Architecture with Components

What Changes?Components reduce the architectural controlRemove some qualities from your direct influence Which can force “how-important-is-this”

decisions about requirements

Search becomes a part of the problem

Searching for workable component ensembles1. Define constraints that the ensemble

must meet2. Define a first cut at other success criteria 3. Try to make it work4. Revise (usually, add to) the success

criteria5. Modify the ensemble6. Repeat 3-5 until

• An adequate ensemble is found, OR• You give up

RememberYou are searching for a working ensemble of componentsWorking one component at a time will probably waste time and energy

Mismatch can make an ensemble unworkable

Each OTS component comes with an architectural styleArchitectural Mismatch! Requires Provides

What to do? Detect mismatch during search and avoid it Detect it during design/implementation and

fix it

Detect mismatch during search

Inspect each candidate component to discover Requires Provides

Make sure each requires can be satisfied by a providesParameterized interfaces can give you some control over requires/providesUnfortunately, examining all assumptions for components is not possible!

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

When qualifying an interface, remember

An interface is more than method signaturesIt 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

Fixing mismatch1. Wrappers2. Bridges3. Mediators

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 componentsExamples: Screen scraping Most legacy wrappers

What experience do you have with wrappers?

Fixing Mismatch 2 - BridgesAn independent componentTranslate a requires of one side to a provides of the otherTranslation is defined at design timeOften independent of the componentsExample: postscript to PDFExperience with bridges?

Fixing Mismatch 3 - Mediators

PlanningIs often a first class component in the architectureExamples: Sensor fusion (p 459) EAI platform

Experience with mediators?