A three –tier architecture:

Emerged period: 1990’s

It consists of Three layers:
1)User interface layer:
Either windows UI or web UI

2) Mid layer:

• Main function:  process management where business logic and rules are executed..

• Database staging, 
• queuing, 
• Application execution

3) DATA ACCESS LAYER:(DAL)
SQL usage for database operation..


Developed to overcome problems of two-tier architecture:
 
Features:

• Performance
• Re-usability
• Maintenance
• Flexibility
• Scalability
• Accommodate 100 of users to do perform operations listed in mid layer
• Hiding the complexity operations of database processing

Application:
Distributed client-server design