Patent Publication Number: US-6986459-B2

Title: System for providing a document associated with a video signal

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present application is a continuation of U.S. application Ser. No. 09/609,139 filed Jun. 30, 2000, now issued as U.S. Pat. No. 6,824,044, the entire contents of which are herein incorporated by reference. 

   FIELD OF INVENTION 
   The present invention relates generally to methods, systems and apparatus for interacting with computers. More particularly, the invention relates to obtaining a document related to content of a video signal, utilizing such methods, systems and apparatus. 
   The invention has been developed primarily to allow a large number of distributed users to interact with networked information via printed matter and optical sensors, thereby to obtain interactive printed matter on demand via high-speed networked color printers. Although the invention will largely be described herein with reference to this use, it will be appreciated that the invention is not limited to use in this field. 
   CO-PENDING APPLICATIONS 
   Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications/granted patents filed by the applicant or assignee of the present invention simultaneously with the present application: 
   
     
       
         
             
             
             
             
             
           
             
                 
             
           
          
             
               09/609,139, 
               9/608,970, 
               6,678,499, 
               6,679,420, 
               09/663,599, 
             
             
               09/607,852, 
               09/607,656, 
               6,766,942, 
               09/663,701, 
               6,720,985, 
             
             
               09/609,303, 
               09/610,095, 
               9/609,596, 
               09/693,705, 
               9/607,843, 
             
             
               09/607,605, 
               9/608,178, 
               9/609,553, 
               09/609,233, 
               9/609,149, 
             
             
               09/608,022, 
               09/609,232, 
               9/607,844, 
               6,457,883, 
               9/608,920, 
             
             
               09/607,985, 
               6,398,332, 
               6,394,573, 
               6,622,923 
             
             
                 
             
          
         
       
     
   
   The disclosures of these co-pending applications are incorporated herein by cross-reference. 
   Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications/granted patents filed by the applicant or assignee of the present invention on 23 May 2000: 
   
     
       
         
             
             
             
             
             
           
             
                 
                 
             
           
          
             
                 
               09/575,197, 
               09/575,195, 
               09/575,159, 
               09/575,132, 
             
             
                 
               09/575,123, 
               09/575,148, 
               09/575,130, 
               09/575,165, 
             
             
                 
               09/575,153, 
               09/575,118, 
               09/575,131, 
               09/575,116, 
             
             
                 
               09/575,144, 
               09/575,139, 
               09/575,186, 
               6,681,045, 
             
             
                 
               6,728,000, 
               09/575,145, 
               09/575,192, 
               09/575,181, 
             
             
                 
               09/575,193, 
               09/575,156, 
               09/575,183, 
               09/575,160, 
             
             
                 
               09/575,150, 
               09/575,169, 
               6,644,642, 
               6,502,614, 
             
             
                 
               6,622,999, 
               6,669,385, 
               6,549,935, 
               09/575,187, 
             
             
                 
               6,727,996, 
               6,591,884, 
               6,439,706, 
               6,760,119, 
             
             
                 
               09/575,198, 
               6,290,349, 
               6,428,155, 
               09/575,146, 
             
             
                 
               09/575,174, 
               09/575,163, 
               6,737,591, 
               09/575,154, 
             
             
                 
               09/575,129, 
               09/575,124, 
               09/575,188 
               09/575,189, 
             
             
                 
               09/575,162, 
               09/575,172, 
               09/575,170, 
               09/575,171, 
             
             
                 
               09/575,161, 
               6,428,133, 
               6,526,658, 
               6,315,399, 
             
             
                 
               6,338,548, 
               6,540,319, 
               6,328,431, 
               6,328,425, 
             
             
                 
               09/575,127, 
               6,383,833, 
               6,464,332, 
               6,390,591, 
             
             
                 
               09/575,152, 
               6,328,417, 
               6,409,323, 
               6,281,912, 
             
             
                 
               6,604,810, 
               6,318,920, 
               6,488,422, 
               09/575,108, 
             
             
                 
               09/575,109, 
               09/575,110 
             
             
                 
                 
             
          
         
       
     
   
   The disclosures of these co-pending applications are incorporated herein by cross-reference. 
   BACKGROUND 
   Infotainment programs on television often provide associated informational material to viewers. This information is usually posted or faxed to the viewer on request, or is available in an associated print publication. Increasingly this information is being made available over the Internet on the program&#39;s associated Web site. 
   SUMMARY OF INVENTION 
   According to a first aspect, the present invention provides a method of obtaining a document associated with a video signal using a computer system, a sensing device and coded data on a surface, wherein: 
   the sensing device is operable to sense the coded data and generate indicating data indicative of a request for the document; and, 
   the computer system is operable to extract document identity data identifying the document from the video signal; 
   the method comprising the steps of: 
   placing the sensing device in an operative position relative to the surface for generating the indicating data using at least some of the coded data; 
   providing the computer system with the indicating data for extracting the document identity data; 
   identifying the document; and
         retrieving the document.       

   Preferably, the method includes the further step displaying the document. 
   Preferably, the method includes the further step of printing the document. 
   Preferably, the video signal is derived from at least one video playback device. 
   Preferably, the playback device is a cassette-based video player or a disk-based video player. 
   Preferably, the video signal is derived from at least one video transmission. 
   Preferably, the video transmission is a broadcast television transmission, a cable television transmission, a satellite television transmission, or an Internet video transmission. 
   Preferably, the video signal has an analogue format. 
   Preferably, the video signal has a digital format. 
   Preferably, the coded data is indicative of an identity of a region of the surface and of a plurality of reference points of the region, and the indicating data is indicative of the identity of the region and a position of the sensing device relative to the region. 
   Preferably, the document identity data is extracted from at least one data channel of the video signal. 
   Preferably, the data channel is a caption data channel, a text data channel, or an extended data channel. 
   Preferably, the method includes the further steps of: 
   receiving, from the sensing device, user identity data indicative of an identity of the user; 
   identifying, using the user identity data, a user profile; and 
   customizing, using the user profile, the document. 
   Preferably, the coded data is substantially invisible to the unaided human eye. 
   According to a second aspect, the invention provides a system for enabling a user to obtain a document associated with a video signal, the system comprising: 
   a surface with coded data disposed on it; 
   a sensing device operable to sense at least some of the coded data and generate indicating data indicative of a request for the document when placed in an operative position relative to the surface; 
   a receiver for receiving the indicating data from the sensing device; 
   a decoder for extracting document identity data indicative of an identity of the document, from the video signal; and 
   a processing means operable to identify and retrieve the document. 
   Preferably, the system includes a display device for displaying the document. 
   Preferably, the system includes a printer for printing the document. 
   According to a third aspect, the invention provides a printer for printing a document associated with a video signal, the printer comprising: 
   a receiver for receiving indicating data indicative of a request for the document; 
   a decoder for extracting document identity data indicative of an identity of the document from the video signal; 
   a network interface; and 
   a processor for transmitting the indicating data and the document identity data to a server and via the network interface, and receiving the document from the server via the network interface; and
         a printhead for printing the document.       

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Preferred and other embodiments of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic of a the relationship between a sample printed netpage and its online page description; 
       FIG. 2  is a schematic view of a interaction between a netpage pen, a netpage printer, a netpage page server, and a netpage application server; 
       FIG. 3  illustrates a collection of netpage servers and printers interconnected via a network; 
       FIG. 4  is a schematic view of a high-level structure of a printed netpage and its online page description; 
       FIG. 5  is a plan view showing a structure of a netpage tag; 
       FIG. 6  is a plan view showing a relationship between a set of the tags shown in  FIG. 5  and a field of view of a netpage sensing device in the form of a netpage pen; 
       FIG. 7  is a flowchart of a tag image processing and decoding algorithm; 
       FIG. 8  is a perspective view of a netpage pen and its associated tag-sensing field-of-view cone; 
       FIG. 9  is a perspective exploded view of the netpage pen shown in  FIG. 8 ; 
       FIG. 10  is a schematic block diagram of a pen controller for the netpage pen shown in  FIGS. 8 and 9 ; 
       FIG. 11  is a perspective view of a wall-mounted netpage printer; 
       FIG. 12  is a section through the length of the netpage printer of  FIG. 11 ; 
       FIG. 12   a  is an enlarged portion of  FIG. 12  showing a section of the duplexed print engines and glue wheel assembly; 
       FIG. 13  is a detailed view of the ink cartridge, ink, air and glue paths, and print engines of the netpage printer of  FIGS. 11 and 12 ; 
       FIG. 14  is a schematic block diagram of a printer controller for the netpage printer shown in  FIGS. 11 and 12 ; 
       FIG. 15  is a schematic block diagram of duplexed print engine controllers and Memjet™ printheads associated with the printer controller shown in  FIG. 14 ; 
       FIG. 16  is a schematic block diagram of the print engine controller shown in  FIGS. 14 and 15 ; 
       FIG. 17  is a perspective view of a single Memjet™ printing element, as used in, for example, the netpage printer of  FIGS. 10 to 12 ; 
       FIG. 18  is a perspective view of a small part of an array of Memjet™ printing elements; 
       FIG. 19  is a series of perspective views illustrating the operating cycle of the Memjet™ printing element shown in  FIG. 13 ; 
       FIG. 20  is a perspective view of a short segment of a pagewidth Memjet™ printhead; 
       FIG. 21  is a schematic view of a user class diagram; 
       FIG. 22  is a schematic view of a printer class diagram; 
       FIG. 23  is a schematic view of a pen class diagram; 
       FIG. 24  is a schematic view of an application class diagram; 
       FIG. 25  is a schematic view of a document and page description class diagram; 
       FIG. 26  is a schematic view of a document and page ownership class diagram; 
       FIG. 27  is a schematic view of a terminal element specialization class diagram; 
       FIG. 28  is a schematic view of a static element specialization class diagram; 
       FIG. 29  is a schematic view of a hyperlink element class diagram; 
       FIG. 30  is a schematic view of a hyperlink element specialization class diagram; 
       FIG. 31  is a schematic view of a hyperlinked group class diagram; 
       FIG. 32  is a schematic view of a form class diagram; 
       FIG. 33  is a schematic view of a digital ink class diagram; 
       FIG. 34  is a schematic view of a field element specialization class diagram; 
       FIG. 35  is a schematic view of a checkbox field class diagram; 
       FIG. 36  is a schematic view of a text field class diagram; 
       FIG. 37  is a schematic view of a signature field class diagram; 
       FIG. 38  is a flowchart of an input processing algorithm; 
       FIG. 38   a  is a detailed flowchart of one step of the flowchart of  FIG. 38 ; 
       FIG. 39  is a schematic view of a page server command element class diagram; 
       FIG. 40  is a schematic view of a subscription delivery protocol; 
       FIG. 41  is a schematic view of a hyperlink request class diagram; 
       FIG. 42  is a schematic view of a hyperlink activation protocol; 
       FIG. 43  is a schematic view of a form submission protocol; 
       FIG. 44  is a schematic block diagram of a netpage printer with a closed caption decoder; 
       FIG. 45  is a schematic block diagram of a television with a closed caption decoder; 
       FIG. 46  is a schematic block diagram of a netpage printer controller with a closed caption decoder; 
       FIG. 47  is a schematic view of a program information hyperlink class diagram; and 
       FIG. 48  is a schematic view of a television related document class diagram. 
   

   DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS 
   Note: Memjet™ is a trade mark of Silverbrook Research Pty Ltd, Australia. 
   In the preferred embodiment, the invention is configured to work with the netpage networked computer system, a detailed overview of which follows. It will be appreciated that not every implementation will necessarily embody all or even most of the specific details and extensions discussed below in relation to the basic system. However, the system is described in its most complete form to reduce the need for external reference when attempting to understand the context in which the preferred embodiments and aspects of the present invention operate. 
   In brief summary, the preferred form of the netpage system employs a computer interface in the form of a mapped surface, that is, a physical surface which contains references to a map of the surface maintained in a computer system. The map references can be queried by an appropriate sensing device. Depending upon the specific implementation, the map references may be encoded visibly or invisibly, and defined in such a way that a local query on the mapped surface yields an unambiguous map reference both within the map and among different maps. The computer system can contain information about features on the mapped surface, and such information can be retrieved based on map references supplied by a sensing device used with the mapped surface. The information thus retrieved can take the form of actions which are initiated by the computer system on behalf of the operator in response to the operator&#39;s interaction with the surface features. 
   In its preferred form, the netpage system relies on the production of, and human interaction with, netpages. These are pages of text, graphics and images printed on ordinary paper, but which work like interactive web pages. Information is encoded on each page using ink which is substantially invisible to the unaided human eye. The ink, however, and thereby the coded data, can be sensed by an optically imaging pen and transmitted to the netpage system. 
   In the preferred form, active buttons and hyperlinks on each page can be clicked with the pen to request information from the network or to signal preferences to a network server. In one embodiment, text written by hand on a netpage is automatically recognized and converted to computer text in the netpage system, allowing forms to be filled in. In other embodiments, signatures recorded on a netpage are automatically verified, allowing e-commerce transactions to be securely authorized. 
   As illustrated in  FIG. 1 , a printed netpage  1  can represent a interactive form which can be filled in by the user both physically, on the printed page, and “electronically”, via communication between the pen and the netpage system. The example shows a “Request” form containing name and address fields and a submit button. The netpage consists of graphic data  2  printed using visible ink, and coded data  3  printed as a collection of tags  4  using invisible ink. The corresponding page description  5 , stored on the netpage network, describes the individual elements of the netpage. In particular it describes the type and spatial extent (zone) of each interactive element (i.e. text field or button in the example), to allow the netpage system to correctly interpret input via the netpage. The submit button  6 , for example, has a zone  7  which corresponds to the spatial extent of the corresponding graphic  8 . 
   As illustrated in  FIG. 2 , the netpage pen  101 , a preferred form of which is shown in  FIGS. 8 and 9  and described in more detail below, works in conjunction with a netpage printer  601 , an Internet-connected printing appliance for home, office or mobile use. The pen is wireless and communicates securely with the netpage printer via a short-range radio link  9 . 
   The netpage printer  601 , a preferred form of which is shown in  FIGS. 11 to 13  and described in more detail below, is able to deliver, periodically or on demand, personalized newspapers, magazines, catalogs, brochures and other publications, all printed at high quality as interactive netpages. Unlike a personal computer, the netpage printer is an appliance which can be, for example, wall-mounted adjacent to an area where the morning news is first consumed, such as in a user&#39;s kitchen, near a breakfast table, or near the household&#39;s point of departure for the day. It also comes in tabletop, desktop, portable and miniature versions. 
   Netpages printed at their point of consumption combine the ease-of-use of paper with the timeliness and interactivity of an interactive medium. 
   As shown in  FIG. 2 , the netpage pen  101  interacts with the coded data on a printed netpage  1  and communicates, via a short-range radio link  9 , the interaction to a netpage printer. The printer  601  sends the interaction to the relevant netpage page server  10  for interpretation. In appropriate circumstances, the page server sends a corresponding message to application computer software running on a netpage application server  13 . The application server may in turn send a response which is printed on the originating printer. 
   The netpage system is made considerably more convenient in the preferred embodiment by being used in conjunction with high-speed microelectromechanical system (MEMS) based inkjet (Memjet™) printers. In the preferred form of this technology, relatively high-speed and high-quality printing is made more affordable to consumers. In its preferred form, a netpage publication has the physical characteristics of a traditional newsmagazine, such as a set of letter-size glossy pages printed in full color on both sides, bound together for easy navigation and comfortable handling. 
   The netpage printer exploits the growing availability of broadband Internet access. Cable service is available to 95% of households in the United States, and cable modem service offering broadband Internet access is already available to 20% of these. The netpage printer can also operate with slower connections, but with longer delivery times and lower image quality. Indeed, the netpage system can be enabled using existing consumer inkjet and laser printers, although the system will operate more slowly and will therefore be less acceptable from a consumer&#39;s point of view. In other embodiments, the netpage system is hosted on a private intranet. In still other embodiments, the netpage system is hosted on a single computer or computer-enabled device, such as a printer. 
   Netpage publication servers  14  on the netpage network are configured to deliver print-quality publications to netpage printers. Periodical publications are delivered automatically to subscribing netpage printers via pointcasting and multicasting Internet protocols. Personalized publications are filtered and formatted according to individual user profiles. 
   A netpage printer can be configured to support any number of pens, and a pen can work with any number of netpage printers. In the preferred implementation, each netpage pen has a unique identifier. A household may have a collection of colored netpage pens, one assigned to each member of the family. This allows each user to maintain a distinct profile with respect to a netpage publication server or application server. 
   A netpage pen can also be registered with a netpage registration server  11  and linked to one or more payment card accounts. This allows e-commerce payments to be securely authorized using the netpage pen. The netpage registration server compares the signature captured by the netpage pen with a previously registered signature, allowing it to authenticate the user&#39;s identity to an e-commerce server. Other biometrics can also be used to verify identity. A version of the netpage pen includes fingerprint scanning, verified in a similar way by the netpage registration server. 
   Although a netpage printer may deliver periodicals such as the morning newspaper without user intervention, it can be configured never to deliver unsolicited junk mail. In its preferred form, it only delivers periodicals from subscribed or otherwise authorized sources. In this respect, the netpage printer is unlike a fax machine or e-mail account which is visible to any junk mailer who knows the telephone number or email address. 
   1 Netpage System Architecture 
   Each object model in the system is described using a Unified Modeling Language (UML) class diagram. A class diagram consists of a set of object classes connected by relationships, and two kinds of relationships are of interest here: associations and generalizations. An association represents some kind of relationship between objects, i.e. between instances of classes. A generalization relates actual classes, and can be understood in the following way: if a class is thought of as the set of all objects of that class, and class A is a generalization of class B, then B is simply a subset of A. The UML does not directly support second-order modelling—i.e. classes of classes. 
   Each class is drawn as a rectangle labelled with the name of the class. It contains a list of the attributes of the class, separated from the name by a horizontal line, and a list of the operations of the class, separated from the attribute list by a horizontal line. In the class diagrams which follow, however, operations are never modelled. 
   An association is drawn as a line joining two classes, optionally labelled at either end with the multiplicity of the association. The default multiplicity is one. An asterisk (*) indicates a multiplicity of “many”, i.e. zero or more. Each association is optionally labelled with its name, and is also optionally labelled at either end with the role of the corresponding class. An open diamond indicates an aggregation association (“is-part-of”), and is drawn at the aggregator end of the association line. 
   A generalization relationship (“is-a”) is drawn as a solid line joining two classes, with an arrow (in the form of an open triangle) at the generalization end. 
   When a class diagram is broken up into multiple diagrams, any class which is duplicated is shown with a dashed outline in all but the main diagram which defines it. It is shown with attributes only where it is defined. 
   1.1 Netpages 
   Netpages are the foundation on which a netpage network is built. They provide a paper-based user interface to published information and interactive services. 
   A netpage consists of a printed page (or other surface region) invisibly tagged with references to an online description of the page. The online page description is maintained persistently by a netpage page server. The page description describes the visible layout and content of the page, including text, graphics and images. It also describes the input elements on the page, including buttons, hyperlinks, and input fields. A netpage allows markings made with a netpage pen on its surface to be simultaneously captured and processed by the netpage system. 
   Multiple netpages can share the same page description. However, to allow input through otherwise identical pages to be distinguished, each netpage is assigned a unique page identifier. This page ID has sufficient precision to distinguish between a very large number of netpages. 
   Each reference to the page description is encoded in a printed tag. The tag identifies the unique page on which it appears, and thereby-indirectly identifies the page description. The tag also identifies its own position on the page. Characteristics of the tags are described in more detail below. 
   Tags are printed in infrared-absorptive ink on any substrate which is infrared-reflective, such as ordinary paper. Near-infrared wavelengths are invisible to the human eye but are easily sensed by a solid-state image sensor with an appropriate filter. 
   A tag is sensed by an area image sensor in the netpage pen, and the tag data is transmitted to the netpage system via the nearest netpage printer. The pen is wireless and communicates with the netpage printer via a short-range radio link. Tags are sufficiently small and densely arranged that the pen can reliably image at least one tag even on a single click on the page. It is important that the pen recognize the page ID and position on every interaction with the page, since the interaction is stateless. Tags are error-correctably encoded to make them partially tolerant to surface damage. 
   The netpage page server maintains a unique page instance for each printed netpage, allowing it to maintain a distinct set of user-supplied values for input fields in the page description for each printed netpage. 
   The relationship between the page description, the page instance, and the printed netpage is shown in  FIG. 4 . The printed netpage may be part of a printed netpage document  45 . The page instance is associated with both the netpage printer which printed it and, if known, the netpage user who requested it. 
   1.2 Netpage Tags 
   1.2.1 Tag Data Content 
   In a preferred form, each tag identifies the region in which it appears, and the location of that tag within the region. A tag may also contain flags which relate to the region as a whole or to the tag. One or more flag bits may, for example, signal a tag sensing device to provide feedback indicative of a function associated with the immediate area of the tag, without the sensing device having to refer to a description of the region. A netpage pen may, for example, illuminate an “active area” LED when in the zone of a hyperlink. 
   As will be more clearly explained below, in a preferred embodiment, each tag contains an easily recognized invariant structure which aids initial detection, and which assists in minimizing the effect of any warp induced by the surface or by the sensing process. The tags preferably tile the entire page, and are sufficiently small and densely arranged that the pen can reliably image at least one tag even on a single click on the page. It is important that the pen recognize the page ID and position on every interaction with the page, since the interaction is stateless. 
   In a preferred embodiment, the region to which a tag refers coincides with an entire page, and the region ID encoded in the tag is therefore synonymous with the page ID of the page on which the tag appears. In other embodiments, the region to which a tag refers can be an arbitrary subregion of a page or other surface. For example, it can coincide with the zone of an interactive element, in which case the region ID can directly identify the interactive element. 
   
     
       
         
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               Tag data 
             
          
         
         
             
             
             
          
             
                 
               Field 
               Precision (bits) 
             
             
                 
                 
             
             
                 
               Region ID 
               100 
             
             
                 
               Tag ID 
                16 
             
             
                 
               Flags 
                4 
             
             
                 
               Total 
               120 
             
             
                 
                 
             
          
         
       
     
   
   Each tag contains 120 bits of information, typically allocated as shown in Table 1. Assuming a maximum tag density of 64 per square inch, a 16-bit tag ID supports a region size of up to 1024 square inches. Larger regions can be mapped continuously without increasing the tag ID precision simply by using abutting regions and maps. The 100-bit region ID allows 2 100  (˜10 30  or a million trillion trillion) different regions to be uniquely identified. 
   1.2.2 Tag Data Encoding 
   The 120 bits of tag data are redundantly encoded using a (15, 5) Reed-Solomon code. This yields 360 encoded bits consisting of 6 codewords of 15 4-bit symbols each. The (15, 5) code allows up to 5 symbol errors to be corrected per codeword, i.e. it is tolerant of a symbol error rate of up to 33% per codeword. 
   Each 4-bit symbol is represented in a spatially coherent way in the tag, and the symbols of the six codewords are interleaved spatially within the tag. This ensures that a burst error (an error affecting multiple spatially adjacent bits) damages a minimum number of symbols overall and a minimum number of symbols in any one codeword, thus maximising the likelihood that the burst error can be fully corrected. 
   1.2.3 Physical Tag Structure 
   The physical representation of the tag, shown in  FIG. 5 , includes fixed target structures  15 ,  16 ,  17  and variable data areas  18 . The fixed target structures allow a sensing device such as the netpage pen to detect the tag and infer its three-dimensional orientation relative to the sensor. The data areas contain representations of the individual bits of the encoded tag data. 
   To achieve proper tag reproduction, the tag is rendered at a resolution of 256×256 dots. When printed at 1600 dots per inch this yields a tag with a diameter of about 4 mm. At this resolution the tag is designed to be surrounded by a “quiet area” of radius 16 dots. Since the quiet area is also contributed by adjacent tags, it only adds 16 dots to the effective diameter of the tag. 
   The tag includes six target structures. A detection ring  15  allows the sensing device to initially detect the tag. The ring is easy to detect because it is rotationally invariant and because a simple correction of its aspect ratio removes most of the effects of perspective distortion. An orientation axis  16  allows the sensing device to determine the approximate planar orientation of the tag due to the yaw of the sensor. The orientation axis is skewed to yield a unique orientation. Four perspective targets  17  allow the sensing device to infer an accurate two-dimensional perspective transform of the tag and hence an accurate three-dimensional position and orientation of the tag relative to the sensor. 
   All target structures are redundantly large to improve their immunity to noise. 
   The overall tag shape is circular. This supports, amongst other things, optimal tag packing on an irregular triangular grid. In combination with the circular detection ring, this makes a circular arrangement of data bits within the tag optimal. To maximise its size, each data bit is represented by a radial wedge in the form of an area bounded by two radial lines and two concentric circular arcs. Each wedge has a minimum dimension of 8 dots at 1600 dpi and is designed so that its base (its inner arc), is at least equal to this minimum dimension. The height of the wedge in the radial direction is always equal to the minimum dimension. Each 4-bit data symbol is represented by an array of 2×2 wedges. 
   The 15 4-bit data symbols of each of the six codewords are allocated to the four concentric symbol rings  18   a  to  18   d  in interleaved fashion. Symbols are allocated alternately in circular progression around the tag. 
   The interleaving is designed to maximise the average spatial distance between any two symbols of the same codeword. 
   In order to support “single-click” interaction with a tagged region via a sensing device, the sensing device must be able to see at least one entire tag in its field of view no matter where in the region or at what orientation it is positioned. The required diameter of the field of view of the sensing device is therefore a function of the size and spacing of the tags. 
   Assuming a circular tag shape, the minimum diameter of the sensor field of view is obtained when the tags are tiled on a equilateral triangular grid, as shown in  FIG. 6 . 
   1.2.4 Tag Image Processing and Decoding 
   The tag image processing and decoding performed by a sensing device such as the netpage pen is shown in  FIG. 7 . While a captured image is being acquired from the image sensor, the dynamic range of the image is determined (at  20 ). The center of the range is then chosen as the binary threshold for the image  21 . The image is then thresholded and segmented into connected pixel regions (i.e. shapes  23 ) (at  22 ). Shapes which are too small to represent tag target structures are discarded. The size and centroid of each shape is also computed. 
   Binary shape moments  25  are then computed (at  24 ) for each shape, and these provide the basis for subsequently locating target structures. Central shape moments are by their nature invariant of position, and can be easily made invariant of scale, aspect ratio and rotation. 
   The ring target structure  15  is the first to be located (at  26 ). A ring has the advantage of being very well behaved when perspective-distorted. Matching proceeds by aspect-normalizing and rotation-normalizing each shape&#39;s moments. Once its second-order moments are normalized the ring is easy to recognize even if the perspective distortion was significant. The ring&#39;s original aspect and rotation  27  together provide a useful approximation of the perspective transform. 
   The axis target structure  16  is the next to be located (at  28 ). Matching proceeds by applying the ring&#39;s normalizations to each shape&#39;s moments, and rotation-normalizing the resulting moments. Once its second-order moments are normalized the axis target is easily recognized. Note that one third order moment is required to disambiguate the two possible orientations of the axis. The shape is deliberately skewed to one side to make this possible. Note also that it is only possible to rotation-normalize the axis target after it has had the ring&#39;s normalizations applied, since the perspective distortion can hide the axis target&#39;s axis. The axis target&#39;s original rotation provides a useful approximation of the tag&#39;s rotation due to pen yaw  29 . 
   The four perspective target structures  17  are the last to be located (at  30 ). Good estimates of their positions are computed based on their known spatial relationships to the ring and axis targets, the aspect and rotation of the ring, and the rotation of the axis. Matching proceeds by applying the ring&#39;s normalizations to each shape&#39;s moments. Once their second-order moments are normalized the circular perspective targets are easy to recognize, and the target closest to each estimated position is taken as a match. The original centroids of the four perspective targets are then taken to be the perspective-distorted corners  31  of a square of known size in tag space, and an eight-degree-of-freedom perspective transform  33  is inferred (at  32 ) based on solving the well-understood equations relating the four tag-space and image-space point pairs (see Heckbert, P., Fundamentals of Texture Mapping and Image Warping, Masters Thesis, Dept. of EECS, U. of California at Berkeley, Technical Report No. UCB/CSD 89/516, June 1989, the contents of which are herein incorporated by cross-reference). 
   The inferred tag-space to image-space perspective transform is used to project (at  36 ) each known data bit position in tag space into image space where the real-valued position is used to bilinearly interpolate (at  36 ) the four relevant adjacent pixels in the input image. The previously computed image threshold  21  is used to threshold the result to produce the final bit value  37 . 
   Once all 360 data bits  37  have been obtained in this way, each of the six 60-bit Reed-Solomon codewords is decoded (at  38 ) to yield 20 decoded bits  39 , or 120 decoded bits in total. Note that the codeword symbols are sampled in codeword order, so that codewords are implicitly de-interleaved during the sampling process. 
   The ring target  15  is only sought in a subarea of the image whose relationship to the image guarantees that the ring, if found, is part of a complete tag. If a complete tag is not found and successfully decoded, then no pen position is recorded for the current frame. Given adequate processing power and ideally a non-minimal field of view  193 , an alternative strategy involves seeking another tag in the current image. 
   The obtained tag data indicates the identity of the region containing the tag and the position of the tag within the region. An accurate position  35  of the pen nib in the region, as well as the overall orientation  35  of the pen, is then inferred (at  34 ) from the perspective transform  33  observed on the tag and the known spatial relationship between the pen&#39;s physical axis and the pen&#39;s optical axis. 
   1.2.5 Tag Map 
   Decoding a tag results in a region ID, a tag ID, and a tag-relative pen transform. Before the tag ID and the tag-relative pen location can be translated into an absolute location within the tagged region, the location of the tag within the region must be known. This is given by a tag map, a function which maps each tag ID in a tagged region to a corresponding location. The tag map class diagram is shown in  FIG. 22 , as part of the netpage printer class diagram. 
   A tag map reflects the scheme used to tile the surface region with tags, and this can vary according to surface type. When multiple tagged regions share the same tiling scheme and the same tag numbering scheme, they can also share the same tag map. 
   The tag map for a region must be retrievable via the region ID. Thus, given a region ID, a tag ID and a pen transform, the tag map can be retrieved, the tag ID can be translated into an absolute tag location within the region, and the tag-relative pen location can be added to the tag location to yield an absolute pen location within the region. 
   1.2.6 Tagging Schemes 
   Two distinct surface coding schemes are of interest, both of which use the tag structure described earlier in this section. The preferred coding scheme uses “location-indicating” tags as already discussed. An alternative coding scheme uses object-indicating tags. 
   A location-indicating tag contains a tag ID which, when translated through the tag map associated with the tagged region, yields a unique tag location within the region. The tag-relative location of the pen is added to this tag location to yield the location of the pen within the region. This in turn is used to determine the location of the pen relative to a user interface element in the page description associated with the region. Not only is the user interface element itself identified, but a location relative to the user interface element is identified. Location-indicating tags therefore trivially support the capture of an absolute pen path in the zone of a particular user interface element. 
   An object-indicating tag contains a tag ID which directly identifies a user interface element in the page description associated with the region. All the tags in the zone of the user interface element identify the user interface element, making them all identical and therefore indistinguishable. Object-indicating tags do not, therefore, support the capture of an absolute pen path. They do, however, support the capture of a relative pen path. So long as the position sampling frequency exceeds twice the encountered tag frequency, the displacement from one sampled pen position to the next within a stroke can be unambiguously determined. 
   With either tagging scheme, the tags function in cooperation with associated visual elements on the netpage as user interactive elements in that a user can interact with the printed page using an appropriate sensing device in order for tag data to be read by the sensing device and for an appropriate response to be generated in the netpage system. 
   1.3 Document and Page Descriptions 
   A preferred embodiment of a document and page description class diagram is shown in  FIGS. 25 and 26 . 
   In the netpage system a document is described at three levels. At the most abstract level the document  836  has a hierarchical structure whose terminal elements  839  are associated with content objects  840  such as text objects, text style objects, image objects, etc. Once the document is printed on a printer with a particular page size and according to a particular user&#39;s scale factor preference, the document is paginated and otherwise formatted. Formatted terminal elements  835  will in some cases be associated with content objects which are different from those associated with their corresponding terminal elements, particularly where the content objects are style-related. Each printed instance of a document and page is also described separately, to allow input captured through a particular page instance  830  to be recorded separately from input captured through other instances of the same page description. 
   The presence of the most abstract document description on the page server allows a user to request a copy of a document without being forced to accept the source document&#39;s specific format. The user may be requesting a copy through a printer with a different page size, for example. Conversely, the presence of the formatted document description on the page server allows the page server to efficiently interpret user actions on a particular printed page. 
   A formatted document  834  consists of a set of formatted page descriptions  5 , each of which consists of a set of formatted terminal elements  835 . Each formatted element has a spatial extent or zone  58  on the page. This defines the active area of input elements such as hyperlinks and input fields. 
   A document instance  831  corresponds to a formatted document  834 . It consists of a set of page instances  830 , each of which corresponds to a page description  5  of the formatted document. Each page instance  830  describes a single unique printed netpage  1 , and records the page ID  50  of the netpage. A page instance is not part of a document instance if it represents a copy of a page requested in isolation. 
   A page instance consists of a set of terminal element instances  832 . An element instance only exists if it records instance-specific information. Thus, a hyperlink instance exists for a hyperlink element because it records a transaction ID  55  which is specific to the page instance, and a field instance exists for a field element because it records input specific to the page instance. An element instance does not exist, however, for static elements such as textflows. 
   A terminal element can be a static element  843 , a hyperlink element  844 , a field element  845  or a page server command element  846 , as shown in  FIG. 27 . A static element  843  can be a style element  847  with an associated style object  854 , a textflow element  848  with an associated styled text object  855 , an image element  849  with an associated image element  856 , a graphic element  850  with an associated graphic object  857 , a video clip element  851  with an associated video clip object  858 , an audio clip element  852  with an associated audio clip object  859 , or a script element  853  with an associated script object  860 , as shown in  FIG. 28 . 
   A page instance has a background field  833  which is used to record any digital ink captured on the page which does not apply to a specific input element. 
   In the preferred form of the invention, a tag map  811  is associated with each page instance to allow tags on the page to be translated into locations on the page. 
   1.4 the Netpage Network 
   In a preferred embodiment, a netpage network consists of a distributed set of netpage page servers  10 , netpage registration servers  11 , netpage ID servers  12 , netpage application servers  13 , netpage publication servers  14 , and netpage printers  601  connected via a network  19  such as the Internet, as shown in  FIG. 3 . 
   The netpage registration server  11  is a server which records relationships between users, pens, printers, applications and publications, and thereby authorizes various network activities. It authenticates users and acts as a signing proxy on behalf of authenticated users in application transactions. It also provides handwriting recognition services. As described above, a netpage page server  10  maintains persistent information about page descriptions and page instances. The netpage network includes any number of page servers, each handling a subset of page instances. Since a page server also maintains user input values for each page instance, clients such as netpage printers send netpage input directly to the appropriate page server. The page server interprets any such input relative to the description of the corresponding page. 
   A netpage ID server  12  allocates document IDs  51  on demand, and provides load-balancing of page servers via its ID allocation scheme. 
   A netpage printer uses the Internet Distributed Name System (DNS), or similar, to resolve a netpage page ID  50  into the network address of the netpage page server handling the corresponding page instance. 
   A netpage application server  13  is a server which hosts interactive netpage applications. A netpage publication server  14  is an application server which publishes netpage documents to netpage printers. They are described in detail in Section 2. 
   Netpage servers can be hosted on a variety of network server platforms from manufacturers such as IBM, Hewlett-Packard, and Sun. Multiple netpage servers can run concurrently on a single host, and a single server can be distributed over a number of hosts. Some or all of the functionality provided by netpage servers, and in particular the functionality provided by the ID server and the page server, can also be provided directly in a netpage appliance such as a netpage printer, in a computer workstation, or on a local network. 
   1.5 The Netpage Printer 
   The netpage printer  601  is an appliance which is registered with the netpage system and prints netpage documents on demand and via subscription. Each printer has a unique printer ID  62 , and is connected to the netpage network via a network such as the Internet, ideally via a broadband connection. 
   Apart from identity and security settings in non-volatile memory, the netpage printer contains no persistent storage. As far as a user is concerned, “the network is the computer”. Netpages function interactively across space and time with the help of the distributed netpage page servers  10 , independently of particular netpage printers. 
   The netpage printer receives subscribed netpage documents from netpage publication servers  14 . Each document is distributed in two parts: the page layouts, and the actual text and image objects which populate the pages. Because of personalization, page layouts are typically specific to a particular subscriber and so are pointcast to the subscriber&#39;s printer via the appropriate page server. Text and image objects, on the other hand, are typically shared with other subscribers, and so are multicast to all subscribers&#39; printers and the appropriate page servers. 
   The netpage publication server optimizes the segmentation of document content into pointcasts and multicasts. After receiving the pointcast of a document&#39;s page layouts, the printer knows which multicasts, if any, to listen to. 
   Once the printer has received the complete page layouts and objects that define the document to be printed, it can print the document. 
   The printer rasterizes and prints odd and even pages simultaneously on both sides of the sheet. It contains duplexed print engine controllers  760  and print engines utilizing Memjet™ printheads  350  for this purpose. 
   The printing process consists of two decoupled stages: rasterization of page descriptions, and expansion and printing of page images. The raster image processor (RIP) consists of one or more standard DSPs  757  running in parallel. The duplexed print engine controllers consist of custom processors which expand, dither and print page images in real time, synchronized with the operation of the printheads in the print engines. 
   Printers not enabled for IR printing have the option to print tags using IR-absorptive black ink, although this restricts tags to otherwise empty areas of the page. Although such pages have more limited functionality than IR-printed pages, they are still classed as netpages. 
   A normal netpage printer prints netpages on sheets of paper. More specialised netpage printers may print onto more specialised surfaces, such as globes. Each printer supports at least one surface type, and supports at least one tag tiling scheme, and hence tag map, for each surface type. The tag map  811  which describes the tag tiling scheme actually used to print a document becomes associated with that document so that the document&#39;s tags can be correctly interpreted. 
     FIG. 2  shows the netpage printer class diagram, reflecting printer-related information maintained by a registration server  11  on the netpage network. 
   A preferred embodiment of the netpage printer is described in greater detail in Section 6 below, with reference to  FIGS. 11 to 16 . 
   1.5.1 Memjet™ Printheads 
   The netpage system can operate using printers made with a wide range of digital printing technologies, including thermal inkjet, piezoelectric inkjet, laser electrophotographic, and others. However, for wide consumer acceptance, it is desirable that a netpage printer have the following characteristics:
         photographic-quality color printing   high quality text printing   high reliability   low printer cost   low ink cost   low paper cost   simple operation   nearly silent printing   high printing speed   simultaneous double sided printing   compact form factor   low power consumption       

   No commercially available printing technology has all of these characteristics. 
   To enable to production of printers with these characteristics, the present applicant has invented a new print technology, referred to as Memjet™ technology. Memjet™ is a drop-on-demand inkjet technology that incorporates pagewidth printheads fabricated using microelectromechanical systems (MEMS) technology.  FIG. 17  shows a single printing element  300  of a Memjet™ printhead. The netpage wallprinter incorporates 168960 printing elements  300  to form a 1600 dpi pagewidth duplex printer. This printer simultaneously prints cyan, magenta, yellow, black, and infrared inks as well as paper conditioner and ink fixative. 
   The printing element  300  is approximately 110 microns long by 32 microns wide. Arrays of these printing elements are formed on a silicon substrate  301  that incorporates CMOS logic, data transfer, timing, and drive circuits (not shown). 
   Major elements of the printing element  300  are the nozzle  302 , the nozzle rim  303 , the nozzle chamber  304 , the fluidic seal  305 , the ink channel rim  306 , the lever arm  307 , the active actuator beam pair  308 , the passive actuator beam pair  309 , the active actuator anchor  310 , the passive actuator anchor  311 , and the ink inlet  312 . 
   The active actuator beam pair  308  is mechanically joined to the passive actuator beam pair  309  at the join  319 . Both beams pairs are anchored at their respective anchor points  310  and  311 . The combination of elements  308 ,  309 ,  310 ,  311 , and  319  form a cantilevered electrothermal bend actuator  320 . 
     FIG. 18  shows a small part of an array of printing elements  300 , including a cross section  315  of a printing element  300 . The cross section  315  is shown without ink, to clearly show the ink inlet  312  that passes through the silicon wafer  301 . 
     FIGS. 19(   a ),  19 ( b ) and  19 ( c ) show the operating cycle of a Memjet™ printing element  300 . 
     FIG. 19(   a ) shows the quiescent position of the ink meniscus  316  prior to printing an ink droplet. Ink is retained in the nozzle chamber by surface tension at the ink meniscus  316  and at the fluidic seal  305  formed between the nozzle chamber  304  and the ink channel rim  306 . 
   While printing, the printhead CMOS circuitry distributes data from the print engine controller to the correct printing element, latches the data, and buffers the data to drive the electrodes  318  of the active actuator beam pair  308 . This causes an electrical current to pass through the beam pair  308  for about one microsecond, resulting in Joule heating. The temperature increase resulting from Joule heating causes the beam pair  308  to expand. As the passive actuator beam pair  309  is not heated, it does not expand, resulting in a stress difference between the two beam pairs. This stress difference is partially resolved by the cantilevered end of the electrothermal bend actuator  320  bending towards the substrate  301 . The lever arm  307  transmits this movement to the nozzle chamber  304 . The nozzle chamber  304  moves about two microns to the position shown in  FIG. 19(   b ). This increases the ink pressure, forcing ink  321  out of the nozzle  302 , and causing the ink meniscus  316  to bulge. The nozzle rim  303  prevents the ink meniscus  316  from spreading across the surface of the nozzle chamber  304 . 
   As the temperature of the beam pairs  308  and  309  equalizes, the actuator  320  returns to its original position. This aids in the break-off of the ink droplet  317  from the ink  321  in the nozzle chamber, as shown in  FIG. 19(   c ). The nozzle chamber is refilled by the action of the surface tension at the meniscus  316 . 
     FIG. 20  shows a segment of a printhead  350 . In a netpage printer, the length of the printhead is the full width of the paper (typically 210 mm) in the direction  351 . The segment shown is 0.4 mm long (about 0.2% of a complete printhead). When printing, the paper is moved past the fixed printhead in the direction  352 . The printhead has 6 rows of interdigitated printing elements  300 , printing the six colors or types of ink supplied by the ink inlets  312 . 
   To protect the fragile surface of the printhead during operation, a nozzle guard wafer  330  is attached to the printhead substrate  301 . For each nozzle  302  there is a corresponding nozzle guard hole  331  through which the ink droplets are fired. To prevent the nozzle guard holes  331  from becoming blocked by paper fibers or other debris, filtered air is pumped through the air inlets  332  and out of the nozzle guard holes during printing. To prevent ink  321  from drying, the nozzle guard is sealed while the printer is idle. 
   1.6 The Netpage Pen 
   The active sensing device of the netpage system is typically a pen  101 , which, using its embedded controller  134 , is able to capture and decode IR position tags from a page via an image sensor. The image sensor is a solid-state device provided with an appropriate filter to permit sensing at only near-infrared wavelengths. As described in more detail below, the system is able to sense when the nib is in contact with the surface, and the pen is able to sense tags at a sufficient rate to capture human handwriting (i.e. at 200 dpi or greater and 100 Hz or faster). Information captured by the pen is encrypted and wirelessly transmitted to the printer (or base station), the printer or base station interpreting the data with respect to the (known) page structure. 
   The preferred embodiment of the netpage pen operates both as a normal marking ink pen and as a non-marking stylus. The marking aspect, however, is not necessary for using the netpage system as a browsing system, such as when it is used as an Internet interface. Each netpage pen is registered with the netpage system and has a unique pen ID  61 .  FIG. 23  shows the netpage pen class diagram, reflecting pen-related information maintained by a registration server  11  on the netpage network. 
   When either nib is in contact with a netpage, the pen determines its position and orientation relative to the page. The nib is attached to a force sensor, and the force on the nib is interpreted relative to a threshold to indicate whether the pen is “up.” or “down”. This allows a interactive element on the page to be ‘clicked’ by pressing with the pen nib, in order to request, say, information from a network. Furthermore, the force is captured as a continuous value to allow, say, the full dynamics of a signature to be verified. 
   The pen determines the position and orientation of its nib on the netpage by imaging, in the infrared spectrum, an area  193  of the page in the vicinity of the nib. It decodes the nearest tag and computes the position of the nib relative to the tag from the observed perspective distortion on the imaged tag and the known geometry of the pen optics. Although the position resolution of the tag may be low, because the tag density on the page is inversely proportional to the tag size, the adjusted position resolution is quite high, exceeding the minimum resolution required for accurate handwriting recognition. 
   Pen actions relative to a netpage are captured as a series of strokes. A stroke consists of a sequence of time-stamped pen positions on the page, initiated by a pen-down event and completed by the subsequent pen-up event. A stroke is also tagged with the page ID  50  of the netpage whenever the page ID changes, which, under normal circumstances, is at the commencement of the stroke. 
   Each netpage pen has a current selection  826  associated with it, allowing the user to perform copy and paste operations etc. The selection is timestamped to allow the system to discard it after a defined time period. The current selection describes a region of a page instance. It consists of the most recent digital ink stroke captured through the pen relative to the background area of the page. It is interpreted in an application-specific manner once it is submitted to an application via a selection hyperlink activation. 
   Each pen has a current nib  824 . This is the nib last notified by the pen to the system. In the case of the default netpage pen described above, either the marking black ink nib or the non-marking stylus nib is current. Each pen also has a current nib style  825 . This is the nib style last associated with the pen by an application, e.g. in response to the user selecting a color from a palette. The default nib style is the nib style associated with the current nib. Strokes captured through a pen are tagged with the current nib style. When the strokes are subsequently reproduced, they are reproduced in the nib style with which they are tagged. 
   Whenever the pen is within range of a printer with which it can communicate, the pen slowly flashes its “online” LED. When the pen fails to decode a stroke relative to the page, it momentarily activates its “error” LED. When the pen succeeds in decoding a stroke relative to the page, it momentarily activates its “ok” LED. 
   A sequence of captured strokes is referred to as digital ink. Digital ink forms the basis for the digital exchange of drawings and handwriting, for online recognition of handwriting, and for online verification of signatures. 
   The pen is wireless and transmits digital ink to the netpage printer via a short-range radio link. The transmitted digital ink is encrypted for privacy and security and packetized for efficient transmission, but is always flushed on a pen-up event to ensure timely handling in the printer. 
   When the pen is out-of-range of a printer it buffers digital ink in internal memory, which has a capacity of over ten minutes of continuous handwriting. When the pen is once again within range of a printer, it transfers any buffered digital ink. 
   A pen can be registered with any number of printers, but because all state data resides in netpages both on paper and on the network, it is largely immaterial which printer a pen is communicating with at any particular time. 
   A preferred embodiment of the pen is described in greater detail in Section 6 below, with reference to  FIGS. 8 to 10 . 
   1.7 Netpage Interaction 
   The netpage printer  601  receives data relating to a stroke from the pen  101  when the pen is used to interact with a netpage  1 . The coded data  3  of the tags  4  is read by the pen when it is used to execute a movement, such as a stroke. The data allows the identity of the particular page and associated interactive element to be determined and an indication of the relative positioning of the pen relative to the page to be obtained. The indicating data is transmitted to the printer, where it resolves, via the DNS, the page ID  50  of the stroke into the network address of the netpage page server  10  which maintains the corresponding page instance  830 . It then transmits the stroke to the page server. If the page was recently identified in an earlier stroke, then the printer may already have the address of the relevant page server in its cache. Each netpage consists of a compact page layout maintained persistently by a netpage page server (see below). The page layout refers to objects such as images, fonts and pieces of text, typically stored elsewhere on the netpage network. 
   When the page server receives the stroke from the pen, it retrieves the page description to which the stroke applies, and determines which element of the page description the stroke intersects. It is then able to interpret the stroke in the context of the type of the relevant element. 
   A “click” is a stroke where the distance and time between the pen down position and the subsequent pen up position are both less than some small maximum. An object which is activated by a click typically requires a click to be activated, and accordingly, a longer stroke is ignored. The failure of a pen action, such as a “sloppy” click, to register is indicated by the lack of response from the pen&#39;s “ok” LED. 
   There are two kinds of input elements in a netpage page description: hyperlinks and form fields. Input through a form field can also trigger the activation of an associated hyperlink. 
   1.7.1 Hyperlinks 
   A hyperlink is a means of sending a message to a remote application, and typically elicits a printed response in the netpage system. 
   A hyperlink element  844  identifies the application  71  which handles activation of the hyperlink, a link ID  54  which identifies the hyperlink to the application, an “alias required” flag which asks the system to include the user&#39;s application alias ID  65  in the hyperlink activation, and a description which is used when the hyperlink is recorded as a favorite or appears in the user&#39;s history. The hyperlink element class diagram is shown in  FIG. 29 . 
   When a hyperlink is activated, the page server sends a request to an application somewhere on the network. The application is identified by an application ID  64 , and the application ID is resolved in the normal way via the DNS. There are three types of hyperlinks: general hyperlinks  863 , form hyperlinks  865 , and selection hyperlinks  864 , as shown in  FIG. 30 . A general hyperlink can implement a request for a linked document, or may simply signal a preference to a server. A form hyperlink submits the corresponding form to the application. A selection hyperlink submits the current selection to the application. If the current selection contains a single-word piece of text, for example, the application may return a single-page document giving the word&#39;s meaning within the context in which it appears, or a translation into a different language. Each hyperlink type is characterized by what information is submitted to the application. 
   The corresponding hyperlink instance  862  records a transaction ID  55  which can be specific to the page instance on which the hyperlink instance appears. The transaction ID can identify user-specific data to the application, for example a “shopping cart” of pending purchases maintained by a purchasing application on behalf of the user. 
   The system includes the pen&#39;s current selection  826  in a selection hyperlink activation. The system includes the content of the associated form instance  868  in a form hyperlink activation, although if the hyperlink has its “submit delta” attribute set, only input since the last form submission is included. The system includes an effective return path in all hyperlink activations. 
   A hyperlinked group  866  is a group element  838  which has an associated hyperlink, as shown in  FIG. 31 . When input occurs through any field element in the group, the hyperlink  844  associated with the group is activated. A hyperlinked group can be used to associate hyperlink behavior with a field such as a checkbox. It can also be used, in conjunction with the “submit delta” attribute of a form hyperlink, to provide continuous input to an application. It can therefore be used to support a “blackboard” interaction model, i.e. where input is captured and therefore shared as soon as it occurs. 
   1.7.2 Forms 
   A form defines a collection of related input fields used to capture a related set of inputs through a printed netpage. A form allows a user to submit one or more parameters to an application software program running on a server. 
   A form  867  is a group element  838  in the document hierarchy. It ultimately contains a set of terminal field elements  839 . A form instance  868  represents a printed instance of a form. It consists of a set of field instances  870  which correspond to the field elements  845  of the form. Each field instance has an associated value  871 , whose type depends on the type of the corresponding field element. Each field value records input through a particular printed form instance, i.e. through one or more printed netpages. The form class diagram is shown in  FIG. 32 . 
   Each form instance has a status  872  which indicates whether the form is active, frozen, submitted, void or expired. A form is active when first printed. A form becomes frozen once it is signed or once its freeze time is reached. A form becomes submitted once one of its submission hyperlinks has been activated, unless the hyperlink has its “submit delta” attribute set. A form becomes void when the user invokes a void form, reset form or duplicate form page command. A form expires when its specified expiry time is reached, i.e. when the time the form has been active exceeds the form&#39;s specified lifetime. While the form is active, form input is allowed. Input through a form which is not active is instead captured in the background field  833  of the relevant page instance. When the form is active or frozen, form submission is allowed. Any attempt to submit a form when the form is not active or frozen is rejected, and instead elicits an form status report. 
   Each form instance is associated (at  59 ) with any form instances derived from it, thus providing a version history. This allows all but the latest version of a form in a particular time period to be excluded from a search. 
   All input is captured as digital ink. Digital ink  873  consists of a set of timestamped stroke groups  874 , each of which consists of a set of styled strokes  875 . Each stroke consists of a set of timestamped pen positions  876 , each of which also includes pen orientation and nib force. The digital ink class diagram is shown in  FIG. 33 . 
   A field element  845  can be a checkbox field  877 , a text field  878 , a drawing field  879 , or a signature field  880 . The field element class diagram is shown in  FIG. 34 . Any digital ink captured in a field&#39;s zone  58  is assigned to the field. 
   A checkbox field has an associated boolean value  881 , as shown in  FIG. 35 . Any mark (a tick, a cross, a stroke, a fill zigzag, etc.) captured in a checkbox field&#39;s zone causes a true value to be assigned to the field&#39;s value. 
   A text field has an associated text value  882 , as shown in  FIG. 36 . Any digital ink captured in a text field&#39;s zone is automatically converted to text via online handwriting recognition, and the text is assigned to the field&#39;s value. Online handwriting recognition is well-understood (see, for example, Tappert, C., C. Y. Suen and T. Wakahara, “The State of the Art in On-Line Handwriting Recognition”, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol.12, No.8, August 1990, the contents of which are herein incorporated by cross-reference). 
   A signature field has an associated digital signature value  883 , as shown in  FIG. 37 . Any digital ink captured in a signature field&#39;s zone is automatically verified with respect to the identity of the owner of the pen, and a digital signature of the content of the form of which the field is part is generated and assigned to the field&#39;s value. The digital signature is generated using the pen user&#39;s private signature key specific to the application which owns the form. Online signature verification is well-understood (see, for example, Plamondon, R. and G. Lorette, “Automatic Signature Verification and Writer Identification—The State of the Art”, Pattern Recognition, Vol.22, No.2, 1989, the contents of which are herein incorporated by cross-reference). 
   A field element is hidden if its “hidden” attribute is set. A hidden field element does not have an input zone on a page and does not accept input. It can have an associated field value which is included in the form data when the form containing the field is submitted. 
   “Editing” commands, such as strike-throughs indicating deletion, can also be recognized in form fields. 
   Because the handwriting recognition algorithm works “online” (i.e. with access to the dynamics of the pen movement), rather than “offline” (i.e. with access only to a bitmap of pen markings), it can recognize run-on discretely-written characters with relatively high accuracy, without a writer-dependent training phase. A writer-dependent model of handwriting is automatically generated over time, however, and can be generated up-front if necessary, 
   Digital ink, as already stated, consists of a sequence of strokes. Any stroke which starts in a particular element&#39;s zone is appended to that element&#39;s digital ink stream, ready for interpretation. Any stroke not appended to an object&#39;s digital ink stream is appended to the background field&#39;s digital ink stream. 
   Digital ink captured in the background field is interpreted as a selection gesture. Circumscription of one or more objects is generally interpreted as a selection of the circumscribed objects, although the actual interpretation is application-specific. 
   Table 2 summarises these various pen interactions with a netpage. 
   
     
       
         
             
           
             
               TABLE 2 
             
           
          
             
                 
             
             
               Summary of pen interactions with a netpage 
             
          
         
         
             
             
             
             
          
             
               Object 
               Type 
               Pen input 
               Action 
             
             
                 
             
             
               Hyperlink 
               General 
               Click 
               Submit action to application 
             
             
                 
               Form 
               Click 
               Submit form to application 
             
             
                 
               Selection 
               Click 
               Submit selection to 
             
             
                 
                 
                 
               application 
             
             
               Form field 
               Checkbox 
               Any mark 
               Assign true to field 
             
             
                 
               Text 
               Handwriting 
               Convert digital ink to text; 
             
             
                 
                 
                 
               assign text to field 
             
             
                 
               Drawing 
               Digital ink 
               Assign digital ink to field 
             
             
                 
               Signature 
               Signature 
               Verify digital ink signature; 
             
             
                 
                 
                 
               generate digital signature of 
             
             
                 
                 
                 
               form; assign digital signature 
             
             
                 
                 
                 
               to field 
             
             
               None 
               — 
               Circumscription 
               Assign digital ink to current 
             
             
                 
                 
                 
               selection 
             
             
                 
             
          
         
       
     
   
   The system maintains a current selection for each pen. The selection consists simply of the most recent stroke captured in the background field. The selection is cleared after an inactivity timeout to ensure predictable behavior. 
   The raw digital ink captured in every field is retained on the netpage page server and is optionally transmitted with the form data when the form is submitted to the application. This allows the application to interrogate the raw digital ink should it suspect the original conversion, such as the conversion of handwritten text. This can, for example, involve human intervention at the application level for forms which fail certain application-specific consistency checks. As an extension to this, the entire background area of a form can be designated as a drawing field. The application can then decide, on the basis of the presence of digital ink outside the explicit fields of the form, to route the form to a human operator, on the assumption that the user may have indicated amendments to the filled-in fields outside of those fields. 
     FIG. 38  shows a flowchart of the process of handling pen input relative to a netpage. The process consists of receiving (at  884 ) a stroke from the pen; identifying (at  885 ) the page instance  830  to which the page ID  50  in the stroke refers; retrieving (at  886 ) the page description  5 ; identifying (at  887 ) a formatted element  839  whose zone  58  the stroke intersects; determining (at  888 ) whether the formatted element corresponds to a field element, and if so appending (at  892 ) the received stroke to the digital ink of the field value  871 , interpreting (at  893 ) the accumulated digital ink of the field, and determining (at  894 ) whether the field is part of a hyperlinked group  866  and if so activating (at  895 ) the associated hyperlink; alternatively determining (at  889 ) whether the formatted element corresponds to a hyperlink element and if so activating (at  895 ) the corresponding hyperlink; alternatively, in the absence of an input field or hyperlink, appending (at  890 ) the received stroke to the digital ink of the background field  833 ; and copying (at  891 ) the received stroke to the current selection  826  of the current pen, as maintained by the registration server. 
     FIG. 38   a  shows a detailed flowchart of step  893  in the process shown in  FIG. 38 , where the accumulated digital ink of a field is interpreted according to the type of the field. The process consists of determining (at  896 ) whether the field is a checkbox and (at  897 ) whether the digital ink represents a checkmark, and if so assigning (at  898 ) a true value to the field value; alternatively determining (at  899 ) whether the field is a text field and if so converting (at  900 ) the digital ink to computer text, with the help of the appropriate registration server, and assigning (at  901 ) the converted computer text to the field value; alternatively determining (at  902 ) whether the field is a signature field and if so verifying (at  903 ) the digital ink as the signature of the pen&#39;s owner, with the help of the appropriate registration server, creating (at  904 ) a digital signature of the contents of the corresponding form, also with the help of the registration server and using the pen owner&#39;s private signature key relating to the corresponding application, and assigning (at  905 ) the digital signature to the field value. 
   1.7.3 Page Server Commands 
   A page server command is a command which is handled locally by the page server. It operates directly on form, page and document instances. 
   A page server command  907  can be a void form command  908 , a duplicate form command  909 , a reset form command  910 , a get form status command  911 , a duplicate page command  912 , a reset page command  913 , a get page status command  914 , a duplicate document command  915 , a reset document command  916 , or a get document status command  917 , as shown in  FIG. 39 . 
   A void form command voids the corresponding form instance. A duplicate form command voids the corresponding form instance and then produces an active printed copy of the current form instance with field values preserved. The copy contains the same hyperlink transaction IDs as the original, and so is indistinguishable from the original to an application. A reset form command voids the corresponding form instance and then produces an active printed copy of the form instance with field values discarded. A get form status command produces a printed report on the status of the corresponding form instance, including who published it, when it was printed, for whom it was printed, and the form status of the form instance. 
   Since a form hyperlink instance contains a transaction ID, the application has to be involved in producing a new form instance. A button requesting a new form instance is therefore typically implemented as a hyperlink. 
   A duplicate page command produces a printed copy of the corresponding page instance with the background field value preserved. If the page contains a form or is part of a form, then the duplicate page command is interpreted as a duplicate form command. A reset page command produces a printed copy of the corresponding page instance with the background field value discarded. If the page contains a form or is part of a form, then the reset page command is interpreted as a reset form command. A get page status command produces a printed report on the status of the corresponding page instance, including who published it, when it was printed, for whom it was printed, and the status of any forms it contains or is part of. 
   The netpage logo which appears on every netpage is usually associated with a duplicate page element. 
   When a page instance is duplicated with field values preserved, field values are printed in their native form, i.e. a checkmark appears as a standard checkmark graphic, and text appears as typeset text. Only drawings and signatures appear in their original form, with a signature accompanied by a standard graphic indicating successful signature verification. 
   A duplicate document command produces a printed copy of the corresponding document instance with background field values preserved. If the document contains any forms, then the duplicate document command duplicates the forms in the same way a duplicate form command does. A reset document command produces a printed copy of the corresponding document instance with background field values discarded. If the document contains any forms, then the reset document command resets the forms in the same way a reset form command does. A get document status command produces a printed report on the status of the corresponding document instance, including who published it, when it was printed, for whom it was printed, and the status of any forms it contains. 
   If the page server command&#39;s “on selected” attribute is set, then the command operates on the page identified by the pen&#39;s current selection rather than on the page containing the command. This allows a menu of page server commands to be printed. If the target page doesn&#39;t contain a page server command element for the designated page server command, then the command is ignored. 
   An application can provide application-specific handling by embedding the relevant page server command element in a hyperlinked group. The page server activates the hyperlink associated with the hyperlinked group rather than executing the page server command. 
   A page server command element is hidden if its “hidden” attribute is set. A hidden command element does not have an input zone on a page and so cannot be activated directly by a user. It can, however, be activated via a page server command embedded in a different page, if that page server command has its “on selected” attribute set. 
   1.8 Standard Features of Netpages 
   In the preferred form, each netpage is printed with the netpage logo at the bottom to indicate that it is a netpage and therefore has interactive properties. The logo also acts as a copy button. In most cases pressing the logo produces a copy of the page. In the case of a form, the button produces a copy of the entire form. And in the case of a secure document, such as a ticket or coupon, the button elicits an explanatory note or advertising page. 
   The default single-page copy function is handled directly by the relevant netpage page server. Special copy functions are handled by linking the logo button to an application. 
   1.9 User Help System 
   In a preferred embodiment, the netpage printer has a single button labelled “Help”. When pressed it elicits a single help page 46 of information, including:
         status of printer connection   status of printer consumables   top-level help menu   document function menu   top-level netpage network directory       

   The help menu provides a hierarchical manual on how to use the netpage system. 
   The document function menu includes the following functions:
         print a copy of a document   print a clean copy of a form   print the status of a document       

   A document function is initiated by selecting the document and then pressing the button. The status of a document indicates who published it and when, to whom it was delivered, and to whom and when it was subsequently submitted as a form. 
   The help page is obviously unavailable if the printer is unable to print. In this case the “error” light is lit and the user can request remote diagnosis over the network. 
   2 Personalized Publication Model 
   In the following description, news is used as a canonical publication example to illustrate personalization mechanisms in the netpage system. Although news is often used in the limited sense of newspaper and newsmagazine news, the intended scope in the present context is wider. 
   In the netpage system, the editorial content and the advertising content of a news publication are personalized using different mechanisms. The editorial content is personalized according to the reader&#39;s explicitly stated and implicitly captured interest profile. The advertising content is personalized according to the reader&#39;s locality and demographic. 
   2.1 Editorial Personalization 
   A subscriber can draw on two kinds of news sources: those that deliver news publications, and those that deliver news streams. While news publications are aggregated and edited by the publisher, news streams are aggregated either by a news publisher or by a specialized news aggregator. News publications typically correspond to traditional newspapers and newsmagazines, while news streams can be many and varied: a “raw” news feed from a news service, a cartoon strip, a freelance writer&#39;s column, a friend&#39;s bulletin board, or the reader&#39;s own e-mail. 
   The netpage publication server supports the publication of edited news publications as well as the aggregation of multiple news streams. By handling the aggregation and hence the formatting of news streams selected directly by the reader, the server is able to place advertising on pages over which it otherwise has no editorial control. 
   The subscriber builds a daily newspaper by selecting one or more contributing news publications, and creating a personalized version of each. The resulting daily editions are printed and bound together into a single newspaper. The various members of a household typically express their different interests and tastes by selecting different daily publications and then customizing them. 
   For each publication, the reader optionally selects specific sections. Some sections appear daily, while others appear weekly. The daily sections available from The New York Times online, for example, include “Page One Plus”, “National”, “International”, “Opinion”, “Business”, “Arts/Living”, “Technology”, and “Sports”. The set of available sections is specific to a publication, as is the default subset. 
   The reader can extend the daily newspaper by creating custom sections, each one drawing on any number of news streams. Custom sections might be created for e-mail and friends&#39; announcements (“Personal”), or for monitoring news feeds for specific topics (“Alerts” or “Clippings”). 
   For each section, the reader optionally specifies its size, either qualitatively (e.g. short, medium, or long), or numerically (i.e. as a limit on its number of pages), and the desired proportion of advertising, either qualitatively (e.g. high, normal, low, none), or numerically (i.e. as a percentage). 
   The reader also optionally expresses a preference for a large number of shorter articles or a small number of longer articles. Each article is ideally written (or edited) in both short and long forms to support this preference. 
   An article may also be written (or edited) in different versions to match the expected sophistication of the reader, for example to provide children&#39;s and adults&#39; versions. The appropriate version is selected according to the reader&#39;s age. The reader can specify a “reading age” which takes precedence over their biological age. 
   The articles which make up each section are selected and prioritized by the editors, and each is assigned a useful lifetime. By default they are delivered to all relevant subscribers, in priority order, subject to space constraints in the subscribers&#39; editions. 
   In sections where it is appropriate, the reader may optionally enable collaborative filtering. This is then applied to articles which have a sufficiently long lifetime. Each article which qualifies for collaborative filtering is printed with rating buttons at the end of the article. The buttons can provide an easy choice (e.g. “liked” and “disliked”), making it more likely that readers will bother to rate the article. 
   Articles with high priorities and short lifetimes are therefore effectively considered essential reading by the editors and are delivered to most relevant subscribers. 
   The reader optionally specifies a serendipity factor, either qualitatively (e.g. do or don&#39;t surprise me), or numerically. A high serendipity factor lowers the threshold used for matching during collaborative filtering. A high factor makes it more likely that the corresponding section will be filled to the reader&#39;s specified capacity. A different serendipity factor can be specified for different days of the week. 
   The reader also optionally specifies topics of particular interest within a section, and this modifies the priorities assigned by the editors. 
   The speed of the reader&#39;s Internet connection affects the quality at which images can be delivered. The reader optionally specifies a preference for fewer images or smaller images or both. If the number or size of images is not reduced, then images may be delivered at lower quality (i.e. at lower resolution or with greater compression). 
   At a global level, the reader specifies how quantities, dates, times and monetary values are localized. This involves specifying whether units are imperial or metric, a local timezone and time format, and a local currency, and whether the localization consist of in situ translation or annotation. These preferences are derived from the reader&#39;s locality by default. 
   To reduce reading difficulties caused by poor eyesight, the reader optionally specifies a global preference for a larger presentation. Both text and images are scaled accordingly, and less information is accommodated on each page. 
   The language in which a news publication is published, and its corresponding text encoding, is a property of the publication and not a preference expressed by the user. However, the netpage system can be configured to provide automatic translation services in various guises. 
   2.2 Advertising Localization and Targeting 
   The personalization of the editorial content directly affects the advertising content, because advertising is typically placed to exploit the editorial context. Travel ads, for example, are more likely to appear in a travel section than elsewhere. The value of the editorial content to an advertiser (and therefore to the publisher) lies in its ability to attract large numbers of readers with the right demographics. 
   Effective advertising is placed on the basis of locality and demographics. Locality determines proximity to particular services, retailers etc., and particular interests and concerns associated with the local community and environment. Demographics determine general interests and preoccupations as well as likely spending patterns. 
   A news publisher&#39;s most profitable product is advertising “space”, a multi-dimensional entity determined by the publication&#39;s geographic coverage, the size of its readership, its readership demographics, and the page area available for advertising. 
   In the netpage system, the netpage publication server computes the approximate multi-dimensional size of a publication&#39;s saleable advertising space on a per-section basis, taking into account the publication&#39;s geographic coverage, the section&#39;s readership, the size of each reader&#39;s section edition, each reader&#39;s advertising proportion, and each reader&#39;s demographic. 
   In comparison with other media, the netpage system allows the advertising space to be defined in greater detail, and allows smaller pieces of it to be sold separately. It therefore allows it to be sold at closer to its true value. 
   For example, the same advertising “slot” can be sold in varying proportions to several advertisers, with individual readers&#39; pages randomly receiving the advertisement of one advertiser or another, overall preserving the proportion of space sold to each advertiser. 
   The netpage system allows advertising to be linked directly to detailed product information and online purchasing. It therefore raises the intrinsic value of the advertising space. 
   Because personalization and localization are handled automatically by netpage publication servers, an advertising aggregator can provide arbitrarily broad coverage of both geography and demographics. The subsequent disaggregation is efficient because it is automatic. This makes it more cost-effective for publishers to deal with advertising aggregators than to directly capture advertising. Even though the advertising aggregator is taking a proportion of advertising revenue, publishers may find the change profit-neutral because of the greater efficiency of aggregation. The advertising aggregator acts as an intermediary between advertisers and publishers, and may place the same advertisement in multiple publications. 
   It is worth noting that ad placement in a netpage publication can be more complex than ad placement in the publication&#39;s traditional counterpart, because the publication&#39;s advertising space is more complex. While ignoring the full complexities of negotiations between advertisers, advertising aggregators and publishers, the preferred form of the netpage system provides some automated support for these negotiations, including support for automated auctions of advertising space. Automation is particularly desirable for the placement of advertisements which generate small amounts of income, such as small or highly localized advertisements. 
   Once placement has been negotiated, the aggregator captures and edits the advertisement and records it on a netpage ad server. Correspondingly, the publisher records the ad placement on the relevant netpage publication server. When the netpage publication server lays out each user&#39;s personalized publication, it picks the relevant advertisements from the netpage ad server. 
   2.3 User Profiles 
   2.3.1 Information Filtering 
   The personalization of news and other publications relies on an assortment of user-specific profile information, including:
         publication customizations   collaborative filtering vectors   contact details   presentation preferences       

   The customization of a publication is typically publication-specific, and so the customization information is maintained by the relevant netpage publication server. 
   A collaborative filtering vector consists of the user&#39;s ratings of a number of news items. It is used to correlate different users&#39; interests for the purposes of making recommendations. Although there are benefits to maintaining a single collaborative filtering vector independently of any particular publication, there are two reasons why it is more practical to maintain a separate vector for each publication: there is likely to be more overlap between the vectors of subscribers to the same publication than between those of subscribers to different publications; and a publication is likely to want to present its users&#39; collaborative filtering vectors as part of the value of its brand, not to be found elsewhere. Collaborative filtering vectors are therefore also maintained by the relevant netpage publication server. 
   Contact details, including name, street address, ZIP Code, state, country, telephone numbers, are global by nature, and are maintained by a netpage registration server. 
   Presentation preferences, including those for quantities, dates and times, are likewise global and maintained in the same way. 
   The localization of advertising relies on the locality indicated in the user&#39;s contact details, while the targeting of advertising relies on personal information such as date of birth, gender, marital status, income, profession, education, or qualitative derivatives such as age range and income range. 
   For those users who choose to reveal personal information for advertising purposes, the information is maintained by the relevant netpage registration server. In the absence of such information, advertising can be targeted on the basis of the demographic associated with the user&#39;s ZIP or ZIP+4 Code. 
   Each user, pen, printer, application provider and application is assigned its own unique identifier, and the netpage registration server maintains the relationships between them, as shown in  FIGS. 21 ,  22 ,  23  and  24 . For registration purposes, a publisher is a special kind of application provider, and a publication is a special kind of application. 
   Each user  800  may be authorized to use any number of printers  802 , and each printer may allow any number of users to use it. Each user has a single default printer (at  66 ), to which periodical publications are delivered by default, whilst pages printed on demand are delivered to the printer through which the user is interacting. The server keeps track of which publishers a user has authorized to print to the user&#39;s default printer. A publisher does not record the ID of any particular printer, but instead resolves the ID when it is required. The user may also be designated as having administrative privileges  69  on the printer, allowing the user to authorize other users to use the printer. This only has meaning if the printer requires administrative privileges  84  for such operations. 
   When a user subscribes  808  to a publication  807 , the publisher  806  (i.e. application provider  803 ) is authorized to print to a specified printer or the user&#39;s default printer. This authorization can be revoked at any time by the user. Each user may have several pens  801 , but a pen is specific to a single user. If a user is authorized to use a particular printer, then that printer recognizes any of the user&#39;s pens. 
   The pen ID is used to locate the corresponding user profile maintained by a particular netpage registration server, via the DNS in the usual way. 
   A Web terminal  809  can be authorized to print on a particular netpage printer, allowing Web pages and netpage documents encountered during Web browsing to be conveniently printed on the nearest netpage printer. 
   The netpage system can collect, on behalf of a printer provider, fees and commissions on income earned through publications printed on the provider&#39;s printers. Such income can include advertising fees, click-through fees, e-commerce commissions, and transaction fees. If the printer is owned by the user, then the user is the printer provider. 
   Each user also has a netpage account  820  which is used to accumulate micro-debits and credits (such as those described in the preceding paragraph); contact details  815 , including name, address and telephone numbers; global preferences  816 , including privacy, delivery and localization settings; any number of biometric records  817 , containing the user&#39;s encoded signature  818 , fingerprint  819  etc; a handwriting model  819  automatically maintained by the system; and SET payment card accounts  821 , with which e-commerce payments can be made. 
   In addition to the user-specific netpage account, each user also has a netpage account  936  specific to each printer the user is authorized to use. Each printer-specific account is used to accumulate micro-debits and credits related to the user&#39;s activities on that printer. The user is billed on a regular basis for any outstanding debit balances. 
   A user optionally appears in the netpage user directory  823 , allowing other users to locate and direct e-mail (etc.) to the user. 
   2.4 Intelligent Page Layout 
   The netpage publication server automatically lays out the pages of each user&#39;s personalized publication on a section-by-section basis. Since most advertisements are in the form of pre-formatted rectangles, they are placed on the page before the editorial content. 
   The advertising ratio for a section can be achieved with wildly varying advertising ratios on individual pages within the section, and the ad layout algorithm exploits this. The algorithm is configured to attempt to co-locate closely tied editorial and advertising content, such as placing ads for roofing material specifically within the publication because of a special feature on do-it-yourself roofing repairs. 
   The editorial content selected for the user, including text and associated images and graphics, is then laid out according to various aesthetic rules. 
   The entire process, including the selection of ads and the selection of editorial content, must be iterated once the layout has converged, to attempt to more closely achieve the user&#39;s stated section size preference. The section size preference can, however, be matched on average over time, allowing significant day-to-day variations. 
   2.5 Document Format 
   Once the document is laid out, it is encoded for efficient distribution and persistent storage on the netpage network. 
   The primary efficiency mechanism is the separation of information specific to a single user&#39;s edition and information shared between multiple users&#39; editions. The specific information consists of the page layout. The shared information consists of the objects to which the page layout refers, including images, graphics, and pieces of text. 
   A text object contains fully-formatted text represented in the Extensible Markup Language (XML) using the Extensible Stylesheet Language (XSL). XSL provides precise control over text formatting independently of the region into which the text is being set, which in this case is being provided by the layout. The text object contains embedded language codes to enable automatic translation, and embedded hyphenation hints to aid with paragraph formatting. 
   An image object encodes an image in the JPEG 2000 wavelet-based compressed image format. A graphic object encodes a 2D graphic in Scalable Vector Graphics (SVG) format. 
   The layout itself consists of a series of placed image and graphic objects, linked textflow objects through which text objects flow, hyperlinks and input fields as described above, and watermark regions. These layout objects are summarized in Table 3. The layout uses a compact format suitable for efficient distribution and storage. 
                   TABLE 3                  netpage layout objects                                 Layout       Format of           object   Attribute   linked object                       Image   Position   —               Image object ID   JPEG 2000           Graphic   Position   —               Graphic object ID   SVG           Textflow   Textflow ID   —               Zone   —               Optional text object ID   XML/XSL           Hyperlink   Type   —               Zone   —               Application ID, etc.   —           Field   Type   —               Meaning   —               Zone   —           Watermark   Zone   —                        
2.6 Document Distribution
 
   As described above, for purposes of efficient distribution and persistent storage on the netpage network, a user-specific page layout is separated from the shared objects to which it refers. 
   When a subscribed publication is ready to be distributed, the netpage publication server allocates, with the help of the netpage ID server  12 , a unique ID for each page, page instance, document, and document instance. 
   The server computes a set of optimized subsets of the shared content and creates a multicast channel for each subset, and then tags each user-specific layout with the names of the multicast channels which will carry the shared content used by that layout. The server then pointcasts each user&#39;s layouts to that user&#39;s printer via the appropriate page server, and when the pointcasting is complete, multicasts the shared content on the specified channels. After receiving its pointcast, each page server and printer subscribes to the multicast channels specified in the page layouts. During the multicasts, each page server and printer extracts from the multicast streams those objects referred to by its page layouts. The page servers persistently archive the received page layouts and shared content. 
   Once a printer has received all the objects to which its page layouts refer, the printer re-creates the fully-populated layout and then rasterizes and prints it. 
   Under normal circumstances, the printer prints pages faster than they can be delivered. Assuming a quarter of each page is covered with images, the average page has a size of less than 400 KB. The printer can therefore hold in excess of 100 such pages in its internal 64 MB memory, allowing for temporary buffers etc. The printer prints at a rate of one page per second. This is equivalent to 400 KB or about 3 Mbit of page data per second, which is similar to the highest expected rate of page data delivery over a broadband network. 
   Even under abnormal circumstances, such as when the printer runs out of paper, it is likely that the user will be able to replenish the paper supply before the printer&#39;s 100-page internal storage capacity is exhausted. 
   However, if the printer&#39;s internal memory does fill up, then the printer will be unable to make use of a multicast when it first occurs. The netpage publication server therefore allows printers to submit requests for re-multicasts. When a critical number of requests is received or a timeout occurs, the server re-multicasts the corresponding shared objects. 
   Once a document is printed, a printer can produce an exact duplicate at any time by retrieving its page layouts and contents from the relevant page server. 
   2.7 On-Demand Documents 
   When a netpage document is requested on demand, it can be personalized and delivered in much the same way as a periodical. However, since there is no shared content, delivery is made directly to the requesting printer without the use of multicast. 
   When a non-netpage document is requested on demand, it is not personalized, and it is delivered via a designated netpage formatting server which reformats it as a netpage document. A netpage formatting server is a special instance of a netpage publication server. The netpage formatting server has knowledge of various Internet document formats, including Adobe&#39;s Portable Document Format (PDF), and Hypertext Markup Language (HTML). In the case of HTML, it can make use of the higher resolution of the printed page to present Web pages in a multi-column format, with a table of contents. It can automatically include all Web pages directly linked to the requested page. The user can tune this behavior via a preference. 
   The netpage formatting server makes standard netpage behavior, including interactivity and persistence, available on any Internet document, no matter what its origin and format. It hides knowledge of different document formats from both the netpage printer and the netpage page server, and hides knowledge of the netpage system from Web servers. 
   3 Security 
   3.1 Cryptography 
   Cryptography is used to protect sensitive information, both in storage and in transit, and to authenticate parties to a transaction. There are two classes of cryptography in widespread use: secret-key cryptography and public-key cryptography. The netpage network uses both classes of cryptography. 
   Secret-key cryptography, also referred to as symmetric cryptography, uses the same key to encrypt and decrypt a message. Two parties wishing to exchange messages must first arrange to securely exchange the secret key. 
   Public-key cryptography, also referred to as asymmetric cryptography, uses two encryption keys. The two keys are mathematically related in such a way that any message encrypted using one key can only be decrypted using the other key. One of these keys is then published, while the other is kept private. The public key is used to encrypt any message intended for the holder of the private key. Once encrypted using the public key, a message can only be decrypted using the private key. Thus two parties can securely exchange messages without first having to exchange a secret key. To ensure that the private key is secure, it is normal for the holder of the private key to generate the key pair. 
   Public-key cryptography can be used to create a digital signature. The holder of the private key can create a known hash of a message and then encrypt the hash using the private key. Anyone can then verify that the encrypted hash constitutes the “signature” of the holder of the private key with respect to that particular message by decrypting the encrypted hash using the public key and verifying the hash against the message. If the signature is appended to the message, then the recipient of the message can verify both that the message is genuine and that it has not been altered in transit. 
   To make public-key cryptography work, there has to be a way to distribute public keys which prevents impersonation. This is normally done using certificates and certificate authorities. A certificate authority is a trusted third party which authenticates the connection between a public key and someone&#39;s identity. The certificate authority verifies the person&#39;s identity by examining identity documents, and then creates and signs a digital certificate containing the person&#39;s identity details and public key. Anyone who trusts the certificate authority can use the public key in the certificate with a high degree of certainty that it is genuine. They just have to verify that the certificate has indeed been signed by the certificate authority, whose public key is well-known. 
   In most transaction environments, public-key cryptography is only used to create digital signatures and to securely exchange secret session keys. Secret-key cryptography is used for all other purposes. 
   In the following discussion, when reference is made to the secure transmission of information between a netpage printer and a server, what actually happens is that the printer obtains the server&#39;s certificate, authenticates it with reference to the certificate authority, uses the public key-exchange key in the certificate to exchange a secret session key with the server, and then uses the secret session key to encrypt the message data. A session key, by definition, can have an arbitrarily short lifetime. 
   3.2 Netpage Printer Security 
   Each netpage printer is assigned a pair of unique identifiers at time of manufacture which are stored in read-only memory in the printer and in the netpage registration server database. The first ID  62  is public and uniquely identifies the printer on the netpage network. The second ID is secret and is used when the printer is first registered on the network. 
   When the printer connects to the netpage network for the first time after installation, it creates a signature public/private key pair. It transmits the secret ID and the public key securely to the netpage registration server. The server compares the secret ID against the printer&#39;s secret ID recorded in its database, and accepts the registration if the IDs match. It then creates and signs a certificate containing the printer&#39;s public ID and public signature key, and stores the certificate in the registration database. 
   The netpage registration server acts as a certificate authority for netpage printers, since it has access to secret information allowing it to verify printer identity. 
   When a user subscribes to a publication, a record is created in the netpage registration server database authorizing the publisher to print the publication to the user&#39;s default printer or a specified printer. Every document sent to a printer via a page server is addressed to a particular user and is signed by the publisher using the publisher&#39;s private signature key. The page server verifies, via the registration database, that the publisher is authorized to deliver the publication to the specified user. The page server verifies the signature using the publisher&#39;s public key, obtained from the publisher&#39;s certificate stored in the registration database. 
   The netpage registration server accepts requests to add printing authorizations to the database, so long as those requests are initiated via a pen registered to the printer. 
   3.3 Netpage Pen Security 
   Each netpage pen is assigned a unique identifier at time of manufacture which is stored in read-only memory in the pen and in the netpage registration server database. The pen ID  61  uniquely identifies the pen on the netpage network. 
   A netpage pen can “know” a number of netpage printers, and a printer can “know” a number of pens. A pen communicates with a printer via a radio frequency signal whenever it is within range of the printer. Once a pen and printer are registered, they regularly exchange session keys. Whenever the pen transmits digital ink to the printer, the digital ink is always encrypted using the appropriate session key. Digital ink is never transmitted in the clear. 
   A pen stores a session key for every printer it knows, indexed by printer ID, and a printer stores a session key for every pen it knows, indexed by pen ID. Both have a large but finite storage capacity for session keys, and will forget a session key on a least-recently-used basis if necessary. 
   When a pen comes within range of a printer, the pen and printer discover whether they know each other. If they don&#39;t know each other, then the printer determines whether it is supposed to know the pen. This might be, for example, because the pen belongs to a user who is registered to use the printer. If the printer is meant to know the pen but doesn&#39;t, then it initiates the automatic pen registration procedure. If the printer isn&#39;t meant to know the pen, then it agrees with the pen to ignore it until the pen is placed in a charging cup, at which time it initiates the registration procedure. 
   In addition to its public ID, the pen contains a secret key-exchange key. The key-exchange key is also recorded in the netpage registration server database at time of manufacture. During registration, the pen transmits its pen ID to the printer, and the printer transmits the pen ID to the netpage registration server. The server generates a session key for the printer and pen to use, and securely transmits the session key to the printer. It also transmits a copy of the session key encrypted with the pen&#39;s key-exchange key. The printer stores the session key internally, indexed by the pen ID, and transmits the encrypted session key to the pen. The pen stores the session key internally, indexed by the printer ID. 
   Although a fake pen can impersonate a pen in the pen registration protocol, only a real pen can decrypt the session key transmitted by the printer. 
   When a previously unregistered pen is first registered, it is of limited use until it is linked to a user. A registered but “un-owned” pen is only allowed to be used to request and fill in netpage user and pen registration forms, to register a new user to which the new pen is automatically linked, or to add a new pen to an existing user. 
   The pen uses secret-key rather than public-key encryption because of hardware performance constraints in the pen. 
   3.4 Secure Documents 
   The netpage system supports the delivery of secure documents such as tickets and coupons. The netpage printer includes a facility to print watermarks, but will only do so on request from publishers who are suitably authorized. The publisher indicates its authority to print watermarks in its certificate, which the printer is able to authenticate. 
   The “watermark” printing process uses an alternative dither matrix in specified “watermark” regions of the page. Back-to-back pages contain mirror-image watermark regions which coincide when printed. The dither matrices used in odd and even pages&#39; watermark regions are designed to produce an interference effect when the regions are viewed together, achieved by looking through the printed sheet. 
   The effect is similar to a watermark in that it is not visible when looking at only one side of the page, and is lost when the page is copied by normal means. 
   Pages of secure documents cannot be copied using the built-in netpage copy mechanism described in Section 1.9 above. This extends to copying netpages on netpage-aware photocopiers. 
   Secure documents are typically generated as part of e-commerce transactions. They can therefore include the user&#39;s photograph which was captured when the user registered biometric information with the netpage registration server, as described in Section 2. 
   When presented with a secure netpage document, the recipient can verify its authenticity by requesting its status in the usual way. The unique ID of a secure document is only valid for the lifetime of the document, and secure document IDs are allocated non-contiguously to prevent their prediction by opportunistic forgers. A secure document verification pen can be developed with built-in feedback on verification failure, to support easy point-of-presentation document verification. 
   Clearly neither the watermark nor the user&#39;s photograph are secure in a cryptographic sense. They simply provide a significant obstacle to casual forgery. Online document verification, particularly using a verification pen, provides an added level of security where it is needed, but is still not entirely immune to forgeries. 
   3.5 Non-Repudiation 
   In the netpage system, forms submitted by users are delivered reliably to forms handlers and are persistently archived on netpage page servers. It is therefore impossible for recipients to repudiate delivery. 
   E-commerce payments made through the system, as described in Section 4, are also impossible for the payee to repudiate. 
   4 Electronic Commerce Model 
   4.1 Secure Electronic Transaction (Set) 
   The netpage system uses the Secure Electronic Transaction (SET) system as one of its payment systems. SET, having been developed by MasterCard and Visa, is organized around payment cards, and this is reflected in the terminology. However, much of the system is independent of the type of accounts being used. 
   In SET, cardholders and merchants register with a certificate authority and are issued with certificates containing their public signature keys. The certificate authority verifies a cardholder&#39;s registration details with the card issuer as appropriate, and verifies a merchant&#39;s registration details with the acquirer as appropriate. Cardholders and merchants store their respective private signature keys securely on their computers. During the payment process, these certificates are used to mutually authenticate a merchant and cardholder, and to authenticate them both to the payment gateway. 
   SET has not yet been adopted widely, partly because cardholder maintenance of keys and certificates is considered burdensome. Interim solutions which maintain cardholder keys and certificates on a server and give the cardholder access via a password have met with some success. 
   4.2 SET Payments 
   In the netpage system the netpage registration server acts as a proxy for the netpage user (i.e. the cardholder) in SET payment transactions. 
   The netpage system uses biometrics to authenticate the user and authorize SET payments. Because the system is pen-based, the biometric used is the user&#39;s on-line signature, consisting of time-varying pen position and pressure. A fingerprint biometric can also be used by designing a fingerprint sensor into the pen, although at a higher cost. The type of biometric used only affects the capture of the biometric, not the authorization aspects of the system. 
   The first step to being able to make SET payments is to register the user&#39;s biometric with the netpage registration server. This is done in a controlled environment, for example a bank, where the biometric can be captured at the same time as the user&#39;s identity is verified. The biometric is captured and stored in the registration database, linked to the user&#39;s record. The user&#39;s photograph is also optionally captured and linked to the record. The SET cardholder registration process is completed, and the resulting private signature key and certificate are stored in the database. The user&#39;s payment card information is also stored, giving the netpage registration server enough information to act as the user&#39;s proxy in any SET payment transaction. 
   When the user eventually supplies the biometric to complete a payment, for example by signing a netpage order form, the printer securely transmits the order information, the pen ID and the biometric data to the netpage registration server. The server verifies the biometric with respect to the user identified by the pen ID, and from then on acts as the user&#39;s proxy in completing the SET payment transaction. 
   4.3 Micro-Payments 
   The netpage system includes a mechanism for micro-payments, to allow the user to be conveniently charged for printing low-cost documents on demand and for copying copyright documents, and possibly also to allow the user to be reimbursed for expenses incurred in printing advertising material. The latter depends on the level of subsidy already provided to the user. 
   When the user registers for e-commerce, a network account is established which aggregates micro-payments. The user receives a statement on a regular basis, and can settle any outstanding debit balance using the standard payment mechanism. 
   The network account can be extended to aggregate subscription fees for periodicals, which would also otherwise be presented to the user in the form of individual statements. 
   4.4 Transactions 
   When a user requests a netpage in a particular application context, the application is able to embed a user-specific transaction ID  55  in the page. Subsequent input through the page is tagged with the transaction ID, and the application is thereby able to establish an appropriate context for the user&#39;s input. 
   When input occurs through a page which is not user-specific, however, the application must use the user&#39;s unique identity to establish a context. A typical example involves adding items from a pre-printed catalog page to the user&#39;s virtual “shopping cart”. To protect the user&#39;s privacy, however, the unique user ID  60  known to the netpage system is not divulged to applications. This is to prevent different application providers from easily correlating independently accumulated behavioral data. 
   The netpage registration server instead maintains an anonymous relationship between a user and an application via a unique alias ID  65 , as shown in  FIG. 24 . Whenever the user activates a hyperlink tagged with the “registered” attribute, the netpage page server asks the netpage registration server to translate the associated application ID  64 , together with the pen ID  61 , into an alias ID  65 . The alias ID is then submitted to the hyperlink&#39;s application. 
   The application maintains state information indexed by alias ID, and is able to retrieve user-specific state information without knowledge of the global identity of the user. 
   The system also maintains an independent certificate and private signature key for each of a user&#39;s applications, to allow it to sign application transactions on behalf of the user using only application-specific information. 
   To assist the system in routing product bar code (UPC) “hyperlink” activations, the system records a favorite application on behalf of the user for any number of product types. 
   Each application is associated with an application provider, and the system maintains an account on behalf of each application provider, to allow it to credit and debit the provider for click-through fees etc. 
   An application provider can be a publisher of periodical subscribed content. The system records the user&#39;s willingness to receive the subscribed publication, as well as the expected frequency of publication. 
   5 Communications Protocols 
   A communications protocol defines an ordered exchange of messages between entities. In the netpage system, entities such as pens, printers and servers utilise a set of defined protocols to cooperatively handle user interaction with the netpage system. 
   Each protocol is illustrated by way of a sequence diagram in which the horizontal dimension is used to represent message flow and the vertical dimension is used to represent time. Each entity is represented by a rectangle containing the name of the entity and a vertical column representing the lifeline of the entity. During the time an entity exists, the lifeline is shown as a dashed line. During the time an entity is active, the lifeline is shown as a double line. Because the protocols considered here do not create or destroy entities, lifelines are generally cut short as soon as an entity ceases to participate in a protocol. 
   5.1 Subscription Delivery Protocol 
   A preferred embodiment of a subscription delivery protocol is shown in  FIG. 40 . 
   A large number of users may subscribe to a periodical publication. Each user&#39;s edition may be laid out differently, but many users&#39; editions will share common content such as text objects and image objects. The subscription delivery protocol therefore delivers document structures to individual printers via pointcast, but delivers shared content objects via multicast. 
   The application (i.e. publisher) first obtains a document ID  51  for each document from an ID server  12 . It then sends each document structure, including its document ID and page descriptions, to the page server  10  responsible for the document&#39;s newly allocated ID. It includes its own application ID  64 , the subscriber&#39;s alias ID  65 , and the relevant set of multicast channel names. It signs the message using its private signature key. 
   The page server uses the application ID and alias ID to obtain from the registration server the corresponding user ID  60 , the user&#39;s selected printer ID  62  (which may be explicitly selected for the application, or may be the user&#39;s default printer), and the application&#39;s certificate. 
   The application&#39;s certificate allows the page server to verify the message signature. The page server&#39;s request to the registration server fails if the application ID and alias ID don&#39;t together identify a subscription  808 . 
   The page server then allocates document and page instance IDs and forwards the page descriptions, including page IDs  50 , to the printer. It includes the relevant set of multicast channel names for the printer to listen to. 
   It then returns the newly allocated page IDs to the application for future reference. 
   Once the application has distributed all of the document structures to the subscribers&#39; selected printers via the relevant page servers, it multicasts the various subsets of the shared objects on the previously selected multicast channels. Both page servers and printers monitor the appropriate multicast channels and receive their required content objects. They are then able to populate the previously pointcast document structures. This allows the page servers to add complete documents to their databases, and it allows the printers to print the documents. 
   5.2 Hyperlink Activation Protocol 
   A preferred embodiment of a hyperlink activation protocol is shown in  FIG. 42 . 
   When a user clicks on a netpage with a netpage pen, the pen communicates the click to the nearest netpage printer  601 . The click identifies the page and a location on the page. The printer already knows the ID  61  of the pen from the pen connection protocol. 
   The printer determines, via the DNS, the network address of the page server  10   a  handling the particular page ID  50 . The address may already be in its cache if the user has recently interacted with the same page. The printer then forwards the pen ID, its own printer ID  62 , the page ID and click location to the page server. 
   The page server loads the page description  5  identified by the page ID and determines which input element&#39;s zone  58 , if any, the click lies in. Assuming the relevant input element is a hyperlink element  844 , the page server then obtains the associated application ID  64  and link ID  54 , and determines, via the DNS, the network address of the application server hosting the application  71 . 
   The page server uses the pen ID  61  to obtain the corresponding user ID  60  from the registration server  11 , and then allocates a globally unique hyperlink request ID  52  and builds a hyperlink request  934 . The hyperlink request class diagram is shown in  FIG. 41 . The hyperlink request records the IDs of the requesting user and printer, and identifies the clicked hyperlink instance  862 . The page server then sends its own server ID  53 , the hyperlink request ID, and the link ID to the application. 
   The application produces a response document according to application-specific logic, and obtains a document ID  51  from an ID server  12 . It then sends the document to the page server  10   b  responsible for the document&#39;s newly allocated ID, together with the requesting page server&#39;s ID and the hyperlink request ID. 
   The second page server sends the hyperlink request ID and application ID to the first page server to obtain the corresponding user ID and printer ID  62 . The first page server rejects the request if the hyperlink request has expired or is for a different application. 
   The second page server allocates document instance and page IDs  50 , returns the newly allocated page IDs to the application, adds the complete document to its own database, and finally sends the page descriptions to the requesting printer. 
   The hyperlink instance may include a meaningful transaction ID  55 , in which case the first page server includes the transaction ID in the message sent to the application. This allows the application to establish a transaction-specific context for the hyperlink activation. 
   If the hyperlink requires a user alias, i.e. its “alias required” attribute is set, then the first page server sends both the pen ID  61  and the hyperlink&#39;s application ID  64  to the registration server  11  to obtain not just the user ID corresponding to the pen ID but also the alias ID  65  corresponding to the application ID and the user ID. It includes the alias ID in the message sent to the application, allowing the application to establish a user-specific context for the hyperlink activation. 
   5.3 Handwriting Recognition Protocol 
   When a user draws a stroke on a netpage with a netpage pen, the pen communicates the stroke to the nearest netpage printer. The stroke identifies the page and a path on the page. 
   The printer forwards the pen ID  61 , its own printer ID  62 , the page ID  50  and stroke path to the page server  10  in the usual way. 
   The page server loads the page description  5  identified by the page ID and determines which input element&#39;s zone  58 , if any, the stroke intersects. Assuming the relevant input element is a text field  878 , the page server appends the stroke to the text field&#39;s digital ink. 
   After a period of inactivity in the zone of the text field, the page server sends the pen ID and the pending strokes to the registration server  11  for interpretation. The registration server identifies the user corresponding to the pen, and uses the user&#39;s accumulated handwriting model  822  to interpret the strokes as handwritten text. Once it has converted the strokes to text, the registration server returns the text to the requesting page server. The page server appends the text to the text value of the text field. 
   5.4 Signature Verification Protocol 
   Assuming the input element whose zone the stroke intersects is a signature field  880 , the page server  10  appends the stroke to the signature field&#39;s digital ink. 
   After a period of inactivity in the zone of the signature field, the page server sends the pen ID  61  and the pending strokes to the registration server  11  for verification. It also sends the application ID  64  associated with the form of which the signature field is part, as well as the form ID  56  and the current data content of the form. The registration server identifies the user corresponding to the pen, and uses the user&#39;s dynamic signature biometric  818  to verify the strokes as the user&#39;s signature. Once it has verified the signature, the registration server uses the application ID  64  and user ID  60  to identify the user&#39;s application-specific private signature key. It then uses the key to generate a digital signature of the form data, and returns the digital signature to the requesting page server. The page server assigns the digital signature to the signature field and sets the associated form&#39;s status to frozen. 
   The digital signature includes the alias ID  65  of the corresponding user. This allows a single form to capture multiple users&#39; signatures. 
   5.5 Form Submission Protocol 
   A preferred embodiment of a form submission protocol is shown in  FIG. 43 . 
   Form submission occurs via a form hyperlink activation. It thus follows the protocol defined in Section 5.2, with some form-specific additions. 
   In the case of a form hyperlink, the hyperlink activation message sent by the page server  10  to the application  71  also contains the form ID  56  and the current data content of the form. If the form contains any signature fields, then the application verifies each one by extracting the alias ID  65  associated with the corresponding digital signature and obtaining the corresponding certificate from the registration server  11 . 
   6 Netpage Pen Description 
   6.1 Pen Mechanics 
   Referring to  FIGS. 8 and 9 , the pen, generally designated by reference numeral  101 , includes a housing  102  in the form of a plastics moulding having walls  103  defining an interior space  104  for mounting the pen components. The pen top  105  is in operation rotatably mounted at one end  106  of the housing  102 . A semi-transparent cover  107  is secured to the opposite end  108  of the housing  102 . The cover  107  is also of moulded plastics, and is formed from semi-transparent material in order to enable the user to view the status of the LED mounted within the housing  102 . The cover  107  includes a main part  109  which substantially surrounds the end  108  of the housing  102  and a projecting portion  110  which projects back from the main part  109  and fits within a corresponding slot  111  formed in the walls  103  of the housing  102 . A radio antenna  112  is mounted behind the projecting portion  110 , within the housing  102 . Screw threads  113  surrounding an aperture  113 A on the cover  107  are arranged to receive a metal end piece  114 , including corresponding screw threads  115 . The metal end piece  114  is removable to enable ink cartridge replacement. 
   Also mounted within the cover  107  is a tri-color status LED  116  on a flex PCB  117 . The antenna  112  is also mounted on the flex PCB  117 . The status LED  116  is mounted at the top of the pen  101  for good all-around visibility. 
   The pen can operate both as a normal marking ink pen and as a non-marking stylus. An ink pen cartridge  118  with nib  119  and a stylus  120  with stylus nib  121  are mounted side by side within the housing  102 . Either the ink cartridge nib  119  or the stylus nib  121  can be brought forward through open end  122  of the metal end piece  114 , by rotation of the pen top  105 . Respective slider blocks  123  and  124  are mounted to the ink cartridge  118  and stylus  120 , respectively. A rotatable cam barrel  125  is secured to the pen top  105  in operation and arranged to rotate therewith. The cam barrel  125  includes a cam  126  in the form of a slot within the walls  181  of the cam barrel. Cam followers  127  and  128  projecting from slider blocks  123  and  124  fit within the cam slot  126 . On rotation of the cam barrel  125 , the slider blocks  123  or  124  move relative to each other to project either the pen nib  119  or stylus nib  121  out through the hole  122  in the metal end piece  114 . The pen  101  has three states of operation. By turning the top  105  through 90° steps, the three states are:
         Stylus  120  nib  121  out;   Ink cartridge  118  nib  119  out; and   Neither ink cartridge  118  nib  119  out nor stylus  120  nib  121  out.       

   A second flex PCB  129 , is mounted on an electronics chassis  130  which sits within the housing  102 . The second flex PCB  129  mounts an infrared LED  131  for providing infrared radiation for projection onto the surface. An image sensor  132  is provided mounted on the second flex PCB  129  for receiving reflected radiation from the surface. The second flex PCB  129  also mounts a radio frequency chip  133 , which includes an RF transmitter and RF receiver, and a controller chip  134  for controlling operation of the pen  101 . An optics block  135  (formed from moulded clear plastics) sits within the cover  107  and projects an infrared beam onto the surface and receives images onto the image sensor  132 . Power supply wires  136  connect the components on the second flex PCB  129  to battery contacts  137  which are mounted within the cam barrel  125 . A terminal  138  connects to the battery contacts  137  and the cam barrel  125 . A three volt rechargeable battery  139  sits within the cam barrel  125  in contact with the battery contacts. An induction charging coil  140  is mounted about the second flex PCB  129  to enable recharging of the battery  139  via induction. The second flex PCB  129  also mounts an infrared LED  143  and infrared photodiode  144  for detecting displacement in the cam barrel  125  when either the stylus  120  or the ink cartridge  118  is used for writing, in order to enable a determination of the force being applied to the surface by the pen nib  119  or stylus nib  121 . The IR photodiode  144  detects light from the IR LED  143  via reflectors (not shown) mounted on the slider blocks  123  and  124 . 
   Rubber grip pads  141  and  142  are provided towards the end  108  of the housing  102  to assist gripping the pen  101 , and top  105  also includes a clip  142  for clipping the pen  101  to a pocket. 
   6.2 Pen Controller 
   The pen  101  is arranged to determine the position of its nib (stylus nib  121  or ink cartridge nib  119 ) by imaging, in the infrared spectrum, an area of the surface in the vicinity of the nib. It records the location data from the nearest location tag, and is arranged to calculate the distance of the nib  121  or  119  from the location tab utilising optics  135  and controller chip  134 . The controller chip  134  calculates the orientation of the pen and the nib-to-tag distance from the perspective distortion observed on the imaged tag. 
   Utilising the RF chip  133  and antenna  112  the pen  101  can transmit the digital ink data (which is encrypted for security and packaged for efficient transmission) to the computing system. 
   When the pen is in range of a receiver, the digital ink data is transmitted as it is formed. When the pen  101  moves out of range, digital ink data is buffered within the pen  101  (the pen  101  circuitry includes a buffer arranged to store digital ink data for approximately 12 minutes of the pen motion on the surface) and can be transmitted later. 
   The controller chip  134  is mounted on the second flex PCB  129  in the pen  101 .  FIG. 10  is a block diagram illustrating in more detail the architecture of the controller chip  134 .  FIG. 10  also shows representations of the RF chip  133 , the image sensor  132 , the tri-color status LED  116 , the IR illumination LED  131 , the IR force sensor LED  143 , and the force sensor photodiode  144 . 
   The pen controller chip  134  includes a controlling processor  145 . Bus  146  enables the exchange of data between components of the controller chip  134 . Flash memory  147  and a 512 KB DRAM  148  are also included. An analog-to-digital converter  149  is arranged to convert the analog signal from the force sensor photodiode  144  to a digital signal. 
   An image sensor interface  152  interfaces with the image sensor  132 . A transceiver controller  153  and base band circuit  154  are also included to interface with the RF chip  133  which includes an RF circuit  155  and RF resonators and inductors  156  connected to the antenna  112 . 
   The controlling processor  145  captures and decodes location data from tags from the surface via the image sensor  132 , monitors the force sensor photodiode  144 , controls the LEDs  116 ,  131  and  143 , and handles short-range radio communication via the radio transceiver  153 . It is a medium-performance (˜40 MHz) general-purpose RISC processor. 
   The processor  145 , digital transceiver components (transceiver controller  153  and baseband circuit  154 ), image sensor interface  152 , flash memory  147  and 512 KB DRAM  148  are integrated in a single controller ASIC. Analog RF components (RF circuit  155  and RF resonators and inductors  156 ) are provided in the separate RF chip. 
   The image sensor is a 215×215 pixel CCD (such a sensor is produced by Matsushita Electronic Corporation, and is described in a paper by Itakura, K T Nobusada, N Okusenya, R Nagayoshi, and M Ozaki, “A 1 mm 50 k-Pixel IT CCD Image Sensor for Miniature Camera System”, IEEE Transactions on Electronic Devices, Volt 47, number 1, January 2000, which is incorporated herein by reference) with an IR filter. 
   The controller ASIC  134  enters a quiescent state after a period of inactivity when the pen  101  is not in contact with a surface. It incorporates a dedicated circuit  150  which monitors the force sensor photodiode  144  and wakes up the controller  134  via the power manager  151  on a pen-down event. 
   The radio transceiver communicates in the unlicensed 900 MHz band normally used by cordless telephones, or alternatively in the unlicensed 2.4 GHz industrial, scientific and medical (ISM) band, and uses frequency hopping and collision detection to provide interference-free communication. 
   In an alternative embodiment, the pen incorporates an Infrared Data Association (IrDA) interface for short-range communication with a base station or netpage printer. 
   In a further embodiment, the pen  101  includes a pair of orthogonal accelerometers mounted in the normal plane of the pen  101  axis. The accelerometers  190  are shown in  FIGS. 9 and 10  in ghost outline. 
   The provision of the accelerometers enables this embodiment of the pen  101  to sense motion without reference to surface location tags, allowing the location tags to be sampled at a lower rate. Each location tag ID can then identify an object of interest rather than a position on the surface. For example, if the object is a user interface input element (e.g. a command button), then the tag ID of each location tag within the area of the input element can directly identify the input element. 
   The acceleration measured by the accelerometers in each of the x and y directions is integrated with respect to time to produce an instantaneous velocity and position. 
   Since the starting position of the stroke is not known, only relative positions within a stroke are calculated. Although position integration accumulates errors in the sensed acceleration, accelerometers typically have high resolution, and the time duration of a stroke, over which errors accumulate, is short. 
   7 Netpage Printer Description 
   7.1 Printer Mechanics 
   The vertically-mounted netpage wallprinter  601  is shown fully assembled in  FIG. 11 . It prints netpages on Letter/A4 sized media using duplexed 8½″ Memjet™ print engines  602  and  603 , as shown in  FIGS. 12 and 12   a . It uses a straight paper path with the paper  604  passing through the duplexed print engines  602  and  603  which print both sides of a sheet simultaneously, in full color and with full bleed. 
   An integral binding assembly  605  applies a strip of glue along one edge of each printed sheet, allowing it to adhere to the previous sheet when pressed against it. This creates a final bound document  618  which can range in thickness from one sheet to several hundred sheets. 
   The replaceable ink cartridge  627 , shown in  FIG. 13  coupled with the duplexed print engines, has bladders or chambers for storing fixative, adhesive, and cyan, magenta, yellow, black and infrared inks. The cartridge also contains a micro air filter in a base molding. The micro air filter interfaces with an air pump  638  inside the printer via a hose  639 . This provides filtered air to the printheads to prevent ingress of micro particles into the Memjet™ printheads  350  which might otherwise clog the printhead nozzles. By incorporating the air filter within the cartridge, the operational life of the filter is effectively linked to the life of the cartridge. The ink cartridge is a fully recyclable product with a capacity for printing and gluing 3000 pages (1500 sheets). 
   Referring to  FIG. 12 , the motorized media pick-up roller assembly  626  pushes the top sheet directly from the media tray past a paper sensor on the first print engine  602  into the duplexed Memjet™ printhead assembly. The two Memjet™ print engines  602  and  603  are mounted in an opposing in-line sequential configuration along the straight paper path. The paper  604  is drawn into the first print engine  602  by integral, powered pick-up rollers  626 . The position and size of the paper  604  is sensed and full bleed printing commences. Fixative is printed simultaneously to aid drying in the shortest possible time. 
   The paper exits the first Memjet™ print engine  602  through a set of powered exit spike wheels (aligned along the straight paper path), which act against a rubberized roller. These spike wheels contact the ‘wet’ printed surface and continue to feed the sheet  604  into the second Memjet™ print engine  603 . 
   Referring to  FIGS. 12 and 12   a , the paper  604  passes from the duplexed print engines  602  and  603  into the binder assembly  605 . The printed page passes between a powered spike wheel axle  670  with a fibrous support roller and another movable axle with spike wheels and a momentary action glue wheel. The movable axle/glue assembly  673  is mounted to a metal support bracket and it is transported forward to interface with the powered axle  670  via gears by action of a camshaft. A separate motor powers this camshaft. 
   The glue wheel assembly  673  consists of a partially hollow axle  679  with a rotating coupling for the glue supply hose  641  from the ink cartridge  627 . This axle  679  connects to a glue wheel, which absorbs adhesive by capillary action through radial holes. A molded housing  682  surrounds the glue wheel, with an opening at the front. Pivoting side moldings and sprung outer doors are attached to the metal bracket and hinge out sideways when the rest of the assembly  673  is thrust forward. This action exposes the glue wheel through the front of the molded housing  682 . Tension springs close the assembly and effectively cap the glue wheel during periods of inactivity. 
   As the sheet  604  passes into the glue wheel assembly  673 , adhesive is applied to one vertical edge on the front side (apart from the first sheet of a document) as it is transported down into the binding assembly  605 . 
   7.2 Printer Controller Architecture 
   The netpage printer controller consists of a controlling processor  750 , a factory-installed or field-installed network interface module  625 , a radio transceiver (transceiver controller  753 , baseband circuit  754 , RF circuit  755 , and RF resonators and inductors  756 ), dual raster image processor (RIP) DSPs  757 , duplexed print engine controllers  760   a  and  760   b , flash memory  658 , and 64 MB of DRAM  657 , as illustrated in  FIG. 14 . 
   The controlling processor handles communication with the network  19  and with local wireless netpage pens  101 , senses the help button  617 , controls the user interface LEDs  613 – 616 , and feeds and synchronizes the RIP DSPs  757  and print engine controllers  760 . It consists of a medium-performance general-purpose microprocessor. The controlling processor  750  communicates with the print engine controllers  760  via a high-speed serial bus  659 . 
   The RIP DSPs rasterize and compress page descriptions to the netpage printer&#39;s compressed page format. Each print engine controller expands, dithers and prints page images to its associated Memjet™ printhead  350  in real time (i.e. at over 30 pages per minute). The duplexed print engine controllers print both sides of a sheet simultaneously. 
   The master print engine controller  760   a  controls the paper transport and monitors ink usage in conjunction with the master QA chip  665  and the ink cartridge QA chip  761 . 
   The printer controller&#39;s flash memory  658  holds the software for both the processor  750  and the DSPs  757 , as well as configuration data. This is copied to main memory  657  at boot time. 
   The processor  750 , DSPs  757 , and digital transceiver components (transceiver controller  753  and baseband circuit  754 ) are integrated in a single controller ASIC  656 . Analog RF components (RF circuit  755  and RF resonators and inductors  756 ) are provided in a separate RF chip  762 . The network interface module  625  is separate, since netpage printers allow the network connection to be factory-selected or field-selected. Flash memory  658  and the 2×256 Mbit (64 MB) DRAM  657  is also off-chip. The print engine controllers  760  are provided in separate ASICs. 
   A variety of network interface modules  625  are provided, each providing a netpage network interface  751  and optionally a local computer or network interface  752 . Netpage network Internet interfaces include POTS modems, Hybrid Fiber-Coax (HFC) cable modems, ISDN modems, DSL modems, satellite transceivers, current and next-generation cellular telephone transceivers, and wireless local loop (WLL) transceivers. Local interfaces include IEEE 1284 (parallel port), 10Base-T and 100Base-T Ethernet, USB and USB 2.0, IEEE 1394 (Firewire), and various emerging home networking interfaces. If an Internet connection is available on the local network, then the local network interface can be used as the netpage network interface. 
   The radio transceiver  753  communicates in the unlicensed 900 MHz band normally used by cordless telephones, or alternatively in the unlicensed 2.4 GHz industrial, scientific and medical (ISM) band, and uses frequency hopping and collision detection to provide interference-free communication. 
   The printer controller optionally incorporates an Infrared Data Association (IrDA) interface for receiving data “squirted” from devices such as netpage cameras. In an alternative embodiment, the printer uses the IrDA interface for short-range communication with suitably configured netpage pens. 
   7.2.1 Rasterization and Printing 
   Once the main processor  750  has received and verified the document&#39;s page layouts and page objects, it runs the appropriate RIP software on the DSPs  757 . 
   The DSPs  757  rasterize each page description and compress the rasterized page image. The main processor stores each compressed page image in memory. The simplest way to load-balance multiple DSPs is to let each DSP rasterize a separate page. The DSPs can always be kept busy since an arbitrary number of rasterized pages can, in general, be stored in memory. This strategy only leads to potentially poor DSP utilization when rasterizing short documents. 
   Watermark regions in the page description are rasterized to a contone-resolution bi-level bitmap which is losslessly compressed to negligible size and which forms part of the compressed page image. 
   The infrared (IR) layer of the printed page contains coded netpage tags at a density of about six per inch. Each tag encodes the page ID, tag ID, and control bits, and the data content of each tag is generated during rasterization and stored in the compressed page image. 
   The main processor  750  passes back-to-back page images to the duplexed print engine controllers  760 . Each print engine controller  760  stores the compressed page image in its local memory, and starts the page expansion and printing pipeline. Page expansion and printing is pipelined because it is impractical to store an entire 114 MB bi-level CMYK+IR page image in memory. 
   7.2.2 Print Engine Controller 
   The page expansion and printing pipeline of the print engine controller  760  consists of a high speed IEEE 1394 serial interface  659 , a standard JPEG decoder  763 , a standard Group 4 Fax decoder  764 , a custom halftoner/compositor unit  765 , a custom tag encoder  766 , a line loader/formatter unit  767 , and a custom interface  768  to the Memjet™ printhead  350 . 
   The print engine controller  360  operates in a double buffered manner. While one page is loaded into DRAM  769  via the high speed serial interface  659 , the previously loaded page is read from DRAM  769  and passed through the print engine controller pipeline. Once the page has finished printing, the page just loaded is printed while another page is loaded. 
   The first stage of the pipeline expands (at  763 ) the JPEG-compressed contone CMYK layer, expands (at  764 ) the Group 4 Fax-compressed bi-level black layer, and renders (at  766 ) the bi-level netpage tag layer according to the tag format defined in section 1.2, all in parallel. The second stage dithers (at  765 ) the contone CMYK layer and composites (at  765 ) the bi-level black layer over the resulting bi-level CMYK layer. The resultant bi-level CMYK+IR dot data is buffered and formatted (at  767 ) for printing on the Memjet™ printhead  350  via a set of line buffers. Most of these line buffers are stored in the off-chip DRAM. The final stage prints the six channels of bi-level dot data (including fixative) to the Memjet™ printhead  350  via the printhead interface  768 . 
   When several print engine controllers  760  are used in unison, such as in a duplexed configuration, they are synchronized via a shared line sync signal  770 . Only one print engine  760 , selected via the external master/slave pin  771 , generates the line sync signal  770  onto the shared line. 
   The print engine controller  760  contains a low-speed processor  772  for synchronizing the page expansion and rendering pipeline, configuring the printhead  350  via a low-speed serial bus  773 , and controlling the stepper motors  675 ,  676 . 
   In the 8½″ versions of the netpage printer, the two print engines each prints 30 Letter pages per minute along the long dimension of the page (11″), giving a line rate of 8.8 kHz at 1600 dpi. In the 12″ versions of the netpage printer, the two print engines each prints 45 Letter pages per minute along the short dimension of the page (8½″), giving a line rate of 10.2 kHz. These line rates are well within the operating frequency of the Memjet™ printhead, which in the current design exceeds 30 kHz. 
   8 Printing Video-Related Documents 
   The netpage system provides a mechanism whereby users watching infotainment programs on television can print the associated informational material on their netpage printer by pressing the “print” button on their remote control at the appropriate time. The “print” button may be a printed button on a netpage document, or may be a physical button on a manufacturer&#39;s remote control. 
   In the case of the manufacturer&#39;s remote control, the remote control and/or television set is suitably modified or augmented to route the print request to the netpage printer. The television or remote control may, for example, include a radio transmitter or transceiver which allows it to communicate with the netpage printer. When the print button is pressed, a message is sent to the netpage printer which contains the current program document information. 
   The program document information may include information such as the television channel ID, date and time. This information uniquely identifies a document associated with the program at that time. The printer or page server constructs a URI (Universal Resource Identifier) based on the television channel ID and determines the address of the television channel&#39;s document server via the DNS in the usual way. It then retrieves the document from the document server based on date and time. Alternatively the program document information may contain a netpage document identifier, which allows the printer or page server to retrieve the document from the page server handling that particular document. 
   A potentially more flexible approach embeds the URI of the document in the video signal itself, for example as a closed caption. In analog video signals there is plenty of room for information in the vertical blanking interval (VBI). The advantage of leveraging support for closed captioning, in particular, is twofold. Closed caption decoders are now standard components in normal-sized television sets, and closed captioning is fully supported in digital television standards that are now being deployed. Other VBI-based schemes require custom decoders and may not survive the transition to digital television. 
   By routing the television set&#39;s video output to the netpage printer, and locating a closed caption decoder in the printer, modification of the television set can be avoided entirely. Other video devices are also then trivially supported. 
   8.1 Embedding Program Information in Video Signals 
   Currently there are standards relating to embedding information in video signals for both analog and digital transmission. 
   8.1.1 Analog Television and Video 
   The Vertical Blanking Interval (VBI) of an analog video signal contains the first 21 scan lines of the video picture, and can contain non-picture data. Line  21  of the VBI is reserved for closed caption information. 
   Field  1  of line  21  contains two captioning channels (CC1 and CC2) and two text channels (TEXT-1 and TEXT-2). Field  2  of line  21  contains two captioning channels, two text channels, and can also contain Extended Data Services (XDS) packets. XDS contains information such as the time of day, station call letters, name of the current program, program content advisory (e.g. V-chip data), etc. The caption data specification and XDS data structure is defined in the Electronic Industries Alliance standard EIA-608 (EIA-608-A “Recommended Practice for Line 21 Data Service”, Electronic Industries Alliance Standard, December 1999, the contents of which are herein incorporated by cross-reference). The general standard for XDS data is EIA-766 (EIA-766 “U.S. Region Rating Table (RRT) and Content Advisory Descriptor for Transport of Content Advisory Information Using ATSC A/65 Program and System Information Protocol (PSIP)”, Electronic Industries Alliance Standard, September 1998, the contents of which are herein incorporated by cross-reference). 
   EIA-746 (EIA-746-A “Transport of Internet Uniform Resource Locator (URL) Information Using Text-2 (T-2) Service”, Electronic Industries Alliance Standard, September 1998, the contents of which are herein incorporated by cross-reference) defines the use of Text-2 for the transport of Internet URLs, or Interactive Television Links. These URLs point to Web pages that contain more information about the current TV program or advertisement. 
   The program document information used by the netpage system can be transmitted using these standards. Either the document URI can be transported in Text-2, or other program document information can be transported in the XDS. As discussed earlier, the netpage system can also utilize the channel, date, time program information normally transmitted in the XDS channel to construct the document URI. 
   8.1.2 Digital Television and Video 
   Digital television broadcasts also carry captioning information and non-caption data (such as that carried in XDS). EIA-708 (EIA-708-B “Digital Television (DTV) Closed Captioning”, Electronic Industries Alliance Standard, December 1999, the contents of which are herein incorporated by cross-reference) defines the standard for Digital Television Closed Captioning. 
   Non-caption data, such as program name and network ID, is transported in a separate data stream using the Program and System Information Protocol (PSIP), which is defined by the ATSC A/65 standard (ATSC A/65 Program and System Information Protocol (PSIP) Standard, Advanced Television System Committee (ATSC), the contents of which are herein incorporated by cross-reference). 
   The program document information used by netpage can be transmitted in the digital TV broadcast in the caption or non-caption data streams. A document URI can be included in the Text-2 equivalent caption field. Other program document information can be transported in the XDS-equivalent non-caption data stream. 
   8.1.3 Netpage Program Document Information 
   The program document information may contain the netpage document identifier of the document associated with the current broadcast, which is used to retrieve the netpage document from the relevant page server. 
   Alternatively the netpage program document information may contain the time of day, channel ID, and program name for the current broadcast. This information is sent to the broadcaster&#39;s application and is used to look up the appropriate document. The document may be formatted as a netpage document by the broadcaster&#39;s application, or by a netpage formatting server. The requested document is printed on the user&#39;s netpage printer. 
   A video recording of a broadcast also records the program&#39;s closed caption data. A user can watch the recording at any time after the original broadcast and request the related document. This applies equally to pre-recorded video tapes and other video media such as laser disc, DVD, etc. 
   8.2 Requesting a Television Related Document 
   A television broadcast may have associated with it one or more documents. The user may request to print the related document while watching the broadcast by pressing a print button on a netpage document or on their manufacturer&#39;s remote control. 
   To extract the program document information from the TV signal a closed caption decoder is required, such as the Zilog “NTSC Line 21 Decoder”. This is a chip-based decoder which accepts the video input signal, extracts, decodes, and outputs the required closed caption or XDS data. 
   The closed caption decoder  500  may be embedded either in the netpage printer  601 , as illustrated in  FIG. 44 , or in the television  501  (or other video device), as illustrated in  FIG. 45 . 
   8.2.1 Decoder Embedded in the Netpage Printer 
   A more detailed block diagram of the netpage printer controller  656  with an embedded closed caption decoder  500  is shown in  FIG. 46 . A low speed serial interface  503 , such as an I 2 C interface, is also needed in the printer controller  656  to allow it to query the decoder. 
   The printer  601  and television  501  are connected so that the “video out” signal from the television is directed to the decoder  500  within the printer. The program document information is decoded and extracted from the TV signal, and is timestamped and stored in the printer in a circular buffer. 
   When the user presses the &lt;Print&gt; button on a netpage document the click is sent by the user&#39;s netpage pen to the netpage printer in the usual way. It is then sent to the relevant page server for interpretation. The &lt;Print&gt; button is implemented as a program information hyperlink  504  (see  FIG. 47 ). When the page server identifies a program information hyperlink  504  activation, it instructs the printer to look up the time-stamped program document information in its closed caption buffer. 
   If this lookup provides a netpage document identifier the page server can retrieve the netpage document directly from the relevant page server. Otherwise the page server sends the request to the broadcaster&#39;s application to look up and return the document  507  relevant to the supplied program document information  506  (see  FIG. 48 ). The application is identified by the hyperlink&#39;s application ID  64 . The document is then printed on the user&#39;s netpage printer  601 . 
   8.2.2 Decoder Embedded in the TV 
   A television  501  (or other video device) may have an embedded closed caption decoder  500  for the purposes of printing TV-related (or other video-related) documents. The manufacturer&#39;s remote control may have a &lt;Print&gt; button, which is pressed by the user to request a TV related document. 
   When the user presses &lt;Print&gt; the program document information is decoded and extracted from the TV signal, and is sent to the netpage printer  601  via a short-range transceiver  502  in the TV. The netpage printer receives the “Print” Program Document Information  508  via its RF chip  762 , then sends this information to the page server  10  which retrieves the appropriate document and prints it on the user&#39;s netpage printer. 
   CONCLUSION 
   The present invention has been described with reference to a preferred embodiment and number of specific alternative embodiments. However, it will be appreciated by those skilled in the relevant fields that a number of other embodiments, differing from those specifically described, will also fall within the spirit and scope of the present invention. Accordingly, it will be understood that the invention is not intended to be limited to the specific embodiments described in the present specification, including documents incorporated by cross-reference as appropriate. The scope of the invention is only limited by the attached claims.