Introduction

At its very beginning, Tripal was created to enable the use of Chado schema under Drupal CMS. Since its version 3, Tripal design changed in order to be ontology driven (like Chado) but database agnostic. However, Tripal version 3 was only able to support the Chado database schema. With version 4, a new biological database layer has been added: the Biological Database layer. This layer provides a database API extending Drupal database API that enables the use of other database schemas in Drupal. While it is currently limited to PostgreSQL database type, it has no number or type of schema limit. It means that it supports querying more than one schema at a time, and it is not limited to Chado or Drupal.

Since the Biological Database layer is an API, it does not work on it own but is rather a basis to build other extensions that will work on proprietary schema definitions like Chado. Therefore, the Tripal Chado extension is provided within Tripal package as an implementation of the Biological Database Layer for Chado.

To sum up:

• The Biological Database API provides an abstraction layer to support any biological database schema.

• It supports multiple schemas and cross-schema queries.

• Tripal Chado extension is an implementation of the Biological Database API to support Chado schema.