Abstract:
An improved electronic spreadsheet is provided for applications that require the processing of continuous data streams over a time-based data interval of size greater than one. The improved spreadsheet supports the creation of expressions involving clocked delay line objects instantiated within spreadsheet cells. The delay line object includes data storage and a member function that implements a shift register. Data stream input functions supply the clocking signals that trigger the execution of the shift register function of the delay line object. Spreadsheet functions are provided that support random access of elements and other analysis over the buffered data interval The forgoing improvements extend the effective range of spreadsheet programming to include a wider range of applications than was previously possible, including signal processing, machine vision, and time evolution studies.

Description:
This is a continuation of application Ser. No. 09/370,808, filed Aug. 9, 1999, now U.S. Pat. No. 6,490,600 B1. 

   FIELD OF THE INVENTION 
   The present invention relates to electronic spreadsheets, and particularly to spreadsheets applied to processing continuous data streams. 
   BACKGROUND OF THE INVENTION 
   The superior ease-of-use characteristics of electronic spreadsheets are well-known, especially in the field of office automation. The use of electronic spreadsheets in other fields is also known, although in the past, certain computer applications have been unable to take full advantage of the spreadsheet metaphor. One reason for this is that a large class of computer applications require algorithms that operate over time-based intervals of a continuous data stream, and conventional spreadsheets provide no intrinsic support for continuous data processing over more than one processing interval. 
   An electronic spreadsheet is, essentially, a means of graphically representing a set of expressions as a grid of cells. Each cell in the spreadsheet grid represents a parenthetical expression that can, in turn, be a function of some number of other cellular expressions. 
   A spreadsheet program updates its grid, as necessary, to maintain the programmed relationship between cellular expressions. Electronic spreadsheets are intended to provide immediate response to any modifications of the programmed expressions. However, in conventional electronic spreadsheets, cellular expressions have no means for accessing previously evaluated results from prior processing intervals. Absent this capability, it is impossible for a conventional spreadsheet to process a continuous data stream of incoming data on a time-based interval of a duration greater than one processing interval. 
   Although methods for implementing algorithms that operate on continuous data streams are well-known in computer programming, no methods are known for implementing this class of processing within the context of an electronic spreadsheet. 
   SUMMARY OF THE INVENTION 
   The invention provides an electronic spreadsheet adapted for programming the processing of continuous data streams. The invention also provides means and methods that, to a high degree, preserve the fundamental characteristics of conventional electronic spreadsheets. The invention also provides means and methods, which are uncomplicated and intuitive to use. 
   These benefits and features are accomplished by extending the spreadsheet paradigm to include apparatuses and methods of clocked data buffering, such as by using shift registers, delay lines, FIFOs, pipelines, and even random access memory. The use of shift registers is preferred because shift registers do not require addressing. Delay lines objects are instantiated (memory is allocated for each delay line object) and assigned to spreadsheet cells (each allocated memory is associated with the coordinates of a cell). A delay line object includes a data buffer configured as a variable length shift register, and a method for clocking data through the buffer. In a preferred embodiment, input data streams supply the clocking signals, and “tap functions” support random access of elements, and other analysis over the buffered interval. 
   The invention extends the conventional electronic spreadsheet paradigm to include the processing of continuous data streams on finite intervals. 

   
     BRIEF DESCRIPTION OF DRAWING 
     The invention will be more fully understood from the following detailed description, in conjunction with the following figures, wherein: 
       FIG. 1  is an example illustrating methods of electronic spreadsheet programming for processing continuous data streams of the invention; 
       FIG. 2  is an example output sequence illustrating the response of the example program of  FIG. 1  to a specific input sequence; 
       FIG. 3  is a diagram illustrating the components of a delay line object; and 
       FIG. 3A  is a diagram of the parameters of the delay line object of  FIG. 3 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a sequence of user interface screens  1 ,  2 ,  3 ,  4 ,  5 , and  6  illustrates how a spreadsheet processes a continuous data stream according to the invention. Displayed is a spreadsheet program that computes the square root of the sum of the squares of the last three data elements of a continuous data stream. The spreadsheet program of  FIG. 1  is constructed in  6  expressions entered in cells B 1 , B 2 , B 3 , B 4 , B 5 , and B 6 . 
   Cell B 1  contains an external input function “INPUT( 1 )”. The input function “INPUT( 1 )” accesses a data source “1” external to the spreadsheet. In this example, we assume that cell B 1  updates periodically as a function of some unspecified external event, e.g., in response to data on the lines of a parallel port whenever a line is toggled, or in response to a pixel value at specified coordinates in an image at a particular time. 
   Cell B 2  contains an instance of a delay line object, and is parameterized with four parameters: the input data stream (B 1 *B 1 ), the clock source (B 1 ), the number of elements in the shift register ( 3 ), and the clock divider ( 1 ). 
   Referring to  FIG. 3 , a delay line object  30  consists of a data buffer  32  configured as a variable length shift register (or as a delay line, FIFO, pipeline, etc.), and a method for clocking data through the buffer  34 . The clock signal  34  indicates when data is valid for processing in the spreadsheet. Input data streams supply the clock signals  34 , and “buffered interval” spreadsheet functions support the random access of elements and other analysis over the buffered interval. For example, parallel random access of data elements is performed using “tap functions”  36  that independently access single values from the delay line buffer  32  at particular specified locations by calling methods  37  of the delay line object. Analysis over the buffered interval includes any vector operation on the data buffer, including summing the buffer, and performing a standard deviation or other statistical analysis on the buffer. Further, other sources of clocking signals include a timer (e.g., a clock edge every 20 seconds), an image acquire signal, or a parallel port, or any external event, for example. Other spreadsheet entities can also provide clock signals. The delay line object also includes a plurality of parameters  40 , as detailed in  FIG. 3A . 
   Referring to  FIG. 3A , the delay line object is parameterized by four arguments. The first argument is the input data stream  31 ; the second argument is the clock source  33 ; the third argument is the number of elements in the shift register buffer (delay line)  35 ; and the forth argument is a clock divider  39 . 
   In the example of  FIG. 1 , the data source is defined by an expression that squares the input data stream B 1 ; the clock source is referenced to cell B 1 ; the number of data elements in the shift register is three; and the sample rate is one per cycle. So, when data is received in B 1 , it is squared and input to a three-element delay line. 
   Cells B 3 , B 4 , and B 5  access the delay line instantiated in B 2  to return the values of all three elements in the delay line data buffer. The tap function TAP(B 2 , 0 ) in cell B 3  accesses the last data item to be input to the delay line in cell B 2 . The tap functions TAP(B 2 , 1 ) and TAP(B 2 , 2 ) in cells B 4  and B 5 , respectively, access data that was input on the previous two clock cycles  1  and  2 . 
   Cell B 6  completes the processing by referencing B 3 , B 4 , and B 5  in a computation of the square root of the sum of the three values B 3 , B 4 , and B 5  returned from the delay line&#39;s buffer. 
     FIG. 2  shows the final four spreadsheet display states that result when the spreadsheet program of  FIG. 1  processes the input data stream 
   {1.00,2.00,3.00,4.00,5.00,6.00}: 
   At time (T-3) cells B 3 , B 4  and B 5  display the values 9.00, 4.00, and 1.00, respectively, resulting from the squaring of the first three input data elements 3.00, 2.00, and 1.00; 
   At time (T-2) the value 16.00, the square of the input data value B 1 =4.00 (B 1 *B 1 ), shifts into the delay line; 
   At time (T-1) the value 25.00, the square of the input data value B 1 =5.00 (B 1 *B 1 ) shifts into the delay line; and 
   At time (T-0) the value 36.00, the square of the input data value B 1 =6.00 (B 1 *B 1 ) shifts into the delay line. 
   For every cycle, the square root of the sum of the delay line contents (Mag) is computed by the expression assigned to cell B 6 : (B 6 =SQRT(B 3 +B 4 +B 5 )). 
   The input function INPUT( 1 ) receives data from an external source and updates the value assigned to B 1 . The delay line object in B 2  (B 2 =DELAY(B 1 *B 1 ,B 1 , 3 , 1 ) is clocked by the input function, and a new value is shifted into the data buffer upon each new input. The three tap functions TAP(B 2 , 0 Y, TAP(B 2 , 1 ),and TAP(B 2 , 2 ) are dependent on the contents of the delay line B 2 , and update in an unspecified order. Finally, the expression in B 6  (SQRT(B 3 +B 4 +B 5 )) is dependent on B 3 , B 4 , and B 5 , and is evaluated, the result being assigned to B 6 . At this point, all dependencies have been satisfied, and the contents of the spreadsheet remain unchanged until the next input event occurs. 
   In the forgoing example, the delay line expression in B 2  behaves in a way very different from a conventional spreadsheet expression. First, the delay line is not a function; rather, it is an object instance, i.e., there is data storage (memory) allocated. Delay line class objects combine data storage with a member function that implements the shift register, for example. 
   Second, unlike a conventional spreadsheet expression that is evaluated only as necessary to update the spreadsheet, according to the invention, the evaluation of the delay line member function is executed only upon triggering by a clock signal. The value of the input to the delay line member function does not need to change to force the evaluation of the delay line member function. The state of the source data argument is irrelevant; the shift register action can only be activated by a signal from a valid clock source, such as the input function in the example. 
   Referring to  FIG. 3 , the delay line object  30  consists of a data buffer  32  configured as a variable length shift register (or as a delay line, FIFO, pipeline, etc.), and a method for clocking data through the buffer  34 . The clock signal  36  indicates when data is valid for processing in the spreadsheet. Input data streams supply the clock signals  36 , and buffered interval functions support the random access of elements, and other analysis over the buffered interval. For example, parallel random access of data elements is performed using “tap functions”  38  that independently access single values from the delay line buffer  32  at particular specified locations by calling methods  37  of the delay line object. Analysis over the buffered interval includes any vector operation on the data buffer, including summing the buffer, and performing a standard deviation or other statistical analysis on the buffer. Further, other sources of clocking signals include a timer (e.g., every 20 seconds), an image acquire signal, a parallel port, or any external event, for example. Other spreadsheet entities can also provide clock signals. 
   The delay line object  30  also includes a plurality of parameters  40 , as detailed in  FIG. 3A , including, for example, the input data stream  31 , the clock source  33 , the number of elements in the shift register, and the clock divider  39 . 
   Other modifications and implementations will occur to those skilled in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the above description is not intended to limit the invention except as indicated in the following claims.