Abstract:
The present disclosure includes, among other things, systems, methods and program products for using, storing and retrieving scale information.

Description:
BACKGROUND 
       [0001]    Annotations are used to add helpful information to two dimensional (2D) and three dimensional (3D) computer aided design drawings. Examples of annotations include text labels and hatch patterns. A view is a rectangle or other planar shape that a drawing, or portion thereof, is projected onto and in turn viewed by a user on a display device. A view is of a model space or a paper space (e.g., a preview of a printed drawing plan), and has a scale associated with it that specifies a ratio of units, such as drawing units to paper units. Objects in a drawing are given sizes in terms of units (e.g., inches, feet, centimeters) and appear in the correct proportions depending on a view&#39;s scale and space. For example, if a view scale is 1″ drawing units to ¼″ paper units, a drawing will be rendered as though every inch was a quarter inch in a paper space view. Typically, an annotation is created for a specific view scale. In order for the annotation to appear in the correct proportion at other scales, a version of the annotation needs to be created for each view scale that is desired. This is cumbersome since creating more than one version of an annotation is time consuming, prone to errors, and requires that a change to an annotation be propagated to each version. 
       SUMMARY 
       [0002]    In general, one or more aspects of the subject matter described in this specification can be embodied in one or more methods that include identifying a drawing scale for a graphical view of a drawing, the scale specifying a ratio of two units. One or more annotations associated with the view that support the scale are selected, each of the selected annotations associated with context for the scale, the context specifying one or more of: the annotation&#39;s position in the view, the annotation&#39;s size in the view, the annotation&#39;s style in the view, or the annotation&#39;s rotation in the view. A graphical representation of each of the selected annotations is added to the view according to the scale and each annotation&#39;s respective context. Any annotation that does not support the scale is removed from the view. Other implementations of this aspect include corresponding systems, apparatus, and computer program products. 
         [0003]    These and other implementations can optionally include one or more of the following features. The two units can be paper units and drawing units. The annotation can be one or more of: text, a hatch pattern, a dimension, a leader, a block or a block attribute. 
         [0004]    In general, one or more aspects of the subject matter described in this specification can be embodied in one or more methods that include identifying an annotation in a graphical view of a drawing, the annotation having a graphical representation in the drawing and is associated with a plurality of drawing scales, each of the plurality of drawing scales associated with a context where the context and the associated scale determine the graphical representation of an associated annotation in the drawing when the scale matches a view scale. For each scale associated with the annotation: 1) storing in a the file that stores the drawing the scale including storing first units and second units that determine the scale; and 2) storing in the file the associated context including storing one or more of: the annotation&#39;s position in the view, the annotation&#39;s size in the view, the annotation&#39;s style in the view, or the annotation&#39;s rotation in the view. Other implementations of this aspect include corresponding systems, apparatus, and computer program products. 
         [0005]    These and other implementations can optionally include one or more of the following features. The association between the annotation and the scale can be stored in the file. The association between the scale and the associated context can be stored in the file. The two units can be paper units and drawing units. The annotation can be one or more of: text, a hatch pattern, a dimension, a leader, a block or a block attribute. 
         [0006]    In general, one or more aspects of the subject matter described in this specification can be embodied in one or more methods that include identifying an annotation in a graphical view of a drawing, the annotation having a graphical representation in the drawing and associated with a plurality of drawing scales, each of the plurality of drawing scales associated with a context where a context and an associated scale determine the graphical representation of an associated annotation in the drawing when the scale matches a view scale. For each scale associated with the annotation: 1) retrieving from a the file that stores the drawing the scale including storing first units and second units that determine the scale; and; 2) retrieving from the file the associated context including storing one or more of: the annotation&#39;s position in the view, the annotation&#39;s size in the view, the annotation&#39;s style in the view, or the annotation&#39;s rotation in the view. Other implementations of this aspect include corresponding systems, apparatus, and computer program products. 
         [0007]    These and other implementations can optionally include one or more of the following features. The association between the annotation and the scale can be retried from the file. The association between the scale and the associated context can be retrieved from the file. The two units can be paper units and drawing units. The annotation can be one or more of: text, a hatch pattern, a dimension, a leader, a block or a block attribute. 
         [0008]    In general, one or more aspects of the subject matter described in this specification can be embodied in a memory for storing data for access by an application program being executed on a data processing system, the memory comprising a data structure stored in said memory, said data structure including: 1) an annotation for a graphical view of a drawing, the annotation having a graphical representation in the drawing; 2) a plurality of drawing scales associated with the annotation, each drawing scale having first and second units that determine the scale; and 3) a context associated with each drawing scale, where a context and an associated scale determine the graphical representation of an associated annotation in the drawing. 
         [0009]    These and other implementations can optionally include one or more of the following features. The two units can be paper units and drawing units. The annotation can be one or more of: text, a hatch pattern, a dimension, a leader, a block or a block attribute. 
         [0010]    Particular implementations of the subject matter described in this specification can be implemented to realize one or more of the following advantages. Drawing annotations can be rendered in a constant size, regardless of the scale. Annotations are automatically added to or removed from views depending on the current scale of the view and the scale(s) supported by the annotations. Scales are stored in a drawing&#39;s file instead of elsewhere on a user&#39;s system. A single drawing annotation can appear in different positions for different scales. 
         [0011]    The details of one or more implementations of the invention are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1A and 1B  illustrate example annotations shown in views having different scales. 
           [0013]      FIG. 2  is a flowchart of a method for updating a graphical view of a drawing. 
           [0014]      FIG. 3A  is an illustration of a data store that includes scale information. 
           [0015]      FIG. 3B  is an illustration of an example annotation shown in multiple views. 
           [0016]      FIG. 4  illustrates an example class hierarchy for storing context data associated with scales. 
           [0017]      FIG. 5  is a flowchart of a method for storing a drawing&#39;s annotation scale information. 
           [0018]      FIG. 6  is a flowchart of a method for retrieving a drawing&#39;s annotation scale information. 
           [0019]      FIG. 7  is a schematic diagram of a generic computer system. 
       
    
    
       [0020]    Like reference numbers and designations in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0021]      FIGS. 1A and 1B  illustrate example annotations shown in views having different scales. An annotation (also known as an annotative entity) is an explanatory item on a drawing, which can be used to label or describe other, non-annotative drawing objects. Annotations can be of several types. For example, annotations can be text, hatch patterns (e.g., shading consisting of multiple crossing lines), dimensions (e.g., a measure of spatial extent, such as a width or height), leaders (e.g., explanatory text with an arrow pointing to the object being described), blocks (e.g., an object, such as a door, which is defined once and referenced multiple times in a drawing) and block attributes (e.g., an attribute of a block, such as a door number, which distinguishes one door block reference from another). 
         [0022]    A view  100  in  FIG. 1A  has a scale of “1:1” (the “1:1” can be read as “one to one”). A scale specifies a ratio between two units. For example, a scale of “1:1” can specify a ratio of one paper unit to one drawing unit. A paper unit can be used to specify the size of a drawing item (such as an annotation) as it appears on paper. A drawing unit can be used to specify the size of an item in model space (e.g., a physical size). A view  102  in  FIG. 1B  has a scale of “1:2”, which specifies a ratio of one paper unit to two drawing units. 
         [0023]    The user may desire to control the appearance of annotations. For example, a user may wish to control the size of an annotation, such as showing an annotative text item in a particular size in every view (i.e., keeping the size of a text item constant, even if other items on the drawing appear smaller or larger in views with different scales). As another example, the user may desire the position, rotation or style of an annotation to be different when viewed in different scales (e.g., an annotative text item may fit better at different positions or rotations in views having different scales). As a third example, the user may desire that some annotations appear only in views having particular scales (e.g., showing a certain subset of dimensions in a view with a “1:4” scale and showing a different subset of dimensions in a view having a “1:8” scale). 
         [0024]    An annotation can be configured to support particular scales, and an annotation can have associated context settings which control the appearance of the annotation in a view having a particular scale. For example, annotative text items  104  and  106  in view  100  are each configured to support a “1:1” scale. Since the view  100  has a 1:1 scale, the annotative text items  104  and  106  are visible in the view  100 . The annotative text item  106  also supports a scale of “1:2”, so the annotative text item  106  also appears in the view  102 , which has a scale of “1:2”. Since the annotative text item  104  does not support the scale of “1:2”, it does not appear in the view  102 . 
         [0025]    If a scale of a view is changed, annotations supporting the new scale appear in the view, and annotations supporting the old, but not the new scale, are automatically hidden from the view. Additionally, for annotations that support both the old and the new scales, but have different context settings for the old and new scales (e.g., different size, style, rotation or position), the annotations can be displayed using the context settings associated with the new scale. 
         [0026]    The annotative text item  106  is configured to appear in the same size in both the “1:1” and “1:2” scales. Non-annotative items appear in different sizes in views having different scales. For example, the view  100  includes a rectangle  108  and a non-annotative text item  110 . A corresponding rectangle  112  and non-annotative text item  114  appear in the view  102 . The rectangle  112  and text item  114  appear smaller than the corresponding rectangle  108  and text item  110  due to the scale difference between the two views (a size difference can also occur if a user performs a zoom command in one of the views). 
         [0027]      FIG. 2  is a flowchart of an example method  200  for updating a graphical view of a drawing. A drawing scale for a graphical view of a drawing is determined, where the scale specifies a ratio of two units (step  202 ). For example, the scale of 1 paper unit to 2 drawing units for the view  102 , or the scale of 1 paper unit to 1 drawing unit for the view  100  can be determined. The scale can be determined, for example, when the user changes a scale in a view to a new scale value. 
         [0028]    One or more annotations associated with the view that support the scale are then selected (step  204 ). For example, if scale of “1:1” is determined for the view  100 , the annotations  104  and  106 , which both support a “1:1” scale, can be selected. 
         [0029]    Next, a graphical representation of each of the selected annotations is added to the view according to the scale and each annotation&#39;s respective context (step  206 ). For example, the annotations  104  and  106  can be rendered in the view  100 , according to size, style, position and rotation context associated with each annotation and with the “1:1” scale. 
         [0030]    Next, any annotations that do not support the scale are removed from the view (step  208 ). For example, if the annotative text item  104  supported a “1:2” scale but not a “1:1” scale, it could be removed from the view  100 . 
         [0031]      FIG. 3A  is an illustration of a data store  300  that includes scale information. The data store  300  stores a drawing model, which includes information associated with non-annotative entities  302  and  304  and an annotative entity (e.g., text)  306 . Information stored for the annotative entity  306  includes a list of supported scales  308 . The list  308  is a list of view scales (e.g., “1:1”, “1:2”, “2:1”) that the annotative entity  306  supports. Information stored for the annotative entity  306  also includes, for each supported scale, context associated with the scale. For example, for the scale “1:1”, associated context settings  310  include size, position and rotation values (i.e., when viewed in the scale “1:1”, the annotative entity  306  can be displayed according to the context settings  310 ). In some implementations, the supported scales  308  and associated context settings  310  can be stored using key-value data structures. 
         [0032]      FIG. 3B  is an illustration of an example annotation shown in multiple views having differing scales. As described above, a list  308  of supported scales is stored for the annotative entity  306  in the drawing model  300 , and for each supported scale, a set of context settings  310  can be stored. A view  340  displays the non-annotative entities  302  and  304 , along with the annotative entity  306 , using a “1:1” scale. The annotative entity  306  is shown according to context settings  310  associated with the scale used in the view  340  (i.e., associated with a “1:1” scale). 
         [0033]    A view  350  has a scale of “2:1”, and entities  302   a ,  304   a , and  306   a  are shown in a larger size as compared to the corresponding entities  302 ,  304 , and  306  in the view  340 . The annotative entity  306   a  is shown according to context settings associated with the “2:1” scale. A view  360  has a scale of “1:2”, and entities  302   b ,  304   b , and  306   b  are shown in a smaller size as compared to the corresponding entities  302 ,  304 , and  306  in the view  340 . The annotative entity  306   b  is shown according to context settings associated with the “1:2” scale. In addition, the annotative entity  306   b  is shown with a different rotation than the corresponding annotative entity  306 . As mentioned above, an annotative entity can have context settings associated with a scale that can control the appearance of the annotative entity when displayed in a view using that particular scale. 
         [0034]      FIG. 4  illustrates an example class hierarchy  400  for storing context data associated with scales. A class represents an object type. The class hierarchy  400  shows multiple classes representing multiple annotation object types. A class can define context information that is stored on a per scale basis for a particular annotation type. Base classes ObjectContextData  402  and AnnotScaleObjectContextData  404  define information that is stored for all types of annotation objects. Objects of the ObjectContextData class  402  can store a data version and a boolean value indicating whether the context data stored is the default context data for the annotation. Objects of the AnnotScaleObjectContextData class  404  can store an identifier associated with a scale object that the context data is associated with. 
         [0035]    Objects of the BlkRefObjectContextData class  406  can store context information associated with block reference annotations, such as the rotation, position and scale factors for the block reference. 
         [0036]    Objects of the MLeaderObjectContextData class  408  can store context information associated with “multiple leader” (MLeader) objects, such as the number of leader lines stored, whether the MLeader has an associated multiple-line text item, the number of characters in the multiple-line text item, and the content, location, direction vector, rotation, line-spacing factor, width and height of the multiple-line text item. For each column of the multiple-line text item, a column height and a boolean value indicating whether to use word break for the content can be stored. 
         [0037]    Objects of the MTextObjectContextData class  410  can store context information associated with multiple-line annotative text objects, such as an attachment point, a direction vector, a location point, a width and height of the multiple-line text area, whether columns are associated with the multiple-line text area, the number of columns, and for each column, a column width and an auto height flag. 
         [0038]    Objects of the LeaderObjectContextData class  412  can store context information associated with leader objects, such as the number of vertices in the leader, the vertex point location for each vertex, a horizontal direction, a boolean value indicating whether the leader “hook line” is in the same direction as the horizontal direction for the leader, an offset between the last leader vertex and the leader&#39;s block insertion location, and an annotation offset for the leader. 
         [0039]    Objects of the DimensionObjectContextData class  414  can store context information associated with dimension objects. Dimension context information can vary based on the type of dimension object. For each dimension object, a location, rotation and arrow orientation can be stored. For angular dimension objects, an arc point of the angular dimension can be stored. For aligned dimension objects, a dimension line point specifying the location of the dimension line can be stored. For radial dimension objects, a chord point specifying the point where the dimension line intersects the curve being dimensioned can be stored. For diametric dimension objects, a chord point specifying where the dimension line intersects the curve being dimensioned (and extends outside the curve, if the text is outside the curve) can be stored. Also for diametric dimension objects, a far chord point can be stored. A far chord point is the point on the curve being dimensioned that is diametrically opposite the point where the dimension line extends outside the curve, if the text is outside the curve. For ordinate dimension objects, an origin point defining a reference point for distance calculations can be stored, along with an endpoint specifying the dimension leader&#39;s endpoint. 
         [0040]    Objects of the TextObjectContextData class  416  can store context information associated with annotative text objects, such as a horizontal mode, a rotation value, a position value and an alignment point. 
         [0041]    Objects of the HatchScaleContextData class  418  can store context information associated with hatch annotative objects, such as the number of hatch pattern lines, and for each line in the hatch pattern, a line angle, a base position value of the line, a horizontal offset direction of the line, a vertical offset direction of the line, and the number of dashes in the line. Also, a dash length, a hatch pattern base angle (used for paper orientation) and the number of boundary loops in the hatch can be stored. For each boundary loop in the hatch, a value indicating the type of the boundary loop can be stored, as well as a boolean flag indicating whether the boundary loop has bulges, a boolean value indicating whether the boundary loop is closed, the number of points in the boundary loop, and number of edges in the boundary loop. 
         [0042]    For each edge of the hatch object, an edge type can be stored indicating whether the edge is a line, circular arc, elliptical arc, or spline. For line edges, starting and ending points of the boundary loop edge can be stored. For circular arc edges, a center point, radius, start angle, end angle and boolean value indicating whether the circular arc is measured clockwise can be stored. For elliptical arc edges, a center point, major axis, radius ratio specifying the ratio of the minor radius divided by major radius, start angle, end angle and a boolean value indicating whether the elliptical arc is measured clockwise can be stored. For spline edges, the degree of the spline boundary loop edge, a boolean value indicating whether the spline edge is rational, a boolean value indicating whether the spline edge is periodic, and the number of control points in the spline edge can be stored. 
         [0043]      FIG. 5  is a flowchart of an example method  500  for storing a drawing&#39;s annotation scale information. First, an annotation in a graphical view of a drawing is identified (step  502 ). For example, the annotative entity  306  in the view  340  can be identified. 
         [0044]    A scale associated with the annotation is then identified (step  504 ). For example, the “1:1” scale supported by the annotative entity  306  and used in the view  340  can be identified. 
         [0045]    An association between the annotation and the scale is then stored in a file that stores the drawing (step  506 ). For example, an association between the annotative entity  306  and the scale “1:1” can be stored in a file that stores the drawing model  300 . The scale value of “1:1” can be included in the supported scales list  310 , and the supported scales list  310  can be associated with the annotative entity  306 , for example, by using a key-value data structure. 
         [0046]    Next, the scale, including first units and second units that determine the scale, is stored in the file (step  508 ). For example, the supported scales list  308 , which includes a supported scale value of “1:1” (which specifies a ratio of 1 paper units to 1 drawing units) can be stored in a file which stores the drawing model  300 . 
         [0047]    An association between the scale and the associated context is then stored in the file (step  510 ). For example, an entry in the supported scales list  308  corresponding to a “1:1” scale value can be associated with context setting  310 , for example, by using a key-value data structure, and the key-value data structure can be stored in a file that stores the drawing model  300 . The associated context is then stored in the file, including storing one or more of: the annotation&#39;s position in the view, the annotation&#39;s size in the view, the annotation&#39;s style in the view, and the annotation&#39;s rotation in the view (step  512 ). For example, the context settings  310 , which include values for the annotative entity  306 &#39;s size, position and rotation, can be stored in a file that stores the drawing model  300 . 
         [0048]    It is then determined whether more scales are associated with the annotation (step  514 ). If there are no more scales associated with the annotation, the method ends. If there are more scales associated with the annotation, an association between the annotation and the scale is stored in the file (step  506 ), and steps  508  to  514  are performed. For example, it can be determined that, in addition to a “1:1” scale, the annotative entity  306  is associated with a second scale of “1:2”, as indicated by the contents of the supported scales list  308 . 
         [0049]      FIG. 6  is a flowchart of an example method  600  for retrieving a drawing&#39;s annotation scale information. First, an annotation in a graphical view of a drawing is identified (step  602 ). For example, the annotative entity  306  in the view  340  can be identified. A scale is then associated with the annotation is identified (step  604 ). For example, the “1:1” scale supported by the annotative entity  306  and used in the view  340  can be identified. 
         [0050]    An association between the annotation and the scale is then retrieved from a file that stores the drawing (step  606 ). For example, an association between the supported scales list  308  and the annotative entity  306  can be retrieved, for example, from a key-value data structure that is stored in a file that stores the drawing model  300 . 
         [0051]    Next, the scale, including first units and second units that determine the scale, is retrieved from the file (step  608 ). For example, the supported scales list  308  can be retrieved from a file that stores the drawing model  300 , and the scale value of “1:1” can be read from the supported scales list  308  and converted to a ratio of 1 paper unit to 1 drawing unit. 
         [0052]    An association between the scale and the associated context is then retrieved from the file (step  610 ). For example, an association between a scale value of “1:1” and the context settings  310  can be retrieved from a file that stores the drawing model  300 , for example, by retrieving a key-value data structure. 
         [0053]    The associated context is then retrieved from the file, including retrieving one or more of: the annotation&#39;s position in the view, the annotation&#39;s size in the view, the annotation&#39;s style in the view, and the annotation&#39;s rotation in the view (step  612 ). For example, the context settings  310  can be retrieved from a file that stores the drawing model  300 , and position, size and rotation values can be retrieved from the context settings  310 . 
         [0054]    Next, it is determined whether more scales are associated with the annotation (step  614 ). If there are no more scales associated with the annotation, the method ends. If there are more scales associated with the annotation, an association between the annotation and the scale is retrieved from the file (step  606 ), and steps  608  to  614  are performed. For example, it can be determined that there are additional scales (e.g., “1:2”) in the retrieved supported scales list  308 . 
         [0055]      FIG. 7  is a schematic diagram of a generic computer system  700 . The system  700  can be used for practicing operations described in association with the techniques  200 ,  500  and  600 . The system  700  can include a processor  710 , a memory  720 , a storage device  730 , and input/output devices  740 . Each of the components  710 ,  720 ,  730 , and  740  are interconnected using a system bus  750 . The processor  710  is capable of processing instructions for execution within the system  700 . In one implementation, the processor  710  is a single-threaded processor. In another implementation, the processor  710  is a multi-threaded processor. The processor  710  is capable of processing instructions stored in the memory  720  or on the storage device  730  to display graphical information for a user interface on the input/output device  740 . 
         [0056]    The memory  720  is a computer readable medium such as volatile or non volatile that stores information within the system  700 . The memory  720  could store data structures representing annotations, annotation scales, and associated context, for example. The storage device  730  is capable of providing persistent storage for the system  700 . The storage device  730  may be a floppy disk device, a hard disk device, an optical disk device, or a tape device, or other suitable persistent storage means. The input/output device  740  provides input/output operations for the system  700 . In one implementation, the input/output device  740  includes a keyboard and/or pointing device. In another implementation, the input/output device  740  includes a display unit for displaying graphical user interfaces. 
         [0057]    The input/output device  740  can provide input/output operations for a CAD system. The CAD system can be, for example, AutoCad®, Autodesk Architectural Desktop® or Autodesk Building Systems®, available from Autodesk, Inc., of San Rafael, Calif., or another CAD application or other software application. The CAD system can include computer software components that annotation scales. Such software components can be persisted in storage device  730 , memory  720  or can be obtained over a network connection, to name a few examples. 
         [0058]    A CAD drawing does not necessarily correspond to a file. A drawing may be stored in a portion of a file that holds other content, in a single file dedicated to the drawing in question, or in multiple coordinated files. Moreover, a drawing can be stored in a memory without having first been stored in a file. 
         [0059]    Implementations of the subject matter and the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer-readable medium for execution by, or to control the operation of, data processing apparatus. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus. 
         [0060]    A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
         [0061]    The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). 
         [0062]    Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio player, a Global Positioning System (GPS) receiver, to name just a few. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. 
         [0063]    To provide for interaction with a user, implementations of the subject matter described in this specification can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. 
         [0064]    Implementations of the subject matter described in this specification can be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described is this specification, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet. 
         [0065]    The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
         [0066]    While this specification contains many specifics, these should not be construed as limitations on the scope of the invention or of what may be claimed, but rather as descriptions of features specific to particular implementations of the invention. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
         [0067]    Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
         [0068]    Thus, particular implementations of the invention have been described. Other implementations are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results.