Data access layer: Difference between revisions

Revision as of 03:30, 8 December 2010

Revision as of 06:05, 26 January 2011

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A '''data access layer''' (DAL) is a [[layer (object-oriented design)|layer]] of a [[computer program]] which provides simplified [[access]] to [[data]] stored in [[persistent storage]] of some kind, such as an [[entity relationship|entity-relational]] [[database]]. This layer is mainly responsible for maintaining the integrity of the database and the underlying database engine is also placed here.<ref>[http://www.aspnetbook.com/basics/app_design_two_layer.php Data Access Layer] Two-Layer Architecture ASPNET Book 2010</ref>

For example, the DAL might return a reference to an [[object (computer science)|object]] (in terms of [[object-oriented programming]]) complete with its attributes instead of a [[row]] of [[Field (computer science)|fields]] from a database [[table (database)|table]]. This allows the client (or user) modules to be created with a higher level of [[abstraction]]. This kind of model could be implemented by creating a class of data access methods that directly reference a corresponding set of database stored procedures. Another implementation could potentially retrieve or write records to or from a file system. The DAL hides this complexity of the underlying data store from the external world.