such as “.com,” and then scan the text immediately preceding and following the domain identifier to determine whether it can be combined with the domain identifier to form a valid URL. 
     URL parsing techniques are known in the art. For example, the Eudora electronic mail software program commercially available from Qualcomm, Inc. can scan an email message and recognize text that is in the form of a valid URL. 
     In an alternate embodiment, upon completion of the parsing operation, the system  2  reads each URL in the URL list  30  and attempts to connect to the website identified in the URL through the Internet  50 . This is done by issuing the HTTP GET command, with the URL as an argument. If the domain name of the server included in the URL is not listed in the DNS, or if no server at the URL responds within a pre-determined timeout period (such as 30 seconds), an error condition is raised and the URL is deleted from the URL list  30 . 
     If the HTTP GET command is successful, the home page or initial page of the website identified by the URL is retrieved to a cache memory of the system  2 . Preferably the home page is retrieved in complete form by following all hyperlinks to embedded images in the page and retrieving all graphic images and other non-textual information that is referenced in the page. The system  2  then constructs a website image file  32  by making a bitmapped, scaled-down representation of the complete home page. In one embodiment, the system  2  carries out the step of constructing the image file  32  while the user is engaged in another activity, such as watching television. Use of the website image files  32  is described below. The home pages in the cache are retained in cache memory or, alternatively, written to the data storage devices  172 ,  173  for later retrieval. 
     The step of testing the URLs identified by the system  2  against live websites available through the World Wide Web effectively operates as an additional validity check on the URLs. In this way, use of the OCR and parsing processors is significantly improved. 
     The system  2  then constructs an HTML file  40  having the structure shown in FIG.  3 . The HTML format is used for the HTML file  40  so that the user can later retrieve the HTML file  40  using the browser  3  and conveniently visit a website identified in a URL captured from the video signal. Generally, the HTML file  40  contains: information about the signal that the user was watching when a frame grab was requested; a representation of the current frame; and the URL or URLs located by the OCR processor and the parser in the frame. In the embodiment shown in FIG. 3, the HTML file  40  contains a block of general information  80 , a frame grab  82 , a URL list  84 , and a plurality of Web pages  86   a ,  86   b ,  86   c . The general information  80  comprises the current date and current time at which the frame grab occurred, and the channel or frequency that the user was watching when the frame grab occurred. 
     In an alternate embodiment, while building the HTML file  40 , the system  2  connects to an online TV information server  60  using the Internet  50 . The online TV information server  60  has a searchable database of program information that can be retrieved by channel, date, and time. It provides an automated way to obtain information about any TV program broadcast at any time on any channel in any broadcast market. The system  2  provides the date, time, and channel of the current frame to the online TV information server  60 , and requests the online TV information server  60  to provide any information available in the database about the identified program. The information from the database is displayed as part of the general information  80 . 
     The frame grab  82  of the HTML file  40  is a reproduction of the frame grabbed by the frame grabber  20 . In one embodiment, the frame grab  82  is a hyperlink to a copy of the image file  22 . Thus, when a Web browser program is interpreting the HTML file  40 , the browser follows the frame grab  82  hyperlink, reads the image file  22  at the location identified by the hyperlink, and displays the image file  22  within the Web page defined by the HTML file  40 . In another embodiment, the frame grab  82  is a hyperlink to a copy of the image file  22  that is reduced in size from the original by one half, and the frame grab  82  is an active graphic associated with a hyperlink to a full size copy of the image file  22 . The reduced size image file loads far more quickly when the browser displays the reduced size image file; however, the user can click on the frame grab  82  and the browser will then display the full size copy of the image file  22 . 
     Preferably, to save storage space, the fill-sized copy of the image file  22  is deleted from the data storage device  107  after seven days of storage, and the reduced size copy is deleted after fourteen days. 
     The frame grab  82  is included in the HTML file  40  in order to increase the probability that the user will remember why he or she decided to capture a URL from that image. In this way, when a user displays the HTML file  40  after a significant time has passed, the user will recall that URLs shown in the HTML file  40  are associated with a particular program, product or advertiser. 
     The URL list  84  is a text listing of each URL identified by the parser  28 . Each URL is formatted as a hypertext link before it is inserted into the HTML file  40 . In this way, when a browser displays the HTML file  40 , a user can click on any of the URLs and connect to the website identified by the URL. 
     The HTML file  40  also has a plurality of hypertext links which, when followed by the browser  3 , cause the browser  3  to display Web page images  86   a ,  86   b ,  86   c . Each of the Web page images  86   a ,  86   b ,  86   c  is a display of one of the website image files  32  constructed by the system  2 . As described above, each website image file  32  is constructed by the system by making a bitmapped representation of a page of a website identified by a URL captured from the video signal and stored in a cache memory of the system  2 . In a preferred embodiment, the Web page images  86   a ,  86   b ,  86   c  and their associated website image files  32  are scaled-down representations of the associated website pages. For example, the Web page images  86   a ,  86   b ,  86   c  may represent a website page reduced by 50% from its standard display size. Each of the Web page images  86   a ,  86   b ,  86   c  represents a different URL that was captured from the video signal. Three Web page images  86   a ,  86   b ,  86   c  are shown in FIG. 3, but any number of links to Web page images can be stored in the HTML file  40 . For example, if the parser  28  outputs only one URL for a frame grabbed from the video signal, then only one Web page image  86   a  is displayed as part of the HTML file  40 . 
     In one embodiment, each of the Web page images  86   a ,  86   b ,  86   c  is stored as an active graphic in the HTML file  40 . Active graphic images are associated with a hypertext link. When the browser  3  displays an active graphic, and a user clicks on the active graphic, the browser  3  retrieves the Web page identified by the hypertext link. Each of the Web page images  86   a ,  86   b ,  86   c  is associated in the HTML file  40  with a hypertext link to the website represented by that Web page image, such as a URL captured from the video signal. When the HTML file  40  is displayed to the user in the form shown in FIG. 3, the user can click on one of the Web page images  86   a ,  86   b ,  86   c . In response the browser  3  will follow the associated hypertext link to the website represented by the selected Web page image. 
     Thus, the Web page images  86   a ,  86   b ,  86   c  provide a way for a user to mentally associate a visual representation of a Web page with the URLs recognized from the video signal, and with a frame of the video signal. Also, the user can rapidly display the website associated with the video signal simply by clicking on its representation that is displayed as part of the HTML file  40 . 
     In an alternate embodiment, in addition to or in place of the remote control  16 , the system  2  includes a microphone coupled to a speech recognition processor  19 . The speech recognition processor is coupled to the bus  150  and operates under control of a voice recognition program  72 . The user can command the system  2  to capture information from a signal arriving from the signal source  10  by stating the command to the system  2 . For example, when a desired URL appears on a TV program, the user says “SAVE WEBSITE” to the microphone. The microphone  17  converts the spoken command to an audio signal that is provided to the voice recognition processor  19 . The voice recognition processor  19  and voice recognition program  72  scan the audio signal to recognize spoken words, and write a speech file  13  of recognized words to one of the data storage devices  172 ,  173 . The voice recognition processor  19  then commands the system  2  to read the speech file  13 , e.g., by an interrupt. In response, the system  2  reads the speech file  13  and responds to the command in the manner described above with respect to the remote control  16 . 
     In one embodiment, concurrently with or instead of writing the summary information file or the HTML file, the system  2  writes the retrieved URL to a To-Do List  31 . The To-Do List  31  is an ordered list of network addresses such as URLs that is writable by the system  2  and readable and writable by the browser  3 . Preferably, each list element in the To-Do List  31  comprises the data fields shown in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 To-Do List Format 
               
             
          
           
               
                 Field 
                 Type 
                 Function 
               
               
                   
               
               
                 Network Address Identifier 
                 integer 
                 Array index 
               
               
                 Network Address 
                 string 
                 Web reference object or URL 
               
               
                 Timestamp 
                 date/time 
                 identifies date and time when 
               
               
                   
                   
                 Network Address was first 
               
               
                   
                   
                 written to To-Do List, or date 
               
               
                   
                   
                 and time of last failed 
               
               
                   
                   
                 connection attempt 
               
               
                 Pending flag 
                 Boolean 
                 identifies whether a connection 
               
               
                   
                   
                 to the Web reference object 
               
               
                   
                   
                 identified by the Network 
               
               
                   
                   
                 Address is pending 
               
               
                 User Delay Factor 
                 integer 
                 represents the number of hours 
               
               
                   
                   
                 to wait before re-trying a 
               
               
                   
                   
                 Network Address that is 
               
               
                   
                   
                 Pending 
               
               
                 Attempts 
                 integer 
                 represents the number of 
               
               
                   
                   
                 attempts that have been made to 
               
               
                   
                   
                 connect to the Network Address 
               
               
                   
               
             
          
         
       
     
     In this embodiment, the system  2  provides a way to automatically receive a network address from a source document and store the network address for subsequent use. The URL in a television broadcast signal is an example of a network address in a source document. Subsequent use of the network address is described below. 
     FIG. 4A is a flowchart of one embodiment of a method according to the invention wherein the source document is a television broadcast signal. 
     In step  402 , a signal is received, for example, by receiving a broadcast video signal to a memory continuously in real time. Using a remote signaling device, such as the remote control  16  shown in FIG. 1B, a user signals that information in a current frame of the video signal is to be captured. In response, in step  404  the current frame is converted into an image file. The conversion step can be carried out by digitizing a frame retrieved from a frame buffer  17  that receives the video signal in real time. Alternatively, a frame grabber  20  without a frame buffer can grab a frame from the video signal, digitize the grabbed frame, and write a digital image file representing the grabbed frame. 
     When a frame has been grabbed, in step  406  any text items in the image file are identified. The identification step  406  can be carried out using an OCR processor  24  that reads the image file and writes a text file containing any text strings or characters identified in the image file. 
     When the text file has been written, in step  408  the text file is parsed to identify any references to other information, for example, by identifying URLs or domain names in the text file. The parsing step  408  can be carried out by scanning the text file, compiling character strings into words, testing the words against a vocabulary of valid items or against a template of valid URL semantics, and building in memory a list of valid items. For example, the parsing step  408  can be carried out in the manner described above with respect to the parser  28 . Valid words or URLs identified in the parsing step  408  are written to a list of words or URLs. 
     The words identified in the parsing step  408  are further validated in step  414 . In one embodiment, the validation step  414  is the step of checking that each word or URL represents a valid website. 
     FIG. 4B is a flow chart of one embodiment of a method for carrying out the validation step. 
     In step  422 , a URL is read from the URL list. In step  424 , the system attempts to connect to a Web server at that URL, for example, by opening an HTTP connection and issuing the HTTP GET command with the selected URL as an argument as shown in step  426 . 
     In step  428  the system tests whether the connection was successful. If no website responds, or if the retrieval attempt generates an HTTP error, then in step  428  the system  2  generates an error message and displays it on the display device. Also, in step  440  the requested URL is deleted from the URL list. Next, in step  442  the system tests whether the URL list contains more URLs. If so, control is passed to step  422  and the process is repeated for the next URL. 
     If a page is successfully retrieved from the website, in step  416  the page is stored in a cache memory of the system  2 , and a graphic representation of the page is written to a website image file  32 . This may involve steps  430  to  436  of FIG.  4 B. In step  430 , the home page of the website identified by the selected URL is retrieved, and a local copy of its HTML code is stored. In step  432 , the system follows all hyperlinks in the home page that lead to embedded graphic images. Each image is retrieved and stored locally. When all images are retrieved, the complete page is displayed on the display device. A bitmap image of the complete page is constructed in memory, as shown in step  434 . In step  436 , the bitmap image is written to a website image file in a standard format. 
     When the validation step  414  is complete, in step  410  a summary file is written. As an example, the summary file is an HTML file, and may have the exemplary format shown in FIG.  3 . The summary file contains information about the video signal from which the frame was grabbed, a representation of the frame that was grabbed, and a list of the URLs that were found in the frame. Alternatively, the summary file may also contain a representation of a home page of each website identified by an URL in the list of URLs. 
     In one embodiment, concurrently with or instead of writing the summary information file or the HTML file, in step  411  the retrieved URL is written to a To-Do List. The To-Do List is an ordered list of network addresses such as URLs that is readable and writable by the browser  3 . In this embodiment, the invention provides a way to automatically receive a network address from a source document and store the network address for subsequent use. The URL in a television broadcast signal is an example of a network address in a source document. Subsequent use of the network address is described below. 
     FIG. 4C is a flowchart of an exemplary method for building and writing the HTML file. In step  450 , the system opens the HTML file and writes a header comprising general purpose HTML tags. In step  452 , the date, channel, and time of the program that contained the URL grabbed by the system are written in HTML format to the HTML file. 
     At this point, in an alternate embodiment, additional information about the program is obtained through steps  462  through  470 . In step  462 , the system opens a connection to an online TV program information server (TV server) of the type described above, for example, by opening an HTTP connection to a TV information Web server connected to the Internet. In step  464 , the system submits a database query to the TV server to request any available TV program information. The query may comprise the channel, date, and time. In step  466 , the system receives a response from the TV server containing any available information, such as the program name. In step  467 , this additional information is formatted in HTML form and then written to the HTML file in step  470 . 
     In step  454 , the grabbed frame is written to the summary file. This may be done by storing a copy of the grabbed frame, full size or in a reduced size, and writing a hyperlink identifying the location of the copy into the summary file. In step  456  the list of URLs associated with the grabbed frame is written to the summary file. In step  458  an image of a Web page associated with each of the URLs is written to the summary file. This can be done by writing an HTML hyperlink in the summary file that identifies the location of a copy of the Web page image. In step  460  the system writes any miscellaneous other HTML tags that are needed for proper formatting, and closes the summary file. 
     In a preferred embodiment, in general, the invention integrates a Web browser with a “to-do” list that is automatically constructed by user actions on Web reference objects (URLs). The list is automatically pruned when the user visits the Web reference objects in the list. 
     FIG. 5A is a block diagram of a browser and To-Do List configured according to one embodiment of the invention. As in FIG. 2, the browser  3  runs on top of and under the control of an operating system (OS)  78 . The browser  3  has an Add To List module  500  and a Get From List module  502 . In the preferred embodiment, the Add To List module  500  and Get From List module  502  are computer program segments that are integrated into the browser  3 , for example, by compiling. Alternatively, the modules  500 ,  502  are browser plug-ins. In another alternate embodiment, the modules  500 ,  502  are applets that are downloaded into the end user&#39;s browser  3  from the Web server  62  when the end user uses the browser  3  to connect to the Web server  62  and read a Web page on it. 
     The user&#39;s web browser  3  is coupled to and internally maintains a delayed-intention web-tour list in the form of a To-Do List  31  of network addresses such as web reference objects or URLs. The list is organized as an ordered list. For example, the To Do List is an ordered data structure that can store a collection of text items. In one embodiment, the To Do List is a data structure comprising an array of a pre-determined number of network addresses, and each network address is a string of characters. For example, the To Do List is a C struct that is an array of the elements shown in Table 1. In an alternate embodiment, the To Do List is a linked list of network addresses. 
     In another embodiment, as shown in FIG. 5A, the To Do List  31  is a sequentially ordered text file of fixed-length records  552   a ,  552   b ,  552   c ,  552   n . Each record is a set of the elements shown in Table 1. For clarity, in FIG. 5A only the Network Address element of Table 1 is shown. The designation n in reference numeral  552   n  indicates that the To Do List  31  may store any number n of network addresses. 
     It is preferred that the To Do List is persistently stored in a non-volatile memory device such as the data storage device  107 . 
     Whenever the user comes across a URL that he or she would like to visit later, the user activates an “Add To To-Do List” command, and the URL is added to the end of the list. In one embodiment, as described above, the Add To To-Do List command is activated by pressing a button on the remote control  16  when the user is viewing a broadcast television signal that contains a URL. 
     In another embodiment, the Add To To-Do List is a function of the Add To List module  500  of the browser  3 . In operation, during a network communication session the browser  3  generates a screen display as shown in FIG.  5 B. In conventional manner, the screen display comprises a browser window  501  that displays a Web page  517 . The Web page  517  is an HTML document located on a Web server  62  to which the user is then connected by a network such as the Internet  50 . A URL pane  530  in the browser window  501  displays a URL  536  that identifies the Web page  517 . A portion of the Web page  517  includes a text item  532  that has a hyperlink  534 . When the user positions the cursor  538  on the hyperlink  534 , the URL pane  530  displays a URL that is associated within the Web page  517  with the hyperlink  534  as the URL  536 . 
     The browser  3  also has pull-down menus that display functions of the browser  3 , such as a File function  503 , an Edit function  504 , and a View function  506 . When a user positions the cursor  538  on the File pull-down menu  503  using the mouse  140 , and presses a button on the mouse  140 , a File pull-down menu  510  is displayed over the Web page  517 . The File pull-down menu  510  has conventional commands such as an Open command  512  and a Save command  514 . In this embodiment of the invention, the File pull-down menu  510  also has a Get Page From To-Do List function  516  that is associated with the Get From List module  502 . 
     The user activates the Add To To-Do List command is done by pointing the cursor  538  to a hyperlink  534  and pressing a key that pops up a browser menu providing functions to act on links. In one embodiment, the key is pressed by holding down the right button of the mouse  140 . In response, the browser  3  and the Add To List module  500  display a pull-down menu  520  of special options. In response to pressing the right mouse button, known browser programs provide a pull-down menu that has functions such as the Open In New Window function  522  and the Copy To Clipboard function  524 . In this embodiment of the invention, the pull-down menu  520  further includes an Add To To-Do List function  526 . The Add To To-Do List command is activated by positioning the cursor  538  on the Add To To-Do List function  526  and clicking the left button of the mouse  140 . 
     In still another embodiment, the “Add To To-Do List” is activated when the user speaks a vocal command. The user speaks a pre-determined voice command, such as “Save URL.” The pre-determined voice command is spoken into the microphone  17 . The microphone  17  converts sound waves of the voice command to an electric analog voice signal. The microphone is coupled to a voice recognition processor  19  that converts the analog voice signal to a digital signal. The voice recognition program  72  converts the digital signal to digital command if the digital signal is within a known range associated with the voice command. 
     In response to activation of the Add To To-Do List command, in the preferred embodiment, the system  2  carries out the processing step  606  shown in FIG.  6 A. To provide context, FIG. 6A also shows other processing steps of an embodiment of the invention. 
     In step  602 , a network address, web reference object or URL is received. The web reference object may be received in any of several different ways as described above. For example, the web reference object is received in an email message to a user of the method that identifies a “cool site” that the sender of the email suggests that the user consider visiting. The web reference object also may be encountered when the user is viewing a broadcast signal. As another example, the web reference object is received when it is encountered while the user is reviewing or browsing a page of a web server. 
     In step  604 , the user activates an Add To To-Do List command of the browser. The activation step may be carried out in several different ways as described above. 
     In step  606  the designated network address or URL is written to the To Do List. In one embodiment, the display interface  125  has a local memory called a display buffer that stores an array of the characters that are displayed on the display  120 . In step  606 , the system copies the URL at which the cursor is positioned from the display buffer to a temporary storage area, such as a local variable. 
     In an alternative embodiment, step  606  also includes the step of parsing the URL at which the cursor is positioned to verify that it is a valid web reference object. 
     The URL is then written or appended to the To Do List  31 . Preferably, step  606  includes the step of writing the To-Do List to the data storage device  107 . 
     In this way, a network address is selected during a network communication session and is added to a list. 
     At some subsequent time, the user activates the Get Page From To-Do List command as shown in step  608 . In the preferred embodiment, the user executes the browser  3  and positions the cursor  538  over the File function  503  and the Get Page From To-Do List command  516  of the File pull-down menu  520 . In response, the browser  3  and the Get From List module  520  carry out the steps shown in FIGS. 6A to  6 C. 
     Preferably, when the To-Do List is empty, the Get Page From To-Do List command is not available. For example, when the user positions the cursor over the File pull-down menu  520 , the Get From List module  520  checks whether the To-Do List is empty. If so, the browser  3  displays the Get Page From To-Do List command  516  in a grayed-out format. 
     FIG. 6A illustrates steps in a process carried out immediately after a network address is added to the To Do List  31 , or carried out at some later time when the user wishes to visit one or all of the network addresses in the To Do List  31 . In general, according to one embodiment of the invention, when the user activates the “Get Page From To-Do List” command, in response, the browser reads the next URL from the To-Do List, and attempts to establish an HTTP connection to the website or page described by the URL and retrieve the page. If the URL is retrieved successfully, the browser deletes the URL from the To Do List. If the URL is not successfully retrieved, then the browser attempts to retrieve the next URL on the list. If no pages in the To Do List can be retrieved, then the browser displays an error message to the user. 
     If a URL cannot be retrieved successfully in three attempts, after the third failed attempt the browser marks the URL as Pending, and makes no further attempt to retrieve the URL for a pre-determined time interval, such as 24 hours. The next time the system attempts to retrieve the URL, that is, after the pre-determined time interval, if retrieval is still unsuccessful, an error message is displayed to the user and the user is prompted to take one of two actions. The user may choose to remove the URL from the To Do List. Alternatively, the user may choose to keep the URL on the To Do List and attempt retrieval again after a time interval defined by the user. 
     In the embodiment shown in FIG. 6A, in response to activation of the Get Page From To-Do List command, the browser opens the To-Do List  31  as shown in step  609 . This is done by opening a disk file that contains the To-Do List  31  or by copying the To-Do List data structure to local memory. In step  610  the To Do List  31  is tested to determine whether it is empty. If the To-Do List is empty, then there are no web reference objects to retrieve, so the method concludes as shown in step  612 . 
     If the To-Do List is not empty, then in step  616  the next web reference object in the To-Do List is read from the To-Do List. 
     In step  618 , the web reference object is tested to determine whether it is marked Pending. The process uses a Pending mark to identify web reference objects for which a connection has been attempted previously without success. If the web reference object is marked Pending, then in step  620  the current system time is tested to determine whether a predetermined period of time has elapsed, such as a day or 24 hours. This is done by comparing the current system time with a timestamp associated with the web reference object. If the pre-determined time has not elapsed, then in step  622  a user-set time factor associated with the web reference object is tested to determine whether it has expired. If not, then control returns to step  616 . If so, or if the test of step  620  is affirmative, then in step  624  an attempt is made to retrieve the Web page or other object that is identified by the current web reference object or network address. 
     The logical order of steps  620  and  622  is not critical. These steps may be carried out in inverse order or concurrently. 
     In step  624 , an HTTP connection is opened to the Website or Web page identified by the current network address in the To-Do List, and an attempt is made to retrieve the home page at the network address. For example, the HTTP GET command is issued with the network address as an argument. In step  626 , an Attempts counter variable associated with the network address is incremented. 
     In step  628 , the status of the HTTP connection is tested to determine whether the connection was successful or failed. If the GET command results in an error condition, for example, when the requested Website fails to answer or returns an error message indicating that the requested Web page does not exist, then the connection attempt is a failure and control is passed to step  630 . In step  630 , the Pending flag is tested to determine whether the current web reference object is already marked Pending. If the web reference object is not marked Pending, then in step  632  the Attempts variable is tested to determine whether three failed attempts to connect to the Website identified by the web reference object have occurred. If three failed attempts have occurred, then in step  634  the Pending flag for the current web reference object is set in the To-Do List. 
     If fewer than three failed attempts have occurred, then control is passed to step  624  so that another attempt to connect can be made. More or less than three connection attempts can be carried out in this way. The number three has been selected as an example but it is not a critical value. 
     If the test of step  630  is true, that is, if a failed connection attempt has occurred and the web reference object is already marked pending, in step  636  an error message is displayed by the browser  3 , and the user is presented with two options as indicated by the parallel paths leading from step  636  in FIG.  6 C. 
     The user may choose to keep the current web reference object in the To-Do List, as indicated by step  638 . In that case, in step  642  the user is prompted to enter a user-defined time factor in hours, after which another attempt to connect to the web reference object will be made. In the preferred embodiment, the default value of the user-defined time factor is  24  hours, and the user may enter any other positive integer value. The value entered by the user is stored in association with the current web reference object in the To-Do List. 
     Alternatively, as shown in step  640 , the user may choose to remove the current web reference object from the To-Do List. If the user selects that option, in step  644  the current web reference object is deleted from the To-Do List. Control returns to step  616  so that the next web reference object can be visited. 
     If the test of step  628  is negative, that is, if a successful connection is made to the current web reference object, in step  646  the current web reference object is deleted from the To-Do List. In this way, the To-Do List is automatically pruned as the user visits Websites identified by the entries in the To-Do List. In step  648 , the process is done. The term “done” in step  648  refers to completion of processing of the To-Do List. In the preferred embodiment, in step  648  control is returned to the browser  3  so that the Website identified by the current web reference object can be displayed and browsed in conventional manner. 
     While certain embodiments described herein are described with respect to identifying URLs in a video signal, the invention encompasses and is equally applicable to capturing other information from other types of signals. For example, the invention can be used to capture spoken information in a radio signal by substituting appropriate voice recognition equipment for the frame grabber and frame buffer. 
     Also, while this description has referred to advertisements as an exemplary signal containing information to be captured, the information to be captured can appear in any portion of the video signal, such as a news program, entertainment program, or other program type. 
     In addition, while certain embodiments have been described in terms of URLs, the term “network address” is intended to refer broadly to any type of hypertext link or other reference in a source document to another network location or document. The term “web reference object” is intended to refer broadly to any type of document or site accessible over a network such as the World Wide Web. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.