n tiering

NTiering

A guide to N-Tier application design

NTiering

A guide to N-Tier application design

Badly Drawn Bob, NTiering logo

The Good Old Days

An application typically used command line Performed only one function Used by trained operators

Nowadays !

Complex GUI's Multiple functions in one application Apps expect little or no user training

What is N-Tier?

The practice of breaking an application into well defined regions.

Each region has high cohesion Well defined paths into each regions

Advantages

Lower TOC (total cost of ownership) Less “code rot” Looser coupling

What does it look like?

Typically 3 layers (or tiers)

UI ServiceData

What does it look like?

Typically 3 layers (or tiers)

UI ServiceData

What does it look like?

Common Mistakes !

UI ServiceData

DTO / Common Classes

What does it look like?

Common Mistakes !

UI ServiceData

DTO / Common Classes

Using a common class toMove data means the UI

Layer is coupled to the data layer

What does it look like?

Common Mistakes !

UI ServiceData

ValidationValidation

Validation

What does it look like?

Common Mistakes !

UI ServiceData

ValidationValidation

Validation

Repeated validation is the single most common mistake in n-tier apps.

Not only does this duplicate effort, butWhat happens if the validation

changes on the data layer but not in the UI

How does NTiering fix this?

Enforces clear separation of tiers Encapsulates validation (business rules) in the

service layer Provides tools to produce “boiler plate” code

What does NTiering look like?

3 Tier application

UI ServiceData

What does NTiering look like?

3 Tier application

UINtiering.UIExample

ServiceNtierning.Service

DataNtierning.Data

What does NTiering look like?

3 Tier application

UINtiering.

UIExample

ServiceNtierning.Service

DataNtierning.

DataModels

DTO's

Customer Service Order Service

What does NTiering look like?

3 Tier application

UINtiering.

UIExample

ServiceNtierning.Service

DataNTierning.Data

Models

DTO's

Customer Service Order Service

Models invoke validation usingServices, allowing new UI's

To be developed

Add new services without impact to existing application

No longer tied to one databaseprovider

Change UI easily. Business logic is in the service layer

What does it cost ?

Free (as in beer!). Use it anyway you see fit. See Licence.txt Need help ? Mail me

simonsmith.uk@gmail.com