1. Architecture with Components

2. What Changes? Components reduce the architectural control
Remove some qualities from your direct influence
Which can force “how-important-is-this” decisions about requirements
Search becomes a part of the problem

3. Searching for workable component ensembles
Define constraints that the ensemble must meet
Define a first cut at other success criteria
Try to make it work
Revise (usually, add to) the success criteria
Modify the ensemble
Repeat 3-5 until
An adequate ensemble is found, OR
You give up

4. Remember You are searching for a working ensemble of components
Working one component at a time will probably waste time and energy

5. Mismatch can make an ensemble unworkable
Each OTS component comes with an architectural style
Architectural Mismatch!
Requires
Provides
What to do?
Detect mismatch during search and avoid it
Detect it during design/implementation and fix it

6. Detect mismatch during search
Inspect each candidate component to discover
Requires
Provides
Make sure each requires can be satisfied by a provides
Parameterized interfaces can give you some control over requires/provides
Unfortunately, examining all assumptions for components is not possible!

7. Detect mismatch during design/implementation
Qualify the interfaces by discovering requires and provides while
Designing the architecture
Integrating the ensemble
Prototyping
Building a skeletal system

8. When qualifying an interface, remember
An interface is more than method signatures
It may also include assumptions about
Ordering of method calls
Threading
Resource availability and consumption
Authorization
Security
Persistent storage
Network access
Error reporting and handling
Logging

9. Fixing mismatch
Wrappers
Bridges
Mediators

10. Fixing Mismatch 1 - Wrappers
Encase the component to
Translate an element
Hide an element
Preserving an element without change
Usually specific to the using and used components
Examples:
Screen scraping
Most legacy wrappers
What experience do you have with wrappers?

11. Fixing Mismatch 2 - Bridges
An independent component
Translate a requires of one side to a provides of the other
Translation is defined at design time
Often independent of the components
Example: postscript to PDF
Experience with bridges?

12. Fixing Mismatch 3 - Mediators
Planning
Is often a first class component in the architecture
Examples:
Sensor fusion (p 459)
EAI platform
Experience with mediators?