METHOD AND SYSTEM FOR PROVIDING A COPY OF A PRINTED PAGE

Abstract: A method for providing a copy of a page from a printed document, the document including coded data indicative of an identity of the document and of a plurality of reference points on the document, the method including: receiving, in a computer system, indicating data from a sensing device operated by a user, the indicating data regarding the identity of the document and a position of the sensing device relative to the document, the sensing device, when placed in an operative position relative to the document, sensing the indicating data using at least some of the coded data; and identifying, in the computer system and from the indicating data, a request for a copy of the page of the document.

Description: METHOD AND SYSTEM FOR PROVIDING A COPY OF A PRINTED PAGE FIELD OF INVENTION The present invention relates generally to distributed computing systems and, more particularly, to a system and method for providing a copy of a page from a printed document 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 PCT/ AU00/00518, PCT/AU00/00519, PCT/AUOO/00520, PCT/ AU00/00521 , PCT/AU00/00523, PCT/AU00/00524, PCT/AU00/00525, PCT/AU00/00526, PCT/AUOO/00527, PCT/AU00/00528, PCT/AU00/00529, PCT/AUOO/00530, PCT/AU00/00531 , PCT/AU00/00532, PCT/AU00/00533, PCT/AUOO/00534. PCT/AU00/00535, PCT/AUOO/00536, PCT/AU00/00537, PCT/AU00/00538, PCT/AU00/00539, PCT/AUOO/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/AU00/00570, PCT/AU00/00571 , PCT/AU00/00572, PCT/AU00/00573, PCT/AU00/00574, PCT/AU00/00575, PCT/AU00/00576, PCT/AU00/00577, PCT/AU00/00578, PCT/AU00/00579, PCT/AU00/00581 , PCT/AU00/00580, PCT/AU00/00582, PCT/AUOO/00587, PCT/AU00/00588, PCT/AU00/ 00589, PCT/AU00/00583, PCT/AU00/00593, PCT/AU00/00590, PCT/AU00/00591 , PCT/AU00/00592, PCT/AU00/00594, PCT/AU00/00595, PCT/AU00/00596, PCT/AU00/00597, PCT/AU00/00598, PCT/AU00/00516, and PCT/AU00/00517 The disclosures of these co-pending applications are incorporated herein by cross-reference BACKGROUND The netpage system provides a paper-based user interface to published information and interactive services On occasion, users of the netpage system will want to obtain copies of pages of a printed document provided by the netpage system SUMMARY OF INVENTION It is an obiective of the present invention to provide a new system and method for providing copies of pages of a printed document and in particular, copies of pages of an interactive document The present invention provides, in one aspect, a method of providing a copy of at least one page of a printed document, the document including coded data indicative of the identity of the document and of at least one reference point of the document, the method including the steps of receiving, in a computer system, indicating data from a sensing device operated by the user, said indicating data regarding the identity of the document and a position of the sensing device relative to the document, the sensing device, when placed in an operative position relative to the document, sensing the indicating data using at least some of the coded data identifying in the computer system and from the indicating data, a request for a copy of at least one page of the document, and transmitting, from the computer system, relevant document data to at least one printer to effect printing of the copy of the at least one page In a further aspect, the invention provides a method of providing a copy of at least one page of a printed document, the document including coded data indicative of a request for a copy of the at least one page of the document, the method including the steps of receiving, in a computer system, data from a sensing device operated by the user regarding the request, the lncludmg coded data indicative of a request for a copy of at least one page of the document , the system including a computer system for receiving data from a sensmg device operated by a user, said data regarding the request and regardmg movement of the sensmg device relative to the document, the sensmg device, when moved relative to the document, sensmg the data regardmg said request usmg at least some of the coded data, and generating the data regardmg its own movement relative to the document, the computer system bemg configured to mterpret said movement as designating the request, and bemg configured to transmit relevant document data to at least one printer to effect printing of the copy of the at least one page In still another aspect, the present invention provides a system for providing a copy of at least one page of a printed document, the document including coded data indicative of the identity of the document, the system including a computer system for receiving from a sensmg device data regardmg an identity of the user of the sensmg device and the identity of the document, and for identifying, from said received data, a request for a copy of at least one page of the document, the sensmg device containing the data regardmg the identity of the user and sensmg the data regardmg the identity of the document usmg at least some of the coded data, the computer system bemg configured to transmit relevant document data to at least one printer to effect printing of the copy of the at least one page BRIEF DESCRIPTION OF DRAWINGS Preferred and other embodiments of the invention will now be described, by way of non-lrmitmg 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 description, Figure 2 is a schematic view of a interaction between a netpage pen, a netpage printer, a netpage page server, and a netpage application server, Figure 3 illustrates a collection of netpage servers and printers interconnected via a network, Figure 4 is a schematic view of a high-level structure of a printed netpage and its online page description, 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 of the tags shown m Figure 5 and a field of view of a netpage sensmg device m the form of a netpage pen, Figure 7 is a flowchart of a tag image processmg and decoding algorithm, 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 of the netpage pen shown m Figure 8, Figure 10 is a schematic block diagram of a pen controller for the netpage pen shown m Figures 8 and 9, Figure 11 is a perspective view of a wall-mounted netpage printer, Figure 12 is a section through the length of the netpage printer of Figure 11, Figure 12a is an enlarged portion of Figure 12 showing a section of the duplexed print engmes and glue wheel assembly, Figure 13 is a detailed view of the ink cartridge, ink, air and glue paths, and print engmes of the netpage printer of Figures 11 and 12, Figure 14 is a schematic block diagram of a printer controller for the netpage printer shown m Figures 11 and 12, Figure 15 is a schematic block diagram of duplexed print engme controllers and Memjet™ pπntheads associated with the printer controller shown m Figure 14, Figure 16 is a schematic block diagram of the print engme controller shown m Figures 14 and 15, Figure 17 is a perspective view of a single Memjet™ printing element, as used in, for example, the netpage printer 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 m 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 description 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 mput processmg algorithm, Figure 38a is a detailed flowchart of one step of the 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 resource description class diagram, Figure 41 is a schematic view of a favorites list class diagram, Figure 42 is a schematic view of a history list class diagram, Figure 43 is a schematic view of a subscription delivery protocol, Figure 44 is a schematic view of a hyperlink request class diagram, Figure 45 is a schematic view of a hyperlink activation protocol, Figure 46 is a schematic view of a form submission protocol, Figure 47 is a schematic view of a commission payment protocol, Figure 48 is a schematic view of a set of user interface flow document icons, and Figure 49 is a schematic view of a set of user interface page layout element icons 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 necessaπly embody all or even most of the specific details and extensions discussed below m relation to the basic system However, the system is described m its most complete form to reduce the need for external reference when attemptmg to understand the context m which the preferred embodiments and aspects of the present invention operate In brief summary, the preferred form of the netpage system employs a computer interface m the form of a mapped surface, that is, a physical surface which contams references to a map of the surface mamtamed m a computer system The map references can be queried by an appropnate sensmg device Depending upon the specific lmplementation, the map references may be encoded visibly or mvisibly, and defined m 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 sensmg 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 m 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 usmg 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 wπtten bv hand on a netpage is automatically recognized and converted to computer text m the netpage system, allowing forms to be filled m In other embodiments, signatures recorded on a netpage are automatically verified, allowing e-commerce transactions to be securely authorized As illustrated in Figure 1, a printed netpage 1 can represent a interactive form which can be filled m by the user both physically, on the printed page, and "electronically", via communication between the pen and the netpage system The example shows a "Request" form containing name and address fields and a submit button The netpage consists of graphic data 2 printed usmg visible ink, and coded data 3 printed as a collection of tags 4 usmg invisible ink The corresponding page description 5, stored on the netpage network, descπbes the individual elements of the netpage In particular it describes the type and spatial extent (zone) of each interactive element (1 e text field or button m the example), to allow the netpage system to correctly mterpret mput 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 m Figure 2, the netpage pen 101, a preferred form of which is shown m Figures 8 and 9 and descπbed m 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 m Figures 11 to 13 and descπbed m more detail below, is able to deliver, penodically 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 m a user's kitchen, near a breakfast table, or near the household's pomt of departure for the day It also comes m tabletop, desktop, portable and miniature versions Netpages printed at their pomt of consumption combine the ease-of-use of paper with the timeliness and interactivity of an interactive medium As shown m Figure 2, the netpage pen 101 mteracts with the coded data on a printed netpage 1 and communicates, via a short-range radio link 9, the interaction to a netpage printer The printer 601 sends the interaction to the relevant netpage page server 10 for interpretation In appropnate circumstances, the page server sends a coπesponding message to application computer software running on a netpage application server 13 The application server may m turn send a response which is printed on the onginating printer The netpage system is made considerably more convenient m the prefeπed embodiment by bemg used m conjunction with high-speed imcroelectromechanical system (MEMS) based Inkjet (Memjet™) printers In the preferred form of this technology, relatively high-speed and high-quality prmtmg is made more affordable to consumers In its preferred form, a netpage publication has the physical charactenstics of a traditional newsmagazme, such as a set of letter-size glossy pages printed 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 m the United States, and cable modem service offering broadband Internet access is already available to 20% of these The netpage printer can also operate with slower connections, but with longer delivery times and lower image quality Indeed, the netpage system can be enabled usmg existing consumer Inkjet and laser printers, although the system will operate more slowly and will therefore be less acceptable from a consumer's pomt of view In other embodiments, the netpage system is hosted on a pnvate intranet In still other embodiments, the netpage system is hosted on a smgle computer or computer-enabled device, such as a printer Netpage publication servers 14 on the netpage network are configured to deliver pπnt-quahty publications to netpage printers Peπodical publications are delivered automatically to subscnbing netpage printers via pomtcasting and multicasting Internet protocols Personalized publications are filtered and formatted according to individual user profiles A netpage printer can be configured to support any number of pens, and a pen can work with any number of netpage printers In the prefeπed implementation, each netpage pen has a unique identifier A household may have a collection of colored netpage pens, one assigned to each member of the family This allows each user to maintain a distinct profile with respect to a netpage publication server or application server A netpage pen can also be registered with a netpage registration server 11 and linked to one or more payment card accounts This allows e-commerce payments to be securely authorized usmg 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 biometncs can also be used to veπfy identity A version of the netpage pen includes fingerprint scanning, venfied m a similar way by the netpage registration server Although a netpage prmter may deliver peπodicals 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 penodicals from subscnbed or otherwise authorized sources In this respect, the netpage prmter 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 m the system is descπbed usmg a Unified Modelmg 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 m 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 - 1 e classes of classes Each class is drawn as a rectangle labelled with the name of the class It contams a list of the attπbutes of the class, separated from the name by a horizontal lme, and a list of the operations of the class, separated from the attπbute list by a horizontal lme In the class diagrams which follow, however, operations are never modelled An association is drawn as a lme joining two classes, optionally labelled at either end with the multiplicity of the association The default multiplicity is one An astensk (*) 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 of the association lme A generalization relationship ("ls-a") is drawn as a solid lme joining two classes, with an arrow (m the form of an open tπangle) at the generalization end When a class diagram is broken up mto multiple diagrams, any class which is duplicated is shown with a dashed outline m all but the main diagram which defines it It is shown with attπbutes only where it is defined 1.1 NETPAGES Netpages are the foundation on which a netpage network is built They provide a paper-based user interface to published information and interactive services A netpage consists of a printed page (or other surface region) mvisibly tagged with references to an onlme descπption of the page The onlme page descπption is mamtamed persistently by a netpage page server The page descnption descπbes the visible layout and content of the page, mcludmg text, graphics and images It also descnbes the mput elements on the page, mcludmg buttons, hyperlinks, and mput fields A netpage allows markmgs 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 descnption However, to allow mput through otherwise identical pages to be distmgtushed, each netpage is assigned a umque page identifier This page ID has sufficient precision to distinguish between a very large number of netpages Each reference to the page descnption is encoded m a printed tag The tag identifies the umque page on which it appears, and thereby indirectly identifies the page descnption The tag also identifies its own position on the page Charactenstics of the tags are descnbed 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 appropnate filter A tag is sensed by an area image sensor m the netpage pen, and the tag data is transmitted to the netpage system via the nearest netpage prmter The pen is wireless and communicates with the netpage printer via a short-range radio link Tags are sufficiently small and densely ananged that the pen can reliably image at least one tag even on a smgle click on the page It is important that the pen recognize the page ID and p isi+ion on every interaction with the page, smce the interaction is stateless Tags are eπor-correctably encoded to π.<_A"e them partially tolerant to surface damage The netpage page server maintains a umque page instance for each printed netpage, allowing it to maintain a distinct set of user-supplied values for mput fields in the page descπption for each printed netpage The relationship between the page descπption, the page instance, and the printed netpage is shown m Figure 4 The page instance is associated with both the netpage prmter which printed it and, if known, the netpage user who requested it 1.2 NETPAGE TAGS 1.2.1 Tag Data Content In a preferred form, each tag identifies the region m 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 sensmg device to provide feedback indicative of a function associated with the immediate area of the tag, without the sensmg device havmg to refer to a descnption of the region A netpage pen may, for example, illuminate an "active area" LED when m the zone of a hyperlink As will be more clearly explained below, m a preferred embodiment, each tag contams an easily recognized mvanant structure which aids initial detection, and which assists m minimizing the effect of any warp mduced by the surface or by the sensmg 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 smgle click on the page It is important that the pen recognize the page ID and position on every interaction with the page, smce 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 of the page on which the tag appears In other embodiments, the region to which a tag refers can be an arbitrary subregion of a page or other surface For example, it can comcide 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 contams 120 bits of information, typically allocated as shown m Table 1 Assuming a maximum tag density of 64 per square mch, a 16-bit tag ID supports a region size of up to 1024 square mches Larger regions can be mapped continuously without mcreasmg the tag ID precision simply by usmg abutting regions and maps The 100-bit region ID allows 2 100 (~10 30 or a million tnlhon tπlhon) different regions to be uniquely identified 1.2.2 Tag Data Encoding The 120 bits of tag data are redundantly encoded usmg 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, l 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 m the tag, and the symbols of the six codewords are mterleaved 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 m 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 m Figure 5, mcludes fixed target structures 15, 16, 17 and vanable data areas 18 The fixed target structures allow a sensmg device such as the netpage pen to detect the tag and infer its three-dimensional oπentation relative to the sensor The data areas contain representations of the individual bits of the encoded tag data To achieve proper tag reproduction, the tag is rendered at a resolution of 256x256 dots When printed at 1600 dots per mch 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 Smce the quiet area is also contnbuted by adjacent tags, it only adds 16 dots to the effective diameter of the tag The tag mcludes six target structures A detection ring 15 allows the sensmg device to initially detect the tag The ring is easy to detect because it is rotationally mvanant and because a simple correction of its aspect ratio removes most of the effects of perspective distortion An oπentation axis 16 allows the sensmg device to determine the approximate planar onentation of the tag due to the yaw of the sensor The onentation axis is skewed to yield a umque oπentation Four perspective targets 17 allow the sensmg device to infer an accurate two-dimensional perspective transform of the tag and hence an accurate three-dimensional position and oπentation of the tag relative to the sensor All target structures are redundantly large to improve their immunity to noise The overall tag shape is circular This supports, amongst other things, optimal tag packing on an irregular tnangular gnd 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 lmes and two concentnc 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 of the six codewords are allocated to the four concentnc symbol rings 18a to 18d m mterleaved 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 sensmg device, the sensmg device must be able to see at least one entire tag m its field of view no matter where m the region or at what onentation it is positioned The required diameter of the field of view of the sensmg device is therefore a function of the size and spacmg of the tags Assuming a circular tag shape, the minimum diameter of the sensor field of view is obtained when the tags are tiled on a equilateral tnangular gnd, as shown m Figure 6 1.2.4 Tag Image Processing and Decoding The tag image processmg and decoding performed by a sensmg device such as the netpage pen is shown in Figure 7 While a captured image is bemg acquired from the image sensor, the dynamic range of the image is determined (at 20) The center of the range is then chosen as the binary threshold for the image 21 The image is then thresholded and segmented mto 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 locatmg target structures Central shape moments are by their nature mvanant of position, and can be easily made mvanant of scale, aspect ratio and rotation The ring target structure 15 is the first to be located (at 26) A ring has the advantage of bemg 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 ring's ongmal 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 applymg the ring's normalizations to each shape's moments, and rotation-normalizing the resulting moments Once its second-order moments are normalized the axis target is easilv recognized Note that one third order moment is required to disambiguate the two possible oπentations 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, smce the perspective distortion can hide the axis target's axis The axis target's ongmal 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 then positions are computed based on their known spatial relationships to the ring and axis targets, the aspect and rotation of the ring, and the rotation of the axis Matching proceeds by applymg the ring'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 ongmal centroids of the four perspective targets are then taken to be the perspective-distorted comers 31 of a square of known size m 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 pomt pairs The inferred tag-space to image-space perspective transform is used to project (at 36) each known data bit position m tag space mto image space where the real-valued position is used to bilmearly mterpolate (at 36) the four relevant adjacent pixels m the mput 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 m 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 m total Note that the codeword symbols are sampled m codeword order, so that codewords are implicitly de-interleaved during the sampling process The ring target 15 is only sought m a subarea of the image whose relationship to the image guarantees that the ring, if found, is part of a complete tag If a complete tag is not found and successfully decoded, then no pen position is recorded for the current frame Given adequate processing power and ideally a non-minimal field of view 193, an alternative strategy mvolves seeking another tag m the current image The obtained tag data indicates the identity of the region containing the tag and the position of the tag within the region An accurate position 35 of the pen mb m the region, as well as the overall oπentation 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 mto an absolute location within the tagged region, the location of the tag within the region must be known This is given by a tag map, a function which maps each tag ID m a tagged region to a corresponding location The tag map class diagram is shown m Figure 22, as part of the netpage prmter 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 retnevable via the region ID Thus, given a region ID, a tag ID and a pen transform, the tag map can be retneved, the tag ID can be translated mto 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 mterest, both of which use the tag structure descπbed earlier m 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 contams a tag ID which, when translated through the tag map associated with the tagged region, yields a unique tag location within the region The tag-relative location of the pen is added to this tag location to yield the location of the pen within the region This m turn is used to determine the location of the pen relative to a user interface element m the page descnption 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 tπvially support the capture of an absolute pen path m the zone of a particular user interface element An object-mdicatmg tag contams a tag ID which directly identifies a user interface element m the page descnption associated with the region All the tags m the zone of the user interface element identify the user interface element, makmg 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 m that a user can interact with the printed page usmg an appropnate sensmg device m order for tag data to be read by the sensmg device and for an appropnate response to be generated m the netpage system 1.3 DOCUMENT AND PAGE DESCRIPTIONS A prefened embodiment of a document and page descnption class diagram is shown in Figures 25 and 26 In the netpage system a document is descnbed 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 prmter 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 m some cases be associated with content objects which are different from those associated with their coπesponding terminal elements, particularly where the content objects are style-related Each printed instance of a document and page is also descnbed separately, to allow mput captured through a particular page instance 830 to be recorded separately from mput captured through other instances of the same page descnption The presence of the most abstract document descπption on the page server allows a user to request a copy of a document without bemg forced to accept the source document's specific format The user may be requesting a copy through a prmter with a different page size, for example Conversely, the presence of the formatted document descnption on the page server allows the page server to efficiently mterpret 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 mput elements such as hyperlinks and mput fields A document instance 831 corresponds to a formatted document 834 ( t consists of a set of page instances 830, each of which corresponds to a page descπption 5 of the formatted document Each page instance 830 descnbes a smgle umque 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 mput 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 scnpt element 853 with an associated scnpt 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 mput element In the preferred form of the invention, a tag map 811 is associated with each page instance to allow tags on the page to be translated mto locations on the page 1.4 THE NETPAGE NETWORK In a prefened embodiment, a netpage network consists of a distnbuted set of netpage page servers 10, netpage registration servers 11, netpage ID servers 12, netpage application servers 13, netpage publication servers 14, and netpage printers 601 connected via a network 19 such as the Internet, as shown m Figure 3 The netpage registration server 11 is a server which records relationships between users, pens, printers, applications and publications, and thereby authorizes vanous network activities It authenticates users and acts as a signing proxy on behalf of authenticated users m application transactions It also provides handwriting recogmtion services As descnbed above, a netpage page server 10 maintains persistent information about page descnptions and page instances The netpage network mcludes any number of page servers, each handling a subset of page instances Smce a page server also maintains user mput values for each page instance, clients such as netpage printers send netpage mput directly to the appropnate page server The page server mterprets any such mput relative to the descnption of the corresponding page A netpage ID server 12 allocates document IDs 51 on demand, and provides load-balancing of page servers via its ED allocation scheme A netpage printer uses the Internet Distnbuted Name System (DNS), or similar, to resolve a netpage page ID 50 mto the network address of the netpage page server handling the conespondmg 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 descπbed m detail m Section 2 Netpage servers can be hosted on a vanety of network server platforms from manufacturers such as IBM, Hewlett-Packard, and Sun Multiple netpage servers can run concurrently on a smgle host, and a smgle server can be distnbuted over a number of hosts Some or all of the functionality provided by netpage servers, and m 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 prmter, m a computer workstation, or on a local network 1.5 THE NETPAGE PRINTER The netpage prmter 601 is an appliance which is registered with the netpage system and prints netpage documents on demand and via subscnption Each prmter has a unique prmter 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 secunty settings m non- volatile memory, the netpage printer contams no persistent storage As far as a user is concerned, "the network is the computer" Netpages function interactively across space and time with the help of the distnbuted netpage page servers 10, independently of particular netpage printers The netpage prmter receives subscπbed netpage documents from netpage publication servers 14 Each document is distnbuted m 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 subscnber and so are pomtcast to the subscπber's prmter via the appropnate page server Text and image objects, on the other hand are typically shared with other subscnbers, and so are multicast to all subscnbers' printers and the appropnate page servers The netpage publication server optimizes the segmentation of document content mto pomtcasts and multicasts After receivmg the pomtcast of a document's page layouts, the prmter knows which multicasts, if any, to listen to Once the prmter has received the complete page layouts and objects that define the document to be printed, it can print the document The prmter rastenzes and prints odd and even pages simultaneously on both sides of the sheet It contams duplexed print engme controllers 760 and print engmes utilizing Memjet™ pnntheads 350 for this purpose The prmtmg process consists of two decoupled stages rasterization of page descnptions, and expansion and printing of page images The raster image processor (RIP) consists of one or more standard DSPs 757 running m parallel The duplexed prmt engme controllers consist of custom processors which expand, dither and print page images in real time, synchronized with the operation of the pnntheads in the prmt engines Printers not enabled for IR prmtmg have the option to pπnt tags usmg IR-absorptive black ink, although this restncts 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 printers may pπnt onto more specialised surfaces, such as globes Each prmter supports at least one surface type, and supports at least one tag tilmg scheme, and hence tag map, for each surface type The tag map 811 which descnbes the tag tilmg scheme actually used to prmt a document becomes associated with that document so that the document's tags can be correctly interpreted Figure 2 shows the netpage prmter class diagram, reflecting printer-related information mamtamed by a registration server 11 on the netpage network A prefened embodiment of the netpage prmter is descπbed m greater detail m Section 6 below, with reference to Figures 11 to 16 1.5.1 Memjet™ Printheads The netpage system can operate usmg printers made with a wide range of digital prmtmg technologies, mcludmg thermal Inkjet, piezoelectnc inkjet, laser electrophotographic, and others However, for wide consumer acceptance, it is desirable that a netpage prmter have the following charactenstics • photographic quality color prmtmg • high quality text prmtmg high reliability • low prmter cost • low paper cost • simple operation • nearly silent prmtmg • high prmtmg speed • simultaneous double sided prmtmg • compact form factor • low power consumption No commercially available prmtmg technology has all of these charactenstics To enable to production of printers with these charactenstics, the present applicant has mvented a new prmt technology, referred to as Memjet™ technology Memjet™ is a drop-on-demand inkjet technology that incorporates pagewidth pnntheads fabπcated usmg microelectromechamcal systems (MEMS) technology Figure 17 shows a smgle prmtmg element 300 of a Memjet™ pπnthead The netpage wallpnnter incorporates 168960 prmtmg elements 300 to form a 1600 dpi pagewidth duplex prmter This prmter simultaneously prints cyan, magenta, yellow, black, and infrared inks as well as paper conditioner and ink fixative The printing element 300 is approximately 110 microns long by 32 microns wide Arrays of these prmtmg elements are formed on a silicon substrate 301 that incorporates CMOS logic, data transfer, timing, and dnve circuits (not shown) Major elements of the prmtmg element 300 are the nozzle 302, the nozzle nm 303, the nozzle chamber 304, the flmdic 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 311, and the ink inlet 312 The active actuator beam pair 308 is mechanically jomed to the passive actuator beam pan 309 at the jom 319 Both beams pairs are anchored at their respective anchor points 310 and 311 The combination of elements 308, 309, 310, 311, and 319 form a cantilevered electrothermal bend actuator 320 Figure 18 shows a small part of an array of prmtmg elements 300, mcludmg a cross section 315 of a prmtmg 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™ prmtmg element 300 Figure 19(a) shows the quiescent position of the ink meniscus 316 pπor to prmtmg an ink droplet Ink is retained m the nozzle chamber by surface tension at the ink memscus 316 and at the fluidic seal 305 formed between the nozzle chamber 304 and the ink channel nm 306 While prmtmg, the prmthead CMOS circuitry distπbutes data from the pπnt engme controller to the correct prmtmg element, latches the data, and buffers the data to dnve the electrodes 318 of the active actuator beam pair 308 This causes an electncal current to pass through the beam pair 308 for about one microsecond, resulting m Joule heatmg The temperature mcrease resulting from Joule heat g causes the beam pair 308 to expand As the passive actuator beam pair 309 is not heated, it does not expand, resulting m 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 mcreases the ink pressure, forcmg ink 321 out of the nozzle 302, and causing the ink memscus 316 to bulge The nozzle nm 303 prevents the ink memscus 316 from spreading across the surface of the nozzle chamber 304 As the temperature of the beam pairs 308 and 309 equalizes, the actuator 320 returns to its ongmal position This aids m the break-off of the ink droplet 317 from the ink 321 m the nozzle chamber, as shown m Figure 19(c) The nozzle chamber is refilled by the action of the surface tension at the memscus 316 Figure 20 shows a segment of a prmthead 350 In a netpage prmter, the length of the prmthead is the full width of the paper (typically 210 mm) m the direction 351 The segment shown is 04 mm long (about 02% of a complete prmthead) When prmtmg, the paper is moved past the fixed prmthead m the direction 352 The prmthead has 6 rows of interdigitated prmtmg elements 300, printing the six colors or types of ink supplied by the ink inlets 312 To protect the fragile surface of the prmthead during operation, a nozzle guard wafer 330 is attached to the prmthead substrate 301 For each nozzle 302 there is a correspondmg nozzle guard hole 331 through which the ink droplets are fired To prevent the nozzle guard holes 331 from becommg blocked by paper fibers or other debns, filtered air is pumped through the air rnlets 332 and out of the nozzle guard holes duπng printing To prevent ink 321 from drying, the nozzle guard is sealed while the prmter is idle 1.6 The Netpage Pen The active sensmg device of the netpage system is typically a pen 101, which, usmg 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 appropnate filter to permit sensmg at only near-infrared wavelengths As descnbed in more detail below, the system is able to sense when the mb is m contact with the surface, and the pen is able to sense tags at a sufficient rate to capture human handwntmg (l e at 200 dpi or greater and 100 Hz or faster) Information captured by the pen is encrypted and wirelessly transmitted to the prmter (or base station), the prmter or base station interpreting the data with respect to the (known) page structure The preferred embodiment of the netpage pen operates both as a normal markmg ink pen and as a non- marking stylus The markmg aspect, however, is not necessary for usmg the netpage system as a browsmg system, such as when it is used as an Internet mterface Each netpage pen is registered with the netpage system and has a umque pen ID 61 Figure 23 shows the netpage pen class diagram, reflectmg pen-related information mamtamed by a registration server 11 on the netpage network When either rub is m contact with a netpage, the pen determines its position and oπentation relative to the page The mb is attached to a force sensor, and the force on the rub is interpreted relative to a threshold to indicate whether the pen is "up" or "down" This allows a interactive element on the page to be 'clicked' by pressmg with the pen mb, m 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 veπfied The pen determines the position and oπentation of its mb on the netpage by imaging, m the infrared spectrum, an area 193 of the page m the vicinity of the mb It decodes the nearest tag and computes the position of the mb 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 mversely proportional to the tag size, the adjusted position resolution is quite high, exceeding the minimum resolution required for accurate handwriting recogmtion Pen actions relative to a netpage are captured as a senes of strokes A stroke consists of a sequence of time- stamped pen positions on the page, initiated by a pen-down event and completed by the subsequent pen-up event A stroke is also tagged with the page ID 50 of the netpage whenever the page ID changes, which, under normal circumstances, is at the commencement of the stroke Each netpage pen has a current selection 826 associated with it, allowing the user to perform copy and paste operations etc The selection is tunestamped to allow the system to discard it after a defined time penod The current selection descnbes a region of a page instance It consists of the most recent digita 1 ink stroke captured through the pen relative to the background area of the page It is interpreted in an application-specific manner once it is submitted to an application via a selection hyperlink activation Each pen has a current mb 824 This is the mb last notified by the pen to the system In the case of the default netpage pen descnbed above, either the markmg black ink b or the non-marking stylus mb is current Each pen also has a current mb style 825 This is the mb style last associated with the pen by an application, e g m response to the user selecting a color from a palette The default mb style is the mb style associated with the current mb Strokes captured through a pen are tagged with the current mb style When the strokes are subsequently reproduced, they are reproduced m the mb style with which they are tagged Whenever the pen is within range of a prmter with which it can communicate, the pen slowly flashes its "onlme" LED When the pen fails to decode a stroke relative to the page, it momentanly activates its "error" LED When the pen succeeds m decoding a stroke relative to the page, it momentanly 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 onlme recogmtion of handwriting, and for onlme veπfication of signatures The pen is wireless and transmits digital ink to the netpage prmter via a short-range radio link The transmitted digital ink is encrypted for pπvacy and secunty and packetized for efficient transmission, but is always flushed on a pen-up event to ensure timely handling m the prmter When the pen is out-of-range of a prmter it buffers digital ink m internal memory, which has a capacity of over ten mmutes of contmuous handwriting When the pen is once agam within range of a prmter, 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 lmmatenal which printer a pen is communicating with at any particular time A preferred embodiment of the pen is descnbed m greater detail m Section 6 below, with reference to Figures 8 to 10 1.7 NETPAGE INTERACTION The netpage prmter 601 receives data relating to a stroke from the pen 101 when the pen is used to mteract 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 prmter, where it resolves, via the DNS, the page ID 50 of the stroke mto the network address of the netpage page server 10 which maintains the correspondmg page instance 830 It then transmits the stroke to the page server If the page was recently identified m an earlier stroke, then the prmter may already have the address of the relevant page server m its cache Each netpage consists of a compact page layout mamtamed 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 retneves the page descnption to which the stroke applies, and determines which element of the page descnption the stroke intersects It is then able to mterpret the stroke m the context of the type of the relevant element A "click" is a stroke where the distance and time between the pen down position and the subsequent pen up position are both less than some small maximum An object which is activated by a click typically requires a click to be activated, and accordingly, a longer stroke is ignored The failure of a pen action, such as a "sloppy" click, to register is indicated by the lack of response from the pen's "ok" LED There are two lands of mput elements m a netpage page descnption hyperlinks and form fields Input through a form field can also tπgger 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 mclude the user's application alias ID 65 m the hyperlink activation, and a descπption which is used when the hyperlink is recorded as a favonte 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 m the normal way via the DNS There are three types of hyperlinks general hyperlinks 863, form hyperlinks 865, and selection hyperlinks 864, as shown m 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 correspondmg form to the application A selection hyperlink submits the current selection to the application If the current selection contams a smgle-word piece of text, for example, the application may return a smgle-page document givmg the word's meaning within the context m which it appears, or a translation mto a different language Each hyperlink type is characterized by what information is submitted to the application The correspondmg hyperlink mstance 862 records a transaction ID 55 which can be specific to the page mstance on which the hyperlink mstance appears The transaction ID can identify user-specific data to the application, for example a "shopping cart" of pending purchases mamtamed by a purchasing application on behalf of the user The system mcludes the pen's current selection 826 m a selection hyperlink activation The system mcludes the content of the associated form mstance 868 in a form hyperlink activation, although if the hyperlink has its "submit delta" attnbute set, only mput smce the last form submission is mcluded The system mcludes an effective return path m all hyperlink activations A hyperlinked group 866 is a group element 838 which has an associated hyperlink, as shown m Figure 31 When mput occurs through any field element m the group, the hyperlink 844 associated with the group is activated A hyperlinked group can be used to associate hyperlink behavior with a field such as a checkbox It can also be used, m conjunction with the "submit delta" attnbute of a form hyperlink, to provide contmuous mput to an application It can therefore be used to support a "blackboard" interaction model, I e where mput is captured and therefore shared as soon as it occurs 1.7.2 Forms A form defines a collection of related mput fields used to capture a related set of inputs through a printed netpage A form allows a user to submit one or more parameters to an application software program runnmg on a server A form 867 is a group element 838 m the document hierarchy It ultimately contams a set of terminal field elements 839 A form mstance 868 represents a printed mstance of a form It consists of a set of field instances 870 which correspond to the field elements 845 of the form Each field mstance has an associated value 871, whose type depends on the type of the correspondmg field element Each field value records mput through a particular printed form mstance, l e through one or more printed netpages The form class diagram is shown m Figure 32 Each form mstance has a status 872 which indicates whether the form is active, frozen, submitted, void or expired A form is active when first printed A form becomes frozen once it is signed A form becomes submitted once one of its submission hyperlinks has been activated, unless the hyperlink has its "submit delta" attnbute set A form becomes void when the user mvokes a void form, reset form or duplicate form page command A form expires when the time the form has been active exceeds the form's specified lifetime While the form is active, form mput is allowed Input through a form which is not active is mstead captured in the background field 833 of the relevant page mstance 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 mstead elicits an form status report Each form mstance is associated (at 59) with any form instances deπved from it, thus providing a version history This allows all but the latest version of a form m a particular tune penod to be excluded from a search All mput 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 mcludes pen oπentation and mb 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 m 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 m Figure 35 Any mark (a tick, a cross, a stroke, a fill zigzag, etc ) captured m 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 m Figure 36 Any digital ink captured m a text field's zone is automatically converted to text via onlme handwriting recogmtion, and the text is assigned to the field's value Onlme handwriting recogmtion is well-understood (see for example Tappert, C , C Y Suen and T Wakahara, "The State of the Art m On-Line Handwriting Recogmtion", IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol 12, No 8, August 1990) A signature field has an associated digital signature value 883, as shown in Figure 37 Any digital ink captured m a signature field's zone is automatically venfied 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 usmg the pen user's pnvate signature key specific to the application which owns the form Onlme signature veπfication is well-understood (see for example Plamondon, R and G Lorette, "Automatic Signature Veπfication and Wnter Identification - The State of the Art", Pattern Recogmtion, Vol 22, No 2, 1989) A field element is hidden if its "hidden" attnbute is set A hidden field element does not have an mput zone on a page and does not accept mput It can have an associated field value which is mcluded m 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 recogmtion algoπthm works "onlme" (I e with access to the dynamics of the pen movement), rather than "offline" (l e with access only to a bitmap of pen markmgs), it can recognize run-on discretely- wntten 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 m a particular element's zone is appended to that element's digital ink stream, ready for interpretation Any stroke not appended to an object's digital ink stream is appended to the background field's digital ink stream Digital ink captured m the background field is interpreted as a selection gesture Circumscπption of one or more objects is generally interpreted as a selection of the circumscnbed objects, although the actual interpretation is application-specific Table 2 summanses these vanous 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 m the background field The selection is cleared after an inactivity timeout to ensure predictable behavior The raw digital ink captured m 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 ongmal conversion, such as the conversion of handwritten text This can, for example, mvolve human mtervention at the application level for forms which fail certam 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 mdicated amendments to the filled-in fields outside of those fields Figure 38 shows a flowchart of the process of handling pen mput relative to a netpage The process consists of receiving (at 884) a stroke from the pen, identifying (at 885) the page mstance 830 to which the page ID 50 m the stroke refers, retneving (at 886) the page descπption 5, identifying (at 887) a formatted element 839 whose zone 58 the stroke intersects, detemuning (at 888) whether the formatted element corresponds to a field element, and if so appending (at 892) the received stroke to the digital ink of the field value 871, interpreting (at 893) the accumulated digital ink of the field, and determining (at 894) whether the field is part of a hyperlinked group 866 and if so activating (at 895) the associated hyperlink, alternatively determining (at 889) whether the formatted element corresponds to a hyperlink element and if so activating (at 895) the correspondmg hyperlink, alternatively, m the absence of an mput field or hyperlink, appending (at 890) the received stroke to the digital ink of the background field 833, and copying (at 8 1 ) the received stroke to the current selection 826 of the current pen, as mamtamed by the registration server Figure 38a shows a detailed flowchart of step 893 m the process shown m Figure 38, where the accumulated digital ink of a field is interpreted according to the type of the field The process consists of deterπurung (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 appropnate 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 venfying (at 903) the digital ink as the signature of the pen's owner, with the help of the appropnate registration server, creating (at 904) a digital signature of the contents of the correspondmg form, also with the help of the registration server and usmg the pen owner's pnvate signature key relating to the coπesponding application, and assigmng (at 905) the digital signature to the field value 1.7.3 Page Server Commands A page server command is a command which is handled locally by the page server It operates directly on form, page and document instances A page server command 907 can be a void form command 908, a duplicate form command 909, a reset form command 910, a get form status command 911, a duplicate page command 912, a reset page command 913, a get page status command 914, a duplicate document command 915, a reset document command 916, or a get document status command 917, as shown m Figure 39 A void form command voids the coπesponding form mstance A duplicate form command voids the correspondmg form mstance and then produces an active printed copy of the current form mstance with field values preserved The copy contams the same hyperlink transaction IDs as the ongmal, and so is indistinguishable from the ongmal to an application A reset form command voids the correspondmg form mstance and then produces an active printed copy of the form mstance with field values discarded A get form status command produces a printed report on the status of the correspondmg form mstance, mcludmg who published it, when it was printed, for whom it was printed, and the form status of the form mstance Smce a form hyperlink mstance contams a transaction ID, the application has to be mvolved m producmg a new form mstance A button requesting a new form mstance is therefore typically implemented as a hyperlink A duplicate page command produces a prmted copy of the correspondmg page mstance with the background field value preserved If the page contains a form or is part of a form, then the duplicate page command is mterpreted as a duplicate form command A reset page command produces a printed copy of the correspondmg page mstance with the background field value discarded If the page contams a form or is part of a form, then the reset page command is mterpreted as a reset form command A get page status command produces a prmted report on the status of the corresponding page instance, mcludmg who published it, when it was prmted, for whom it was prmted, and the status of any forms it contams or is part of The netpage logo which appears on every netpage is usually associated with a duplicate page element When a page mstance is duplicated with field values preserved, field values are prmted m their native form, l e a checkmark appears as a standard checkmark graphic, and text appears as typeset text Only drawings and signatures appear m their ongmal form, with a signature accompanied by a standard graphic indicating successful signature venfication A duplicate document command produces a prmted copy of the coπesponding document mstance with background field values preserved If the document contams 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 prmted copy of the coπesponding document mstance with background field values discarded If the document contams any forms, then the reset document command resets the forms m the same way a reset form command does A get document status command produces a prmted report on the status of the coπesponding document mstance, mcludmg who published it, when it was prmted, for whom it was prmted, and the status of any forms it contams If the page server command's "on selected" attnbute is set, then the command operates on the page identified by the pen's current selection rather than on the page containing the command This allows a menu of page server commands to be prmted 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 m a hyperlinked group The page server activates the hyperlink associated with the hyperlinked group rather than executing the page server command A page server command element is hidden if its "hidden" attnbute is set A hidden command element does not have an mput zone on a page and so cannot be activated directly by a user It can, however, be activated via a page server command embedded m a different page, if that page server command has its "on selected" attnbute set 1.8 STANDARD FEATURES OF NETPAGES In the preferred form, each netpage is prmted 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 pressmg the logo produces a copy of the page In the case of a form, the button produces a copy of the entire form And m the case of a secure document, such as a ticket or coupon, the button elicits an explanatory note or advertising page The default smgle-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 prefeπed embodiment, the netpage prmter has a smgle button labelled "Help" When pressed it elicits a smgle page of information, mcludmg • status of prmter connection • status of prmter 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 mcludes the following functions • prmt a copy of a document • pπnt a clean copy of a form • pπnt the status of a document A document function is initiated by simply pressmg the button and then touching any page of the document The status of a document mdicates who published it and when, to whom it was delivered, and to whom and when it was subsequently submitted as a form The netpage network directory allows the user to navigate the hierarchy of publications and services on the network As an alternative, the user can call the netpage network "900" number "yellow pages" and speak to a human operator The operator can locate the desired document and route it to the user's prmter Dependmg on the document type, the publisher or the user pays the small "yellow pages" service fee The help page is obviously unavailable if the prmter is unable to pπnt In this case the "error" light is lit and the user can request remote diagnosis over the network 2 PERSONALIZED PUBLICATION MODEL In the following descπption, 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 newsmagazme news, the mtended scope m the present context is wider In the netpage system, the editonal content and the advertising content of a news publication are personalized usmg different mechanisms The editonal content is personalized according to the reader's explicitly stated and implicitly captured mterest profile The advertising content is personalized according to the reader's locality and demographic 2.1 EDITORIAL PERSONALIZATION A subscnber can draw on two lands 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 coπespond to traditional newspapers and newsmagazines, while news streams can be many and vaπed a "raw" news feed from a news service, a cartoon stnp, a freelance wnter'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 editonal control The subscnber builds a daily newspaper by selecting one or more contributing news publications, and creating a personalized version of each The resulting daily editions are prmted and bound together mto a smgle newspaper The vanous members of a household typically express their different mterests 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 onlme, for example, mclude "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 momtormg 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 numencally (1 e as a limit on its number of pages), and the desired proportion of advertising, either qualitatively (e g high, normal, low, none), or numencally (I e as a percentage) The reader also optionally expresses a preference for a large number of shorter articles or a small number of longer articles Each article is ideally written (or edited) m both short and long forms to support this preference An article may also be wntten (or edited) m different versions to match the expected sophistication of the reader, for example to provide children's and adults' versions The appropnate version is selected accordmg 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 pnoπtized by the editors, and each is assigned a useftd lifetime By default they are delivered to all relevant subscnbers, m pπonty order, subject to space consframts m the subscnbers' editions In sections where it is appropnate, 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 prmted with rating buttons at the end of the article The buttons can provide an easy choice (e g "liked" and "disliked'), makmg it more likely that readers will bother to rate the article Articles with high pnonties 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 suipnse me), or numencally A high serendipity factor lowers the threshold used for matching duπng collaborative filtering A high factor makes it more likely that the correspondmg section will be filled to the reader's specified capacity A different serendipity factor can be specified for different days of the week The reader also optionally specifies topics of particular mterest within a section, and this modifies the pnonties 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, tunes and monetary values are localized This mvolves specifying whether units are unpenal or metnc, a local timezone and time format, and a local currency, and whether the localization consist of m 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 m which a news publication is published, and its coπesponding 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 vanous guises 2.2 ADVERTISING LOCALIZATION AND TARGETING The personalization of the editonal content directly affects the advertising content, because advertising is typically placed to exploit the editonal context Travel ads, for example, are more likely to appear m a travel section than elsewhere The value of the editonal content to an advertiser (and therefore to the publisher) lies m its ability to attract large numbers of readers with the πght demographics Effective advertismg is placed on the basis of locality and demographics Locality determines proximity to particular services, retailers etc , and particular mterests and concerns associated with the local commumfy and environment Demographics determine general mterests and preoccupations as well as likely spending patterns A news publisher's most profitable product is advertismg "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 advertismg In the netpage system, the netpage pubhcation server computes the approximate multi-dimensional size of a publication's saleable advertismg space on a per-section basis, taking mto account the publication's geographic coverage, the section's readership, the size of each reader's section edition, each reader's advertismg proportion, and each reader's demographic In companson with other media, the netpage system allows the advertismg space to be defined m 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 advertismg "slot" can be sold m 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 advertismg to be linked directly to detailed product information and onlme purchasing It therefore raises the intrinsic value of the advertismg space Because personalization and localization are handled automatically by netpage publication servers, an advertismg aggregator can provide arbitranly 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 advertismg aggregators than to directly capture advertismg Even though the advertismg aggregator is taking a proportion of advertismg revenue, publishers may find the change profit-neutral because of the greater efficiency of aggregation The advertismg aggregator acts as an intermediary between advertisers and publishers, and may place the same advertisement m multiple publications It is worth noting that ad placement m a netpage publication can be more complex than ad placement m the publication's traditional counterpart, because the publication's advertismg space is more complex While ignoring the full complexities of negotiations between advertisers, advertismg aggregators and publishers, the preferred form of the netpage system provides some automated support for these negotiations, mcludmg support for automated auctions of advertismg space Automation is particularly desirable for the placement of advertisements which generate small amounts of mcome, 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 Coπespondrngly, 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, mcludmg • publication customizations • collaborative filtering vectors • contact details • presentation preferences The customization of a publication is typically publication-specific, and so the customization information is mamtamed 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 coπelate different users' mterests for the purposes of makmg recommendations Although there are benefits to mamtammg a smgle collaborative filtenng vector mdependenfly of any particular publication, there are two reasons why it is more practical to mamtam a separate vector for each publication there is likely to be more overlap between the vectors of subscnbers to the same publication than between those of subscnbers to different publications, and a publication is likely to want to present its users' collaborative filtenng vectors as part of the value of its brand, not to be found elsewhere Collaborative filtenng vectors are therefore also mamtamed by the relevant netpage publication server Contact details, mcludmg name, street address, ZIP Code, state, country, telephone numbers, are global by nature, and are mamtamed by a netpage registration server Presentation preferences, mcludmg those for quantities, dates and times, are likewise global and mamtamed m the same way The localization of advertismg relies on the locality mdicated m the user's contact details, while the targeting of advertismg relies on personal information such as date of birth, gender, mantal status, come, profession, education, or qualitative denvatives such as age range and mco e range For those users who choose to reveal personal information for advertismg purposes, the information is mamtamed by the relevant netpage registration server In the absence of such information, advertismg can be targeted on the basis of the demographic associated with the user's ZIP or ZDP+4 Code Each user, pen, prmter, application provider and application is assigned its own umque identifier, and the netpage registration server maintains the relationships between them, as shown m Figures 21, 22, 23 and 24 For registration purposes, a publisher is a special land of application provider, and a publication is a special kind of application Each user 800 may be authorized to use any number of printers 802, and each prmter may allow any number of users to use it Each user has a smgle default prmter (at 66), to which penodical publications are delivered by default, whilst pages prmted on demand are delivered to the prmter through which the user is interacting The server keeps track of which publishers a user has authorized to pπnt to the user's default prmter A publisher does not record the ID of any particular prmter, but mstead resolves the ID when it is required When a user subscnbes 808 to a publication 807, the publisher 806 (l e application provider 803) is authorized to pπnt to a specified printer or the user's default prmter This authorization can be revoked at any tune by the user Each user may have several pens 801, but a pen is specific to a smgle user If a user is authorized to use a particular prmter, then that prmter recognizes any of the user's pens The pen ID is used to locate the coπesponding user profile mamtamed by a particular netpage registration server, via the DNS m the usual way A Web terminal 809 can be authorized to prmt on a particular netpage prmter, allowing Web pages and netpage documents encountered duπng Web browsmg to be conveniently prmted on the nearest netpage printer The netpage system can collect, on behalf of a prmter provider, fees and commissions on mcome earned through publications prmted on the provider's printers Such mcome can mclude advertismg fees, click-through fees, e- commerce commissions, and transaction fees If the prmter is owned bv the user, then the user is the prmter provider Each user also has a netpage account 820 which is used to accumulate micro-debits and credits (such as those descπbed m the preceding paragraph), contact details 815, mcludmg name, address and telephone numbers, global preferences 816, mcludmg pnvacy, delivery and localization settings, any number of biometnc records 817, containmg the user's encoded signature 818, fingerprint 819 etc, a handwriting model 819 automatically mamtamed by the system, and SET payment card accounts 821 with which e-commerce payments can be made 2.3.2 Favorites List A netpage user can mamtam a list 922 of "favontes" - links to useftd documents etc on the netpage network The list is mamtamed by the system on the user's behalf It is organized as a hierarchy of folders 924, a preferrred embodiment of which is shown m the class diagram m Figure 41 2.3.3 History List The system maintains a history list 929 on each user's behalf, containmg links to documents etc accessed by the user through the netpage system It is organized as a date-ordered list, a prefeπed embodiment of which is shown m the class diagram m Figure 42 2.4 INTELLIGENT PAGE LAYOUT The netpage publication server automatically lays out the pages of each user's personalized publication on a section-by-section basis Smce most advertisements are m the form of pre-tormatted rectangles, they are placed on the page before the editonal content The advertismg ratio for a section can be achieved with wildly varying advertismg ratios on individual pages within the section, and the ad layout algoπthm exploits this The algonthm is configured to attempt to co-locate closely tied editonal and advertismg content, such as placmg ads for roofing mateπal specifically within the publication because of a special feature on do-it-yourself roofing repairs The editonal content selected for the user, mcludmg text and associated images and graphics, is then laid out accordmg to vanous aesthetic rules The entire process, mcludmg the selection of ads and the selection of editonal 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 tune, allowing significant day-to-day vaπations 2.5 DOCUMENT FORMAT Once the document is laid out, it is encoded for efficient distπbution and persistent storage on the netpage network The primary efficiency mechanism is the separation of information specific to a smgle user's edition and information shared between multiple users' editions The specific information consists of the page layout The shared information consists of the objects to which the page layout refers, mcludmg images, graphics, and pieces of text A text object contams fully-formatted text represented m the Extensible Markup Language (XML) using the Extensible Stylesheet Language (XSL) XSL provides precise control over text formatting mdependenfly of the region mto which the text is bemg set, which in this case is bemg provided by the layout The text object contams embedded language codes to enable automatic translation, and embedded hyphenation hints to aid with paragraph formatting An image object encodes an image m the JPEG 2000 wavelet-based compressed image format A graphic object encodes a 2D graphic m Scalable Vector Graphics (SVG) format The layout itself consists of a seπes of placed image and graphic objects, linked textflow objects through which text objects flow, hyperlinks and mput fields as descπbed above, and watermark regions These layout objects are summarized m Table 3 The layout uses a compact format suitable for efficient distπbution and storage Table 3 - netpage layout objects 2.6 DOCUMENT DISTRIBUTION As descnbed above, for purposes of efficient distπbution and persistent storage on the netpage network, a user-specific page layout is separated from the shared objects to which it refers When a subscnbed publication is ready to be distnbuted, the netpage publication server allocates, with the help of the netpage ID server 12, a umque ID for each page, page mstance, document, and document mstance 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 prmter via the appropnate page server, and when the pointcasting is complete, multicasts the shared content on the specified channels After receiving its pomtcast, each page server and prmter subscπbes to the multicast channels specified m the page layouts During the multicasts, each page server and prmter extracts from the multicast streams those objects referred to by its page layouts The page servers persistently archive the received page layouts and shared content Once a prmter has received all the objects to which its page layouts refer, the prmter re-creates the fiilly- populated layout and then rasteπzes and pπnts it Under normal circumstances, the prmter 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 p mter can therefore hold m excess of 100 such pages m its internal 64MB memory, allowing for temporary buffers etc The prmter 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 prmter runs out of paper, it is likely that the user will be able to replemsh the paper supply before the prmter' s 100-page internal storage capacity is exhausted However, if the printer' s mtemal memory does fill up, then the prmter will be unable to make use of a multicast when it first occurs The netpage publication server therefore allows printers to submit requests for re- multicasts When a cntical number of requests is received or a timeout occurs, the server re-multicasts the corresponding shared objects Once a document is prmted, a prmter 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 m much the same way as a penodical However, smce there is no shared content, delivery is made directly to the requesting prmter 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 mstance of a netpage publication server The netpage formatting server has knowledge of vanous Internet document formats, mcludmg Adobe's Portable Document Format (PDF), and Hypertext Markup Language (HTML) In the case of HTML, it can make use of the higher resolution of the prmted page to present Web pages m a multi-column format, with a table of contents It can automatically mclude 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, mcludmg interactivity and persistence, available on any Internet document, no matter what its oπgm and format It hides knowledge of different document formats from both the netpage prmter and the netpage page server, and hides knowledge of the netpage system from Web servers 3 SECURITY 3.1 CRYPTOGRAPHY Cryptography is used to protect sensitive information, both m storage and m 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 referred to as symmetnc cryptography, uses the same key to encrypt and decrypt a message Two parties wishing to exchange messages must first arrange to securely exchange the secret key Public-key cryptography, also refeπed to as asymmetπc cryptography, uses two encryption keys The two keys are mathematically related m such a way that any message encrypted usmg one key can only be decrypted usmg the other key One of these keys is then published, while the other is kept pnvate ihe public key is used to encrypt any message intended for the holder of the pnvate key Once encrypted usmg the public key, a message can only be decrypted usmg the pnvate key Thus two parties can securely exchange messages without first havmg to exchange a secret key To ensure that the pnvate key is secure, it is normal for the holder of the pnvate key to generate the key pair Public-key cryptography can be used to create a digital signature The holder of the pnvate key can create a known hash of a message and then encrypt the hash usmg the pnvate key Anyone can then venfy that the encrypted hash constitutes the "signature" of the holder of the pnvate key with respect to that particular message by decrypting the encrypted hash usmg the public key and venfying the hash against the message If the signature is appended to the message, then the recipient of the message can venfy both that the message is genuine and that it has not been altered m transit To make public-key cryptography work, there has to be a way to distribute public keys which prevents impersonation This is normally done usmg certificates and certificate authonties A certificate authonty is a trusted third party which authenticates the connection between a public key and someone's identity The certificate authonty 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 authonty can use the public key m the certificate with a high degree of certainty that it is genuine They just have to venfy that the certificate has mdeed been signed by the certificate authonty, whose public key is well-known In most transaction environments, public-key cryptography is only used to create digital signatures and to securely exchange secret session keys Secret-key cryptography is used for all other purposes In the following discussion, when reference is made to the secure transmission of information between a netpage prmter and a server, what actually happens is that the prmter obtams the server's certificate, authenticates it with reference to the certificate authonfy, uses the public key-exchange key m 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 arbitranly short lifetime 3.2 NETPAGE PRINTER SECURITY Each netpage prmter is assigned a pair of umque identifiers at time of manufacture which are stored m read-only memory m the prmter and m the netpage registration server database The first ID 62 is public and umquely identifies the prmter on the netpage network The second ID is secret and is used when the prmter is first registered on the network When the prmter connects to the netpage network for the first time after installation, it creates a signature pubhc/pnvate 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 m its database, and accepts the registration if the IDs match It then creates and signs a certificate containmg the prmter' s public ID and public signature key, and stores the certificate m the registration database The netpage registration server acts as a certificate authonty for netpage printers, smce it has access to secret information allowing it to venfy printer identity When a user subscnbes to a publication, a record is created m the netpage registration server database authorizing the publisher to pπnt the publication to the user's default prmter or a specified prmter Every document sent to a prmter via a page server is addressed to a particular user and is signed by the publisher usmg the publisher's pnvate signature key The page server venfies, via the registration database, that the publisher is authorized to deliver the publication to the specified user The page server venfies the signature usmg the publisher's public key, obtained from the publisher's certificate stored m the registration database The netpage registration server accepts requests to add printing authorizations to the database, so long as those requests are initiated via a pen registered to the prmter 3.3 NETPAGE PEN SECURITY Each netpage pen is assigned a umque identifier at time of manufacture which is stored m read-only memory m the pen and m the netpage registration server database The pen ID 61 umquely identifies the pen on the netpage network A netpage pen can "know" a number of netpage printers, and a prmter can "know" a number of pens A pen communicates with a prmter via a radio frequency signal whenever it is within range of the printer Once a pen and prmter are registered, they regularly exchange session keys Whenever the pen transmits digital ink to the prmter, the digital ink is always encrypted usmg the appropnate session key Digital ink is never transmitted m the clear A pen stores a session key for every prmter it knows, mdexed by prmter ID, and a prmter stores a session key for every pen it knows, mdexed 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 prmter, the pen and prmter discover whether they know each other If they don't know each other, then the prmter 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 prmter If the pnnter is meant to know the pen but doesn't, then it initiates the automatic pen registration procedure If the pnnter isn't meant to know the pen, then it agrees with the pen to ignore it until the pen is placed m a charging cup, at which time it initiates the registration procedure In addition to its public ID, the pen contams a secret key-exchange key The key-exchange key is also recorded m the netpage registration server database at time of manufacture Duπng registration, the pen transmits its pen ID to the pnnter, and the pnnter transmits the pen ID to the netpage registration server The server generates a session key for the pnnter and pen to use, and securely transmits the session key to the pnnter It also transmits a copy of the session key encrypted with the pen's key-exchange key The pnnter stores the session key internally, mdexed by the pen ID, and transmits the encrypted session key to the pen The pen stores the session key internally, mdexed by the pnnter ID Although a fake pen can impersonate a pen m the pen registration protocol, only a real pen can decrypt the session key transmitted by the pnnter 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 m 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 consframts m the pen 3.4 SECURE DOCUMENTS The netpage system supports the delivery of secure documents such as tickets and coupons The netpage pnnter mcludes a facility to print watermarks, but will only do so on request from publishers who are suitably authorized The publisher mdicates its authonty to print watermarks m its certificate, which the pnnter is able to authenticate The "watermark" printing process uses an alternative dither mafrix in specified "watermark" regions of the page Back-to-back pages contain mirror-image watermark regions which coincide when prmted The dither matnces used m odd and even pages' watermark regions are designed to produce an interference effect when the regions are viewed together, achieved by looking through the prmted sheet The effect is similar to a watermark m 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 usmg the built-in netpage copy mechanism descπbed in Section 1 9 above This extends to copymg netpages on netpage-aware photocopiers Secure documents are typically generated as part of e-commerce transactions They can therefore mclude the user's photograph which was captured when the user registered biometnc information with the netpage registration server, as descnbed m Section 2 When presented with a secure netpage document, the recipient can venfy its authenticity by requesting its status m the usual way The umque 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 venfication pen can be developed with built-in feedback on veπfication failure, to support easy pomt-of-presentation document venfication Clearly neither the watermark nor the user's photograph are secure m a cryptographic sense They simply provide a significant obstacle to casual forgery Onlme document venfication, particularly usmg a venfication pen, provides an added level of secunty where it is needed, but is still not entirely immune to forgenes 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 descπbed m 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, havmg been developed by MasterCard and Visa, is organized around payment cards, and this is reflected m the terminology However, much of the system is mdependent of the type of accounts bemg used In SET, cardholders and merchants register with a certificate authonty and are issued with certificates containmg their public signature keys The certificate authonty venfies a cardholder's regisfration details with the card issuer as appropnate, and venfies a merchant's registration details with the acquirer as appropnate Cardholders and merchants store their respective pnvate signature keys securely on their computers During the payment process, these certificates are used to mutually authenticate a merchant and cardholder, and to authenticate them both to the payment gateway SET has not yet been adopted widely, partly because cardholder maintenance of keys and certificates is considered burdensome Interim solutions which mamtam 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) m SET payment transactions The netpage system uses biometncs to authenticate the user and authorize SET payments Because the system is pen-based, the biometnc used is the user's on-lme signature, consisting of time- varying pen position and pressure A fingerprint biometnc can also be used by designing a fingerprint sensor mto the pen, although at a higher cost The type of biometnc used only affects the capture of the biometnc, not the authorization aspects of the system The first step to bemg able to make SET payments is to register the user's biometnc with the netpage registration server This is done m a controlled environment, for example a bank, where the biometnc can be captured at the same time as the user's identity is venfied The biometnc is captured and stored m the regisfration 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 pnvate signature key and certificate are stored m the database The user's payment card information is also stored, giving the netpage regisfration server enough information to act as the user's proxy m any SET payment transaction When the user eventually supplies the biometnc to complete a payment, for example by signing a netpage order form, the pnnter securely fransmits the order information, the pen ID and the biometnc data to the netpage registration server The server venfies the biometnc with respect to the user identified by the pen ID, and from then on acts as the user's proxy m completing the SET payment transaction 4.3 MICRO-PAYMENTS The netpage system mcludes a mechanism for micro-payments, to allow the user to be conveniently charged for prmtmg low-cost documents on demand and for copymg copynght documents, and possibly also to allow the user to be reimbursed for expenses incuπed m prmtmg advertismg matenal 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 usmg the standard payment mechanism The network account can be extended to aggregate subscnption fees for penodicals, which would also otherwise be presented to the user the form of individual statements 4.4 TRANSACTIONS When a user requests a netpage m a particular application context, the application is able to embed a user- specific fransaction ID 55 m the page Subsequent mput through the page is tagged with the fransaction ID, and the application is thereby able to establish an appropnate context for the user's mput When mput occurs through a page which is not user-specific, however, the application must use the user's umque identity to establish a context A typical example mvolves adding items from a pre-pnnted catalog page to the user's virtual "shoppmg cart" To protect the user's pnvacy, however, the umque user ID 60 known to the netpage system is not divulged to applications This is to prevent different application providers from easily correlating mdependenfly accumulated behavioral data The netpage registration server mstead maintains an anonymous relationship between a user and an application via a umque alias ID 65, as shown m Figure 24 Whenever the user activates a hyperlink tagged with the "registered" attnbute, the netpage page server asks the netpage registration server to translate the associated application ID 64, together with the pen ID 61 , mto an alias ID 65 The alias ID is then submitted to the hyperlink's application The application maintains state information mdexed by alias ID, and is able to retneve user-specific state information without knowledge of the global identity of the user The system also maintains an mdependent certificate and pnvate signature key for each of a user's applications, to allow it to sign application transactions on behalf of the user usmg only application-specific information To assist the system m routing product bar code (UPC) "hyperlink" activations, the system records a favoπte 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 penodical subscπbed content The system records the user's willingness to receive the subscnbed publication, as well as the expected frequen. y of publication 4.5 RESOURCE DESCRIPTIONS AND COPYRIGHT A prefeπed embodiment of a resource descπption class diagram is shown m Figure 40 Each document and content object may be descnbed by one or more resource descnptions 842 Resource descnptions use the Dublin Core metadata element set, which is designed to facilitate discovery of electronic resources Dublm Core metadata conforms to the World Wide Web Consortium (W3C) Resource Descπption Framework (RDF) A resource descnption may identify nghts holders 920 The netpage system automatically transfers copynght fees from users to nghts holders when users pπnt copynght content 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 m 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 containmg 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 lme Duπng the time an entity is active, the lifeline is shown as a double lme Because the protocols considered here do not create or destroy entities, lifelines are generally cut short as soon as an entity ceases to participate m a protocol 5.1 SUBSCRIPTION DELIVERY PROTOCOL A prefeπed embodiment of a subscπption delivery protocol is shown in Figure 43 A large number of users may subscπbe to a penodical 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 subscπption delivery protocol therefore delivers document structures to mdividual prmters via pomtcast, but delivers shared content objects via multicast The application (l e publisher) first obtams a document ID 51 for each document from an ID server 12 It then sends each document structure, mcludmg its document ID and page descnptions, to the page server 10 responsible for the document's newly allocated ID It mcludes its own application ID 64, the subscnber' s alias ID 65, and the relevant set of multicast channel names It signs the message usmg its pnvate signature key The page server uses the application ID and alias ID to obtain from the registration server the coπesponding user ID 60, the user's selected pnnter ID 62 (which may be explicitly selected for the application, or may be the user's default pnnter), and the application's certificate The application's certificate allows the page server to venfy 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 subscnption 808 The page server then allocates document and page mstance IDs and forwards the page descnptions, mcludmg page IDs 50, to the pnnter It mcludes the relevant set of multicast channel names for the pnnter to listen to It then returns the newly allocated page IDs to the application for future reference Once the application has distnbuted all of the document structures to the subscnbers' selected prmters via the relevant page servers, it multicasts the vanous subsets of the shared objects on the previously selected multicast channels Both page servers and printers momtor the appropnate multicast channels and receive their required content objects They are then able to populate the previously pomtcast document structures This allows the page servers to add complete documents to their databases, and it allows the prmters to print the documents 5.2 HYPERLINK ACTIVATION PROTOCOL A prefeπed embodiment of a hyperlink activation protocol is shown m Figure 45 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 of the pen from the pen connection protocol The pnnter determines, via the DNS, the network address of the page server 10a handling the particular page ID 50 The address may already be m its cache if the user has recently mteracted with the same page The pnnter then forwards the pen ID, its own pnnter ID 62, the page ID and click location to the page server The page server loads the page descnption 5 identified by the page ID and determines which mput element's zone 58, if any, the click lies m Assuming the relevant mput element is a hyperlink element 844, the page server then obtams 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 coπesponding user ID 60 from the registration server 11, and then allocates a globally umque hyperlink request ID 52 and builds a hyperlink request 934 The hyperlink request class diagram is shown m Figure 44 The hyperlink request records the IDs of the requesting user and pnnter, and identifies the clicked hyperlink mstance 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 accordmg to application-specific logic, and obtams 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 coπespondmg user ID and pnnter 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 mstance 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 descnptions to the requesting pnnter The hyperlink mstance may mclude a meaningfiil fransaction ID 55, m which case the first page server mcludes the fransaction ID m 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" attnbute is set, then the first page server sends both the pen ID 61 and the hyperlink's application ID 64 to the registration server 11 to obtain not just the user ID coπesponding to the pen ID but also the alias ID 65 coπespondmg to the application ID and the user ID It mcludes the alias ID m 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 pnnter The stroke identifies the page and a path on the page The pnnter forwards the pen ID 61 , its own pnnter ID 62, the page ID 50 and stroke path to the page server 10 m the usual way The page server loads the page descnption 5 identified by the page ID and determines which mput element's zone 58, if any, the stroke intersects Assuming the relevant mput element is a text field 878, the page server appends the stroke to the text field's digital ink After a peπod of inactivity m the zone of the text field, the page server sends the pen ID and the pending strokes to the registration server 11 for interpretation The registration server identifies the user coπespondmg to the pen, and uses the user's accumulated handwriting model 822 to mterpret the strokes as handwritten text Once it has converted the strokes to text, the registration server returns the text to the requesting page server The page server appends the text to the text value of the text field 5.4 SIGNATURE VERIFICATION PROTOCOL Assuming the mput element whose zone the stroke mtersects is a signature field 880, the page server 10 appends the stroke to the signature field's digital ink After a peπod of inactivity m the zone of the signature field, the page server sends the pen ID 61 and the pending strokes to the registration server 11 for venfication 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 coπespondmg to the pen, and uses the user's dynamic signature biometnc 818 to venfy the strokes as the user's signature Once it has venfied the signature, the registration server uses the application ID 64 and user ID 60 to identify the user's application-specific pnvate 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 mcludes the alias ID 65 of the coπespondmg user This allows a smgle form to capture multiple users' signatures 5.5 FORM SUBMISSION PROTOCOL A prefeπed embodiment of a form submission protocol is shown m Figure 46 Form submission occurs via a form hyperlink activation It thus follows the protocol defined m Section 5 2, with some form-specific additions In the case of a form hyperlink, the hyperlink activation message sent by the page server 10 to the application 71 also contains the form ID 56 and the current data content of the form If the form contains any signature fields, then the application venfies each one by extracting the alias ID 65 associated with the coπespondmg digital signature and obtaining the coπespondmg certificate from the registration server 11 5.6 COMMISSION PAYMENT PROTOCOL A prefeπed embodiment of a commission payment protocol is shown m Figure 47 In an e-commerce environment, fees and commissions may be payable from an application provider to a publisher on click-throughs, transactions and sales Commissions on fees and commissions on commissions may also be payable from the publisher to the provider of the pnnter The hyperlink request ID 52 is used to route a fee or commission credit from the target application provider 70a (e g merchant) to the source application provider 70b (I e publisher), and from the source application provider 70b to the pnnter provider 72 The target application receives the hyperlink request ID from the page server 10 when the hyperlink is first activated, as descnbed m Section 5 2 When the target application needs to credit the source application provider, it sends the application provider credit to the ongmal page server together with the hyperlink request ID The page server uses the hyperlink request ID to identify the source application, and sends the credit on to the relevant regisfration server 11 together with the source application ID 64, its own server ID 53, and the hyperlink request ID The regisfration server credits the coπesponding application provider's account 827 It also notifies the application provider If the application provider needs to credit the pnnter provider, it sends the pnnter provider credit to the ongmal page server together with the hyperlink request ID The page server uses the hyperlink request ID to identify the pnnter, and sends the credit on to the relevant registration server together with the pnnter D The regisfration server credits the coπesponding pnnter provider account 814 The source application provider is optionally notified of the identity of the target application provider, and the pnnter provider of the identity of the source application provider 6. NETPAGE PEN DESCRIPTION 6.1 PEN MECHANICS Referring to Figures 8 and 9, the pen, generally designated by reference numeral 101, mcludes a housmg 102 in the form of a plastics moulding havmg walls 103 defining an mtenor space 104 for mounting the pen components The pen top 105 is m operation rotatably mounted at one end 106 of the housmg 102 A semi-transparent cover 107 is secured to the opposite end 108 of the housmg 102 The cover 107 is also of moulded plastics, and is formed from semi-transparent matenal m order to enable the user to view the status of the LED mounted within the housmg 102 The cover 107 mcludes a mam part 109 which substantially surrounds the end 108 of the housmg 102 and a projecting portion 110 which projects back from the mam part 109 and fits within a corresponding slot 111 formed m the walls 103 of the housmg 102 A radio antenna 112 is mounted behind the projecting portion 110, within the housmg 102 Screw threads 113 surrounding an aperture 113A on the cover 107 are arranged to receive a metal end piece 114, mcludmg coπespondmg screw threads 115 The metal end piece 114 is removable to enable ink cartridge replacement Also mounted within the cover 107 is a tn-color status LED 116 on a flex PCB 117 The antenna 112 is also mounted on the flex PCB 117 The status LED 116 is mounted at the top of the pen 101 for good all-around visibility The pen can operate both as a normal markmg ink pen and as a non-marking stylus An ink pen cartridge 118 with mb 119 and a stylus 120 with stylus b 121 are mounted side by side within the housmg 102 Either the ink cartndge mb 119 or the stylus mb 121 can be brought forward through open end 122 of the metal end piece 114, by rotation of the pen top 105 Respective slider blocks 123 and 124 are mounted to the ink cartndge 118 and stylus 120, respectively A rotatable cam baπel 125 is secured to the pen top 105 m operation and arranged to rotate therewith The cam baπel 125 mcludes a cam 126 in the form of a slot within the walls 181 of the cam baπel Cam followers 127 and 128 projecting from slider blocks 123 and 124 fit within the cam slot 126 On rotation of the cam barrel 125, the slider blocks 123 or 124 move relative to each other to project either the pen mb 119 or sfylus mb 121 out through the hole 122 m the metal end piece 114 The pen 101 has three states of operation By turning the top 105 through 90° steps, the three states are Stylus 120 mb 121 out, • Ink cartndge 118 b 119 out, and • Neither ink cartndge 118 mb 119 out nor stylus 120 mb 121 out A second flex PCB 129, is mounted on an electronics chassis 130 which sits within the housmg 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 mcludes an RF transmitter and RF receiver, and a controller chip 134 for controlling operation of the pen 101 An optics block 135 (formed from moulded clear plastics) sits within the cover 107 and projects an infrared beam onto the surface and receives images onto the image sensor 132 Power supply wires 136 connect the components on the second flex PCB 129 to battery contacts 137 which are mounted within the cam barrel 125 A terminal 138 connects to the battery contacts 137 and the cam barrel 125 A three volt rechargeable battery 139 sits within the cam baπel 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 m the cam baπel 125 when either the stylus 120 or the ink cartndge 118 is used for wntmg order to enable a determination of the force bemg applied to the surface by the pen mb 119 or stylus b 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 gnp pads 141 and 142 are provided towards the end 108 of the housmg 102 to assist gnpping the pen 101, and top 105 also mcludes a clip 142 for clipping the pen 101 to a pocket 6.2 PEN CONTROLLER The pen 101 is arranged to determine the position of its mb (stylus mb 121 or ink cartndge mb 119) by imaging, m the infrared spectrum, an area of the surface m the vicinity of the mb It records the location data from the nearest location tag, and is arranged to calculate the distance of the mb 121 or 119 from the location tab utilising optics 135 and controller chip 134 The controller chip 134 calculates the oπentation of the pen and the nib-to-tag distance from the perspective distortion observed on the imaged tag Utilising the RF chip 133 and antenna 112 the pen 101 can transmit the digital ink data (which is encrypted for secuntv and packaged for efficient transmission) to the computing system When the pen is in range of a receiver, the digital ink data is transmitted as it is formed When the pen 101 moves out of range, digital ink data is buffered within the pen 101 (the pen 101 circuitry mcludes a buffer arranged to store digital ink data for approximately 12 mmutes of the pen motion on the surface) and can be transmitted later The controller chip 134 is mounted on the second flex PCB 129 m the pen 101 Figure 10 is a block diagram illustrating m 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 116, the IR illumination LED 131, the IR force sensor LED 143, and the force sensor photodiode 144 The pen controller chip 134 mcludes 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 mcluded An analog-to-digital converter 149 is arranged to convert the analog signal from the force sensor photodiode 144 to a digital signal An image sensor mterface 152 interfaces with the image sensor 132 A transceiver controller 153 and base band circuit 154 are also mcluded to mterface with the RF chip 133 which mcludes an RF circuit 155 and RF resonators and mductors 156 connected to the antenna 112 The controlling processor 145 captures and decodes location data from tags from the surface via the image sensor 132, monitors the force sensor photodiode 144, controls the LEDs 116, 131 and 143, and handles short-range radio communication via the radio transceiver 153 It is a medium-performance (~40MHz) general-purpose RISC processor The processor 145, digital transceiver components (transceiver controller 153 and baseband circuit 154), image sensor mterface 152, flash memory 147 and 512KB DRAM 148 are integrated m a smgle controller ASIC Analog RF components (RF circuit 155 and RF resonators and mductors 156) are provided m the separate RF chip The image sensor is a 215x215 pixel CCD (such a sensor is produced by Matsushita Electronic Corporation, and is descπbed m 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 incorporated herem by reference) with an IR filter The controller ASIC 134 enters a quiescent state after a peπod of inactivity when the pen 101 is not m contact with a surface It incorporates a dedicated circuit 150 which monitors the force sensor photodiode 144 and wakes up the controller 134 via the power manager 151 on a pen-down event The radio transceiver communicates m the unlicensed 900MHz band normally used by cordless telephones, or alternatively m the unlicensed 24GHz mdustnal, scientific and medical (ISM) band, and uses frequency hoppmg and collision detection to provide interference-free communication In an alternative embodiment, the pen incorporates an Infrared Data Association (IrDA) mterface for short- range communication with a base station or netpage pnnter In a further embodiment, the pen 101 mcludes a pair of orthogonal accelerometers mounted m the normal plane of the pen 101 axis The accelerometers 190 are shown m Figures 9 and 10 m 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 mterest rather than a position on the surface For example, if the object is a user mterface mput element (e g a command button), then the tag ID of each location tag within the area of the mput element can directly identify the mput element The acceleration measured by the accelerometers m each of the x and y directions is integrated with respect to time to produce an instantaneous velocity and position Smce the starting position of the stroke is not known, only relative positions within a stroke are calculated Although position integration accumulates eπors m the sensed acceleration, accelerometers typically have high resolution and the time duration of a stroke, over which eπors accumulate, is short 7. NETPAGE PRINTER DESCRIPTION 7.1 PRINTER MECHANICS The vertically-mounted netpage wallpnnter 601 is shown fully assembled m Figure 11 It prints netpages on Letter/A4 sized media usmg duplexed 8' " Memjet™ print engmes 602 and 603, as shown m Figures 12 and 12a It uses a sfraight paper path with the paper 604 passmg through the duplexed pπnt engmes 602 and 603 which pπnt both sides of a sheet simultaneously, m full color and with full bleed An integral binding assembly 605 applies a stnp of glue along one edge of each prmted sheet, allowing it to adhere to the previous sheet when pressed agamst it This creates a final bound document 618 which can range m thickness from one sheet to several hundred sheets The replaceable ink cartndge 627, shown m Figure 13 coupled with the duplexed pπnt engmes, has bladders or chambers for storing fixative, adhesive, and cyan, magenta, yellow, black and infrared inks The cartndge also contams a micro air filter m a base molding The micro air filter interfaces with an air pump 638 mside the pnnter via a hose 639 This provides filtered air to the pnntheads to prevent ingress of micro particles mto the Memjet™ pnntheads 350 which might otherwise clog the prmthead nozzles By incorporating the air filter within the cartndge, the operational life of the filter is effectively linked to the life of the cartndge The ink cartndge is a fully recyclable product with a capacity for printing and gluing 3000 pages (1500 sheets) Referring 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 prmt engme 602 mto the duplexed Memjet™ prmthead assembly The two Memjet™ prmt engmes 602 and 603 are mounted in an opposmg m-lme sequential configuration along the straight paper path The paper 604 is drawn mto the first pπnt engme 602 by integral, powered pick-up rollers 626 The position and size of the paper 604 is sensed and full bleed prmtmg commences Fixative is prmted simultaneously to aid drying m the shortest possible time The paper exits the first Memjet™ prmt engme 602 through a set of powered exit spike wheels (aligned along the straight paper path), which act agamst a rubberized roller These spike wheels contact the 'wet' prmted surface and continue to feed the sheet 604 mto the second Memjet™ pπnt engme 603 Referring to Figures 12 and 12a, the paper 604 passes from the duplexed prmt engmes 602 and 603 mto the bmder assembly 605 The prmted 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 mterface 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 couplmg for the glue supply hose 641 from the ink cartndge 627 This axle 679 connects to a glue wheel, which absorbs adhesive by capillary action through radial holes A molded housmg 682 surrounds the glue wheel, with an opening at the front Pivoting side moldings and sprung outer doors are attached to the metal bracket and lunge out sideways when the rest of the assembly 673 is thrust forward This action exposes the glue wheel through the front of the molded housmg 682 Tension springs close the assembly and effectively cap the glue wheel duπng peπods of inactivity As the sheet 604 passes mto 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 mto the binding assembly 605 7.2 PRINTER CONTROLLER ARCHITECTURE The netpage pnnter controller consists of a controlling processor 750, a factory-installed or field-installed network mterface module 625, a radio transceiver (transceiver controller 753, baseband circuit 754, RF circuit 755, and RF resonators and mductors 756), dual raster image processor (RIP) DSPs 757, duplexed prmt engme controllers 760a and 760b, flash memory 658, and 64MB of DRAM 657, as illustrated m 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 mterface LEDs 613-616, and feeds and synchronizes the RIP DSPs 757 and pπnt engme controllers 760 It consists of a medium-performance general-purpose microprocessor The controlling processor 750 communicates with the pπnt engme controllers 760 via a high-speed seπal bus 659 The RIP DSPs rastenze and compress page descnptions to the netpage printer's compressed page format Each pπnt engme controller expands, dithers and pπnts page images to its associated Memjet™ prmthead 350 m real time (l e at over 30 pages per minute) The duplexed pπnt engme controllers pπnt both sides of a sheet simultaneously The master pπnt engme confroller 760a controls the paper transport and momtors ink usage m conjunction with the master QA chip 665 and the ink cartndge QA chip 761 The pnnter 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 mam memory 657 at boot time The processor 750, DSPs 757, and digital transceiver components (transceiver controller 753 and baseband circuit 754) are integrated m a smgle controller ASIC 656 Analog RF components (RF circuit 755 and RF resonators and mductors 756) are provided m a separate RF chip 762 The network interface module 625 is separate, smce netpage prmters 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 prmt engme controllers 760 are provided m separate ASICs A vanety of network mterface modules 625 are provided, each providing a netpage network mterface 751 and optionally a local computer or network mterface 752 Netpage network Internet interfaces mclude POTS modems, Hybnd Fiber-Coax (HFC) cable modems, ISDN modems, DSL modems, satellite transceivers, current and next- generation cellular telephone transceivers, and wireless local loop (WLL) transceivers Local interfaces mclude IEEE 1284 (parallel port), lOBase-T and 100Base-T Ethernet, USB and USB 2 0, IEEE 1394 (Firewire), and vanous emerging home networking interfaces If an Internet connection is available on the local network, then the local network mterface can be used as the netpage network mterface The radio transceiver 753 communicates m the unlicensed 900MHz band normally used by cordless telephones, or alternatively m the unlicensed 2 4GHz mdustnal, scientific and medical (ISM) band, and uses frequency hoppmg and collision detection to provide interference-free communication The pnnter confroller optionally incorporates an Infrared Data Association (IrDA) mterface for receivmg data "squirted" from devices such as netpage cameras In an alternative embodiment, the pnnter uses the IrDA mterface for short-range communication with suitably configured netpage pens 7.2.1 RASTERIZATION AND PRINTING Once the mam processor 750 has received and venfied the document's page layouts and page objects, it runs the appropnate RIP software on the DSPs 757 The DSPs 757 rastenze each page descnption and compress the rastenzed page image The mam processor stores each compressed page image m memory The simplest way to load-balance multiple DSPs is to let each DSP rastenze a separate page The DSPs can always be kept busy smce an arbitrary number of rastenzed pages can, m general, be stored m memory This strategy only leads to potentially poor DSP utilization when rastenzmg short documents Watermark regions m the page descπption are rastenzed to a contone-resolution bi-level bitmap which is losslessly compressed to negligible size and which forms part of the compressed page image The infrared (IR) layer of the prmted page contams coded netpage tags at a density of about six per mch Each tag encodes the page ID, tag ID, and control bits, and the data content of each tag is generated duπng rasterization and stored m the compressed page image The mam processor 750 passes back-to-back page images to the duplexed prmt engme controllers 760 Each pπnt engme confroller 760 stores the compressed page image m its local memory, and starts the page expansion and prmtmg pipeline Page expansion and printing is pipelined because it is unpractical to store an entire 114MB bi-level CMYK+IR page image m memory 7.2.2 PRINT ENGINE CONTROLLER The page expansion and printing pipeline of the pπnt engme controller 760 consists of a high speed IEEE 1394 senal mterface 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 lme loader/formatter unit 767, and a custom mterface 768 to the Memjet™ prmthead 350 The pπnt engme confroller 360 operates in a double buffered manner While one page is loaded mto DRAM 769 via the high speed senal mterface 659, the previously loaded page is read from DRAM 769 and passed through the prmt engme controller pipeline Once the page has finished printing, the page just loaded is prmted while another page is loaded The first stage of the pipeline expands (at 763) the JPEG-compressed contone CMYK layer, expands (at 764) the Group 4 Fax-compressed bi-level black layer, and renders (at 766) the bi-level netpage tag layer accordmg to the tag format defined m section 1 2, all m parallel The second stage dithers (at 765) the contone CMYK layer and composites (at 765) the bi-level black layer over the resulting bi-level CMYK layer The resultant bi-level CMYK+IR dot data is buffered and formatted (at 767) for printing on the Memjet™ prmthead 350 via a set of lme buffers Most of these lme buffers are stored m the off-chip DRAM The final stage prmts the six channels of bi-level dot data (mcludmg fixative) to the Memjet™ prmthead 350 via the prmthead mterface 768 When several pπnt engme controllers 760 are used m unison, such as m a duplexed configuration, they are synchronized via a shared lme sync signal 770 Only one pπnt engme 760, selected via the external master/slave pm 771, generates the lme sync signal 770 onto the shared lme The pπnt engme controller 760 contams a low-speed processor 772 for « τ τ_ lionizing the page expansion and rendering pipeline, configuring the prmthead 350 via a low-speed senal bus 773, _ιrιd controlling the stepper motors 675, 676 In the 8i " versions of the netpage pnnter, the two pπnt engmes each pπnts 30 Letter pages per minute along the long dimension of the page (11"), givmg a lme rate of 8 8 kHz at 1600 dpi In the 12" versions of the netpage pnnter, the two pπnt engmes each prmts 45 Letter pages per minute along the short dimension of the page (8! "), givmg a lme rate of 102 kHz These lme rates are well within the operating frequency of the Memjet™ prmthead, which m the current design exceeds 30 kHz CONCLUSION The present invention has been descnbed with reference to a prefeπed embodiment and number of specific alternative embodiments However, it will be appreciated by those skilled m the relevant fields that a number of other embodiments, differing from those specifically descnbed, will also fall within the spint and scope of the present mvention Accordingly, it will be understood that the invention is not mtended to be limited to the specific embodiments descnbed m the present specification, mcludmg documents incorporated by cross-reference as appropnate The scope of the mvention is only limited by the attached claims

Claims: C LAI MS 1 A method of providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of the identity of the document and of at least one reference pomt of the document, the method mcludmg the steps of receiving, m a computer system, mdicatmg data from a sensmg device operated by the user, said indicating data regardmg the identity of the document and a position of the sensmg device relative to the document, the sensmg device, when placed m an operative position relative to the document, sensmg the mdicatmg data usmg at least some of the coded data, identifying m the computer system and from the mdicatmg data, a request for a copy of at least one page of the document, and transmitting, from the computer system, relevant document data to at least one pnnter to effect printing of the copy of the at least one page 2 The method of claim 1 m which said request for a copy of at least one page of the document is associated with at least one zone of the document, and m which the method mcludes identifying, m the computer system and from the zone relative to which the sensmg device is located, the request 3 The method of claim 2 which mcludes receivmg, m the computer system, data regardmg movement of the sensmg device relative to the document, the sensmg device sensmg its movement relative to the document usmg at least some of the coded data, and identifying, m the computer system and from said movement bemg at least partially within said at least one zone, the request for a copy of the at least one page of the document 4 A method of providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of a request for a copy of the at least one page of the document, the method mcludmg the steps of receivmg, m a computer system, data from a sensmg device operated by the user regardmg the request, the sensmg device, when placed m an operative position relative to the document, sensmg the data regardmg the request usmg at least some of the coded data, and transmitting, from the computer system, relevant document data to at least one pnnter to effect prmtmg of the copy of the at least one page 5 A method of providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of a request for a copy of at least one page of the document, the method mcludmg the steps of receivmg, m a computer system, data from a sensmg device operated by the user regardmg the request and regardmg movement of the sensmg device relative to the document, the sensmg device, when moved relative to the document, sensmg the data regarding the request usmg at least some of the coded data and generating the data regardmg its own movement relative to the document, interpreting, m the computer system, said movement of the sensmg device as designating the request, and transmitting, from the computer system, relevant document data to at least one pnnter to effect printing of the copy of the at least one page 6 A method of providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of an identity of the document, the method mcludmg the steps of, receivmg, m a computer system, data from a sensmg device regardmg an identity of the user and regardmg the identity of the document and at least one page within the document, the sensmg device containmg the data regarding the identity of the user and sensmg the data regardmg the identity of the document and the at least one page within the document usmg at least some of the coded data, identifying, m the computer system from the data regardmg the identity of the user and the identity of the document and the at least one page within the document, a request for a prmted copy of the at least one page of the document, and transmitting, from the computer system, relevant document data to at least one pnnter to effect prmtmg of the copy of the at least one page 7 The method of claim 6 m which the coded data is also mdicative of a request for a copy of at least one page of the document and the method mcludes receivmg, m the computer system, mdicatmg data from the sensmg device regardmg the request, the sensmg device sensmg the mdicatmg data usmg at least some of the coded data 8 The method of claim 7 which mcludes receivmg, m the computer system, data from the sensmg device regardmg movement of the sensmg device relative to the document, the sensmg device generating data regardmg its own movement relative to the document 9 The method accordmg to any one of claims 1 , 4, 5 or 6 which mcludes printing the document on a surface of a surface-defining means and, at the same time that the document is prmted, printing the coded data on the surface 10 The method of claim 9 which mcludes prmtmg the coded data to be substantially invisible m the visible spectrum 11 The method according to either claim 1, 4 or 5 m which the sensmg device contams an identification means which imparts a umque identify to the sensmg device and identifies it as bemg associated with a particular user and m which the method mcludes momtormg, m the computer system, said identity 12 The method accordmg to any one of claims 1 , 4, 5 or 6 m which the request for a copy of at least one page of the document relates to a page that is part of a form, the method mcludmg the step of requesting a copy of the form 13 The method accordmg to any one of claims 1, 4, 5 or 6 m which the request for a copy of the at least one page results m the printing of multiple pages and m which the method mcludes bmdmg the pages 14 A system for providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of an identity of the document and of at least one reference pomt of the document, the system mcludmg a computer system for receivmg mdicatmg data from a sensmg device for identifying a request for a copy of at least one page of the document, the mdicatmg data bemg mdicative of the identity of the document and a position of the sensmg device relative to the document, the sensmg device, when placed m an operative position relative to the document, sensmg the mdicatmg data usmg at least some of the coded data, the computer system bemg configured to transmit relevant document data to at least one pnnter to effect printing of the copy of the at least one page 15 The system of claim 14 m which said request for a copy of at least one page of the document is associated with at least one zone of the page within the document 16 The system of claim 14 mcludmg the at least one sensmg device, the sensmg device sensmg its movement relative to the document, usmg at least some of the coded data 17 A system for providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of a request for a copy of the at least one page of the document, the system mcludmg a computer system for receivmg data from a sensmg device operated by a user regardmg the request, the sensmg device, when placed m an operative position relative to the document, sensmg the data regardmg the request usmg at least some of the coded data, the computer system bemg configured to transmit relevant document data to at least one pnnter to effect prmtmg of the copy of the at least one page 18 A system for providing a copy of at least one page of a prmted document, the document mcludmg coded data mdicative of a request for a copy of the at least one page of the document, the system mcludmg a computer system for receivmg data from a sensmg device operated by a user, said data regardmg the request and regardmg movement of the sensmg device relative to the document, the sensmg device, when moved relative to the document, sensmg the data regardmg said request usmg at least some of the coded data, and generating the data regardmg its own movement relative to the document, the computer system bemg configured to mterpret said movement as designating the request, and bemg configured to transmit relevant document data to at least one pnnter to effect prmtmg of the copy of the at least one page 1 A system for providing a prmted document, the document mcludmg coded data mdicative of the identity of the document, the system mcludmg a computer system for receivmg from a sensmg device data regardmg an identity of the user of the sensmg device and the identity of the document, and for identifying, from said received data, a request for a copy of at least one page of the document, the sensmg device containmg the data regardmg the identity of the user and sensing the data regardmg the identity of the document usmg at least some of the coded data, the computer system bemg configured to transmit relevant document data to at least one pnnter to effect printing of the copy of the at least one page 20 The system of claim 19 m which the coded data is also mdicative of the request for a copy of at least one page of the document, the computer system receivmg mdicatmg data from the sensmg device regardmg said request, and the sensmg device sensmg the mdicatmg data usmg at least some of the coded data 21 The system of claim 20 which mcludes the sensmg device, the sensmg device sensmg its movement relative to the document 22 The system of claim 14, 17, 18 or 19 m which the sensmg device mcludes a markmg mb 23 The system of claim 14, 17 or 18 m which the sensmg device contams an identification means which imparts a umque identity to the sensmg device and identifies it as bemg associated with a particular user 24 The system of claim 14, 17, 18 or 19 m which the the copy of the at least one page is prmted on a surface of a surface-defining means, and m which the system mcludes a pnnter for prmtmg the copy of the at least one page 25 The system of claim 14, 17, 18 or 19 m which the document is prmted on a surface of a surface- defining means, and in which the system mcludes a pnnter for prmtmg the document on demand 26 The system of claim 25 in which the pnnter prints the coded data at the same time as prmtmg the document 27 The system of claim 14, 17, 18 or 19 m which the coded data is substantially invisible m the visible spectrum 28 The system of claim 24 or 25 m which, to cater for the prmtmg of multiple pages, the pnnter mcludes a bmdmg means for bmdmg the pages

Inventors: LAPSTUN PAUL, LAPSTUN, PAUL
Applicants: LAPSTUN PAUL, SILVERBROOK KIA, SILVERBROOK RES PTY LTD, LAPSTUN, PAUL, SILVERBROOK RESEARCH PTY LTD, SILVERBROOK, KIA
Application year: 2000
Main classification: G06K19
IPC codes: B41J2, B41J5, B41J13, B41J21, B41J29, B42C9, B42C19, B42D15, B65H29, B65H37, G06F3, G06F13, G06F17, G06F21, G06K9, G06K17, G06K19, G06Q10, G06Q30, G06Q50, G06T1, G06T11, G08C17, H04L9, H04N1