Dataset definitions written in ehrQL can be run inside different secure

environments, managed by different providers of EHR data.

For each such secure environment, there is a corresponding "backend"

defined in ehrQL. Each ehrQL backend:

* specifies the datasets available inside each secure environment

* does the necessary translation work to allow the same

  dataset definition to run against data modelled in different ways and

  stored in different systems

When writing a dataset definition you don't need to explicitly reference

any particular backend. But, as not every dataset is available in every

backend, the [table schema](schemas.md) you use to write your dataset

definition will determine which backends it can be run against.

Below are the backends currently supported in ehrQL, together with the

list of [table schemas](schemas.md) each one supports.

---8<-- 'includes/generated_docs/backends.md'