Layered Software Architecture

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Lars-Erik KindbladSenior ConsultantBlog: kindblad.com

Layered Architecture

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Agenda Logical Layer Architecture Example Code Physical Tier Architecture Logical Layer vs Physical Tier Architecture Summary Questions

LOGICAL LAYER ARCHITECTURE

3-Layer Architecture

Presentation Layer Also known as Frontend Layer, User Interface (UI) Layer

Responsible for creating and displaying the user interface and handling user interaction

Data shown is fetched from the Domain Layer

Service Layer Also known as Web Service Layer

Responsible for exposing a web service API and returning the method result as XML or JSON

Data returned is retrieved from the Domain Layer

Domain Layer Also known as Business Layer

Responsible for all the business logic in the application Consists of a Domain Model and Domain Services

Domain Model Also known as Business Model, Business Objects, Entities etc.

Responsible for having a model that reflects how the business stakeholders look at the world

Consists of entities with relationships and behavior Similar to a database model but a domain model is richer

Domain Service Also known as Business Services, Business Managers etc.

Business logic that does not belong within an entity

Infrastructure Layer Also known as Data Access Layer, Repository Layer etc.

Responsible for querying a database, calling a web service, sending e-mail etc.

Example

We want to create a banking application with customers and related accounts. An account consist of an account number, a balance and a credit limit.If the account has been overdrawn then the account and customer is considered to be “sick”, otherwise “healthy”

Use Case 1: As a user I want to see if a customer is healthy or sick Use Case 2: As a user I want to retrieve if a customer is healthy or

sick through a web service

Technology: .NET, ASP.NET MVC, WCF

What do we need?

1. Domain Model for Customer and Account

2. Business logic for deciding if an account and customer is healthy or sick

3. 2 Classes: Fetching Customer and fetch list of Accounts from the database

4. Service Class for building up a Customer Entity with Accounts

Use Case 1:

5. MVC Controller and a View to display the health status for a given customer

Use Case 2:

6. WCF Service for returning whether a customer is healthy or not

Domain Model

Progress

Infrastructure – Fetch Customer

Infrastructure – Fetch Accounts

Progress

Domain Service – Build a Complete Customer

Progress

Use Case 1: Show the result to the user

Progress

Use Case 2: Return the result through a Web Service

Completed

Visual Studio Project Structure

Why should you have many layers?

Less code per layer Reduced complexity Easier to maintain code Easier to add new functionality Easier to test Allows for reuse code across the application

PHYSICAL TIER ARCHITECTURE

Logical Layer vs Physical Tier A Logically Layer is how you logically divide the code in the

application A Physical Tier is how you divide your application into multiple sub-

applications that can run on separate servers

2-Tier Windows Client Architecture

3-Tier Windows Client Architecture

3-Tier Web Architecture

4-Tier Architecture

Why have many tiers? Reuse logic across applications Improve security, e.g. restrict database access for the client by going

through a service Improved performance, the performance critical tiers can be scaled

across multiple servers

Summary Logical Layers

• How you logically divide the code in the application• Three Layer Architecture is most commonoPresentation Layer or Service LayeroDomain Layer with a Domain Model and Domain Serviceso Infrastructure layer for communicating with data sources

Physical Tiers• How you divide the application into many sub-applications

QUESTIONS?

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