A Data access layer is a layer of a computer program which provides simplified access to data stored in persistent storage of some kind, such as an entity-relational database. This Data Access Layer is used in turn by other program modules to access and manipulate the data within the data store without having to deal with the complexities inherent in this access. For example, the DAL might return a reference to an object (in terms of object-oriented programming) complete with its attributes instead of a row of fields from a database table. This allows the client (or using) 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 which directly reference a corresponding set of database stored procedures. Another implementation could potentially retrieve or write records on to a file system. The DAL, hides from the external world, this complexity of the underlying data store. Consider that you have to interact from a specific table in the database (like insert, delete, update) then you just create a class and a few stored procedures in the database, where you call those Stored Procedures from a method inside the class. and class in return on the coding side will return an object containing the requested values. Object-Relational Mapping tools provide data layers in this fashion, following the Active Record model.
