A database abstraction layer is an application programming interface

Application programming interface

An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...

 which unifies the communication between a computer application and database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

s such as SQL Server, DB2

IBM DB2

The IBM DB2 Enterprise Server Edition is a relational model database server developed by IBM. It primarily runs on Unix , Linux, IBM i , z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions...

, MySQL

MySQL

MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...

, PostgreSQL

PostgreSQL

PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...

, Oracle

Oracle database

The Oracle Database is an object-relational database management system produced and marketed by Oracle Corporation....

 or SQLite

SQLite

SQLite is an ACID-compliant embedded relational database management system contained in a relatively small C programming library. The source code for SQLite is in the public domain and implements most of the SQL standard...

. Traditionally, all database vendors provide their own interface tailored to their products which leaves it to the application programmer to implement code for all database interfaces he or she would like to support. Database abstraction layers reduce the amount of work by providing a consistent API to the developer and hide the database specifics behind this interface as much as possible. There exist many abstraction layers with different interfaces in numerous programming languages.

API level abstraction

Libraries like OpenDBX

OpenDBX

The OpenDBX library provides a unified and consistent API for software developers to different database management systems. The function library is written in the C programming language and aims at implementing access to the native database interfaces efficiently via a thin abstraction layer...

 unify access to databases by providing a single low-level programming interface to the application developer. Their advantages are most often speed and flexibility because they are not tied to a specific query language (subset) and only have to implement a thin layer to reach their goal. The application developer can choose from all language features but has to provide configurable statements for querying or changing tables. Otherwise his application would also be tied to one database.

Popular use for database abstraction layers are among object-oriented programming

Object-oriented programming

Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...

 languages, which are similar to API level abstraction layers. In an object oriented language like C++ or Java, a database can be represented through an object

Object (computer science)

In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...

, whose methods and members (or the equivalent thereof in other programming languages) represent various functionalities of the database. They also share the same advantages and disadvantages as API level interfaces.

Language level abstraction

An example of a database abstraction layer on the language level would be ODBC. ODBC is a platform-independent implementation of a database abstraction layer. The user installs specific driver-software, through which ODBC can communicate with a database or set of databases. The user then has the ability to have programs communicate with ODBC, which then relays the results back and forth between the user programs and the database. The downside of this abstraction level is the increased overhead to transform statements into constructs understood by the target database.

Development period

Software developers only have to know the database abstraction layer's API instead of all APIs of the databases his application should support. The more databases should be supported the bigger is the time saving.

Wider potential install-base

Using a database abstraction layer means that there is no requirement for new installations in utilise a specific database, i.e. new users who are unwilling or unable to switch databases can deploy on their existing infrastructure.

Developer Testing

A production database may be replaced with a desktop level implementation of the data for developer level unit tests.

Speed

Any abstraction layer will reduce the overall speed more or less depending on the amount of additional code that have to be executed. The more a database layer abstracts from the native database interface and tries to emulate features not present on all database backends, the slower the overall performance. This is especially true for database abstraction layers that try to unify the query language as well like ODBC.

Dependency

A database abstraction layer provides yet another functional dependency for a software system, i.e. a given database abstraction layer, like anything else, may eventually become obsolete, outmoded or unsupported.

Masked operations

Database abstraction layers likely limit the number of available database operations to a subset of those supported by the supported database backends. In particular, database abstraction layers may not fully support database backend-specific optimizations or debugging features. These problems magnify significantly with database size, scale, and complexity.