About OpenFisca
OpenFisca is the most widely adopted free and open-source engine for coding rules and legislation. It’s lightweight, modular and scalable, and uses Python. OpenFisca was initially developed by the French Government in 2011 to codify the French social security benefits.
At a high level, the OpenFisca coding follows five stages:
- Write test scenarios
- Create entities
- Define parameters
- Create input variables
- Create output variables (using formulas)
Test scenarios: OpenFisca uses test-driven development (TDD), so before you start coding you build test scenarios. These test scenarios are then used to build the Python code out.
Entities: OpenFisca’s concept of entities means rules can be defined for different kinds of entities like person, household.
Parameters: A parameter is a property of the rule that changes over time. The parameters have description, reference and values.
Input variables: Variable attributes include value_type, entity, definition_period, label and reference.
Output variables: The values for output variables is actually a formula. The formula takes the defined parameters and the input variables and then calculates the output.
You can find out more do an OpenFisca tutorial at https://openfisca.org/doc/coding-the-legislation/index.html
Version control in OpenFisca
OpenFisca includes versioning attributes, which makes it easy to create a new rule that will come into effect on a certain date. OpenFisca keeps the historical rules and values, plus the current ones, and you can set up future ones too.