Practical examples of applying DCI @ XING.

1. DCI @ XING
hardwiring brains
Boris Tveritnev

2. XING Architecture at a glance
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3. Index
The problem
Problem by example
DCI
DCI and DDD
DCI and TDD
Application techniques
Takeaway

4. The
problem(s)
Object Oriented Programming
http://donkeykong.wikia.com/wiki/User:CoolHungryYoshi?file=Donkey-kong-clean.gif

5. “I thought of objects being like biological
cells and/or individual computers on a
network, only able to communicate with
messages”
Alan Kay
http://userpage.fu-berlin.de/~ram/pub/pub_jf47ht81Ht/doc_kay_oop_en

6. Something went really wrong
• Simula (1967)
• Smalltalk (1980)
• C++ (1983)
• Java (1995)
• C# (2000)
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7. OOP as it is
•There is little in object orientation, that helps
the developer capture doing in the code
•One can’t reason about system behavior in
runtime
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https://s-media-cache-ak0.pinimg.com/736x/c2/02/1c/c2021c66544d3b66495d7d489f527405.jpg

8. “I made up the term 'object-oriented', and I
can tell you I didn't have C++ in mind”
Alan Kay
OOPSLA '97

9. Payments
domain
@XING
http://www.kimberlywoodstucson.com/uploads/5/5/0/9/55094411/3783591_orig.png

10. Payments domain model
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ONLINE OFFLINE IN-APP
BONUS
B2B
customers
B2C
customers
Pay UsePayUsePay Pay Pay Pay
Pay
More
Pay
More
Use Bonus

11. Runtime vs design-time
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12. Runtime vs design-time
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13. Runtime vs design-time
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14. Data-Context-
Interaction
Hardwiring brains
http://1.bp.blogspot.com/_MyFAOEj9GKk/S-QmbuYk56I/AAAAAAAAAEQ/sHc-mwJBacc/s1600/left-brain-right-
brain.jpg

15. Users’ mental models
•What the system is
•What the system does
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16. Data (Records)
•Data objects express what the system is
•Methods and attributes that describe the data
•In essence they are just dumb DTOs
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http://vignette1.wikia.nocookie.net/uncyclopedia/images/3/3a/Pac_man_pie_chart.jpg

17. Data example
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18. Interaction (Roles)
•Roles describe the algorithms defining what
the system does
•Traits of objects
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19. Roles and Biz Processes
•Customer - Sales
•Debtor - Accounting
•Employer - BizDev
•SupportClient - Support
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https://ruthcatchen.files.wordpress.com/2012/03/artclass.jpg

20. Role example
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21. Context
•Specifies a network of communicating Objects
as interconnected Roles
•Represents a single Use Case
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22. Hide Client Context example
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23. Client Role example
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24. Role example
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25. Renew Contract Context example
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26. Contract Role example
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27. Client Role example
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28. DCI and DDD
Swore friends
http://data.whicdn.com/images/67570097/original.gif

29. Aggregates
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•DDD defines Aggregate Root as an invariant
enforcing entry point
•DCI aids in finding correct aggregate
boundaries
http://petroloco.com/wp-content/uploads/2014/01/Disintegrating-01.jpg

30. Aggregate example
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31. Aggregate example
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32. Perfect match
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•DCI context implements a complete Use Case
•Domain events are results of executing a Use
Case
https://s-media-cache-ak0.pinimg.com/736x/7f/f3/7c/7ff37ca2c4d90a56064d0fc3d42ef58a.jpg

33. Domain events example
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34. Domain events example
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35. Common restrictions
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You need neither of them to build this

36. DCI and TDD
Removing the friction
http://i.dailymail.co.uk/i/pix/2013/02/23/article-2283273-1835CCED000005DC-212_634x438.jpg

37. Promoting BDD
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•Feature-driven top-down approach
•Structures the code and thought
http://www.codelanders.com/wp-content/uploads/2015/04/DDD_TDD_BDD_intersection.png

38. Zero-friction TDD
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•Allows to refactor inner parts without
constantly breaking tests
•With enough attention one can get pretty
close to executable specifications
http://icons.wunderground.com/data/wximagenew/l/ljranch/6.jpg

39. BDD example
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40. BDD example
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41. BDD example
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42. Application
techniques
Different ways in different languages
http://images2.fanpop.com/image/photos/9700000/Penguin-of-Death-penguins-of-madagascar-9714329-800-
600.gif

43. Libraries/Languages
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•C#: with Extension methods or dynamic
•Marvin: .Net CLI compatible language,
designed for DCI
•Ruby: with Method injection or using Maroon
•Javascript: hasOwnProperty and apply
•Java: Apache Zest (former Qi4J)
•Scala: traits
•C++: with Templates

44. Takeaway
http://personal.lse.ac.uk/robert49/ebooks/PhilSciAdventures/img/memory-brain.jpg

45. Win!
Touches key areas of agile process
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•Analysis with User Stories and Use Cases
•Customer can be closely involved in
discussions
•Embracing change separating stable domain
model from changing User Stories
•Aids in DDD application
•Promotes BDD

46. www.xing.com
Thank you
for your
attention!
Boris Tveritnev

47. More info
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1. http://www.artima.com/articles/dci_vision.html
2. DCI Glossary: http://folk.uio.no/trygver/2011/DCI-Glossary.pdf
3. http://fulloo.info/
4. https://groups.google.com/forum/#!forum/object-composition
5. Lean Architecture: for Agile Software Development, J. Coplien,
G. Bjørnvig, ISBN-13: 978-0470684207, Wiley, 2010.
6. A Personal Computer for Children of All Ages:
http://www.mprove.de/diplom/gui/Kay72a.pdf
7. Dr. Alan Kay on the Meaning of “Object-Oriented Programming”:
http://userpage.fu-
berlin.de/~ram/pub/pub_jf47ht81Ht/doc_kay_oop_en