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====== Tool On Objects Language ======

Tools-On-Objects Language, is an interactive language for manipulating structured data objects including multi-dimensioned arrays, sets and geometric objects.  TOOL is the only language needed throughout the whatIf? platform.

===== History =====

TOOL inspired by other array languages such as:
  * APL (a programing language)[[http://en.wikipedia.org/wiki/APL_%28programming_language%29]]
  * S (a statistical programing language) [[http://en.wikipedia.org/wiki/S_%28programming_language%29]]

One of the main concepts taken from these is that one object can inform another.  This is used extensively in TOOL for the dimensions of variables.  Each dimension of a variable is one of 3 types of objects: set, category, or sequence. 

===== One Language to Rule Them All =====
 
TOOL is used throughout the whatIf? platform and is the only language the modeller will need to know.  

In the process of building and using a model there are 4 places where code is required and typically there are at least 2 languages to accomplish these tasks:
  * Preparation and manipulation of historical data
  * Model implementation
  * Data input creation 
  * Displaying data and report writing

In the whatif platform TOOL is used for all of those tasks, more specifically:
  * coding the model itself through a customized editor with features to simplify coding
  * importing/exporting and manipulating data as various types of files and formats: [[concepts:tool#Import/Export channels]]
  * interact with the user to allow them to create data
  * display and analyze data by manipulating the data and displaying tables, graphs, and maps
  * interactively test code and check data through a TOOL console


===== 4GL =====

TOOL is fourth-generation programming language (abbreviated 4GL) [[http://en.wikipedia.org/wiki/4GL]] specifically designed for handling large arrays of multi-dimensional data.  This makes it well suited for model building.

Specialized algorithms for model building are built into TOOL for efficiency and simplicity and they are called tools.  There are currently 137 tools in TOOL and this list is ever growing as a need arises. Here are a few common modelling constructs built into TOOL:
  * Stock flow in various forms for the evolving stocks over time
  * Population cohort model
  * Convolution 
  * Life table
  * ...and many more!



===== Multidimensional Support =====

TOOL handles multidimensional arrays (objects) in a way that makes the math as simple as working with single value variables.  For example to multiply a population stock variable which is broken down by region(reg), gender(gen), time(t) and age(a) by a survival rate by only region time and age the math is simply:
<code>
survivors[reg,gen,t,a] = population[reg,gen,t,a] * survivalRate[reg,t,a]
</code>
TOOL automatically handles the mismatch of dimensions by using the same survival rate for each gender and produces a 4 dimensional output.  All TOOL functions handle multidimensional objects.

===== Dimensional Analysis =====
FIXME

explain "shape" and TOOL inheritance

===== Unit Conversions Handled  =====

All the data stored in TOOL objects is stored in its primary SI units (International System of Units). The units the data is to be displayed, called the alternate unit of measure (altUom), in is set on the object to simplify viewing data.  The relationship between any altUom and SI units are specified in a conversion table. 

For example consider a petajoule and a tonne in SI units,

1e-15 petajoule = 1 m<sup>2</sup>kg/s<sup>2</sup> 

0.001 tonne = 1 kg

is represented internally as: 

| altUom | m | kg | s | C | rad | sterad | conversion |
| petajoule | 2 | 1 | -2 |  | | | 1e-15 |
| tonne |  | 1|  |  |  |  | 0.001 |

===== Import/Export channels  =====

TOOL is used to read and write data external to the model and it supports various formats and file types:

Formats:
  * Record 
  * Coordinate 
  * Odometer

File Types:
  * CSV files 
  * Delimited files - any character but tab is most common
  * dbf
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