What PyRel is, and when you need it

You don't need PyRel to use GND. GND checks models, data and plans with its own checker, which installs with gnd and needs no account, no database and no extra runtime. Everything in the tutorials works that way.

PyRel is an optional extension, for when the facts you want to check live in your company's data platform rather than in files.

Files on GitHub

pyrel_rules.py: the code that writes the PyRel programs
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What PyRel is

PyRel is RelationalAI's Python library (the relationalai package) for writing relational models and queries in Python. The same PyRel program can run in two places:

Where	What you need	What it is for
On your laptop, with DuckDB	the `relationalai` and `duckdb` packages; no account	prototyping: the facts are local files
On RelationalAI's Native App for Snowflake	a Snowflake account with the RelationalAI app	your enterprise data, where it already lives

What GND does with it

GND can write a PyRel program from a model, so the rules you wrote once are checked by PyRel too. gnd export pyrel MODEL --rules duckdb writes a program that runs locally on DuckDB and reports the facts that break each rule. gnd export pyrel MODEL --rules lqp writes the same rules as PyRel requirements for a RelationalAI engine.

What has been tested

Path	Status in GND
GND's own checker	the default; everything in the docs uses it
The PyRel program on DuckDB, locally	tested: it agrees with GND's checker on every recorded plan in these docs
The PyRel program on a RelationalAI engine, such as the Snowflake Native App	compiled and counted, not yet run; Snowflake execution is not yet supported by gnd export

So you can prototype with GND alone, check the same rules on PyRel locally when you want to see them as PyRel, and plan for Snowflake knowing that this last step is not yet tested.

Set up PyRel locally

PyRel runs in its own Python environment, separate from GND's, and GND finds it through GND_PYREL_PYTHON. The PyRel applications page shows how to create that environment and set the variable. Then add --backend pyrel to an example app's check or ask command.