An API or "Application Programming Interface" is a library (for example, C++ or Java) that allows you to link an application to another application by accessing entry points and enabling data exchange between the two applications. For that to be possible, the target application has to have one or more entry points that accept specific data. In 4D Server's case, a list is available that describes the entry points that can be used (see below).

4D's APIs allows communication with 4D Server using functions that fall into four main categories:

Access control: groups and password management.
Structure access: retrieval of structure information (list of field/tables and their attributes).
Selection access: creation of record selections through queries, navigation through selections, creation of temporary selections, and so on.
Data access: creation, edition and deletion of records while respecting a multi-user architecture.
There are 4D Open libraries available for 4th Dimension itself (in the form of a 4D Plug-in), for Java (as class libraries), and for C, C++ or Pascal as a shared library. All of these can be downloaded from the 4th Dimension product downloads page at:

http://www.4D.com/downloads/products.html