The document discusses N-tier application design, which involves breaking an application into well-defined regions or tiers, typically including a user interface (UI) tier, service tier, and data tier. Common mistakes in N-tier design include having the UI tier directly coupled to the data tier or duplicating validation logic across tiers. N-tiering addresses these issues by enforcing clear separation between tiers, encapsulating business rules in the service tier, and allowing new UIs to be developed without impacting existing applications.

1. NTiering A guide to N-Tier application design

2. NTiering A guide to N-Tier application design Badly Drawn Bob, NTiering logo

3. The Good Old Days An application typically used command line Performed only one function Used by trained operators

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

5. 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

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

7. What does it look like? Typically 3 layers (or tiers) UI Service Data

8. What does it look like? Typically 3 layers (or tiers) UI Service Data

9. What does it look like? Common Mistakes ! UI Service Data DTO / Common Classes

10. What does it look like? Common Mistakes ! UI Service Data DTO / Common Classes Using a common class to Move data means the UI Layer is coupled to the data layer

11. What does it look like? Common Mistakes ! UI Service Data Validation Validation Validation

12. What does it look like? Common Mistakes ! UI Service Data Validation Validation Validation Repeated validation is the single most common mistake in n-tier apps. Not only does this duplicate effort, but What happens if the validation changes on the data layer but not in the UI

13. 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

14. What does NTiering look like? 3 Tier application UI Service Data

15. What does NTiering look like? 3 Tier application UI Ntiering. UIExample Service Ntierning. Service Data Ntierning. Data

16. What does NTiering look like? 3 Tier application UI Ntiering. UIExample Service Ntierning. Service Data Ntierning. Data Models DTO's Customer Service Order Service

17. What does NTiering look like? 3 Tier application UI Ntiering. UIExample Service Ntierning. Service Data NTierning.Data Models DTO's Customer Service Order Service Models invoke validation using Services, allowing new UI's To be developed Add new services without impact to existing application No longer tied to one database provider Change UI easily. Business logic is in the service layer

18. 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