Abstract:
The invention concerns methods and apparatus for generating and controlling a slider control for simultaneously changing values of two variables. In the methods and apparatus of the invention a graph having two axes is displayed, wherein the axes correspond to first and second variables. The values of the first and second variables may be simultaneously adjusted using a slider control displayed in a two-dimensional region between the axes. As a user adjusts the slider control and changes values associated with the two variables, the methods of the present invention calculate the effects of the adjustment on a value of a third variable. A graphical component is then used to depict the updated value of the third variable. Additionally, curves corresponding to constant values, or ranges of values, of the third variable are displayed in the two-dimensional region to assist a user in selecting values for the first and second variables.

Description:
TECHNICAL FIELD  
       [0001]     The present invention generally concerns visual optimization tools for use in graphical user interfaces, and more particularly concerns a slider control for simultaneously adjusting values of two variables, wherein a graphical component shows the effect of the adjustment on the value of a third variable, the depiction of the effect on the value of the third variable helping a user to select a combination of values for the first and second variables.  
       BACKGROUND  
       [0002]     Graphical user interfaces and associated controls are becoming more popular as means to set parameters for operations and processes. Slider controls are particularly popular to control processes. Most computer-literate people are familiar with using slider controls to set various computer-related parameters in computer-related processes such as, for example, display resolution; level of virus and firewall security (e.g., from “low” to “high”) etc.  
         [0003]     Such slider controls are particularly useful for those relatively unfamiliar with underlying processes because they provide a level of abstraction with which novice users can relate. The alternative to using a slider control to set levels of virus and firewall protection may be daunting. Typically, the slider control abstracts numerous individual settings which otherwise would have to be individually set. The most common way of making such selections is with check boxes. In a complex security application, the number of check boxes may comprise tens, or even hundreds, of individual settings. If details are not provided to assist a user in making selections, the user may be befuddled as to whether an individual setting increases, or decreases, the level of security. In addition, unless the user has a detailed understanding of interactions between various settings, combinations of settings that conflict with a desired level of protection may be selected.  
         [0004]     As indicated previously, slider controls overcome these problems because they provide a level of abstraction. Although a user typically will have difficulty in determining whether any particular combination of check box selections are optimal, the user will have a much easier time determining that a particular slider control setting is optimal. This occurs because experts are mapping the slider control settings to combinations of check settings in a complex process. Experts understand intuitively how settings combine and interact, and thus are capable of mapping the combinations to slider control settings in terms of, for example, “low protection” or “high protection”.  
         [0005]     Thus, slider controls are particularly useful when a plurality of settings can be abstracted to a single range. Slider controls are less useful, though, when a user is interested in more than one abstract characterization of a process. An archetypal relationship immediately comes to mind, the trade-off between performance level, availability and cost. It is not unusual that there is a direct relationship between cost and the level of availability and performance selected in a complex process. Increasing levels of availability and performance often come at great expense. In such situations, conventional slider controls have been found ineffective. Two slider controls simply do not provide enough information as to whether an optimal combination of values has been selected for two parameters.  
         [0006]     Accordingly, those skilled in the art desire improvements to slider controls that enable them to be used to more effectively select values for two or more operating parameters.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0007]     The foregoing problems and other problems are overcome, and other advantages are realized, in accordance with the following embodiments of the present invention.  
         [0008]     A first embodiment of the invention comprises a signal-bearing medium tangibly embodying a program of machine-readable instructions executable by a digital processing apparatus of a computer system to perform operations for displaying and controlling an interactive graphical user interface, the operations comprising: displaying a graph having two axes corresponding to first and second variables in the interactive graphical user interface, wherein a two-dimensional region between the two axes specifies values the first and second variables may assume, and wherein a combination of values that the two variables assume determines a value of a third variable; displaying a slider control in the two-dimensional region; receiving a command moving the slider control within the two-dimensional region to a new position, wherein the movement of the slider control to a new position determines a new combination of values for the first and second variables; calculating a new value for the third variable based on the new combination of values for the first and second variables; and displaying a graphical component representing the new value for the third variable in the interactive graphical user interface.  
         [0009]     A second embodiment of the invention comprises a method for displaying and controlling an interactive graphical user interface, the method comprising: displaying a graph having two axes corresponding to first and second variables in the interactive graphical user interface, wherein a two-dimensional region between the two axes specifies values the first and second variables may assume, and wherein a combination of values that the first and second variables assume determines a value of a third variable; displaying a discrete number of pre-determined combinations of values for the first and second variables in the two-dimensional region; displaying a slider control in the two-dimensional region; receiving a command moving the slider control toward a position of a particular one of the pre-determined combinations of values for the first and second variables in the two-dimensional region; determining that a trajectory of the slider control is toward the particular one of the pre-determined combinations of values for the first and second variables displayed in the two-dimensional region; snapping a graphical indicator to the position of the particular one of the pre-determined combinations of values for the first and second variables in the two-dimensional region indicating that the particular one of the pre-determined combinations of values for the first and second variables has been selected; determining a new value for the third variable based on the new combination of values for the first and second variables associated with the particular one of the pre-determined combinations of values for the first and second variable; and displaying a graphical component representing the new value of the third variable in the interactive graphical user interface.  
         [0010]     A third embodiment of the invention comprises a computer system for displaying and controlling an interactive graphical user interface, the computer system comprising: at least one memory to store at least one computer program of machine-readable instructions, where the at least one program performs operations to display and control the interactive graphical user interface when executed; a display for displaying the interactive graphical user interface; and at least one processor coupled to the at least one memory and display, wherein the at least one processor performs at least the following operations when the at least one program is executed: displaying a graph having two axes corresponding to first and second variables in the interactive graphical user interface, wherein a two-dimensional region between the two axes specifies values the first and second variables may assume, wherein values that the two variables may assume determines a value of a third variable; displaying a slider control in the two-dimensional region; receiving a command moving the slider control within the two-dimensional region to a new position, wherein the movement of the slider control to a new position determines a new combination of values for the first and second variables; calculating a new value for the third variable based on the new combination of values for the first and second variables; and displaying a graphical component representing the new value for the third variable in the interactive graphical user interface.  
         [0011]     In conclusion, the foregoing summary of the embodiments of the present invention is exemplary and non-limiting. For example, one skilled in the art will understand that one or more aspects or steps from one embodiment can be combined with one or more aspects or steps from another embodiment to create a new embodiment within the scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein:  
         [0013]      FIG. 1  depicts a two-variable slider control operating in accordance with the prior art;  
         [0014]      FIG. 2  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0015]      FIG. 3  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0016]      FIG. 4  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0017]      FIG. 5  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0018]      FIG. 6  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0019]      FIG. 7  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0020]      FIG. 8  depicts a two-dimensional slider control operating in accordance with an embodiment of the invention;  
         [0021]      FIG. 9  depicts a two-dimensional slider control with additional information superimposed in a region of the two-dimensional slider control, all operating in accordance with another embodiment of the invention;  
         [0022]      FIG. 10  depicts a two-dimensional slider control with additional information superimposed in a region of the two-dimensional slider control, all operating in accordance with another embodiment of the invention;  
         [0023]      FIG. 11  depicts a method operating in accordance with the invention;  
         [0024]      FIG. 12  depicts another method operating in accordance with the invention; and  
         [0025]      FIG. 13  depicts a two-dimensional slider control operating in accordance with a further embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]      FIG. 1  depicts a conventional slider control  100  for adjusting values associated with two variables  110 ,  130 . The slider control  100  comprises individual sliders  120 ,  140  associated with corresponding variables, performance  1   10  and availability  130 . Such a slider control can be used to control the operations of, for example, a computer system. It is difficult to determine exactly how optimal the level of control that is achieved with the slider control  100  depicted in  FIG. 100 . For example, since no cost variable is displayed, it is not known whether a particular combination of settings for variables performance and availability is optimal from a cost perspective. In addition, since no maintenance variable is displayed, it is not known whether a particular combination of variables results in a low-maintenance or a maintenance-intensive implementation. Accordingly, so while dual slider controls may make it somewhat easier to control a complex process, those skilled in the art desire greater assistance in determining whether suitable, or even optimal, combinations of values for variables have been selected.  
         [0027]      FIG. 2  depicts a graphical user interface operating in accordance with the invention that overcomes the limitations of the prior art. In particular, the graphical user interface  200  comprises two axes  212 ,  222 , that correspond to, and are associated with, two variables  210 , and  220 , respectively. The two axes  212 ,  222  define a two-dimensional region  240  between the axes. The axes  212 ,  222  and two-dimensional region  240  graphically depict the respective values that variables  210  and  220  may assume. In contrast to the dual slider control depicted in  FIG. 1 , the graphical user interface  200  operating in accordance with the present invention further comprises a graphical component  230  corresponding to a third variable. An indicator  232  visually depicts the current value of the third variable as determined by the current combination of values for the first and second variables. The current combination of values for the availability and performance variables is determined by the current position of a slider control  250 . As is apparent, instead of separately setting the values of two variables with separate slider controls  120 ,  140  as in the case of the conventional control  100 , in the graphical user interface  200  of the present invention, a single control is used to set values of both variables  210 ,  220 .  
         [0028]     An additional advantage is shown in  FIG. 2  as well. Curves  234 ,  236  and  238  correspond to various levels of the third variable as depicted in graphical element  230 . For example, curve  238  shown in two-dimensional area  240  corresponds to cost level “$$$” shown in graphical element  230 . To explain in greater detail, all combinations of values for variables  210 ,  200  falling along curve  238  correspond to, and are associated with, a cost level “$$$”. In addition, all combinations of values for variables  210 ,  220  falling along curve  236  correspond to, and are associated with, a cost level “$$” (which is a lower cost level than that associated with line  238 , which corresponded to a higher cost level “$$$”). Further, all combinations of values for variables  210 ,  220  falling along curve  234  correspond to cost level “$” (which is lower than either cost levels “$$” or “$$$” associated with curves  236 ,  238 ).  
         [0029]     This feature represents a particular advantage of the graphical user interface of the invention. In the conventional dual slider control  100  depicted in  FIG. 1 , no information is provided regarding the effect of the setting of variables  110 ,  130  on other variables. Accordingly, a user is not provided with any guidance regarding whether a particular combination of values is, for example, either cost-effective, or within budgetary constraints. In addition, information is provided in the graphical user interface  200  which is not provided to a user of the dual slider control of  FIG. 1 .  
         [0030]     As an example, a user starting at an initial point along curve  236  as depicted in  FIG. 2  moves the slider control  250  to a new position as shown in  FIG. 3 . As the slider control  250  moves to the new position depicted in  FIG. 3 , indicator  232  associated with the third variable moves downward as well, indicating that the new combination of variables  210 ,  220  associated with the new position of the slider control  250  corresponds to a lower cost option.  
         [0031]     Another advantage of the present invention is that a user can select “optimal” points easily, because optimal portions are readily apparent in the curves  234 ,  236  and  238 . A user can see from optimal portions in the curves where further adjustment of one of the variables comes at an increasingly greater cost to the other variable. For example, a user has decided to operate along curve  234  corresponding to a low-cost option “$” as seen in  FIGS. 4 and 5 . In looking at curve  234 , it is evident in moving the slider control  250  from left to right, that increasing levels of “availability” can be had for relatively low cost in “performance”, up through optimal portion  234   a.  Beyond optimal portion  234   a  further levels of availability come at an ever-increasing cost to performance, until the value of the performance variable bottoms out. Accordingly, in most instances it would make sense to select an operating point (e.g.,  235 ) in optimal portion  234   a,  because point  235  represents a near-optimal combination of performance and availability for a given cost, when performance is valued more highly than availability.  
         [0032]     In contrast, curve  238  corresponding to high cost “$$$” has two optimal portions  238   a  and  238   b.  These help a user of the graphical user interface  200  of the invention to select a combination of values for variables availability and performance  210 ,  200 , respectively, as shown in  FIGS. 6-8 . For example, if a user can accept cost level “$$$” (it fits within budgetary constraints) then the user will make a determination about what variable is most important. For example, if performance and availability are equally important, the user will select a point about midway along curve  238 , which roughly corresponds to medium levels of performance and availability, as shown in  FIG. 6 . Alternatively, if a relatively high level of performance is desired, the user will examine the portion of the curve  238  closer to the performance axis  222 . As is apparent, initially higher levels of availability can be had for relatively little cost to performance. After optimal portion  238   a,  though, improvements in availability come at an increasingly higher cost to performance. Accordingly, a user interested mainly in performance would be expected to select a combination of values for variables  210 ,  220  in optimal portion  238   a  (e.g.,  239   a ), as shown in  FIG. 7 .  
         [0033]     Alternatively, if one using the graphical user interface of the invention is interested in high levels of availability, but performance is relatively less important, than the user would be interested in the portion along curve  238  near the availability axis  212 . As can be seen, as one moves along curve  238  away from axis  212 , initially additional performance can be had for relatively little cost in availability up until optimal portion  238   b.  Beyond optimal portion  238   b,  the cost in availability of higher levels of performance becomes much greater. Accordingly, a user mainly interested in availability and not so interested in performance would pick an operating point in optimal portion  238   b  (e.g.,  239   b ), as shown in  FIG. 8 .  
         [0034]      FIGS. 9-10  display another embodiment of the invention. In this embodiment, it is assumed that a user is relatively constrained in the options that may be chosen. For example, assume that a user is using the invention to select a server configuration, and that there are several pre-existing server configurations available based on particular server models. Region  910  corresponds to a configuration using Blade XXX. There are several pre-existing options based on Blade XXX corresponding to Option T as shown by reference character  912 ; Option U as shown by reference character  914 ; and Option V as shown by reference character  916 . Region  920  corresponds to configurations using Blade YYY. There are several pre-existing options based on Blade YYY corresponding to Option A as shown by reference character  922 ; Option B as shown by reference character  924 ; and Option C as shown by reference character  926 . There are several pre-existing options based on Blade ZZZ corresponding to Option  1  as shown by reference  932  and Option  2  as shown by reference character  934 . In this example, regions  910 ,  920  and  930  are provided as an aid to a user to show the general range of options available.  
         [0035]     In operation, this embodiment of the invention functions as follows. A user moves slider control  250  about two-dimensional region  930 . Slider control does not actually determine the combination of values for the performance and availability variables  210 , 220 . Rather, depending on the movement of slider control, box  960  snaps to the option likely to be selected by the user next. The snapping can be done based on underlying detents within the two-dimensional area, which can be point-based, line-based, or area-based detents. For example, if the user is moving the slider control toward Option B, the methods of the present invention will detect this intention based on analysis of the trajectory of slider control  250 , and will snap selection box  960  to Option B. Alternatively, methods of the present invention can snap the selection box  960  to options adjacent to the slider control. The end result of the operation is shown in  FIG. 9 . In addition, box  962  acts in synchronism with selection box  960  to indicate which Blade the currently selected option is associated with. Indicator  232  will then graphically indicate the value of variable  230  corresponding to the combination of values for the variables availability  210  and performance  220  associated with Option B  924 .  
         [0036]     Further operation of this embodiment of the invention is depicted in  FIG. 10 . As is apparent, a user has moved the slider control nearly to the position of Option  1 . As a result, the selection box  960  has snapped to Option  1 , and box  962  has snapped to Blade ZZZ. Since Option  1  represents a high cost option, indicator  230  remains at a position similar to that depicted in  FIG. 9 .  
         [0037]     In alternative embodiments of the invention, combinations of values falling within regions  910 ,  920  and  930  associated with options Blade XXX, Blade YYY and Blade ZZZ are also available for selection, in addition to the discrete options corresponding to reference characters  912 ,  914 ,  916 ,  922 ,  924 ,  926 ,  932  and  934 . In such an embodiment, a user may toggle a control that disables the operation of selection box  960  which is snapped to discrete options. Instead, the user would use slider control  250  to select combinations of values for the availability and performance variables  210 ,  220 . In this particular embodiment, though, the movement of slider control  250  could be restricted to movement within regions  910 ,  920  and  930 .  
         [0038]      FIG. 11  is a flowchart depicting a method operating in accordance with the invention, which will be described with reference to the preceding figures. The method begins at step  1110 , where a computer programmed to operate in accordance with the methods of the invention displays a graph having two axes  212 ,  222  corresponding to first and second variables  210 ,  220 , wherein a two-dimensional region  240  is defined by the area between the two axes  212 ,  222 . Next, at step  1120 , the computer displays a slider control  250  in the two-dimensional region. Then, at step  1130 , the computer receives a command moving the slider control  250  to a new position within the two-dimensional region, wherein the new position determines a new combination of values for the first and second variables  210 ,  220 . Next, at step  1140 , the computer calculates a new value for a third variable based on the new combination of values for the first and second variables. Then, at step  1150 , the computer displays a graphical component representing the new value for the third variable in the interactive graphical user interface.  
         [0039]     In one variant of the method depicted in  FIG. 11 , an additional step is performed. In the additional step, curves  234 ,  236  and  238  are displayed in the two-dimensional region  240 . Although three curves  234 ,  236  and  238  are displayed in  FIGS. 2-6 , this is not essential; one or more curves may be displayed in this variant of the invention. Curves  234 ,  236  and  238  correspond to constant values for the third variable. As is apparent, curve  234  corresponds to a low-cost option ($); curve  236  corresponds to a mid-cost option ($$); and curve  238  corresponds to a high-cost option ($$$). Curves  234 ,  236  and  238  help a user to select more easily a combination of values for variables  210 ,  220  since the curves indicate where certain values for the third variable fall within the two-dimensional region. If a user desires a relatively low-cost option, then the user would know to immediately move the slider control to a region close to the origin of the two axes  212 ,  222  because of the cue provided by curve  234 . Alternatively, if the user can accept a relatively high-cost option (e.g., cost of service), then the user would know to immediately move the slider control  250  to a region relatively distant from the origin of the axes due to the cue provided by curve  238 .  
         [0040]     In another variant of the method depicted in  FIG. 11  additional steps are performed. In a first step, a computer executing a computer program performing methods in accordance with the invention receives a command to switch one of the first and second variables with the third variable. Thereafter, values the third variable may assume are displayed on one of the axes. A user selects the value of the third variable and a value for the one of the first and second variables not switched with the third variable using the slider control. A combination of values selected for the one of the first and second variables not switched with the third variable and the third variable determine a value for the one of the first and second variables switched with the third variable. Then, the computer receives a command moving the slider control within the two-dimensional region to a new position, wherein the movement of the slider control to a new position determines a new combination of values for the third variable and the one of the first and second variables not switched with the third variable. Next, the computer calculates a new value for the one of the first and second variables switched with the third variable. Then, the computer displays the new value for the one of the first and second variables switched with the third variable in the interactive graphical user interface using a graphical component. In an example of this embodiment, in  FIG. 2 , “availability”  210 , values of which are currently shown on axis  212 , would switch positions with “cost”, values of which are currently shown by graphical element  230  and indicator  232 . After the switch, values for “cost” available for selection would be shown on axis  212 , and a user would simultaneously select values for “performance” and “cost” with slider control  250 . Values selected for “performance” and “cost” would then be used to determine a value for “availability”, the current value of which would be shown using a graphical element similar to  230 .  
         [0041]     In a further variant of the method depicted in  FIG. 11 , in addition to third variable “cost”, values of one or more additional variables may be shown using graphical components like  230 ,  232 . Current values of such additional variables would each be determined by the current values of the first and second variables set with slider control  250 . Any of these additional variables may be switched with one of the first and second variables in a manner similar to that described in the immediately preceding variant.  
         [0042]     In yet another variant of the method depicted in  FIG. 11 , the method is used to control a process such as, for example, a manufacturing process; a security process; or a computer-related process. In these variants, the third variable (the current value of which is shown with elements  230 ,  232 ) may alternatively be cost or maintenance.  
         [0043]      FIG. 12  is a flowchart depicting another method operating in accordance with the invention. The method depicted in  FIG. 12  will be described with reference to the preceding figures. The method begins at step  1210 , where a computer programmed to operate in accordance with the methods of the invention displays a graph having two axes  212 ,  222  corresponding to first and second variables  210 ,  220 , wherein a region  240  between the two axes specifies values that the first and second variables may assume, and wherein values that the two variables assume determine values of a third variable. Then, at step  1220  a discrete number of pre-determined combinations of values of for the first and second variables ( 912 ,  914 ,  916 ,  922 ,  924 ,  926 ,  932  and  934 ) are displayed in the two-dimensional region. Next, at step  1230 , a slider control  250  is displayed in the two-dimensional region  240 . Then, at step  1240 , the computer receives a command moving the slider control  250  toward a position of a particular one  932  of the pre-determined combinations of values for the first and second variables in the two-dimensional region. Next, at step  1250 , the computer determines that a trajectory of the slider control  250  is toward the particular one of the predetermined combinations of values for the first and second variables in the two-dimensional region. Then, at step  1260 , the computer snaps a graphical indicator to the position of the particular one of the pre-determined combinations of values for the first and second variables in the two-dimensional region, thereby indicating that the particular one of the pre-determined combinations of values for the first and second variables has been selected. Next at step  1270 , the computer determines a new value for the third variable based on the new combination of values for the first and second variables associated with the particular one of the pre-determined combination of values for the first and second variables. Then, at step  1280 , the computer displays a graphical component representing the new value for the third variable in the interactive graphical user interface.  
         [0044]     In a variant of the method depicted in  FIG. 12  additional steps are performed. First, the computer receives a command to change to a new mode of operation, wherein when in the new mode of operation a user enters a command switching the third variable with one of the first and second variables. When switched, operations are performed displaying values the third variable may assume on one of the axes. The user then selects a value of the third variable and a value of the one of the first and second variables not switched with the third variable using the slider control. A combination of values selected for the one of the first and second variables not switched with the third variable and the third variable using the slider control determines a value for the one of the first and second variables switched with the third variable. After receiving a command to change to the new mode of operation, the computer then receives a command to switch one of the first and second variables with the third variable. Next, the computer performs operations to display values the third variable may assume on an axis previously occupied by the one of the first and second variables switched with the third variable. Then, the computer receives a command moving the slider control within the two-dimensional region to a new position, wherein the movement of the slider control to a new position determines a new combination of values for the third variable and the one of the first and second variables not switched with the third variable. Next, the computer calculates a new value for the one of the first and second variables switched with the third variable. Then, the computer displays a graphical component representing the new value for the one of the first and second variables switched with the third variable in the interactive graphical user interface.  
         [0045]     As used herein “user” may refer to a person or an automated process.  
         [0046]      FIG. 13  depicts a further embodiment of the invention. In the embodiment depicted in  FIG. 13 a  user has selected a control mode where movement of the slider control is restricted to a region corresponding to a particular value, or ranges of values, of the third variable. The user has selected the particular values for the third variable with control  239 . Control  239  indicates that only combinations of values for the first and second variables which result in a value for the third variable corresponding to at least a high-cost option ($$$) may be selected. The region  241  corresponding to the combinations of values for the first and second variables that may be selected is graphically set apart by shading. When the slider control is moved, it is restricted to region  241 .  
         [0047]     One of ordinary skill in the art will understand that the methods depicted and described herein can be embodied in a tangible machine-readable memory medium. A computer program fixed in a machine-readable memory medium and embodying a method or methods of the present invention perform steps of the method or methods when executed by a digital processing apparatus coupled to the machine-readable memory medium. Tangible machine-readable memory media include, but are not limited to, hard drives, CD- or DVD-ROM, flash memory storage devices or in a RAM memory of a computer system. A machine-readable memory medium tangibly embodying such a computer program comprises an embodiment of the present invention.  
         [0048]     Thus it is seen that the foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best methods and apparatus presently contemplated by the inventors for implementing a slider control movable in a two-dimensional region for simultaneously adjusting values of multiple variables. One skilled in the art will appreciate that the various embodiments described herein can be practiced individually; in combination with one or more other embodiments described herein; or in combination with interactive graphical user interfaces differing from those described herein. Further, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments; that these described embodiments are presented for the purposes of illustration and not of limitation; and that the present invention is therefore limited only by the claims which follow.