.. _external_classifiers:

====================
External Classifiers
====================

External classifiers (third-party) are those which rely on a REST API request for their service.

If an external classifier is used as the local classifier, the instance will act as a proxy for classification.

The only requirement for third-party classifiers is to implement the classification endpoints (see :ref:`rest_api_classify`).

Set up is done by the admin interface of the instance (``/admin/base/externalclassifier``).

**Remote User** reffers to the user the instance will use to authenticate its requests to the external classifier. That authentication is done via a token that the external service must generate and provide to the ``covid-ht`` instance.

**Metrics** are those to be evaluated on the external classifier with the data in the instance. The purpose of them is to evaluate how the classifier performs with the data generated from the instance's population, as the classifier may have been trained or inferred with another population and / or with different fields or variables.

Note that these metrics are **not cross-validated** and hence a "not-so-accurate" estimation of their real or true values (`cross-validated estimations <https://en.wikipedia.org/wiki/Cross-validation_(statistics)>`_ are done at training time) for the instance's population.

If those metrics are not in line with the cross-validated ones reported by the external service, the classifier may not be suitable for the instance's population.

The list of available metrics is `here <docs.scikit-learn>`_.

Values of these metrics, as well as supported and non-available fields differences are calculated and stored in the metadata which can be updated with the link at the bottom of the page of its admin interface.

Other Considerations
====================

Network Nodes are also External Classifiers (which also can share data) and will be listed as such.

If you want the instance to proxy its classification to another instance, set the External Classifier of the Node as the Local Classifier.

If you want to include the External Classifier as a vote in the classification service of the instance, create a Node with no data sharing.

`The R community provides`_ what can be regarded as the most comprehensive implementations of statistical techniques which allows Reproducible Research.

It makes to sense prototyping a classifier in a foreign language (to python) and integrate it as an External Service.

R users may do this with the `plumber`_ package.

Once the classifier is providing the desired results, porting to an Internal Classifier should be evaluated in order to improve system perfomance, reduce complexity and sharing with the network and / or ecosystem.

.. _plumber: https://www.rplumber.io/
.. _The R community provides: https://cloud.r-project.org/web/packages/index.html