METHOD AND SYSTEM FOR NAVIGATING A HISTORY LIST

Abstract: A method of enabling a user to obtain a printed copy of a document previously printed by the user, the method including: maintaining a history list in a computer system of documents previously printed by the user; printing the history list, or a portion of the history list, in a list document including at least one user interface element associated at least one history item in the history list, to allow the user to indicate a request for a copy of the previously printed document associated with the history item by interacting with the interface element using a sensing device which is adapted to transmit request data to the computer system; retrieving the copy via the computer system; and printing the copy.

Description: METHOD AND SYSTEM FOR NAVIGATING A HISTORY LIST FIELD OF INVENTION The present invention relates generally to methods systems and apparatus for interacting with computers More particularly, the invention relates to enabling a user to obtain a printed copy of a previously printed document via a history list of previously printed documents utilizing such methods, systems and apparatus The invention has been developed primarily to allow a large number ol 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 filed by the applicant or assignee of the present invention simultaneously with the present application PPCCTT//AAUU0000//0000776622,, PPCCTT//AAUU0000//0000776633,, PCT/AU00/00761 PCT/AU00/00760, PCT/AUOO/00758, PCT/AU00/00764. PCT/AU00/00765, PCT/AU00/00766, PCT/AU00/00767, PCT/AU00/00768, PCT/AUOO/00773. PCT/AU00/00774. PCT/AU00/00775. PCT/AU00/00776, PCT/AU00/00777, PCT/AUOO/00770, PCT/AU00/00769. PCT/AU00/00771 , PC r/AUOO/00772. PCT/AU00/00754, PCT/AU00/00755, PCT/AU00/00756, PCT/AU00/00757 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 filed by the applicant or assignee of the present invention on 24 May 2000 PCT/AU00/00518, PCT/AU00/00519, PCT/AU00/00520, PCT/AU00/00521 , PCT/AU00/00523, PCT/AU00/00524. PCT/AU00/00525, PCT/AU00/00526, PCT/AU00/00527, PCT/AU00/00528, PPCCTT//AAUU0000//0000552299,, PPCCTT//AAUU0000//0000553300,, PCT/AUOO/00531, PCT/AU00/00532, PCT/AU00/00533, PCT/AU00/00534, PCT/AU00/00535, PCT/AU00/00536, PCT/AU00/00537, PCT/AU00/00538, PCT/AU00/00539, PCT/AU00/00540, PCT/AU00/00541 , PCT/AU00/00542, PCT/AU00/00543, PCT/AU00/00544, PCT/AU00/00545, PCT/AU00/00547, PCT/AU00/00546, PCT/AU00/00554, PCT/AU00/00556, PCT/AU00/00557 PCT/AUOO/00558, PCT/AU00/00559, PCT/AU00/00560, PCT/AU00/00561. PCT/AU00/00562 PCT/AU00/00563, PCT/AU00/00564, PCT/AU00/00566, PCT/AU00/00567, PCT/AU00/00568 PCT/AU00/00569, PCT/AU0O/O0570, PCT/AU00/00571, PCT/AU00/00572, PCT/AU00/00573, PCT/AU00/00574, PCT/AUOO/00575, PCT/AU00/00576, PCT/AU00/00577, PCT/AUOO/00578, PCT/AU00/00579, PCT/AU00/00581, PCT/AU00/00580, PCT/AU00/00582, PCT/AU00/00587, PCT/AUOO/00588, PCT/AU00/00589, PCT/AU00/00583, PPCCTT//AAUU0000//0000559933,, PPCCTT//AAUUOOOO//0000559900,, PCT/AU00/00591 , PCT/AU00/00592, PCT/AU00/00594, PCT/AU00/00595, PCT/AU00/00596, PCT/AU00/00597, PCT/AU00/00598, PCT/AU00/00516, PCT/AU00/00517 and PCT/AU00/00511 The disclosures of these co-pending applications are incorporated herein by cross-reference BACKGROUND Browsers for navigating the World Wide Web are well known to maintain a history list of Web pages retrieved and displayed by a user, to allow the user to easily re-retπeve and display such previously displayed pages OBJECT It is an object of the present invention to provide a method and system for enabling a user to obtain a printed copy of a previously printed document SUMMARY OF INVENTION According to a first aspect, the present invention provides a method of enabling a user to obtain a printed copy of a document previously printed by the user, the method including maintaining a history list in a computer system of documents previously printed by the user, printing the history list, or a portion of the history list, in a list document including at least one user interface element associated with at least one history item in the history list, to allow the user to indicate a request for a copy of a previously printed document associated with the history item by interacting with the interface element using a sensing device which is adapted to transmit request data to the computer system, retrieving the copy via the computer system, and printing the copy Preferably, the at least one previously printed document is identified by a descπption in the list document which presents a link to a corresponding instance of the previously printed document, for retrieval by the computer system Preferably, at least one further user interface element is provided in the list document to allow the history list to be subject to at least one navigation action using the sensing device, the navigation action being indicated to the computer system via the sensing device and resulting in a further list document being pπnted Preferably, the navigation action is at least one of requesting an ordering of the history list by date, requesting an ordering of the history list by description, requesting a chronologically earlier portion ofthe history list, and requesting a summary version ofthe history list Preferably, the method further includes deletion of a history item from the history list upon request from the user, the sensing device being adapted to identify the history item to be deleted and the list document including an appropπate interface element to allow the request to be transmitted to the computer system using the sensing device Preferably, the list document includes coded data indicative of an identity of the list document and of the at least one interface element, and the method includes receiving, m the computer system, indicating data from the sensing device regarding the identity ofthe list document and a position ofthe sensing device relative to the list document in order to identify the list document and determine when the sensing device is used to interact with the interface element to indicate the request Preferably, the method includes receiving, in the computer system, movement data regarding movement of the sensing device relative to the list document, the sensing device sensing its movement relative to the list document using at least some of the coded data, and identifying the request m the computer system from the movement being at least partially within a zone associated with the interface element In a second aspect, the invention provides a system for enabling a user to obtain a printed copy of a document previously printed by the user, the system including a database maintaining a history list of documents previously printed by the user, a computer system for accessing the database and for generating a list document to include the history list, or a portion of the history list, and to include at least one user interface element associated with at least one history item in the history list, to enable a user to indicate a request for a copy of a previously printed document associated with the history item, a printer to print the list document, and a sensing device for interacting with the interface element so as to transmit request data to the computer system which, upon receipt ofthe request data, retrieves the copy for printing at the printer Preferably, the at least one previously printed document is identified by a description in the list document which presents a link to a corresponding instance of the previously printed document, for retrieval by the computer system Preferably, the list document is printed with further user interface elements to allow the history list to be subjected to one or more navigation actions using the sensing device, each navigation action being indicated to the computer system via the sensing device and resulting in a further list document being printed Preferably, the list document includes coded data indicative of an identity of the list document and of the at least one interface element Preferably, the computer system is adapted to receive movement data regarding movement of the sensing device relative to the list document and to interpret said movement of the sensing device as it relates to the interface element, the sensing device, when moved relative to the list document, sensing the data regarding the interface element using at least some ofthe coded data and generating the data regarding its own movement relative to the list document Accordingly, the present invention provides a system and a method which utilizes one or more forms capable of interacting with a computer system Whilst the novel method and system of the present invention may be used in conjunction with a single computer system, in a particularly preferred form it is designed to operate over a computer network, such as the Internet Physically, the form is disposed on a surface medium of any suitable structure However, in a preferred arrangement, the form is disposed on sheet material such as paper or the like which has the coded data pπnted on it and which allows interaction with the computer system The coded data is detectable preferably, but not exclusively, outside the visible spectrum, thereby enabling it to be machine-readable but substantially invisible to the human eye The form may also include visible mateπal which provides information to a user, such as the application or purpose ofthe form, and which visible information may be registered or correlate in position with the relevant hidden coded data The system also includes a sensing device to convey data from the form to the computer system, and in some instances, to contribute additional data Again, the sensing device may take a variety of forms but is preferably compact and easily portable In a particularly preferred arrangement, the sensing device is configured as a pen which is designed to be able to physically mark the form as well as to selectively enable the coded data from the form to be read and transmitted to the computer system The coded data then provides control information, configured such that designation thereof by a user causes instructions to be applied to the software running on the computer system or network The nature of the interaction between the form and the sensing device and the data that each contributes to the computer system may vary In one arrangement, the coded data on the form is indicative ofthe identity ofthe form and of at least one reference point on that form In another embodiment, the form includes coded data which is indicative of a parameter of the form, whereas the sensing device is operative to provide data regarding its own movement relative to that form to the computer system together with coded data from the form In yet another arrangement, the form includes the coded data which at least identifies the form, and the sensing device is designed to provide, to the computer system, data based on the form coded data, and also on data which identifies the user ofthe device In a preferred arrangement, the system and method also employs specially designed pπnters to print the form Further these pπnters constitute or form part of the computer system and are designed to receive data from the sensing device As indicated above, the system and method of the invention is ideally suited to operate over a network In this arrangement, the printers are fully integrated into the network and allow for printing of the forms on demand and also for distributing ofthe forms using a mixture of multicast and pointcast communication protocols Accordingly, in a preferred form, the present invention provides methods and systems which use a paper and pen based interface for a computer system This provides many significant benefits over traditional computer systems The advantage of paper is that it is widely used to display and record information Further, printed information is easier to read than information displayed on a computer screen Moreover, paper does not run on batteries, can be read in bπght light, or robustly accepts coffee spills or the like and is portable and disposable Furthermore, the system allows for hand-drawing and handwriting to be captured which affords greater richness of expression than input via a computer keyboard and mouse The present invention therefore provides a novel method and system for enabling a user to obtain a copy of a previously printed document making use of novel interactive surface media 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 Figure 1 is a schematic of a the relationship between a sample printed netpage and its online page descπption, Figure 2 is a schematic view of a interaction between a netpage pen, a netpage pπnter, a netpage page server, and a netpage application server, Figure 3 illustrates a collection of netpage servers and pπnters interconnected via a network, Figure 4 is a schematic view of a high-level structure of a printed netpage and its online page descπption, Figure 5 is a plan view showing a structure of a netpage tag, Figure 6 is a plan view showing a relationship between a set ofthe tags shown in Figure 5 and a field of view of a netpage sensing device in the form of a netpage pen, Figure 7 is a flowchart of a tag image processing and decoding algoπthm, Figure 8 is a perspective view of a netpage pen and its associated tag-sensing field-of-view cone, Figure 9 is a perspective exploded view ofthe netpage pen shown in Figure 8, Figure 10 is a schematic block diagram of a pen controller for the netpage pen shown in Figures 8 and 9, Figure 1 1 is a perspective view of a wall-mounted netpage pπnter, Figure 12 is a section through the length of the netpage printer of Figure 1 1 , Figure 12a is an enlarged portion of Figure 12 showing a section ofthe duplexed pπnt engines and glue wheel assembly, Figure 13 is a detailed view ofthe ink cartridge, ink, air and glue paths, and pπnt engines ofthe netpage printer of Figures 1 1 and 12, Figure 14 is a schematic block diagram of a pπnter controller for the netpage printer shown m Figures 1 1 and 12, Figure 15 is a schematic block diagram of duplexed print engine controllers and Memjet™ printheads associated with the printer controller shown m Figure 14, Figure 16 is a schematic block diagram ofthe print engine controller shown in Figures 14 and 15, Figure 17 is a perspective view of a single Memjet™ printing element, as used in, for example, the netpage pπnter of Figures 10 to 12, Figure 18 is a perspective view of a small part of an array of Memjet™ printing elements, Figure 19 is a series of perspective views illustrating the operating cycle of the Memjet™ printing element shown in Figure 13, Figure 20 is a perspective view of a short segment of a pagewidth Memjet™ pπnthead, Figure 21 is a schematic view of a user class diagram; Figure 22 is a schematic view of a printer class diagram, Figure 23 is a schematic view of a pen class diagram, Figure 24 is a schematic view of an application class diagram, Figure 25 is a schematic view of a document and page descπption class diagram, Figure 26 is a schematic view of a document and page ownership class diagram, Figure 27 is a schematic view of a terminal element specialization class diagram, Figure 28 is a schematic view of a static element specialization class diagram, Figure 29 is a schematic view of a hyperlink element class diagram, Figure 30 is a schematic view of a hyperlink element specialization class diagram, Figure 31 is a schematic view of a hyperlinked group class diagram, Figure 32 is a schematic view of a form class diagram; Figure 33 is a schematic view of a digital ink class diagram; Figure 34 is a schematic view of a field element specialization class diagram, Figure 35 is a schematic view of a checkbox field class diagram, Figure 36 is a schematic view of a text field class diagram, Figure 37 is a schematic view of a signature field class diagram, Figure 38 is a flowchart of an input processing algoπthm; Figure 38a is a detailed flowchart of one step ofthe flowchart of Figure 38, Figure 39 is a schematic view of a page server command element class diagram, Figure 40 is a schematic view of a subscnption delivery protocol, Figure 41 is a schematic view of a hyperlink request class diagram, Figure 42 is a schematic view of a hyperlink activation protocol, Figure 43 is a schematic view of a form submission protocol, Figure 44 is a schematic view of a set of user interface flow document icons, Figure 45 is a schematic view of a set of user interface page layout element icons, Figure 46 is a schematic view of a history list class diagram, Figure 47 is a schematic view of a history list navigation user interface flow, and Figure 48 is a schematic view of a history list form 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 ofthe present invention operate In brief summary, the preferred form of the netpage system employs a computer interface m 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'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 wntten 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 veπfied, allowing e-commerce transactions to be securely authoπzed As illustrated in Figure 1 , a printed netpage 1 can represent a interactive form which can be filled in by the user both physically, on the pπnted 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 (l 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 Figure 2, the netpage pen 101 , a preferred form of which is shown Figures 8 and 9 and described in more detail below, works m 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 Figures 1 1 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's kitchen, near a breakfast table, or near the household's point of departure for the day It also comes in tabletop, desktop, portable and miniature versions Netpages pπnted at their point of consumption combine the ease-of-use of paper with the timeliness and interactivity of an interactive medium As shown in Figure 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 pπnter 601 sends the interaction to the relevant netpage page server 10 for interpretation In appropπate circumstances, the page server sends a corresponding message to application computer software running on a netpage application server 13 The application server may m turn send a response which is pπnted on the originating pπnter 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™) pπnters In the preferred form of this technology, relatively high-speed and high-quality pπntmg is made more affordable to consumers In its preferred form, a netpage publication has the physical characteπstics of a traditional newsmagazine, such as a set of letter- size glossy pages pπnted m 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 the United States, and cable modem service offeπng broadband Internet access is already available to 20% of these The netpage pπnter 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 pπnters, although the system will operate more slowly and will therefore be less acceptable from a consumer'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 pπnter Netpage publication servers 14 on the netpage network are configured to deliver pπnt-quality publications to netpage pπnters Periodical publications are delivered automatically to subscπbing netpage pπnters via pointcastmg and multicasting Internet protocols Personalized publications are filtered and formatted according to individual user profiles A netpage pπnter can be configured to support any number of pens, and a pen can work with any number of netpage pπnters 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 1 1 and linked to one or more payment card accounts This allows e-commerce payments to be securely authoπzed 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'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 subscπbed 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, l 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 ofthe attributes ofthe class, separated from the name by a hoπzontal line, and a list of the operations of the class, separated from the attribute list by a hoπzontal 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 ("ls-part-of '), and is drawn at the aggregator end ofthe association line A generalization relationship ("ls-a") is drawn as a solid line joining two classes, with an arrow (m the form of an open tπangle) 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 pπnted page (or other surface region) invisibly tagged with references to an online descπption of the page The online page descπption is maintained persistently by a netpage page server The page descπption descπbes 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 descπption 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 descπption The tag also identifies its own position on the page Characteristics ofthe tags are described m more detail below Tags are printed m 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 pπnter 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 m the page description for each printed netpage The relationship between the page description, the page instance, and the pπnted netpage is shown in Figure 4 The printed netpage may be part of a printed netpage document 45 The page instance is associated with both the netpage printer which pπnted 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 ofthe tag, without the sensing device having to refer to a descπption 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, m 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 m the tag is therefore synonymous with the page ID ofthe 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 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 ofthe 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 Figure 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 ofthe encoded tag data To achieve proper tag reproduction, the tag is rendered at a resolution of 256x256 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 ofthe 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 oπentation of the tag due to the yaw of the sensor The oπentation axis is skewed to yield a unique oπentation Four perspective targets 17 allow the sensing device to infer an accurate two-dimensional perspective transform ofthe tag and hence an accurate three-dimensional position and orientation ofthe 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 m 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 2x2 wedges The 15 4-bit data symbols of each ofthe six codewords are allocated to the four concentric symbol rings 18a to 18d m 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 oπentation it is positioned The required diameter of the field of view of the sensing device is therefore a function of the size and spacing ofthe 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 Figure 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 Figure 7 While a captured image is being acquired from the image sensor, the dynamic range of the image is determined (at 20) The center ofthe range is then chosen as the binary threshold for the image 21 The image is then thresholded and segmented into connected pixel regions (l 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 πng target structure 15 is the first to be located (at 26) A πng has the advantage of being very well behaved when perspective-distorted Matching proceeds by aspect-normalizing and rotation-normalizing each shape's moments Once its second-order moments are normalized the ring is easy to recognize even if the perspective distortion was significant The πng'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 πng's normalizations to each shape'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's normalizations applied, since the perspective distortion can hide the axis target's axis The axis target's original rotation provides a useful approximation of the tag'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 πng, and the rotation ofthe axis Matching proceeds by applying the πng's normalizations to each shape'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 oπgmal 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 Waφing, 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 incoφorated by cross-reference) The inferred tag-space to image-space perspective transform is used to project (at 36) each known data bit position m tag space into image space where the real-valued position is used to bilinearly inteφolate (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-mterleaved during the sampling process The ring target 15 is only sought in a subarea ofthe 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-mmimal field of view 193, an alternative strategy involves seeking another tag in the current image The obtained tag data indicates the identity ofthe region containing the tag and the position ofthe 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's physical axis and the pen's optical axis 1.2.5 Tag Map Decoding a tag results m 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 ofthe 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 Figure 22, as part of the netpage pπnter 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 ofthe pen within the region This in turn is used to determine the location ofthe pen relative to a user interface element in the page descπption 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 m the page descπption 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 m the netpage system 1.3 DOCUMENT AND PAGE DESCRIPTIONS A preferred embodiment of a document and page description class diagram is shown in Figures 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'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 pπnted 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'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 inteφret user actions on a particular printed page A formatted document 834 consists of a set of formatted page descπptions 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 descπbes 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 Figure 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 scπpt object 860, as shown in Figure 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 81 1 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 1 1 , 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 Figure 3 The netpage registration server 1 1 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 pπnters send netpage input directly to the appropπate page server The page server mteφrets 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 ofthe 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 subscπption Each pπnter 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 m non-volatile memory, the netpage pπnter 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 ofthe distributed netpage page servers 10, independently of particular netpage pπnters 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 pomtcast to the subscπber's pπnter via the appropπate page server Text and image objects, on the other hand, are typically shared with other subscribers, and so are multicast to all subscπbers' pπnters and the appropπate page servers The netpage publication server optimizes the segmentation of document content into pointcasts and multicasts After receiving the pointcast of a document's page layouts, the pπnter 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 rasteπzes 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 puφose 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 ofthe printheads m the pπnt engines Printers not enabled for IR printing have the option to print tags using IR-absoφtive black ink, although this restricts tags to otherwise empty areas of the page Although such pages have more limited functionality than IR-pπnted pages, they are still classed as netpages A normal netpage printer prints netpages on sheets of paper More specialised netpage pπnters 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 81 1 which describes the tag tiling scheme actually used to print a document becomes associated with that document so that the document's tags can be correctly inteφreted Figure 2 shows the netpage pπnter class diagram, reflecting pπnter-related information maintained by a registration server 1 1 on the netpage network A preferred embodiment ofthe netpage pπnter is described m greater detail in Section 6 below, with reference to Figures 1 1 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 characteπstics photographic quality color printing high quality text pπnting high reliability low printer cost low paper cost simple operation nearly silent pπnting high pπnting speed simultaneous double sided pπnting • compact form factor • low power consumption No commercially available printing technology has all of these charactenstics 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 mkjet technology that incoφorates pagewidth printheads fabricated using microelectromechanical systems (MEMS) technology Figure 17 shows a single pπnting element 300 of a Memjet™ pπnthead The netpage wallpπnter incoφorates 168960 printing elements 300 to form a 1600 dpi pagewidth duplex printer This printer simultaneously pnnts cyan, magenta, yellow, black, and infrared inks as well as paper conditioner and ink fixative The pnntmg element 300 is approximately 110 microns long by 32 microns wide Arrays of these printing elements are formed on a silicon substrate 301 that incoφorates CMOS logic, data transfer, timing, and drive circuits (not shown) Major elements of the printing element 300 are the nozzle 302, the nozzle nm 303, the nozzle chamber 304, the fluidic seal 305, the ink channel nm 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 31 1 , 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 31 1 The combination of elements 308, 309, 310, 31 1 , and 319 form a cantilevered electrothermal bend actuator 320 Figure 18 shows a small part of an array of pnnting 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 Figures 19(a), 19(b) and 19(c) show the operating cycle of a Memjet™ printing element 300 Figure 19(a) shows the quiescent position of the ink meniscus 316 prior to printing an ink droplet Ink is retained m 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 nm 306 While printing, the pnnthead CMOS circuitry distributes data from the pπnt 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 Figure 19(b) This increases the ink pressure, forcing ink 321 out ofthe nozzle 302, and causing the ink meniscus 316 to bulge The nozzle nm 303 prevents the ink meniscus 316 from spreading across the surface ofthe nozzle chamber 304 As the temperature of the beam pairs 308 and 309 equalizes, the actuator 320 returns to its onginal position This aids in the break-off of the ink droplet 317 from the ink 321 in the nozzle chamber, as shown in Figure 19(c) The nozzle chamber is refilled by the action of the surface tension at the meniscus 316 Figure 20 shows a segment of a pnnthead 350 In a netpage pπnter, the length of the pπnthead 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 pnnthead) When printing, the paper is moved past the fixed pnnthead in the direction 352 The pnnthead 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 pπnthead during operation, a nozzle guard wafer 330 is attached to the pnnthead 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 pπnting 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 (l 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 inteφreting 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 Figure 23 shows the netpage pen class diagram, reflecting pen-related information maintained by a registration server 1 1 on the netpage network When either nib is in contact with a netpage, the pen determines its position and oπentation relative to the page The nib is attached to a force sensor, and the force on the nib is inteφreted 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 ofthe page in the vicinity ofthe nib It decodes the nearest tag and computes the position ofthe 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 ofthe netpage whenever the page ID changes, which, under normal circumstances, is at the commencement ofthe 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 penod 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 inteφreted 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 cuπent 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 pπnter 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 pπnter, 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 ofthe pen is described in greater detail in Section 6 below, with reference to Figures 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 pπnter, 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 pπnter may already have the address ofthe 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 descπption to which the stroke applies, and determines which element ofthe page descπption the stroke intersects It is then able to inteφret the stroke in the context ofthe type ofthe 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's "ok" LED There are two kinds of input elements in a netpage page descnption 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'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's history The hyperlink element class diagram is shown in Figure 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 Figure 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'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's current selection 826 in a selection hyperlink activation The system includes the content of the associated form instance 868 m 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 hyperhnked group 866 is a group element 838 which has an associated hyperlink, as shown in Figure 31 When input occurs through any field element in the group, the hyperlink 844 associated with the group is activated A hyperhnked 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 pπnted 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 pπnted 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, l e through one or more pπnted netpages The form class diagram is shown m Figure 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 pπnted A fonn 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, 1 e when the time the form has been active exceeds the form'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 Figure 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 Figure 34 Any digital ink captured in a field's zone 58 is assigned to the field A checkbox field has an associated boolean value 881 , as shown in Figure 35 Any mark (a tick, a cross, a stroke, a fill zigzag, etc ) captured in a checkbox field's zone causes a true value to be assigned to the field's value A text field has an associated text value 882, as shown in Figure 36 Any digital ink captured in a text field's zone is automatically converted to text via online handwriting recognition, and the text is assigned to the field'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 incoφorated by cross-reference) A signature field has an associated digital signature value 883, as shown m Figure 37 Any digital ink captured in a signature field'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's value The digital signature is generated using the pen user's pπvate 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 Veπfication and Wπter Identification - The State of the Art", Pattern Recognition, Vol.22, No 2, 1989, the contents of which are herein incoφorated 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 stnke-throughs indicating deletion, can also be recognized in form fields Because the handwriting recognition algonthm works "online" (I e with access to the dynamics of the pen movement), rather than "offline" (l e with access only to a bitmap of pen markings), it can recognize run-on discretely- written characters with relatively high accuracy, without a wπter-dependent training phase A wnter-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's zone is appended to that element's digital ink stream, ready for mteφretation Any stroke not appended to an object's digital ink stream is appended to the background field's digital ink stream Digital ink captured in the background field is inteφreted as a selection gesture Circumscription of one or more objects is generally inteφreted as a selection of the circumscribed objects, although the actual inteφretation is application-specific Table 2 summarises these various pen interactions with a netpage Table 2 - Summary of pen interactions with a netpage 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 onginal 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 Figure 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 descπption 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 , mteφreting (at 893) the accumulated digital ink ofthe field, and determining (at 894) whether the field is part of a hyperhnked 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 conespondmg 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 ofthe current pen, as maintained by the registration server Figure 38a shows a detailed flowchart of step 893 in the process shown in Figure 38, where the accumulated digital ink of a field is inteφreted 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 appropπate 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 veπfy g (at 903) the digital ink as the signature ofthe pen's owner, with the help ofthe appropπate registration server, creating (at 904) a digital signature of the contents of the conespondmg form, also with the help of the registration server and using the pen owner's private signature key relating to the conespondmg 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 91 1, 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 Figure 39 A void form command voids the corresponding form instance A duplicate fonn command voids the conespondmg form instance and then produces an active pπnted copy of the cunent 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 pπnted copy of the form instance with field values discarded A get form status command produces a printed report on the status of the conespondmg form instance, including who published it, when it was printed, for whom it was pπnted, and the form status ofthe 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 pπnted copy of the conespondmg 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 inteφreted as a duplicate form command A reset page command produces a pπnted copy of the conespondmg 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 inteφreted as a reset form command A get page status command produces a printed report on the status of the conespondmg page instance, including who published it, when it was pπnted, 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 venfication A duplicate document command produces a pπnted copy of the conespondmg document instance with background field values preserved If the document contains any forms, then the duplicate document command duplicates the forms m the same way a duplicate form command does A reset document command produces a pπnted copy of the conespondmg 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 pnnted report on the status of the conespondmg document instance, including who published it, when it was pnnted, for whom it was printed, and the status of any forms it contains If the page server command's "on selected" attribute is set, then the command operates on the page identified by the pen's cunent 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'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 hyperhnked group The page server activates the hyperlink associated with the hyperhnked 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 prefened fonn, 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 prefened embodiment, the netpage pπnter 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 pπnter is unable to pπnt In this case the "enor" 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 m the netpage system Although news is often used in the limited sense of newspaper and newsmagazine news, the intended scope m 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's explicitly stated and implicitly captured interest profile The advertising content is personalized according to the reader'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 conespond 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's column, a friend's bulletin board, or the reader'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 pπnted 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' announcements ("Personal"), or for monitonng 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 (l e as a limit on its number of pages), and the desired proportion of advertising, either qualitatively (e g high, normal, low, none), or numeπcally (l 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's and adults' versions The appropnate version is selected according to the reader'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 pπoπtized by the editors, and each is assigned a useful lifetime By default they are delivered to all relevant subscnbers, in pπoπty order, subject to space constraints in the subscribers' 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 ofthe 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 subscnbers The reader optionally specifies a serendipity factor, either qualitatively (e g do or don't suφπse me), or numerically A high serendipity factor lowers the threshold used for matching duπng collaborative filtering A high factor makes it more likely that the conespondmg section will be filled to the reader's specified capacity A different serendipity factor can be specified for different days ofthe 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'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 (l 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 cunency, and whether the localization consist of in situ translation or annotation These preferences are denved from the reader'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 conespondmg 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 m 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 πght 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's most profitable product is advertising "space", a multi-dimensional entity determined by the publication'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's saleable advertising space on a per-section basis, taking into account the publication's geographic coverage, the section's readership, the size of each reader's section edition, each reader's advertising proportion, and each reader'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' 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's traditional counteφart, because the publication's advertising space is more complex While ignoring the full complexities of negotiations between advertisers, advertising aggregators and publishers, the prefened form ofthe 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 Conespondingly, the publisher records the ad placement on the relevant netpage publication server When the netpage publication server lays out each user'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 customization • collaborative filtenng 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 filtenng vector consists of the user's ratings of a number of news items It is used to correlate different users' interests for the puφoses of making recommendations Although there are benefits to maintaining a single collaborative filtenng 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' 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 m the same way The localization of advertising relies on the locality indicated in the user'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 puφoses, 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'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 Figures 21 , 22, 23 and 24 For registration puφoses, a publisher is a special kind of application provider, and a publication is a special kind of application Each user 800 may be authoπzed to use any number of pnnters 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 pπnted on demand are delivered to the pπnter through which the user is interacting The server keeps track of which publishers a user has authorized to print to the user's default pnnter A publisher does not record the ID of any particular pπnter, 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 pπvileges 84 for such operations When a user subscribes 808 to a publication 807, the publisher 806 (l e application provider 803) is authorized to print to a specified printer or the user's default pnnter This authoπzation 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 pπnter recognizes any ofthe user's pens The pen ID is used to locate the conespondmg user profile maintained by a particular netpage registration server, via the DNS m the usual way A Web terminal 809 can be authorized to pπnt on a particular netpage printer, allowing Web pages and netpage documents encountered during Web browsing to be conveniently pπnted on the nearest netpage pnnter The netpage system can collect, on behalf of a printer provider, fees and commissions on income earned through publications pnnted on the provider's pnnters Such income can include advertising fees, click-through fees, e- commerce commissions, and transaction fees If the pnnter 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 m the preceding paragraph), contact details 815, including name, address and telephone numbers, global preferences 816, including privacy, delivery and localization settings, any number of biomernc records 817, containing the user's encoded signature 818, fingeφπnt 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's activities on that pnnter 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 neφage publication server automatically lays out the pages of each user'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'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's edition and information shared between multiple users' editions The specific information consists of the page layout The shared information consists ofthe 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 senes 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 summaπzed in Table 3 The layout uses a compact format suitable for efficient distribution and storage Table 3 - netpage layout objects 2.6 DOCUMENT DISTRIBUTION As described above, for puφoses 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 ofthe 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 pomtcasts each user's layouts to that user's pπnter via the appropnate page server, and when the pomtcasting is complete, multicasts the shared content on the specified channels After receiving its po tcast, each page server and pπnter subscribes to the multicast channels specified m the page layouts During the multicasts, each page server and pπnter extracts from the multicast streams those objects refened 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 pπnter re-creates the fully- populated layout and then rasteπzes 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 400KB The printer can therefore hold in excess of 100 such pages in its internal 64MB memory, allowing for temporary buffers etc The pπnter pπnts at a rate of one page per second This is equivalent to 400KB or about 3Mbit 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's 100-page internal storage capacity is exhausted However, if the pnnter's internal memory does fill up, then the pnnter will be unable to make use of a multicast when it first occurs The netpage publication server therefore allows pπnters to submit requests for re-multicasts When a cπtical number of requests is received or a timeout occurs, the server re-multicasts the corresponding shared objects Once a document is pπnted, a pπnter 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's Portable Document Format (PDF), and Hypertext Markup Language (HTML) In the case of HTML, it can make use of the higher resolution ofthe 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 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 m widespread use secret-key cryptography and public-key cryptography The netpage network uses both classes of cryptography Secret-key cryptography, also refened to as symmetric cryptography, uses the same key to encrypt and decrypt a message Two parties wishing to exchange messages must first anange to securely exchange the secret key Public-key cryptography, also refened to as asymmetnc 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 pπvate 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 pnvate key is secure, it is normal for the holder ofthe pnvate key to generate the key pair Public-key cryptography can be used to create a digital signature The holder of the pπvate key can create a known hash of a message and then encrypt the hash using the pπvate key Anyone can then verify that the encrypted hash constitutes the "signature" of the holder of the pπvate 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 authoπty is a trusted third party which authenticates the connection between a public key and someone's identity The certificate authority venfies the person's identity by examining identity documents, and then creates and signs a digital certificate containing the person'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 puφoses 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'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 m readonly 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 pπnter 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's secret ID recorded in its database, and accepts the registration if the IDs match It then creates and signs a certificate containing the pπnter's public ID and public signature key, and stores the certificate in the registration database The netpage registration server acts as a certificate authoπty 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'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's pnvate signature key The page server verifies, via the registration database, that the publisher is authonzed to deliver the publication to the specified user The page server verifies the signature using the publisher's public key, obtained from the publisher's certificate stored in the registration database The netpage registration server accepts requests to add pπnting authoπzations to the database, so long as those requests are initiated via a pen registered to the pnnter 3.3 NETPAGE PEN SECURITY Each netpage pen is assigned a unique identifier at time of manufacture which is stored m 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 pπnters, and a printer can "know" a number of pens A pen communicates with a pnnter via a radio frequency signal whenever it is within range ofthe printer Once a pen and pπnter 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 pπnter it knows, indexed by pnnter ID, and a pπnter 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'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 pπnter If the printer is meant to know the pen but doesn't, then it initiates the automatic pen registration procedure If the printer isn'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 pπnter and pen to use, and securely transmits the session key to the pπnter It also transmits a copy of the session key encrypted with the pen'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 pπnter includes a facility to print watermarks, but will only do so on request from publishers who are suitably authonzed 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 minor-image watermark regions which coincide when printed The dither matrices used odd and even pages' 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 descnbed m 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's photograph which was captured when the user registered biometπc information with the netpage registration server, as described in Section 2 When presented with a secure netpage document, the recipient can venfy its authenticity by requesting its status 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 veπfication failure, to support easy pomt-of-presentation document veπfication Clearly neither the watermark nor the user'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 ofthe system is independent ofthe 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's registration details with the card issuer as appropriate, and verifies a merchant's registration details with the acquirer as appropriate Cardholders and merchants store their respective private signature keys securely on their computers Dunng 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 (l e the cardholder) in SET payment transactions The netpage system uses biometrics to authenticate the user and authoπze SET payments Because the system is pen-based, the biometπc used is the user's on-line signature, consisting of time-varying pen position and pressure A fingeφπnt biomefπc can also be used by designing a fingeφnnt sensor into the pen, although at a higher cost The type of biometric used only affects the capture ofthe biometπc, not the authorization aspects ofthe system The first step to being able to make SET payments is to register the user'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's identity is veπfϊed The biometπc is captured and stored in the registration database, linked to the user's record The user's photograph is also optionally captured and linked to the record The SET cardholder registration process is completed, and the resulting pπvate signature key and certificate are stored in the database The user's payment card information is also stored, giving the netpage registration server enough information to act as the user'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 pπnter 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'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 pπnting low-cost documents on demand and for copying copyright documents, and possibly also to allow the user to be reimbursed for expenses mcuned in pπnting 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 m 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's input When input occurs through a page which is not user-specific, however, the application must use the user's unique identity to establish a context A typical example involves adding items from a pre-pnnted catalog page to the user's virtual "shopping cart" To protect the user's pπvacy, 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 conelating 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 Figure 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's application The application maintains state information indexed by alias ID, and is able to retrieve user-specific state information without knowledge ofthe global identity ofthe user The system also maintains an independent certificate and pnvate signature key for each of a user'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 favonte 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 subscπbed content The system records the user's willingness to receive the subscπbed 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 prefened embodiment of a subscription delivery protocol is shown in Figure 40 A large number of users may subscribe to a periodical publication Each user's edition may be laid out differently, but many users' 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's newly allocated ID It includes its own application ID 64, the subscriber'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 conespondmg user ID 60, the user's selected printer ID 62 (which may be explicitly selected for the application, or may be the user's default printer), and the application's certificate The application's certificate allows the page server to verify the message signature The page server's request to the registration server fails if the application ID and alias ID don'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 pπnter to listen to It then returns the newly allocated page IDs to the application for future reference Once the application has distributed all ofthe document structures to the subscribers' selected printers via the relevant page servers, it multicasts the vaπous subsets ofthe 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 pπnters to pπnt the documents 5.2 HYPERLINK ACTIVATION PROTOCOL A prefened embodiment of a hyperlink activation protocol is shown m Figure 42 When a user clicks on a netpage with a netpage pen, the pen communicates the click to the nearest netpage pnnter 601 The click identifies the page and a location on the page The pnnter already knows the ID 61 ofthe pen from the pen connection protocol The pπnter determines, via the DNS, the network address of the page server 10a 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 pπnter 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'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 conespondmg user ID 60 from the registration server 1 1 , and then allocates a globally unique hyperlink request ID 52 and builds a hyperlink request 934 The hyperlink request class diagram is shown in Figure 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 10b responsible for the document's newly allocated ID, together with the requesting page server'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 conespondmg 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 descπptions 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, l e its "alias required" attribute is set, then the first page server sends both the pen ID 61 and the hyperlink's application ID 64 to the registration server 1 1 to obtain not just the user ID conespondmg to the pen ID but also the alias ID 65 conespondmg 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 pπnter ID 62, the page ID 50 and stroke path to the page server 10 in the usual way The page server loads the page descnption 5 identified by the page ID and determines which input element'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'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 1 1 for inteφretation The registration server identifies the user conespondmg to the pen, and uses the user's accumulated handwπting model 822 to teφret 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 ofthe 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'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 1 1 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 conespondmg to the pen, and uses the user's dynamic signature biometric 818 to veπfy the strokes as the user's signature Once it has verified the signature, the registration server uses the application ID 64 and user ID 60 to identify the user'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's status to frozen The digital signature includes the alias ID 65 of the conespondmg user This allows a single form to capture multiple users' signatures 5.5 FORM SUBMISSION PROTOCOL A preferred embodiment of a form submission protocol is shown in Figure 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 cunent data content ofthe form If the form contains any signature fields, then the application verifies each one by extracting the alias ID 65 associated with the conespondmg digital signature and obtaining the conespondmg certificate from the registration server 1 1 6 NETPAGE PEN DESCRIPTION 6.1 PEN MECHANICS Refemng to Figures 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 ofthe 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 m order to enable the user to view the status ofthe LED mounted within the housing 102 The cover 107 includes a mam 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 1 1 1 formed in the walls 103 of the housing 102 A radio antenna 1 12 is mounted behind the projecting portion 110, within the housing 102 Screw threads 113 sunounding an aperture 1 13A on the cover 107 are arranged to receive a metal end piece 1 14, including conespondmg screw threads 1 15 The metal end piece 1 14 is removable to enable ink cartridge replacement Also mounted within the cover 107 is a tπ-color status LED 1 16 on a flex PCB 1 17 The antenna 1 12 is also mounted on the flex PCB 1 17 The status LED 1 16 is mounted at the top ofthe pen 101 for good all-around visibility The pen can operate both as a normal marking ink pen and as a non-markmg stylus An ink pen cartridge 118 with nib 1 19 and a stylus 120 with stylus nib 121 are mounted side by side within the housing 102 Either the ink cartridge nib 1 19 or the stylus nib 121 can be brought forward through open end 122 of the metal end piece 1 14, by rotation of the pen top 105 Respective slider blocks 123 and 124 are mounted to the ink cartridge 1 18 and stylus 120, respectively A rotatable cam barrel 125 is secured to the pen top 105 in operation and ananged to rotate therewith The cam banel 125 includes a cam 126 in the form of a slot within the walls 181 of the cam banel Cam followers 127 and 128 projecting from slider blocks 123 and 124 fit within the cam slot 126 On rotation of the cam banel 125, the slider blocks 123 or 124 move relative to each other to project either the pen nib 1 19 or stylus nib 121 out through the hole 122 in the metal end piece 1 14 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 1 18 nib 1 19 out, and • Neither ink cartridge 1 18 nib 1 19 out nor stylus 120 nib 121 out A second flex PCB 129, is mounted on an electronics chassis 130 which sits withm 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 banel 125 A terminal 138 connects to the battery contacts 137 and the cam banel 125 A three volt rechargeable battery 139 sits within the cam banel 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 banel 125 when either the stylus 120 or the ink cartndge 1 18 is used for writing, in order to enable a determination of the force being applied to the surface by the pen nib 1 19 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 gπpping 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 ananged to determine the position of its nib (stylus nib 121 or ink cartridge nib 1 19) 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 ananged 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 ofthe 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 secuπty and packaged for efficient transmission) to the computing system When the pen is m 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 ananged to store digital ink data for approximately 12 minutes ofthe 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 Figure 10 is a block diagram illustrating in more detail the architecture of the controller chip 134 Figure 10 also shows representations of the RF chip 133, the image sensor 132, the tπ-color status LED 1 16, 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 ananged 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 1 12 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 1 16, 131 and 143, and handles short-range radio communication via the radio transceiver 153 It is a medium-performance (~40MHz) general-puφose RISC processor The processor 145, digital transceiver components (transceiver controller 153 and baseband circuit 154), image sensor interface 152, flash memory 147 and 512KB 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 215x215 pixel CCD (such a sensor is produced by Matsushita Electronic Coφoration, and is described in a paper by Itakura, K T Nobusada, N Okusenya, R Nagayoshi, and M Ozaki, "A 1mm 50k-Pιxel IT CCD Image Sensor for Miniature Camera System", IEEE Transactions on Electronic Devices, Volt 47, number 1 , January 2000, which is incoφorated 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 incoφorates 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 900MHz band normally used by cordless telephones, or alternatively in the unlicensed 2 4GHz industrial, scientific and medical (ISM) band, and uses frequency hopping and collision detection to provide interference-free communication In an alternative embodiment, the pen incoφorates an Infrared Data Association (IrDA) interface for short- range communication with a base station or netpage pπnter In a further embodiment, the pen 101 includes a pair of orthogonal accelerometers mounted in the normal plane ofthe pen 101 axis The accelerometers 190 are shown in Figures 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 withm the area of the input element can directly identify the input element The acceleration measured by the accelerometers in each ofthe 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 enors m the sensed acceleration, accelerometers typically have high resolution, and the time duration of a stroke, over which enors accumulate, is short 7 NETPAGE PRINTER DESCRIPTION 7.1 PRINTER MECHANICS The vertically-mounted netpage wallpπnter 601 is shown fully assembled in Figure 1 1 It prints netpages on Letter/A4 sized media using duplexed 8/2" Memjet™ print engines 602 and 603, as shown m Figures 12 and 12a It uses a straight paper path with the paper 604 passing through the duplexed print engines 602 and 603 which pnnt 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 m Figure 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 pπnter 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 pnnthead nozzles By incoφorating 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 glumg 3000 pages (1500 sheets) Refening to Figure 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™ pπnthead 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 pπnted simultaneously to aid drying m 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 rubbeπzed roller These spike wheels contact the 'wet' pπnted surface and continue to feed the sheet 604 into the second Memjet™ print engine 603 Refening to Figures 12 and 12a, the paper 604 passes from the duplexed print engines 602 and 603 into the binder assembly 605 The pπnted 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 k cartridge 627 This axle 679 connects to a glue wheel, which absorbs adhesive by capillary action through radial holes A molded housing 682 sunounds the glue wheel, with an opening at the front Pivoting side moldings and sprung outer doors are attached to the metal bracket and h ge 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 spnngs close the assembly and effectively cap the glue wheel duπng 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 760a and 760b, flash memory 658, and 64MB of DRAM 657, as illustrated in Figure 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-puφose microprocessor The controlling processor 750 communicates with the print engine controllers 760 via a high-speed serial bus 659 The RIP DSPs rasteπze and compress page descriptions to the netpage printer's compressed page format Each print engine controller expands, dithers and prints page images to its associated Memjet™ pnnthead 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 760a 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'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 ma 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 pπnters allow the network connection to be factory-selected or field-selected Flash memory 658 and the 2x256Mbit (64MB) 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, cunent and next-generation cellular telephone transceivers, and wireless local loop (WLL) transceivers Local interfaces include IEEE 1284 (parallel port), lOBase-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 900MHz band normally used by cordless telephones, or alternatively in the unlicensed 2 4GHz industrial, scientific and medical (ISM) band, and uses frequency hopping and collision detection to provide interference-free communication The pπnter controller optionally incoφorates an Infrared Data Association (IrDA) interface for receiving data "squirted" from devices such as netpage cameras In an alternative embodiment, the pπnter uses the IrDA interface for short-range communication with suitably configured netpage pens 7.2.1 RASTERIZATION AND PRINTING Once the mam processor 750 has received and verified the document's page layouts and page objects, it runs the appropriate RIP software on the DSPs 757 The DSPs 757 rasteπze each page description and compress the rasteπzed 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 rasteπze a separate page The DSPs can always be kept busy since an arbitrary number of rasteπzed pages can, in general, be stored in memory This strategy only leads to potentially poor DSP utilization when rasteπzing short documents Watermark regions in the page description are rasteπzed to a contone-resolution bi-level bitmap which is losslessly compressed to negligible size and which forms part ofthe 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 mam processor 750 passes back-to-back page images to the duplexed pπnt 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 1 14MB 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™ pnnthead 350 The pπnt 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 pπnted while another page is loaded The first stage ofthe 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 pπnting on the Memjet™ pπnthead 350 via a set of line buffers Most of these line buffers are stored in the off-chip DRAM The final stage pπnts the six channels of bi-level dot data (including fixative) to the Memjet™ pπnthead 350 via the pnnthead interface 768 When several pπnt 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, configunng the pnnthead 350 via a low-speed serial bus 773, and controlling the stepper motors 675, 676 In the 8' " versions of the netpage pπnter, the two pπnt engines each pπnts 30 Letter pages per minute along the long dimension ofthe page (1 1"), giving a line rate of 8 8 kHz at 1600 dpi In the 12" versions ofthe netpage pπnter, the two print engines each pπnts 45 Letter pages per minute along the short dimension of the page (δ' "), giving a line rate of 102 kHz These line rates are well within the operating frequency ofthe Memjet™ pπnthead, which m the cunent design exceeds 30 kHz 8 HISTORY LIST A registration server maintains a history list 929 on behalf of each user 800, containing links to documents etc accessed by the user through the netpage system It is organized as a date-ordered list, as shown in the class diagram of Figure 46 Each document 831 printed by or for the user is recorded as a history document 931 , whether delivered as part of a subscription, or requested by the user via a page server command or hyperlink activation Each page 830 printed by the user via a page server command is recorded as a history page 932 Each hyperlink instance activated by the user is recorded as a history hyperlink 933 A hyperlink activation which produces a printed response is therefore recorded twice, and the user has a choice of re-activating the hyperlink to obtain a possibly updated document, or selecting the document instance to obtain an exact duplicate ofthe document Each history document 931 , history page 932 and history hyperlink 933 is recorded as a history item 930, with an associated description The description of a history document is derived from the title of the conespondmg document The description of a history page is derived from the title of the corresponding document and the page number The descπption of a history hyperlink is derived from the description of the conespondmg hyperlink element The history list can be navigated by the user to obtain copies of previously printed documents or pages, or to activate previously activated hyperlinks 8.1 USER INTERFACE DIAGRAM NOTATION Each application user interface flow is illustrated as a collection of documents linked by command anows A command anow indicates that the target document is printed as a result of the user pressing the conespondmg command button on the source page Some command anows are labelled with multiple commands separated by slashes (7's), indicating that any one of the specified commands causes the target document to be printed Although multiple commands may label the same command anow, they typically have different side-effects In application terms, it is important to distinguish between netpage documents and netpage forms Documents contain printed information, as well as command buttons which can be pressed by the user to request further information or some other action Forms, in addition to behaving like normal documents, also contain input fields which can be filled in by the user They provide the system with a data input mechanism It is also useful to distinguish between documents which contain genenc information and documents which contain information specific to a particular interaction between the user and an application Generic documents may be pre-pπnted publications such as magazines sold at news stands or advertising posters encountered in public places Forms may also be pre-pnnted, including, for example, subscπption forms encountered in pre-pπnted publications They may, of course, also be generated on-the-fly by a netpage printer in response to user requests User-specific documents and forms are normally generated on the fly by a netpage pnnter m response to user requests Figure 44 shows a generic document 990, a generic form 991, a user-specific document 992, and a user-specific form 993 Netpages which participate m a user interface flow are further described by abstract page layouts A page layout may contain various kinds of elements, each of which has a unique style to differentiate it from the others As shown m Figure 45, these include fixed information 994, vaπable information 995, input fields 996, command buttons 997, draggable commands 998, and text hyperlinks or hypertext links 999 When a user interface flow is broken up into multiple diagrams, any document which is duplicated is shown with dashed outlines in all but the main diagram which defines it 8.2 HISTORY LIST NAVIGATION The user can browse the history list 929 by date or by item description using the history list navigation form 500 shown in Figure 48 Only a single sheet of history items is printed at a time The number of history items pnnted is dictated by the size ofthe sheet, the user's preferred text size, and whether the sheet is printed on both sides or just on one side, l e according to the capabilities ofthe netpage printer used Each history item shows the type 504 of the item 930, l e whether it refers to a document, page or hyperlink, its creation date and time 505, and its description 506 When presented in descπption order, items are sorted alphabetically When presneted in date order, items are present in time period groups Recent items are grouped more finely than less recent items, l e items in the cunent week are grouped by day, items in the cunent month are grouped by week, etc Recent time periods appear before less recent time periods Items are represented in description order within each time period When the history list 929 is presented in date order, the user can obtain a description-ordered copy of the list via the <order by descπptιon> button 514 When the list is ordered by description, the user can obtain a date-ordered copy ofthe list via the <order by date> button (not shown) The user typically accesses the history list via the <hιstory hst> button on the printer's help page 46 The history list pages thus produced contain the most recent items in the history list Pages of earlier history items can be obtained via the <prevιous> button 513 on any history list page The user can also view the history list in summary form by pressing the <summary> button 51 1 on any history list page This produces a list of time peπods but hides the contents of each time period Each time period acts as a hyperlink which, when activated, produces history list pages showing the contents ofthe selected time period The user can select any number of time periods and/or history items by checking their associated selection checkboxes 515, and delete them permanently from the history list by pressing the <delete selected> button 512 An updated history list is immediately pπnted The user can search for specific history items by entering a full or partial description in the search description field 507 and/or an associated time peπod at 508, and then pressing the <search> button 510 Matching items are presented in description order in a search results list 501 Each item descπption on a history list page or search results page acts as a hyperlink which, when activated, produces a printed copy of the associated document or page, or activates the associated hyperlink which may produce a printed document in response The history list navigation user interface flow is illustrated in Figure 47 CONCLUSION The present invention has been descnbed with reference to a prefened 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, diffenng from those specifically descnbed, will also fall within the spiπt 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 incoφorated by cross-reference as appropπate The scope of the invention is only limited by the attached claims

Claims: CLAIMS 1 A method of enabling a user to obtain a printed copy of a document previously printed by the user, the method including maintaining a history list in a computer system of documents previously printed by the user, printing the history list, or a portion of the history list, in a list document including at least one user interface element associated with at least one history item in the history list, to allow the user to indicate a request for a copy of a previously printed document associated with the history item by interacting with the interface element using a sensing device which is adapted to transmit request data to the computer system, retrieving the copy via the computer system, and printing the copy 2 A method as claimed in claim 1 , wherein the at least one previously pπnted document is identified by a description the list document which presents a link to a conespondmg instance of the previously printed document, for retrieval by the computer system 3 A method as claimed in claim 2, wherein at least one further user interface element is provided in the list document to allow the history list to be subject to at least one navigation action using the sensing device, and wherein the navigation action indicated to the computer system via the sensing device results in a further list document being pπnted 4 A method as claimed in claim 3, wherein the navigation action is at least one of requesting an ordeπng of the history list by date, requesting an ordering of the history list by description, requesting a chronologically earlier portion ofthe history list, and requesting a summary version ofthe history list 5 A method as claimed in claim 1 , further including deletion of a history item from the history list upon request from the user, wherein the sensing device is adapted to identify the history item to be deleted and the list document includes an appropriate interface element to allow the request to be transmitted to the computer system using the sensing device 6 A method as claimed in claim 1 , wherein the list document includes coded data indicative of an identity of the list document and of the at least one interface element, and wherein the method includes receiving, in the computer system, indicating data from the sensing device regarding the identity of the list document and a position of the sensing device relative to the list document in order to identify the list document and determine when the sensing device is used to interact with the interface element to indicate the request 7 A method as claimed in claim 6, including receiving, in the computer system, movement data regarding movement of the sensing device relative to the list document, the sensing device sensing its movement relative to the list document using at least some of the coded data, and identifying the request in the computer system from the movement being at least partially within a zone associated with the interface element 8 A method as claimed m claim 6, wherein the list document is pnnted on a surface of a surface defining structure at the same time as the coded data is pnnted on the surface 9 A method as claimed in claim 6, which includes printing the coded data to be substantially invisible in the visible spectrum 10 A method as claimed in claim 6, including retaining a retrievable record of the printed list document, the list document being retrievable using the identity data as contained in the coded data 1 1 A method as claimed in claim 1, wherein the sensing device includes an identification code associated with a particular user and the method includes monitoπng use ofthe sensing device in the computer system 12 A system for enabling a user to obtain a printed copy of a document previously printed by the user, the system including a database maintaining a history list of documents previously pπnted by the user, a computer system for accessing the database and for generating a list document to include the history list, or a portion of the history list, and to include at least one user interface element associated with at least one history item in the history list, to enable a user to indicate a request for a copy of a previously printed document associated with the history item, a printer to print the list document, and a sensing device for interacting with the interface element so as to transmit request data to the computer system which, upon receipt ofthe request data, retrieves the copy for printing at the printer 13 A system as claimed in claim 12, wherein the at least one previously printed document is identified by a descnption in the list document which presents a link to a conespondmg instance of the previously printed document, for retrieval by the computer system 14 A system as claimed in claim 12, wherein the list document is pπnted with further user interface elements to allow the history list to be subjected to one or more navigation actions using the sensing device, each navigation action indicated to the computer system via the sensing device resulting in a further list document being pπnted 15 A system as claimed in claim 12, wherein the list document includes coded data indicative of an identity ofthe list document and of the at least one interface element 16 A system as claimed in claim 15, wherein the computer system is adapted to receive movement data regarding movement of the sensing device relative to the list document and inteφret said movement of the sensing device as it relates to the interface element, the sensing device, when moved relative to the list document, sensing the data regarding the interface element using at least some of the coded data and generating the data regarding its own movement relative to the list document 17 A system as claimed in claim 10, wherein the sensing device includes an identification code associated with a particular user and the computer system is ananged to monitor the use ofthe sensing device 18 A system as claimed in claim 10, wherein the sensing device includes a marking nib 19 A system as claimed claim 10, wherein the list document is pnnted on a surface of a surface- defining structure and wherein the pnnter prints the list document on demand 20 A system as claimed in claim 15, wherein the pnnter is arranged to pπnt the coded data at the same time as pπnting the list document on a surface-defining structure 21 A system as claimed in claim 15, wherein the coded data is substantially invisible in the visible spectrum 22 The system as claimed in claim 15, including a database for keeping a retrievable record of each list document generated, each list document being retrievable by using its identity, as included in its coded data 23 The system as claimed m claim 15, wherein the printer includes a binding means for binding the list document in the event the list document includes a plurality of pages

Inventors: LAPSTUN PAUL, SILVERBROOK KIA, LAPSTUN, PAUL, SILVERBROOK, KIA
Applicants: LAPSTUN PAUL, SILVERBROOK KIA, SILVERBROOK RES PTY LTD, LAPSTUN, PAUL, SILVERBROOK RESEARCH PTY LTD, SILVERBROOK, KIA
Application year: 2000
Main classification: G06F17
IPC codes: B41J2, B41J13, B42C9, B42C19, B65H29, B65H37, G06F3, G06F15, G06F17, G06K9, H04N1