Abstract:
A graphical user interface which employs logical barriers for temporarily preventing cursor movement between graphical elements under certain circumstances. For example, one embodiment of the invention comprises a data processing device having a memory for storing program code and a processor for processing the program code to generate a graphical user interface (GUI), the GUI comprising: a first predefined region including of a first plurality of selectable graphical elements; a second predefined region including a second plurality of selectable graphical elements; and a logical barrier between the first predefined region and the second predefined region, the logical barrier configured to temporarily prevent movement from a graphical element in the first predetermined region to a graphical element in the second predetermined region in response to a user input directed towards graphical element in the second predetermined region, the logical barrier temporarily preventing the movement for either a specified period of time and/or a specified amount of movement generated by a user input device.

Description:
TECHNICAL FIELD 
   This application relates generally to the field of data processing devices, and more particularly, to versatile input/output and display configurations for a data processing device. 
   BACKGROUND 
   Portable data processing devices such as Personal Digital Assistants (“PDAs”) and programmable wireless telephones are becoming more powerful every day, providing users with a wide range of applications previously only available on personal computers. At the same time, due to advances in silicon processing technology and battery technology, these devices may be manufactured using smaller and smaller form factors. Accordingly, users no longer need to sacrifice processing power for portability when selecting a personal data processing device. 
   Although processing devices with small form factors tend to be more portable, users may find it increasingly difficult to interact with them. For example, entering data may be difficult due to the absence of a full-sized keyboard and reading information may be difficult due to a small, potentially dim Liquid Crystal Display (“LCD”). 
   To solve some of these problems, the assignee of the present application developed two data processing devices known commercially as the “Sidekick” and the “Sidekick II,” respectively. The Sidekick is illustrated in  FIGS. 1   a - c . This data processing device  100  includes a keyboard  101 , a control knob/wheel  102  (e.g., for scrolling between menu items and/or data), and a set of control buttons  105  (e.g., for selecting menu items and/or data). 
   The display  103  is pivotally coupled to the data processing device  100  and pivots around a pivot point  109 , located within a pivot area  104 , from a first position illustrated in  FIG. 1   a  to a second position illustrated in  FIGS. 1   b - c . When in the first position the display  103  covers the keyboard  101 , thereby decreasing the size of the device  100  and protecting the keyboard  101 . Even when the display is in the first position, however, the control knob  102  and control buttons  105  are exposed and therefore accessible by the user. The motion of the display  103  from the first position to a second position is indicated by motion arrow  106  illustrated in  FIGS. 1   a - b . As illustrated, when in the second position, the keyboard  101  is fully exposed. Accordingly, the display is viewable, and data is accessible by the user in both a the first position and the second position (although access to the keyboard is only provided in the first position). 
   In one embodiment, the data processing device  100  is also provided with audio telephony (e.g., cellular) capabilities. To support audio telephony functions, the embodiment illustrated in  FIGS. 1   a - c  includes a speaker  120  for listening and a microphone  121  for speaking during a telephone conversation. Notably, the speaker  120  and microphone  121  are positioned at opposite ends of the data processing device  100  and are accessible when the screen  103  is in a closed position and an open position. 
   The Sidekick II is illustrated in  FIGS. 2   a - b . This data processing device  200  includes many of the same features as the Sidekick such as, for example, a pivoting display  205  which reveals an alphanumeric keyboard  305  and a control wheel  230 . In addition, the Sidekick II includes a directional pad  245  for performing cursor control operations and an integrated speaker  246  and LED (not shown). 
   As mentioned above, the control wheels  102  and  230  in these and other devices may be used to scroll through lists of items such as menu items and/or data entry fields. However, one limitation of the scroll wheel is that it is only capable of navigating within a single dimension. For example, by manipulating the control wheel  112 , a user may move a graphical selection element either “up” or “down” in relation to the orientation of the screen (or “left” or “right” depending on how the user interface is programmed). However, the control wheel does not allow the user to navigate in any desired direction on the screen. Accordingly, a more flexible user interface solution for navigating within a graphical interface of a mobile device is needed. 
   SUMMARY 
   A graphical user interface is described below which employs logical barriers for temporarily preventing cursor movement between graphical elements under certain circumstances. For example, one embodiment comprises a data processing device having a memory for storing program code and a processor for processing the program code to generate a graphical user interface (GUI), the GUI comprising: a first predefined region including a first plurality of selectable graphical elements; a second predefined region including a second plurality of selectable graphical elements; and a logical barrier between the first predefined region and the second predefined region, the logical barrier configured to temporarily prevent movement from a graphical element in the first predefined region to a graphical element in the second predefined region in response to a user input directed towards the graphical element in the second predefined region, the logical barrier temporarily preventing the movement for either a specified period of time and/or a specified amount of movement generated by a user input device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of trackball for a mobile device can be obtained from the following detailed description in conjunction with the following drawings, in which: 
       FIGS. 1   a - c  illustrate a prior art data processing device with a control wheel and an adjustable display. 
       FIGS. 2   a - b  illustrate another prior art data processing device with a control wheel and a display. 
       FIGS. 3   a - b  illustrate one embodiment of a data processing device with a trackball. 
       FIGS. 4   a - b  illustrate one embodiment of a method for navigating within a graphical user interface using a trackball. 
       FIG. 4   c  illustrates an exemplary GUI on which embodiments of the invention may be implemented. 
       FIGS. 5   a - f  illustrate exemplary graphical user interfaces within which the method of  FIGS. 4   a - b  may be employed. 
       FIGS. 6   a - c  illustrate one embodiment of the invention for navigating and editing text fields. 
       FIG. 7  illustrates one embodiment of the invention for selecting text within a graphical user interface. 
       FIG. 8  illustrates additional techniques for selecting text according to one embodiment of the invention. 
       FIGS. 9   a - b  illustrate additional navigation techniques employed within a graphical user interface according to one embodiment of the invention. 
       FIGS. 10   a - e  illustrate the implementation of logical boundaries according to one embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the present invention. 
   Several different techniques for implementing a trackball on a mobile data processing device are described below. As will be apparent from the following description, many of these configurations are particularly beneficial when employed on a dual-purpose data processing device such as a personal digital assistant (“PDA”) or other mobile computing device having integrated wireless telephony capabilities (e.g., a combination PDA and cell phone). However, it should be noted that the underlying principles of the invention are not limited to a wireless telephony configuration. 
   A data processing device  300  according to one embodiment of the invention is illustrated in  FIGS. 3   a - b . Unlike the prior data processing devices described above, this data processing device  300  includes a trackball  301  for navigating through graphical images and text displayed on the data processing device display  305 . In addition, in one embodiment, the trackball  301  may be clicked down into the data processing device to generate a selection function (i.e., similar to the functions provided by a standard mouse button). 
   In one embodiment, the data processing device  300  display adjusts as in the prior data processing devices described above. For example, in one embodiment, the display  305  is pivotally coupled to the data processing device  300  and pivots around a pivot point  309  from a first position illustrated in  FIG. 3   a  to a second position illustrated in  FIG. 3   b.    
   When in the first position the display  305  covers the keyboard  306 , thereby decreasing the size of the device  300  and protecting the keyboard  306 . Even when the display is in the first position, however, the trackball  301  and control buttons, such as directional pad  345 , are exposed and therefore accessible by the user. As illustrated in  FIG. 3   b , when in the second position, the keyboard  306  is fully exposed. Accordingly, the display is viewable, and data is accessible by the user in both the first position and the second position (although access to the keyboard is only provided in the first position). 
   In one embodiment, the data processing device  300  is also provided with audio telephony (e.g., cellular) capabilities. To support audio telephony functions, the embodiment illustrated in  FIGS. 3   a - b  includes a speaker  346  (embedded within the directional pad) for listening and a microphone  321  for speaking during a telephone conversation. Notably, the speaker  346  and microphone  321  are positioned at opposite ends of the data processing device  300  and are accessible when the screen  305  is in a closed position and an open position. 
   Implementing a trackball  301  on a portable data processing devices presents several unique challenges. For example, the relatively small display screen may provide inadequate space for a true “point-and-click” environment (e.g., such as a Windows environment in which is user is provided the ability to move a pointer and click on any graphic on the screen). That is, the graphics displayed on the data processing device display may be so small and close together that moving a cursor to the correct position to identify an icon may be difficult. In addition, with mobile devices, users often do not have the same focus as with a standard personal computer (e.g., users are not sitting at a desk when using a mobile device). Accordingly, simplified navigation techniques for use with a trackball are needed. 
   In one embodiment of the invention, to simplify navigation, in response to user manipulation of the trackball, a “selection element” or “selection graphic” traverses through a limited number of selectable user interface elements displayed within the user interface (e.g., data fields, menu items, text, etc). This approach eliminates unnecessary trackball movement by the user, prevents user errors, and makes the graphical navigation as efficient as possible. 
   General Trackball Navigation 
   One embodiment of a method for selecting elements using a trackball input device is illustrated in  FIGS. 4   a - b . The term “element” is used broadly in this context to refer to any type of image on a display screen including, for example, data input fields, menu items, text and graphical icons. Following the description of  FIGS. 4   a - b , a series of specific examples within a graphical user interface will be provided in  FIGS. 5   a - f.    
   Turning to  FIG. 4   a , at  401 , the data processing device registers a trackball input from a user. At  402  a determination is made as to whether the user input is primarily a horizontal input (e.g., left or right) or primarily a vertical input (e.g., up or down). Given that the user may scroll the trackball in virtually any direction, the input may inadvertently include both horizontal and vertical components. One embodiment of the data processing device  300  determines whether the input is a “horizontal” input or a “vertical” input based on the relative horizontal and vertical components of the input (i.e., the input is a vector with both horizontal and vertical components). If the input has a relatively larger horizontal component, then subsequent trackball movements will be biased to continue horizontally; conversely, if the input has a relatively larger vertical component, then subsequent trackball movements will be biased vertically. 
   If the input is identified as vertical, then the process flows to  FIG. 4   b  (described below). If the input is identified as horizontal, then the process flows to  403  where a determination is made is to whether a manual override exists for the requested motion  403 . For example, in some cases, the core techniques described below for selecting an element within a user interface may not be desirable. In these cases, the user interface programmer may manually identify the desired operation for the user interface. For example, if the techniques described below would cause an element to be selected which is unlikely to be the element that a user would wants to select, then the manual override will cause a different (more likely desired) element to be selected. 
   If no manual override exists, then at  405  a determination is made as to whether elements exist within the same horizontal line as that occupied by the current element—that is, whether another element exists which includes at least some overlapping vertical coordinates with the current element. For example, in  FIG. 4   c , elements  453  and  454  are in the same horizontal “line” as element  452  because at least some of their vertical coordinates overlap. 
   If no elements are in the same horizontal line as the current element, then no new element is selected at  406 . For example, if the user scrolls the trackball  301  to the left/right and if no elements exist to the left/right (within the range of vertical coordinates occupied by the current element), then no new element will be selected. 
   If, however, elements exist within the range of vertical coordinates defined by the current element, then at  407  a determination is made as to whether more than one element exists with overlapping vertical coordinates. If so, then at  406 , the one element is selected. If not, then at  409  the element in the same horizontal line which is closest to the direction of the trackball motion will be selected. For example, in  FIG. 4   c , if element  452  is currently selected and the user scrolls right and slightly upward, then element  453  will be selected. Conversely, if element  452  is currently selected and the user scrolls right and slightly downward, then element  454  will be selected. Alternatively, in one embodiment, the element with a relatively larger vertical coordinate is automatically selected (i.e., the element relatively closer to the top edge of the display—element  453  in the example). 
     FIG. 4   b  illustrates a process for selecting an element in response to a vertical motion (i.e., moving the trackball up or down in relation to the display). At  410 , a determination is made as to whether a manual override exists. If so, then the new element is selected in accordance with the manual override at  411 . If not, then at  412 , the element X which is closest vertically to the current element is identified. For example, in  FIG. 4   c , the element closest vertically to element  450  is element  451 . At  413 , the element in the same horizontal line as element X (or element X if there are no other elements in the same horizontal line) with the closest left-most coordinate to the current element is selected. For example, in  FIG. 4   c , element  452  is selected in response to a downward movement from element  450  because the leftmost coordinate  460  of element  452  is closest to the leftmost coordinate  461  of element  450  (e.g., it is closer on the horizontal axis than the leftmost element  462  of element  453 ). 
   Various alternate and/or additional techniques may be used to select the next element in response to a trackball signal. For example, in one embodiment, in response to a vertical or horizontal movement signal, the element having the largest horizontal range or vertical range, respectively overlapping with the current element may be selected. Various other techniques for selecting the next element may be employed while still complying with the underlying principles of the invention. 
     FIGS. 5   a - f  illustrate specific examples of the foregoing processes (assuming that no manual overrides exist).  FIG. 5   a  illustrates a data entry box  501  with an icon picker element  502  for selecting an icon and data entry fields  503 - 506  for entering the name and nickname of a user. If the icon picker element  502  is initially selected (as shown) and the user scrolls horizontally to the right, then a determination is made that two data entry fields  503 - 504  have overlapping vertical coordinates with the icon picker element  502  (i.e., they are both generally to the right of the icon picker element  502 ). As such, the data entry field which has relatively higher vertical coordinates is selected—in this example, the “first name” field  503 . If the user now the scrolls vertically downward, data fields  504 - 506  will be selected in succession. If the user scrolls to the left from either data entry field  505  or  506 , no new element will be highlighted because no element to the left of these fields has vertical coordinates which overlap with these fields. By contrast, if the user scrolls to the left from either data entry field  503  or  504 , the icon picker element will be selected because it shares overlapping vertical coordinates with these fields. 
     FIG. 5   b  illustrates another data entry box including data entry fields for Job Title  510 , Company  511  and Birthdate  512  as well as a Month Picker element  513 . If the currently selected element is the Company field  511  and the user scrolls down using the trackball, then the Birthdate field  512  will be selected because the leftmost coordinate of the Company element  511  is closest to the leftmost coordinate of the Birthdate element. 
     FIG. 5   c  illustrates an Address data entry box including data entry fields for Label  520 , Street  521 , City  522 , State  523 , Zip  524 , and Country  525 . If the currently selected element is the State field  523  and the user scrolls down using the trackball, then the Country field  525  will be selected because the leftmost coordinate of the Country field  525  is closest to the leftmost coordinate of the State field  523 . Similarly, if the currently selected element is the Country field  525  and the user scrolls up using the trackball, then the State field  523  will be selected because the leftmost coordinate of the State field  523  is closest to the leftmost coordinate of the State field  525 . 
     FIG. 5   d  illustrates a data entry box for specifying calendar event information including data entry fields for an event name  530 , a location  531 , a start date field  532 , a month picker box for the start date  533  a time picker box for the start date  534 , an end date field  535 , a month picker box for the end date  536 , and a time picker box for the end date  537 . In this example, if the month picker box for the end date  536  is currently selected and the user scrolls up, the month picker box for the start date  533  will be selected because the leftmost coordinate of month picker box  536  is closest to the leftmost coordinate of month picker box  533 . Thus, month picker box  533  is selected even though the start date field  532  and time picker box  534  are closer vertically by one pixel. One embodiment of the invention initially groups start date field  532 , the month picker box  533  and the time picker box  534  together because they are in the same horizontal line and then picks the one with the closest left coordinate. 
     FIG. 5   e  illustrates another example that includes (among other elements) an Until check box  540  and a Reminder check box  541 . In this example, if the currently selected element is the Reminder check box  541  and the user scrolls up using the trackball, then the Until check box  540  will be selected because the leftmost coordinate of the Until check box  540  is closest to the leftmost coordinate of the Reminder check box  541 . 
   Similarly,  FIG. 5   f  illustrates an example that includes a default reminder data entry field  550 , an hour data entry field  551 , and a minute data entry field  552 . In this case, if the currently selected element is the default reminder data entry field  550  and the user scrolls up using the trackball, then the minute data entry field  552  will be selected because the leftmost coordinate of the minute data entry field  552  is closest to the leftmost coordinate of the default reminder data entry field  550 . 
   Quick Edit Text Fields 
   One embodiment of the invention employs techniques for navigating and editing text entry fields using the trackball  301 . Specifically, in this embodiment, scrolling the trackball  300  causes each of the text entry fields to be selected according to the techniques described above (e.g., based on leftmost data field coordinate when moving vertically and based on overlapping vertical coordinates when moving horizontally). When a particular text entry field is initially selected, the field is “focused” and a highlight is provided to indicate that the whole text field is selected. At this stage, typing on the keyboard  306  cases the current text within the field to be replaced by the newly entered text. By contrast, clicking the trackball  301  into the data processing device  300  or the directional pad  345  causes a cursor to enter the text entry field, thereby allowing the user to edit the text. Scrolling the trackball  301  with the cursor in the text and/or at the end of the text causes a new field to be selected and focused. By contrast, clicking on the directional pad  345  at this stage causes the cursor to move through the text of the selected field. 
     FIGS. 6   a - c  provide an example of the foregoing operation. In  FIG. 6   a  a text entry field for entering a street  602  is initially selected. The entire text entry field is highlighted to provide an indication that text entry will replace the current contents of the field  602 . In addition, unlike prior user interfaces, the label for the text entry field (e.g., “State”) is provided as text within the field itself. In response to the user scrolling left on the trackball, the city field is once again highlighted. In the illustrated example, the user types a street number and then scrolls down on the trackball to cause a text entry field for entering a city  603  to become highlighted. As the user begins typing the city, the city label is replaced, as indicated in  FIG. 6   b . In response to a rightward scroll after the city is entered, a text entry field for entering a state  604  is highlighted. If the user does not enter text but instead scrolls left, all of the text for the previously-entered city is highlighted, as indicated in  FIG. 6   b . If the user then selects the delete button or types any text, the contents of the city text entry field are deleted or replaced, respectively, as indicated in  FIG. 6   c.    
   In one embodiment, a new text entry field is selected in response to a trackball motion only if the cursor is at the beginning or end of the text within the current text entry field and the cursor is scrolled to the left or right, respectively, or if the trackball is scrolled up or down regardless of the location of the cursor. For example, if the cursor is positioned to the right of the text in text entry box  603  as shown in the first frame of  FIG. 6   b  and the user scrolls right, a new text entry field  604  is selected. However, in one embodiment, if the user scrolls left in this situation, the cursor will responsively move one character at a time through the text within the text entry box  602  until it reaches the beginning of the text. 
   Alternatively, in one embodiment, scrolling the trackball will cause another field to be highlighted regardless of the position of the cursor. In this embodiment, the cursor is moved via the directional pad rather than the trackball. 
   Text Selection 
   One embodiment of the invention provides techniques to select text using the trackball  301  when in a “reading” mode such as, for example, when viewing a Web page or email message. These techniques will be described with respect to  FIG. 7 . 
   In this embodiment, the user is reading a page of an email message containing text, hyperlinks and graphics. Three modes of operation are provided for navigating the page—a “standard” mode, a “targeting/selecting” mode (hereinafter “targeting” mode), and a “selection” mode. When in the standard mode shown in window  700 , only hyperlinks are selected in response to movement of the trackball  301 . That is, in response to the user scrolling the trackball, the highlighter will jump from one hyperlink to the next, bypassing all non-hyperlinked text. This mode may be used to standard Web browsing operations. 
   In one embodiment, the user may cause the device to enter the “targeting” mode by selecting a command from a menu, or pressing and/or holding down a specified shortcut key (e.g., the shift key from the keyboard  306 ). When in targeting mode, both hyperlinked text, non-hyperlinked text and graphical elements are selected in response to the trackball movement. Specifically, as the user moves the trackball, the highlighter highlights each word in succession in the direction of the trackball motion (rather than just hyperlinked words). As illustrated in window  701 , the highlighter may change color and the formatting used for the hyperlinked words may change to indicate that the device is in the targeting mode. The user may position the start of the desired text selection point in either standard mode (if the start is a hyperlink) or targeting mode. 
   Once the start of the desired text selection point is identified, the user can enter into the selection mode by moving the trackball while holding down a specified shortcut key (e.g. Shift) to select a piece of contagious text. In one embodiment, while holding down the designated shortcut key, each additional word in succession will be highlighted along with the currently selected word(s). This is illustrated graphically in window  702 . The user may then copy the text (e.g., using a copy command from the menu or designated key combination), or return to the positioning state by releasing the shortcut key and moving the trackball so that another piece of text can be selected. 
   Selecting on a word-by-word basis as described above is efficient and less error-prone than selecting on a character-by-character basis. However, the underling principles of the invention may still be implemented using character-by-character selection. 
   Assuming a word-by-word selection is employed, in one embodiment a “word” is defined to be any of the following: (a) one or more letters, (b) one or more digits, blocks of spaces, (c) one punctuation/symbol/special characters. In this way, the majority of text selection circumstances are easily captured. The foregoing features are illustrated in  FIG. 8  which shows an exemplary sequence of numbers, letters and other characters: sapien123 1-2234-566!!!. In response to the targeting motion described above, the “sapien” sequence of characters is logically separated from the set of numbers which follow (“123”). This is true even though no space exists between the letters and numbers. As the user holds down the designated control key (e.g., Shift) and scrolls the wheel to the right, the following characters are selected in succession: 123, space, 1, -, 2234, -, 566, !, !, !. Thus, the system selects numbers separated by dashes in groups (e.g., 2234), and highlights special characters such as the dashes, spaces and exclamation points individually. The purpose of the foregoing algorithm is to provide a selection mechanism which is both efficient and which reflects selections which are most likely intended by the user (e.g., it is unlikely that the user would want to highlight only a portion of 2234 in the example above). 
   Browser Navigation 
   In one embodiment, special link navigation features are provided to improve Web browser navigation. For example, on certain Web pages on mobile devices, hyperlinks may be positioned arbitrarily and may have various sizes and lengths. Consequently, users may have a problem knowing which link will be highlighted after they roll the trackball up, down, left or right. For example, in  FIG. 9   a , the mail icon  901  is the currently highlighted link but it is unclear which link will become highlighted when the user scrolls down (e.g., Movies or Horoscopes). 
   To solve these problems, one embodiment of the invention visually identifies the links which will be selected in response to a trackball motion moving away from the current link. In  FIG. 9   b , the current link is “People Search”  902 . To provide an indication of the links which will be selected if the user scrolls the trackball, the potential links are highlighted in a transparent color. In addition, to differentiate the different directions of movement the links to the left/right are provided with different colors than the links above/below the current link  902 . In the illustrated example, the Map link  903  and the TV link  904  are colored purple and the News link  905  and the Personals link  906  are colored gray. In addition, in one embodiment, the further away the link is from the current element, the higher the transparency value associated with the link (e.g., the Geocities link  907  has a higher transparency value, and is therefore more transparent, than the Maps link  903 ). As the user move to a new link, the highlights are regenerated accordingly. 
   Logical Barriers 
   One embodiment of the invention employs logical barriers between windows and other graphical elements to prevent the user from inadvertently navigating in the wrong direction. For example, if the user intends to scroll down a menu structure with the trackball  301  and inadvertently scrolls to the right or left, these embodiments of the invention do not immediately register the right and/or left input. 
     FIGS. 10   a - b  illustrate one embodiment of a logical barrier between two months of a calendar program. In  FIG. 10   a , the month of September is shown in window  1000  and the month of October is shown in window  1003 . In this particular example, the user scrolls down on the trackball from September 13 to September 27 (block  1001 ). Once September 27 has been highlighted, the logical barrier will initially prevent the highlight from moving to the October window  1003  in response to additional downward scrolling motion. In one embodiment, the logical barrier comprises a short duration of time (e.g., 4/10 second, ½ second, etc) during which the user may continue to scroll downward without any effect. Alternatively, or in addition, the logical barrier comprises a specified amount of rotation in the downward direction (e.g., a specified number of downward “clicks” on the trackball). After the short duration of time and/or amount of downward motion, an additional downward scroll on the trackball  301  will move the highlight to the October 4 date  1002  within the October window  1003 . In one embodiment, the logical barriers are user-configurable, allowing the user to specify whether a specified amount of time and/or a measurable downward scroll is to be used as the logical barrier. 
     FIG. 10   b  illustrates the same general principles with a weekly calendar view. In this example, a Wednesday, November 15 entry  1005  is initially selected within the week of Nov. 12, 2006 (window  1006 ). In response to scrolling the trackball to the right, each of the days from Nov. 15 to Nov. 18 are highlighted in succession. When the final day within the window  1006  is highlighted (Nov. 18), a logical barrier will initially prevent the next window  1008  to be displayed in response to additional rightward trackball motion. After a specified amount of time (e.g., 4/10 second, ½ second, etc) and/or a specified amount of additional rightward motion on the trackball, the cursor will move to the first date entry  1007  in the new window  1008 . 
     FIGS. 10   c - e  illustrate a particular type of logical barrier referred to as a “rail guard” for preventing inadvertent trackball movements within a hierarchical menu structure according to one embodiment of the invention. Specifically,  FIG. 10   c  shows a drop down menu  1010  with a plurality of selectable elements which may be selected via an up/down scrolling motion on the trackball  301 . Certain elements, such as element  1011 , have sub-elements associated with them (as indicated by the right-pointing arrow displayed on some of the elements). The user scrolls right on the trackball  301  when the element  1011  is highlighted to expose the sub-elements. For example, scrolling right when element  1011  bring up a set of “Airplane Mode” sub-elements, as illustrated in  FIG. 10   d.    
   In one embodiment, of the invention, the “rail guard” logical barrier is configured on each element to prevent the sub-elements from being exposed in response to an inadvertent right/left scrolling motion. More specifically, the sub-elements will be selected in response to a rightward motion only after a specified amount of time after the vertical motion has stopped (e.g., 2/10 of a second). Thus, any horizontal motion which occurs within the specified amount of time after vertical motion stops is deemed accidental and is ignored. Alternatively, or in addition, the sub-elements may be selected only after a specified amount of additional rightward motion on the trackball. 
   In one embodiment of the invention, the same concepts are applied to the graphical, circular menu structure such as the one illustrated in  FIG. 10   e . That is, certain menu elements such as element  1020  have sub-elements associated with them which will be selected in response to a rightward motion only after a specified amount of time and/or a specified amount of additional rightward motion on the trackball. 
   The end result of the logical barriers described above is that inadvertent motion by a user at the edge of a window or other graphical element will not cause unwanted movements into an adjacent window and/or other graphical element, respectively, thereby improving the navigation experience for the user. 
   Embodiments of the invention may include various steps as set forth above. The steps may be embodied in machine-executable instructions. The instructions can be used to cause a general-purpose or special-purpose processor to perform certain steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
   Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). 
   Throughout the foregoing description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. Accordingly, the scope and spirit of the invention should be judged in terms of the claims which follow.