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IPAT-S Philosophy

The IPAT-S language is a tool: it is a domain language for the domain of scenario development. It was designed with several practical goals in mind, arising from the author’s experience building sustainability scenarios. The IPAT-S suite includes:

• The IPAT-S interpreter, a program that processes IPAT-S scripts
• IPAT Studio, an integrated development environment (IDE) for IPAT-S
• IPAT Data eXchange (IPAT DX), a program for entering and sharing data
• IPAT Scenario Navigator (IPAT SN), a program for interactively exploring IPAT-S scripts

While each element of the suite can be used by itself, they are designed to work well together. Also, they can be used for quick studies or for more involved modeling efforts. For a description of how they can be used to support an involved scenario modeling effort, see the report Workflow Using IPAT-S (a PDF document) and the essay Numbers in Scenario Studies (also a PDF).

Primary goal

The primary goal of IPAT-S is to support rapid development of sustainability scenarios in a participatory process.

Most of the features of IPAT-S follow from this goal. The most important ones are:

• IPAT-S is a programming (scripting) language
  
  Because IPAT-S is a scripting language, it is very flexible: users can make the structure they desire, instead of being tied to someone else’s structure.
  
  
• IPAT-S features a compact syntax
  
  The compact syntax means that scenarios can be built rapidly, and the resulting scripts can be more easily understood than if they were in a general-purpose language like Fortran, C++ or Visual Basic.
  
  
• IPAT-S makes it easy to create new indicators
  
  Indicators are the key to communicating the outcome of a scenario study. In a participatory study, participants might ask for any kind of indicator to illustrate their points. The modeling team should be able to generate new indicators quickly, and IPAT-S makes this easy to do.
  
  
• The IPAT-S interpreter is fast
  
  Because most IPAT-S calculations are converted into fast C routines, the interpreter runs quickly, supporting rapid, interactive development of scenarios.
  
  
• IPAT-S is built around the IPAT framework
  
  The IPAT framework is intuitive, flexible and robust. By emphasizing that framework, scenarios can be developed quickly and communicated easily.
  
  
• IPAT-S improves on the IPAT framework
  
  Most of the factors in the IPAT equation can be given as growth rates, rather than levels. For example, the population growth rate is always important, but you may or may not need to know the level of population. IPAT-S encourages the use of growth rates when specifying problems.
  
  
• IPAT-S is free, and has free supporting tools
  
  Free software encourages participatory processes. Anyone who has an IPAT-S script can download the free interpreter, the IPAT Studio IDE or IPAT Scenario Navigator, run it, view outputs and modify the script if he or she wishes.

Other goals

Many other goals have driven specific features in IPAT-S:

• To encourage transparency and openness, and permit exchange over low-bandwidth connections
  
  The IPAT-S interpreter and IPAT Studio are open-source and freely downloadable, and scripts are text files - open format and very small.
  
  
• To encourage code documentation
  
  IPAT-S offers in-line and block comments, as well as self-documenting features of the language.
  
  
• To simplify development, from quick “sketch” to large study
  
  IPAT-S offers a compact syntax, flexible output formats and modularization through “subfiles”.
  
  
• To support disaggregated analysis
  
  Variables can have “dimensions” that are handled by IPAT-S.
  
  
• To support balances (energy, land, water, food, economy, etc.) and allow optimization sub-models
  
  IPAT-S offers a compact syntax for linear programming (LP) models.
  
  
• To allow extension through external libraries
  
  IPAT-S offers an API for external procedures that can be included using dynamic link libraries (DLLs).
  
  
• To allow other programs to run IPAT-S scripts and use the results
  
  IPAT-S takes a text file as input (the script) and produces a text file as output. Many languages, including Perl, Tcl/Tk, Ruby, PHP, C, C++, Visual Basic and Delphi, can run external programs and use the text output they produce. IPAT-S can be the engine behind the scenes for a custom-built scenario interface.
  
  

Backward compatability

Since it was first created in 2002, there have been many different versions of the IPAT-S language. However, with one exception, all versions have been backward compatible: almost any script written at any time should run under the most recent version of IPAT-S. If it doesn’t, then that is a bug.

The only exception to this is that the “N/A” notation was removed. It is not longer legal to write:

:: N/A >> ratio -> var   Don’t do this!

It never made much sense, and a much more sensible alternative has always been available. To update scripts using N/A, simply delete the N/A and they should run. Use this instead:

:: >> ratio -> var   This is correct