8. Importing other models¶

A model file can (optionally) import (an)other model file(s). An import directive can take two forms:

import: path\filename.yml

or

import:
    - path1\filename1.yml
    - path2\filename2.yml

Each file in the import section will be merged with the current file in the order it appears. Merging means that fields, links, macros and processes from the imported file are added to the ones of the current file. If there is a conflict (something with the same name is defined for the same entity in both files), the “current” file (the model importing the other model) takes priority. This means one can override entity processes defined in imported files, or add fields to an entity defined in the imported model.

Note that both the importing model and the imported model need not be complete/valid models (they do not need to include all required (sub)sections), as long as the combined model is valid. See the examples below.

example (common.yml)

entities:
    person:
        fields:
            - age:      int
            - agegroup: {type: int, initialdata: False}

        processes:
            ageing():
                - age: age + 1
                - agegroup: trunc(age / 10)

simulation:
    processes:
        - person: [ageing]

    # we do not specify output so this model is not valid in itself
    input:
        file: input.h5

    start_period: 2015
    periods: 2

example (variant1.yml)

import: common.yml

entities:
    person:
        processes:
            # override the ageing process
            ageing():
                - age: age + 1
                - agegroup: if(age < 50,
                               5 * trunc(age / 5),
                               10 * trunc(age / 10))

simulation:
    # provide the required "output" section which is missing in common.yml
    output:
        file: variant1.h5

example (variant2.yml)

import: common.yml

entities:
    person:
        fields:
            - severe_illness: {type: bool, initialdata: False}

        processes:
            # adding new processes
            illness():
                - severe_illness: uniform() < 0.001

            death():
                - dead: logit_regr(0.5 * severe_illness,
                                   align='al_p_dead.csv')
                - show('Avg age of death', avg(age, filter=dead))
                - remove(dead)

simulation:
    # since we have new processes, we have to override the *entire* process
    # list, as LIAM2 would not know where to insert the new processes
    # otherwise.
    processes:
        - person: [ageing, illness, death]

    output:
        file: variant2.h5

Imported models can themselves import other models, as for example in variant3.yml.

example (variant3.yml)

import: variant2.yml

entities:
    person:
        processes:
            # use the "alternate" ageing function
            ageing():
                - age: age + 1
                - agegroup: if(age < 50,
                               5 * trunc(age / 5),
                               10 * trunc(age / 10))

This last example could also be achieved by importing both variant1.yml and variant2.yml. Notice that the order of imports is important, since it determines the result of conflicts between variants. For example in variant4.yml below, the process list will be the one from variant2 and the output will go in variant2.h5.

example (variant4.yml)

import:
    - variant1.yml
    - variant2.yml