Domain-Driven Design

1
Domain-Driven Design

• Chapters 4-6
• How to build OO models of business systems

2
Patterns

• Layered Architecture
• Smart UI antipattern
• Entities
• Value objects
• Services
• Modules
• Aggregates
• Factories
• Repositories

3
Real-time System Design

• Patterns for Generating a Layered Architecture,
  Barry Rubin, Pattern Languages of Program Design,
  Addison-Wesley, 1995.
• Layered architecture of real-time systems with an
  operator interface

4
A Typical CMA System
Operator Interface
status, alarms
commands
Health and Status
Tool Control
status
control
feedback
Hardware Interface
control
feedback
status
Mechanical process
5
A CMA Architecture
Layer 5 - Operator interface
Layer 4 - Application layer Model system behavior
Layer 3 - Modeling layer Model of the mechanical
domain (actuator, solenoid, sensor)
Layer 2 - Access layer Model of the EE domain
(I/O ports)
axis of symmetry
Layer 1 - Physical layer Physical hardware or
simulator
Mechanical entities Actuators, solenoid,
sensors, etc
6
Anti-patterns

• AntiPatterns Refactoring Software,
  Architectures, and Projects in Crisis by William
  J. Brown, Raphael C. Malveau, and Thomas J.
  Mowbray

7

• Entities have a unique identity. Cannot make an
  exact copy. Has mutable state.
• Value objects have no identity, and can be
  copied. Stateless. Immutable.

8
Aggregates

• Aggregate consist of one entity that is the root,
  and a set of non-entities.
• Root controls all access to non-value objects
  within the aggregate.
• External objects only hold references to the root.

9

• Service when a significant process is not a
  responsibility of an entity, add an operation to
  the model as a standalone interface described as
  a stateless service.
• Module Choose modules that tell the story of
  the system and contain a cohesive set of concepts.

10

• Factory create new objects
• Repository find old objects