Web services allow two or more applications to share data and instructions with one another across the Internet.
The Migrate API can be used to import content from an older Drupal site (Drupal 7 or older), or any other data source, into the current version of Drupal.
Caching in Drupal
TopicCaching in Drupal is controlled by Drupal's Cache API which is used to store any type of data on a permanent or temporary basis. Some types of data tend to take a long time to compute, but utilizing the Cache API in your module can help your site load data more quickly.
Have you ever wondered "What is the difference between cache keys and cache tags?" One of our Drupalize.Me members wrote in asking about it, and the answer provides insight into how Drupal's Cache API works.
Develop Drupal Sites
Guide
Alter Drupal in Modules
Guide
Develop Custom Pages
Guide
Events
TopicEvents are one of the ways that module developers can alter or extend Drupal without modifying existing code.
Controllers
TopicControllers are the portion of a Drupal module that handle responding to an incoming request with the appropriate response data.