n-tier Architecture

Presentation Layer

 

Here is decided HOW data should appear to the user

Sometimes referred to as the client (not entirely true!!!)

 

Application Logic Layer

Data Processing ('The actual Program')

Here the algorithms are implemented

This Layer is often referred to as

–         services

–         business logic

–         business rules

–         server

 

Resource Management Layer

 

Deals with and implements different data sources of IS

Is the 'data layer' in a restricted interpretation (Database Management System)

Can also be an external system, which recursively uses other ISs

 

 

1 – tier Architectures

 

Were used decades ago..

Monolithic Information Systems

Presentation, application logic, and resource management were merged into a single tier

Many of these 'old' Systems are still in use!

 

Advantages:

Easy to optimize performance

No context switching

No compatibility issues

No client developement, maintainance and deployment cost

Disadvantages:

Monolithic pieces of code (high maintainance)

Hard to modify

Lack of qualified programmers for these systems

 

 

2 - tier Architectures

 

Separation of presentation layer from other 2 layers (app + resource) 

Became popular as 'server/client' systems

Thin clients/fat clients

RPC (Remote Procedure Call)

API (Application Program Interface)

Need for standardization

Advantages

Portability

No need for context switches or calls between component for key operations

Disadvantages

Limited scalability

Legacy problems (blown up clients

 

3 - tier Architectures

 

Can be achieved by separating RM (resource management) from application logic layer

Additional middleware layer between client and server

Integration logic

Application logic

Lead to the introduction of clear RM layer interfaces

Good at dealing with integration of different resources

 

Advantages

Scalability by running each layer on a different server

Scalability by distributing AL (application logic layer) across many nodes

Additional tier for integration logic

Flexibility

Disadvantages

Performance loss if distributed over the internet

Problem when integrating different 3 – tier systems

 

n - tier Architectures

 

2 cases of n – tier

Systems linked with added connectivity through the internet

Resource layer is a full fledged 2 - or 3 - tier system

 

Advantages

Better scalability

Higher fault tolerance

Higher throughput for less cost

Disadvantages

Too much middleware involved

Redundant functionality

Difficulty and cost of development