GdaServerProvider — Base class for all the DBMS providers
Subclassing GdaDataSelect — Base class for all the data models returned by DBMS providers when a SELECT statement is executed
GdaPstmt — Base class for prepared statement's
Quark list — Manages lists of KEY=VALUE pairs
SQL rendering API — Adapting the SQL to the database's own SQL dialect
Misc API for database providers — Methods dedicated to implementing providers

For each database engine, Libgda requires an object which maps Libgda's API to the native API offered by that database engine. That object, a database provider needs to inherit GdaServerProvider and implement its virtual methods.

Database provider objects are generally instantiated once by the Libgda framework and can be used several times to open and work on connections to several databases of the same type.

Since Libgda itself is developed in the C language, and that most providers are also implemented in that language, the Libgda library itself contains a set of helper classes and functions to guide you in the addition of a new provider to the GDA framework. Two reference implementations are provided in the providers/skel-implementation directory of Libgda's sources:

in providers/skel-implementation/capi: a skeleton implementation from scratch for a database accessed through a C API, where all the methods to implement are partially coded
in providers/skel-implementation/models: a skeleton implementation to write a provider for sources which are not databases (which do not implement any SQL) such as the Berkeley DB provider (a BDB database is a key/value collection) or the MDB (MS Access files) provider. This kind of provider "export" tables which are in fact data models.

The helper objects and functions to write database providers are documented in the Providers' support API section.