Many common Web-based apps and systems rely on a form of relational database (including this website!). A relational database is a sophisticated tool for storing information that will be combined in multiple, complex ways. Building and tending a useful database system is a little like gardening: they need planning, updating, and regularly weeding to be fruitful.  CMS systems like Wordpress and Drupal, and CRM systems like Salesforce and Beacon are front for relational databases. Keeping a MailChimp audience fresh and healthy also requires good management.