What is "data access object"

n. (context computing English) an object in programming that provides an abstract interface to some type of persistence mechanism, providing some specific operations without exposing details of the persistence layer.

In computer software, a data access object (DAO) is an object that provides an abstract interface to some type of database or other persistence mechanism. By mapping application calls to the persistence layer, DAO provide some specific data operations without exposing details of the database. This isolation supports the Single responsibility principle. It separates what data accesses the application needs, in terms of domain-specific objects and data types (the public interface of the DAO), from how these needs can be satisfied with a specific DBMS, database schema, etc. (the implementation of the DAO).

Although this design pattern is equally applicable to the following: (1- most programming languages; 2- most types of software with persistence needs; and 3- most types of databases) it is traditionally associated with Java EE applications and with relational databases (accessed via the JDBC API because of its origin in Sun Microsystems' best practice guidelines "Core J2EE Patterns" for that platform).