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Version 2.1 (released 8/9/2004)
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Changes:

* Now possible to build/run PRISM on Windows
* Compilation/installation procedures slightly simplified
* Splash screen on load


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Version 2.0 (released 17/3/2004)
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Changes:

* Completely new graphical user interface, including:
  - Text editor for PRISM language
  - Automated results collection/graph plotting
  
* Enhancements to PRISM language:
  - Types (ints, doubles and booleans) and type checking added
  - Probabilities/rates can now be expressions
  - Variable ranges/initial values can now be expressions
  - Constant/formula definitions can be expressions (including in terms of each other)
  - Process algebra style definitions allowed for MDPs too (via "system" construct)
  
* Enhancements to property specifications:
  - Probability/time bounds in PCTL/CSL properties can now be expressions
  - Use of constants now permitted: both those from the model and newly declared ones
  - Added "init" keyword to PCTL/CSL (atomic proposition true only in initial state)
  - Can define and reuse "labels" (atomic propositions) (like formulas in model files)
  - Can write properties of the form "P=?[...]" which return the actual probability
  
 * Additional features:
  - Automatic handling of multiple model checking computations,
    e.g. check "P~p[true U<=k error]" for k=1..100
  - Added -exportstates switch, exports reachable states to text file
  - Added -nobscc switch for optional bypass of BSCC computation
  - Added explicit versions of export options (including first export option for MDPs)
  - Export options can now be used in conjunction with each other and with model checking
  - Added -version switch to display version
  
* Efficiency improvements
  - Improved heuristics for hybrid engine (sb/sbmax/gsl switches -> sbmax/sbl/gsmax/gsl)
  - More efficient construction process for unstructured models
  - General restructuring/improvements to model construction process implementation
  
* Miscellaneous
  - Various bug fixes
  - Fairness (for MDP model checking) now OFF by default (used to be ON)


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Version 1.3.1 (released 20/2/2003)
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Changes:

* Bug fixes in model construction code


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Version 1.3 (released 10/2/2003)
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Changes:

* Steady-state probability computation improved to include strongly connected component (SCC) computation
* Extended support for CSL time-bounded until operator to include arbitrary intervals
* More flexible parallel composition options in the PRISM language (for DTMCs and CTMCs)
* Added option to import PEPA process algebra descriptions as models
* Improved range of numerical methods: (Backwards) Gauss-Seidel and (Backwards) SOR (plus variants for hybrid engine)
* Added -pctl/-csl switches to allow command line specification of properties
* Improved handling of deadlock states: can add self-loops to these states automatically (e.g. -fixdl switch)
* Steady-state probabilities are no longer automatically computed for CTMCs: use the -ss switch
* Addition of {} operator to PCTL/CSL formulas to support printing of probabilities
* Resolved problem with PRISM language syntax: updates must now be parenthesised
* Default value for maximum number of iterations reduced from 500,000 to (more sensible) 10,000
* Added switches to control CUDD behaviour (-cuddmaxmem, -cuddepsilon)
* Additional example files
* Numerous bug fixlatest.htmles
* Now released under the GPL license


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Version 1.2 (released 17/9/2001)
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First public release