Global Health Policy Simulation model

Configuration and JSON schemas

Health-GPS validates experiment inputs with JSON Schema. Schemas live in the repository under schemas/; the Console loads them from the copy next to the built binary. Your config.json should declare which root schema it follows via the $schema URL.

This page explains how schemas fit together and where to look when validation fails. For field-by-field config guidance and examples, use the User Guide - Configuration. For machine-readable definitions, open the JSON files on GitHub or in your clone.

What gets validated

Input	Typical file	Root schema (v1 path)
Experiment configuration	`config.json`	`schemas/v1/config.json`
Backend data catalogue	`data_index.json` (in downloaded data)	`schemas/v1/data_index.json`
Risk-factor / model JSON	Paths under `modelling`	e.g. `config/models/kevinhall.json`, `hlm.json`, `dynamic.json`, …

At startup the CLI parses JSON, resolves $ref links to sub-schemas (data, inputs, modelling, running, output, model-specific files), and reports validation errors before a long run. Use --dry-run to validate without executing trials (see Developer Guide).

Top-level `config.json` structure

The root schema composes several sections. Optional blocks (such as project_requirements, population_impact_fraction, or output.individual_id_tracking) extend behaviour for FINCH, India, PIF, and per-person tracking without replacing the core layout.


Root `config.json` sections and linked sub-schemas (wide diagram — open the image for full size)

Section	Role
`version`	Config format version (see root schema `const`)
`project_requirements`	Per-project switches: demographics dimensions, income categories, PA, trends (schema)
`data`	Where to fetch or find the backend datastore
`inputs`	Country code, population fraction, age range, validation CSV
`modelling`	SES, risk-factor hierarchy, model file references, baseline adjustments
`running`	Random seeds, trial count, baseline/intervention scenarios
`output`	Result folder, filenames, optional individual ID tracking
`population_impact_fraction`	Optional PIF analysis block

Worked JSON skeleton: examples/config_skeleton.json. Project packs: HealthGPS-examples.

Backend `data_index.json`

Downloaded or local datastore bundles describe countries, demographics, diseases, and analysis metadata in a separate index file. It uses its own root schema and is validated when the Console loads data.


Datastore bundle: `data_index.json` points at country, demographic, disease, analysis, and PIF tables

See User Guide - Backend storage for how this connects to config.json data.

Schema versions (v1, v2, unified)

The repository may contain more than one schema tree while projects migrate:

Tree	Typical use	Notes
`schemas/v1/`	STOP / HLM France, India, many current examples	Root `$schema` URLs often point at `.../main/schemas/v1/config.json`
`schemas/v2/`	Extended FINCH-style model definitions	Extra properties on some model schemas
`schemas/config/`	Target unified layout	Described in the schema migration plan

Your $schema URL must match the tree the Console expects for that release. If validation fails after upgrading Health-GPS, compare your config’s $schema with the example pack for your project and read the update report (config/schema section).

Legacy fields (for example top-level income_categories or trend_type) may still parse when project_requirements is omitted; the root schema marks many of these as deprecated in favour of project_requirements.

How validation works at run time

sequenceDiagram
    participant User
    participant Console as HealthGPS.Console
    participant Local as schemas/ next to binary
    participant Ref as $ref sub-schemas

    User->>Console: -c config.json
    Console->>Console: Read config $schema URL
    Console->>Local: Load vN/config.json + resolve_uri
    Local->>Ref: config/data.json, modelling.json, …
    Console->>Console: validate_json
    alt invalid
        Console-->>User: Schema error (path, message)
    else valid
        Console->>Console: Load CSVs, run simulation
    end

Schema URLs use the prefix https://raw.githubusercontent.com/imperialCHEPI/healthgps/main/schemas/; the Console maps that prefix to {program_dir}/schemas/ (see src/HealthGPS.Input/schema.cpp). Editing $schema in config without updating the matching files under schemas/ in your build causes “Unable to load URL” or validation mismatches.

When validation fails

Read the first schema error (JSON pointer + message).
Open the cited sub-schema on GitHub (table above) or in schemas/v1/config/... in your clone.
Compare with a known-good config (FINCH, France, India).
Run with --dry-run after fixes.
For new optional features (project_requirements, income strata, ID tracking), see the matching technical plans and FINCH guide.

Topic	Document
Config sections and examples	User Guide - Configuration
`project_requirements`	User Guide - Project requirements
Output / ID tracking schema	User Guide - Output
v1 unified migration	Schema migration plan
Architecture / inputs	Software Architecture

Author: Mahima Ghosh