Database abstraction layer: Difference between revisions

Revision as of 23:46, 9 August 2018

Revision as of 03:33, 24 January 2019

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{{RefimproveMore citations needed|date=September 2014}}

A '''database abstraction layer''' ('''DBAL'''<ref>{{cite book|author1=Tim Ambler|author2=Nicholas Cloud|title=JavaScript Frameworks for Modern Web Dev|url=https://books.google.frcom/books?id=2IfDCgAAQBAJ&pg=PA346&dq=%22Database+abstraction+layer%22+DBAL&hl=en&sa=X&redir_esc=y#v=onepage&q=%22Database%20abstraction%20layer%22%20DBAL&f=false|titleyear=JavaScript Frameworks for Modern Web Dev2015|authorspublisher=Tim Ambler, Nicholas CloudApress|editorisbn=Apress978-1-4842-0662-1|datepage=13 October 2015346}}</ref>) is an [[application programming interface]] which unifies the communication between a computer application and [[database]]s such as [[MSSQL|SQL Server]], [[IBM DB2|DB2]], [[MySQL]], [[PostgreSQL]], [[Oracle database|Oracle]] or [[SQLite]]. 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. If an application has such a layer built in, it is called '''database-agnostic'''.<ref>http://searchdatamanagement.techtarget.com/definition/database-agnostic</ref>

== Database levels of abstraction ==

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Implementation of data types and operations are the most database specific at this level.

=== Conceptual or logical level (middle or next highest level) ===

The conceptual level consolidates external concepts and instructions into an intermediate data structure that can be devolved into physical instructions. This layer is the most complex as it spans the external and physical levels. Additionally it needs to span all the supported databases and their quirks, APIs, and problems.

This level is aware of the differences between the databases and able to construct an execution path of operations in all cases. However the conceptual layer defers to the physical layer for the actual implementation of each individual operation.

=== External or view level ===

The external level is exposed to users and developers and supplies a consistent pattern for performing database operations.

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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.

Alternatively, there are thin wrappers, often described as ''lightweight'' abstraction layers, such as OpenDBX<ref>{{cite web |url=https://www.linuxnetworks.de/doc/index.php?title=OpenDBX |title=OpenDBX |author==<!--Not stated--> |date=24 June 2012 |website=linuxnetworks.de |access-date=26 July 2018}}</ref><ref>{{cite web |url=https://en.wikipedia.org/wiki/Wikipedia:Articles_for_deletion/OpenDBX |dead-url=yes |title=OpenDBX | archive-url=https://web.archive.org/web/20060913000000/http://en.wikipedia.org:80/wiki/OpenDBX |archive-date=13 September 2006}}</ref>{{Better source|reason=per WP:CIRCULAR|date=August 2018}} and libzdb.<ref>{{cite web |url=http://www.tildeslash.com/libzdb/ |title=Libzdb |author==<!--Not stated--> |access-date=26 July 2018 |year=2018 |website=tildeslash.com}}</ref> Finally, large projects may develop their own libraries, such as, for example, libgda<ref>{{cite web |url=http://www.gnome-db.org/ |title=GNOME-DB |author==<!--Not stated--> |access-date=26 July 2018 |date=12 June 2015 |quote=Libgda library [...] is mainly a database and data abstraction layer, and includes a GTK+ based UI extension, and some graphical tools.}}</ref> for [[GNOME]].

== Arguments for ==

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=== Added Database Features ===

Depending on the database and the DAL, it may be possible for the DAL to add features to the database. A DAL may use database programming facilities or other methods to create standard but unsupported functionality, or completely new functionality. For instance the DBvolution DAL implements the standard deviation function for several databases that do not support it.

== Arguments against ==