Domain Modelling Paul Stovell

Architecture: Implicit or Explicit? Architecture exists implicitly But if you don’t define it, it probably sucks

Scope of this presentation UI Data Stores (Database, Web Service, etc.)

Domain Modelling Step 1: Understand the problem domain Step 2: Architect around it

Object-Oriented Design Encapsulation Polymorphism Inheritance Abstraction

Design Patterns Gang of Four Concepts Judgement As simple as possible, but no simpler

Object Oriented not Class Oriented

Domain Model What’s in a domain model? Stateful Objects Services Responsibilities: Maintaining their own state Responsibilities: Maintaining their own state Responsibilities: Doing stuff Responsibilities: Doing stuff

Entities : Stateful Objects Have a real-world identity

Value Objects : Stateful Objects Have no real-world identity Value objects with same values are interchangeable

Value Objects : Stateful Objects Value objects are subjective

Domain Services : Stateless Responsibilities: Doing stuff Generally stateless

Relationship Bias Most real-world relationships are one-way

Aggregates Recognise that some things don’t exist without others

Aggregates Timesheet TimesheetEntry Customer Aggregate Timesheet

Locking Timesheet TimesheetEntry Customer Coarse-Grained Lock

Aggregates Timesheet TimesheetEntry Customer Aggregate

Context and Boundaries “Object models don’t scale”

Contexts and Boundaries Sales Application Context Tech Support Application Context Boundary

Gateways Abstract the coordination of services and stateful objects Like your manager: they boss people around but don’t do any work themselves

Domain Models + SOA UI Service Agents Web Services Business Logic Database Service Messages UI Service Agents Web Services Business Logic Database Service Messages

Domain Models + SOA UI Service Agents Web Services Domain Services Database Domain Objects UI Service Agents Web Services Domain Services Database Domain Objects

Recap What’s in a domain model? – Stateful Objects Entities Value Objects – Services Simplified by: – Relationship Bias – Aggregates Scales thanks to: – Contexts and Boundaries – Gateways

I’m still awake! Where can I get more? Head first design patterns Eric & Elizabeth Freeman Domain Driven Design Eric Evans Patterns of Enterprise Application Architecture Martin Fowler

CHEERS! Paul Stovell July 5 th SDNUG (AMP Building) Binding Oriented Programming