CS 691z / 791z Topics on Software Engineering

1
CS 691z / 791zTopics on Software Engineering

• Chapter 17 Interfaces and Subsystems
• Arlow Neustadt, 2002
• March 6, 2007

2
Outline

• Interfaces and subsystems
• Introduction
• Interfaces and component-based development
• Finding interfaces
• Subsystems and interfaces
• Advantages and disadvantages of interfaces

3
Interfaces Introduction

• Chapter 17 roadmap, Fig. 17.1 Arlow Neustadt,
  2002

4
Interfaces .Introduction..

• An interface specifies a named set of operations
• It defines a contract to be implemented by a
  classifier
• It also separates specification from
  implementation
• If the classifier that realizes (implements) the
  interface is physically packaged in a subsystem
  or component and the interface is public in this
  subsystem or component, then the subsystem or
  component also realizes the interface

5
Interfaces ..Introduction.

• Interfaces allow design to contract as compared
  to design to implementation supported by
  classes
• Each operation in an interface must have a
  complete operation signature (name, types of all
  parameters, and return type), semantics (recorded
  as text or pseudo-code) and, optionally, a
  stereotype and set of constraints
• Interfaces may not have
• Attributes
• Operation implementations
• Relationships navigable from the interface

6
Interfaces Introduction

• UML interface syntax, Fig. 17.2 Arlow
  Neustadt, 2002

7
Interfaces and Component-based Development.

• Interfaces are key elements for component-based
  development
• They allow addition of plug-in parts (with
  varied implementations) without changing the
  specification
• Both with components and subsystems, interfaces
  support low coupling and provide high
  architectural flexibility

8
.Interfaces and Component-based Development

• Example of interface, Fig. 17.3 Arlow
  Neustadt, 2002

9
..Interfaces and Component-based Development..

• Example of interfaces
• and subsystems
• Fig. 17.4 Arlow
• Neustadt,2002

10
Interfaces and Component-based Development.

• Another example of interface, Fig. 17.5 Arlow
  Neustadt, 2002

11
. Interfaces and Component-based Development

• Interfaces in Java the
• collection classes
• Fig. 17.6
• Arlow Neustadt,2002

12
Finding Interfaces

• Techniques for finding interfaces in a designed
  system or subsystem
• Challenge each association
• Challenge each message sent
• Factor out groups of operations reusable
  elsewhere
• Factor out sets of operations that repeat in
  classes
• Look at classes that have similar roles in the
  system
• Consider future extensions

13
Subsystems..

• Subsystems are packages stereotyped ltltsubsystemgtgt
• They are used both in design and implementation
• Design subsystems contain
• Design classes and interfaces
• Use case realizations
• Other subsystems
• Specification elements such as use cases
• Subsystems are used to
• Separate design concerns
• Represent large-grained components
• Wrap legacy systems

14
.Subsystems.

• Alternatives for drawing subsystems
• Fig. 17.7 Arlow Neustadt, 2002

15
..Subsystems

• More detailed representation of a subsystem
• Fig. 17.8 Arlow Neustadt, 2002

16
Subsystems and Interfaces..

• By introducing public interfaces in subsystems
  many of the classes in the subsystems could be
  hidden. As such subsystems could act as black
  boxes.
• Using interfaces in a subsystem is different from
  listing subsystem operations (see Figure 17.8).
  In the latter case, public classes must realize
  the operations.
• When a class of a subsystem realizes an
  interface, the subsystem realizes that interface
• A subsystem that provides a set of services by
  realizing one or more interfaces can be seen as a
  component

17
.Subsystems and Interfaces.

• Example of subsystems that realize interfaces
• Fig. 17.9 Arlow Neustadt, 2002

18
..Subsystems and Interfaces

• Physical architecture and the layering pattern,
  Fig. 17.10
• Arlow Neustadt, 2002

19
Advantages and disadvantages of interfaces

• Designing with interfaces increases flexibility
  and extensibility
• Also, using interfaces supports low coupling by
  reducing the number of dependencies between
  classes, subsystems and components
• With interfaces, a model can be neatly separated
  in cohesive subsystems
• Drawbacks of interfaces relate to added
  complexity and increased performance costs
• As a guideline, use interfaces for the more
  fluid parts of the system and dispense of them
  for the more stable parts of the system