what is data access layer ?

Answer:

Data Access layer is a part of Architecture layer.
This Architecture layer has 2 tier,3 tier or N tier Layer.
Generally we use 3 tier Layer.
1) Presentation layer,Business Logic layer and then Data Access Layer.
Data Access layer is a medium to talk between database and Business Logic layer. It helps to maintain flexibility,reusability and even security also. In security SQL Injection can be stopped with 3 tier Architecture.