Spreadsheet
From Wikipedia, the free encyclopedia
A spreadsheet is a rectangular table (or grid) of information, often financial information. The word came from "spread" in its sense of a newspaper or magazine item (text and/or graphics) that covers two facing pages, extending across the center fold and treating the two pages as one large one. The compound word "spread-sheet" came to mean the format used to present bookkeeping ledgers -- with columns for categories of expenditures across the top, invoices listed down the left margin, and the amount of each payment in the cell where its row and column intersect, for example -- which were traditionally a "spread" across facing pages of a bound ledger (book for keeping accounting records) or on oversized sheets of paper ruled into rows and columns in that format and approximately twice as wide as ordinary paper.
One of the first commercial uses of computers was in processing payroll and other financial records, so the programs (and, indeed, the programming languages themselves) were designed to generate reports in the standard "spreadsheet" format bookkeepers and accountants used. The more available and affordable computers themselves became in the last quarter of the 20th century, the more software became available for them, and programs to keep financial records and generate spreadsheet reports were always in demand. Those spreadsheet programs can be used to tabulate many kinds of information, not just financial records, so the term "spreadsheet" has developed a more general meaning as information presented in a rectangular table, usually generated by a computer.
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History
The concept of an electronic spreadsheet was outlined in the 1961 paper "Budgeting Models and System Simulation" by Richard Mattessich. Some credit for the computerized spreadsheet perhaps belongs to Pardo and Landau, who filed a patent (U.S. Patent no. 4,398,249) on some of the related algorithms in 1970. While the patent was originally rejected by the patent office as being a purely mathematical invention, Pardo and Landau won a court case establishing that "something does not cease to become patentable merely because the point of novelty is in an algorithm." This case helped establish the viability of software patents.
The generally recognized inventor of the spreadsheet is Dan Bricklin. Bricklin has spoken of watching his university professor create a table of calculation results on a blackboard. When the professor found an error, he had to tediously erase and rewrite a number of sequential entries in the table, triggering Bricklin to think that he could replicate the process on a computer, using the blackboard as the model to view results of underlying formulas.
His idea became VisiCalc, the first application that turned the personal computer from a hobby for computer enthusiasts into a business tool.
Programming issues
Just as the early programming languages were designed to generate spreadsheet printouts, programming techniques themselves have evolved to process tables (also known as spreadsheets or matrices) of data more efficiently in the computer itself.
Spreadsheets have evolved into powerful programming languages, specifically, they are functional, visual, and multiparadigm languages. Spreadsheets qualify as programming languages because all or most of them are Turing complete, except for the obvious memory/storage issue, which all real programming languages fail too; they can do loops via cyclic dependencies, and have more than enough logic. Disqualifying spreadsheets as programming languages, due to their different, non-linear format, suggests disqualifying all other languages with non-linear formats, such as all visual programming languages.
Many people find it easier to perform calculations, more so complex ones, in spreadsheets than by writing the equivalent sequential program. This power derives from two traits of spreadsheets.
- They use spatial relationships to define program relationships. Like all animals, humans have highly developed intuitions about spaces, and of dependencies between items. Sequential programming usually needs everything to be done by typing line after line of text, which must be read slowly and carefully to be understood and changed.
- They are forgiving, allowing partial results and functions to work. One or more parts of a program can work correctly, even if other parts are unfinished or broken. This makes writing and debugging programs much easier, and faster. Sequential programming usually needs every program line and character to be corect for a program to run. One error usually stops the whole program and prevents any result.
A spreadsheet program is designed to perform general computation tasks using spatial relationships rather than time as the primary organizing principle. Many programs designed to perform general computation use timing, the ordering of computational steps, as their primary way to organize a program. A well defined entry point is used to determine the first instructions, and all other instructions must be reachable from that point.
In a spreadsheet, however, a set of cells is defined, with a spatial relation to one another. In the earliest spreadsheets, these arrangements were a simple two-dimensional grid. Over time, the model has been expanded to include a third dimension, and in some cases a series of named grids. The most advanced examples allow inversion and rotation operations which can slice and project the data set in various ways.
The cells are functionally equivalent to variables in a sequential programming model. Cells often have a formula, a set of instructions which can be used to compute the value of a cell. Formulas can use the contents of other cells or external variables such as the current date and time. It is often convenient to think of a spreadsheet as a mathematical graph, where the nodes are spreadsheet cells, and the edges are references to other cells specified in formulas. This is often called the dependency graph of the spreadsheet. References between cells can take advantage of spatial concepts such as relative position and absolute position, as well as named locations, to make the spreadsheet formulas easier to understand and manage.
Spreadsheets usually attempt to automatically update cells when the cells on which they depend have been changed. The earliest spreadsheets used simple tactics like evaluating cells in a particular order, but modern spreadsheets compute a minimal recomputation order from the dependency graph. Later spreadsheets also include a limited ability to propagate values in reverse, altering source values so that a particular answer is reached in a certain cell. Since spreadsheet cells formulas are not generally invertable, though, this technique is of somewhat limited value.
Many of the concepts common to sequential programming models have analogues in the spreadsheet world. For example, the sequential model of the indexed loop is usually represented as a table of cells, with similar formulas. Cyclic dependency graphs produce the traditional construct known as the infinite loop. Most spreadsheets allow iterative recalculation in the presence of these cyclic dependencies, which can be either directly controlled by a user or which stop when threshold conditions are reached.
List of Spreadsheet Software
- Ability Spreadsheet
- AppleWorks
- Framework
- Gnumeric
- ExcelLite (.NET component)
- KDCalc
- KSpread
- Lotus 1-2-3
- Lotus Improv
- Lotus Symphony
- Origin
- Microsoft_Excel
- OpenOffice.org Calc
- Quantrix Modeler
- Quattro Pro
- SpreadsheetGear for .NET
- The Cruncher (for MacIntosh)
- VisiCalc
- ComplyXL
References
External links
General information
- A Brief History of Spreadsheets by D.J. Power
- A Spreadsheet Programming article on DevX
- comp.apps.spreadsheets FAQ by Russell Schulz
- Extending the Concept of Spreadsheet by Jocelyn Paine
- Develop Training Simulations with Excel
- Linux Spreadsheets by Christopher Browne; much general information on spreadsheets, and some on related Linux issues
- Software Arts and VisiCalc, by Dan Bricklin
- Spreadsheet - Its First Computerization (1961-1964) by Richard Mattessich
- "Spreadsheet Wars" - A classic video showing spreadsheet vendors going head-to-head in the late 80's .
Related software
- Calc OpenOffice spreadsheet (oo-Calc)
- KDCalc Excel compatible spreadsheet engine, converts Excel spreadsheets into web applications for HTML, Java, or .NET
- Microsoft Excel the most widely known and used spreadsheet
- ExcelLite by GemBox Software -- commercial .NET component for accessing Excel and CSV format files. Wiki: ExcelLite
- SpreadsheetGear for .NET Excel compatible spreadsheet component for .NET
- JotSpot Tracker Web-based spreadsheets
- iRows.com Web-based spreadsheets
- Numsum Web-based spreadsheets
- ComplyXL Version recording/management for compliance control of Excel workbooks. ComplyXL plugs a well know gap in Excel because it allows you to record versions. With this functionality you can determine later if changes have been made to a workbook, and display the changes on-screen. Versions are saved within the workbook so are always available to any user of the workbook but are invisible to Excel. Each version is encrypted and can be signed by the person who saves it so the version authenticity can be verified later. An optional comment can be added. ComplyXL can detect ANY change to a workbook and is not restricted to just cell data. Changes to cell formats, column width and row height, macros and many, many other attributes of a workbook will be detected. A graphical view allows you to visualize the changes made to the workbook. Changes to cells across different workbooks or versions are color coded to make the changes clear.
