How to reduce the risk that external dependencies will have a negative effect on your code base.

1. Thank you to our Sponsors
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2. Reducing External Risks
How To Keep Other Software From Messing With Yours

3. External Risks
Any system that you rely on which will potentially have a
negative impact on you when it changes

4. Examples
• Web based asmx/svc/RESTful endpoints
• Internally hosted 3rd party applications
• User Controls
• Databases
• File System

5. Zero Control
• Cloud based service endpoint/api

6. Limited Influence
• 3rd party control suite
• Enterprise message queue (software or message content)
• Internally installed 3rd party application/services

7. Perceived Influence
• Internally created service endpoint/api that doesn’t belong to
your team
• Internally created UI control suite
• Internally installed 3rd party application/services
• Multi-application database
• Computer file system

8. External
Little influence over what changes are made
Some influence over when changes are made
Internal
> influence if it belongs to your project
< influence if it is cross project
cross project == 3rd party

9. Change
is
Guaranteed

10. Don’t fear change – embrace it
Anthony J D’Angelo

11. Don’t fear change –
limit its surface area

12. Don’t fear change –
control it’s impact

13. Limiting Surface Area
• Rooted in Object Oriented Programming
• Based on known design patterns
• Can be implemented by any team and in any language

14. Proxy

15. A proxy, in its most general form, is a
class functioning as an interface to
something else.
http://en.wikipedia.org/wiki/Proxy_pattern

16. Add Service Reference
http://wsf.cdyne.com/WeatherWS/Weather.asmx

17. Add Service Reference

18. …and this is good….right?
• No low level communication code
• Generates all the constructs you may ever need
• Its repeatable

19. Update Service Reference

20. Update Everywhere In Your Application

22. Problem solved…
Technical details of communication are pretty well
encapsulated
Interface changes are isolated and controllable
Technical construct changes are isolated and
controllable
Source interface is limited to only the pieces that are
needed

23. Adapter

24. It (adapter pattern) is often used to
make existing classes work with others
without modifying their source code
http://en.wikipedia.org/wiki/Adapter_pattern

25. Some
Web
Service
Your
application
code
Adapter

26. Adapt the Proxy
• Translate the input parameters and return values
• Convert the input and return structures

27. Parameters and Return Values
On the generated proxy
On the adapter

28. Parameters and Return Structures

29. Some
Web
Service
Your
application
code
Adapter

30. Scope of Change
• If its on the source you adapt it
• True adapter will include all endpoints offered by source

31. Problem solved…
Technical details of communication are pretty well
encapsulated
Interface changes are isolated and controllable
Technical construct changes are isolated and
controllable
Source interface is limited to only the pieces that are
needed

32. Façade
(and the Interface Segregation Principle)

33. A façade is an object that provides a
simplified interface to a larger body of
code…
http://en.wikipedia.org/wiki/Facade_pattern

34. No client should be forced to depend on
methods that it does not use
http://en.wikipedia.org/wiki/Interface_segregation_principle

35. Current Adapter
• Exposes interface that we want
• Exposes all functionality of the source

36. Worst Case Scenario
• The public surface area is *HUGE*
• Each exposed part (not method/property) is a
potential point of change
• Assume 1 parameter and 1 return type for 123
methods == 369 possibly points of change

37. ISP
• Simply don’t implement the unneeded public constructs on
your adapter
• Turns the adapter into a façade

38. Problem solved…
Technical details of communication are pretty well
encapsulated
Interface changes are isolated and controllable
Technical construct changes are isolated and
controllable
Source interface is limited to only the pieces that are
needed

39. The Journey
• Identify the risky dependency
• Use a proxy to abstract connectivity details
• Use an adapter to abstract the data constructs
• Implement ISP via a façade to limit the surface area

40. Your Code
Outside Your
Control
Tilemahos Efthimladis
https://www.flickr.com/photos/telemax/6032760593

41. Thank you
Donald Belcham
@dbelcham
donald.Belcham@igloocoder.com