Processing continuous data streams in electronic spreadsheets

[0002] The present invention relates to electronic spreadsheets, and particularly to spreadsheets applied to processing continuous data streams.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] The invention extends the conventional electronic spreadsheet paradigm to include the processing of continuous data streams on finite intervals.

[0010] The invention will be more fully understood from the following detailed description, in conjunction with the following figures, wherein:

[0011] FIG. 1 is an example illustrating methods of electronic spreadsheet programming for processing continuous data streams of the invention;

[0012] FIG. 2 is an example output sequence illustrating the response of the example program of FIG. 1 to a specific input sequence;

[0013] FIG. 3 is a diagram illustrating the components of a delay line object; and

[0014] FIG. 3A is a diagram of the parameters of the delay line object of FIG. 3.

[0015] 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 B1, B2, B3, B4, B5, and B6.

[0016] Cell B1 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 B1 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.

[0017] Cell B2 contains an instance of a delay line object, and is parameterized with four parameters: the input data stream (B1 *B1), the clock source (B1), the number of elements in the shift register (3), and the clock divider (1).

[0018] 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.

[0019] 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.

[0020] In the example of FIG. 1, the data source is defined by an expression that squares the input data stream B1; the clock source is referenced to cell B1; 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 B1, it is squared and input to a three-element delay line.

[0021] Cells B3, B4, and B5 access the delay line instantiated in B2 to return the values of all three elements in the delay line data buffer. The tap function TAP(B2,0) in cell B3 accesses the last data item to be input to the delay line in cell B2. The tap functions TAP(B2,1) and TAP(B2,2) in cells B4 and B5, respectively, access data that was input on the previous two clock cycles 1 and 2.

[0022] Cell B6 completes the processing by referencing B3, B4, and B5 in a computation of the square root of the sum of the three values B3, B4, and B5 returned from the delay line's buffer.

[0023] 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}:

[0024] At time (T-3) cells B3, B4 and B5 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;

[0025] At time (T-2) the value 16.00, the square of the input data value B1=4.00 (B1*B1), shifts into the delay line;

[0026] At time (T-1) the value 25.00, the square of the input data value B1=5.00 (B1 *B1) shifts into the delay line; and

[0027] At time (T-0) the value 36.00, the square of the input data value B1=6.00 (B1 *B1) shifts into the delay line.

[0028] For every cycle, the square root of the sum of the delay line contents (Mag) is computed by the expression assigned to cell B6: (B6=SQRT(B3+B4+B5)).

[0029] The input function INPUT(1) receives data from an external source and updates the value assigned to B1. The delay line object in B2 (B2=DELAY(B1*B1,B1,3,1) 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(B2,0), TAP(B2,1 ),and TAP(B2,2) are dependent on the contents of the delay line B2, and update in an unspecified order. Finally, the expression in B6 (SQRT(B3+B4+B5)) is dependent on B3, B4, and B5, and is evaluated, the result being assigned to B6. At this point, all dependencies have been satisfied, and the contents of the spreadsheet remain unchanged until the next input event occurs.

[0030] In the forgoing example, the delay line expression in B2 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.