Fields (Content building blocks)
Fields are the building blocks of content in Drupal. For example, all content types (e.g. “Article”, or “Basic Page”) provide content to the end-user via fields that are bundled with the content type. For example, when adding a basic page (a default Drupal content type), the end-user is provided with form elements (or widgets) that allow the user to set the title and the body text for the page. The “Body” is a field. When a basic page is viewed, the body is rendered on the page using formatters, and Drupal stores the values for the body in the database. Every field, therefore, provides three types of functionality: instructions for storage, widgets for allowing input, and formatters for rendering.
Drupal provides a variety of built-in fields, and extension module developers have created a multitude of new fields that can be added by the site admin to add new functionality and support new types of data. Tripal follows this model, but adds a variety of new object oriented classes to support storage of data in biological databases such as Chado.
Note
Not every custom module will require fields. But if you need a new way to store and retrieve data, or if you need data to appear on an existing Tripal content type, then you will want to create a new field for your custom module.