Three-Tier Architecture:
Three-tier architecture typically comprise a presentation tier, a business or data access tier, and a data tier. Three layers in the three tier architecture are as follows:
1) Client layer
2) Business layer
3) Data layer
1) Client layer:
It is also called as Presentation layer which contains UI part of our application. This layer is used for the design purpose where data is presented to the user or input is taken from the user. For example designing registration form which contains text box, label, button etc.
2) Business layer:
In this layer all business logic written like validation of data, calculations, data insertion etc. This acts as a interface between Client layer and Data Access Layer. This layer is also called the intermediary layer helps to make communication faster between client and data layer.
3) Data layer:
In this layer actual database is comes in the picture. Data Access Layer contains methods to connect with database and to perform insert, update, delete, get data from database based on our input data.
- See more at: http://www.softwaretestingclass.com/what-is-difference-between-two-tier-and-three-tier-architecture/#sthash.liLyFj1n.dpuf