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Software Architecture

Software Architecture

The Architecture Hamburger: Layers, Hexagons, Rings with Onion and Clean Architecture.

Henning Schwentner

December 01, 2022

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  1. Starring Directed By Special Appearance Presented by With

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  4. 🇩🇪

  5. Hi, I’m Henning

  6. 👨💻👨🏫👨💼

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  8. @hschwentner Example: A Banking Domain bank account customer teller computer

  9. @hschwentner Example: A Banking Domain computer

  10. @hschwentner A Short History of Software Architecture

  11. @hschwentner Program No Architecture

  12. @hschwentner No Architecture Mess

  13. @hschwentner Structured Programming Edsger Dijkstra Edgar Dijkstra: Go To Statement

    Considered Harmful callable unit callable unit callable unit
  14. @hschwentner Information Hiding David Parnas Programming R. Morris Techniques Editor

    On the Criteria To Be Used in Decomposing Systems into Modules D.L. Parnas Carnegie-Mellon University This paper discusses modularization as a mechanism for improving the flexibility and comprehensibility of a system while allowing the shortening of its development time. The effectiveness of a "modularization" is dependent upon the criteria used in dividing the system into modules. A system design problem is presented and both a conventional and unconventional decomposition are described. It is shown that the unconventional decompositions have distinct advantages for the goals outlined. The criteria used in arriving at the decom- positions are discussed. The unconventional decomposi- tion, if implemented with the conventional assumption that a module consists of one or more subroutines, will be less efficient in most cases. An alternative approach to implementation which does not have this effect is sketched. Key Words and Phrases: software, modules, modularity, software engineering, KWIC index, software design CR Categories: 4.0 Introduction A lucid statement of the philosophy of modular programming can be found in a 1970 textbook on the design of system programs by Gouthier and Pont [1, ¶I0.23], which we quote below: 1 A well-defined segmentation of the project effort ensures system modularity. Each task forms a separate, distinct program module. At implementation time each module and its inputs and outputs are well-defined, there is no confusion in the intended interface with other system modules. At checkout time the in- tegrity of the module is tested independently; there are few sche- duling problems in synchronizing the completion of several tasks before checkout can begin. Finally, the system is maintained in modular fashion; system errors and deficiencies can be traced to specific system modules, thus limiting the scope of detailed error searching. Usually nothing is said about the criteria to be used in dividing the system into modules. This paper will discuss that issue and, by means of examples, suggest some criteria which can be used in decomposing a system into modules. Copyright @ 1972, Association for Computing Machinery, Inc. General permission to republish, but not for profit, all or part of this material is granted, provided that reference is made to this publication, to its date of issue, and to the fact that reprinting privileges were granted by permission of the Association for Com- puting Machinery. Author's address: Department of Computer Science, Carnegie- Mellon University, Pittsburgh, PA 15213. A Brief Status Report The major advancement in the area of modular programming has been the development of coding techniques and assemblers which (l) allow one module to be written with little knowledge of the code in another module, and (2) allow modules to be reas- sembled and replaced without reassembly of the whole system. This facility is extremely valuable for the production of large pieces of code, but the systems most often used as examples of problem systems are highly- modularized programs and make use of the techniques mentioned above. 1 Reprinted by permission of Prentice-Hall, Englewood interface imple- mentation
  15. @hschwentner Loose Coupling/ High Cohesion Ed Yourdon Larry Constantine

  16. @hschwentner 2 Layer Architecture Program “uses” Legend: DB

  17. @hschwentner below The One Rule above Acyclic Dependency Principle allowed

  18. @hschwentner 3 Layer Architecture Presentation Logic Data

  19. @hschwentner 4 Layer Architecture

  20. @hschwentner Patterns Ralph Johnson Erich Gamma Richard Helm John Vlissides

    a.k.a.: Gang of Four
  21. @hschwentner Layered Architecture Frank Buschmann et al. . . .

  22. @hschwentner Strictness allowed forbidden non-strict strict

  23. @hschwentner 4 Layer Architecture User Interface Application Domain Infrastructure

  24. @hschwentner The Problem Infrastructure User Interface Application Domain allowed BAD!

  25. @hschwentner The Problem Domain Infrastructure bank transaction Oracle DB Concrete

  26. @hschwentner below above From above/below to inside/outside out- side inside

  27. @hschwentner port port Hexagonal Architecture Foto: Dennis Hamilton/flickr/CC BY 2.0

    http://alistair.cockburn.us/Hexagonal%2Barchitecture adapter adapter Alistair Cockburn
  28. @hschwentner Kinds of Ports - For UI etc. - Methods

    to be called - “from above” - For DB and infrastructure - Interfaces to be implemented - “from below”
  29. @hschwentner secondary port primary port adapter adapter Kinds of Ports

    Legend: Flow of control Dependency
  30. @hschwentner Domain The Solution Domain Infrastructure bank transaction Oracle DB

    Infrastructure bank transaction Oracle DB port adapter Step 1
  31. @hschwentner uses implements Legend:

  32. @hschwentner Dependency Inversion Depend on abstractions, not on concretions! Robert

    C. Martin “Uncle Bob”
  33. @hschwentner Onion Architecture U I “application core” domain services domain

    model infra app ture struc serv lication ices 🧅
  34. @hschwentner The 4 Tenets •The application is built around an

    independent object model •Inner layers define interfaces. Outer layers implement interfaces •Direction of coupling is toward the center •All application core code can be compiled and run separate from infrastructure Jeffrey Palermo 🧅
  35. @hschwentner Designed for Testability “All application code can be compiled,

    run, and tested separate from infrastructure” Easy unit tests Plays well with TDD 🧅
  36. Clean Architecture Robert C. Martin “Uncle Bob” interactor = use

    case object U I entities DB devices w eb control use cases gate presenters lers ways
  37. Explicit Architecture Herberto Graca

  38. @hschwentner Patterns Languages

  39. @hschwentner Patterns for the UI Layer

  40. @hschwentner Model—View—Controller controller view model Variants: Model—View—Presenter Model—View—Viewmodel Trygve Reenskaug

  41. @hschwentner Patterns for the Domain Layer

  42. @hschwentner Domain-Driven Design Eric Evans

  43. @hschwentner Domain Modeling BankAccount withdraw() deposit() Amount

  44. Entity Value Object Aggregate Service Factory Repository Tactical Design

  45. @hschwentner Entity vs. Value - Identity - Life cycle -

    Can be mutable - No identity - Always immutable Contract Map Name Amount Length 12.5 m $ 100.00 “John Miller”
  46. @hschwentner Rules of Thumb Things become Entities The properties of

    the Things become Values
  47. @hschwentner Repository repository interface repository implementation DB uses impleme port

    adapter Legend:
  48. @hschwentner Expressing Architecture https://xmolecules.org

  49. @hschwentner Putting it all together

  50. @hschwentner Architecture Hamburger Application Domain Infrastructure UI coarse grained

  51. @hschwentner Architecture Hamburger fine grained model repository interface controller use

    case service entity value object view data model repository implementation widget library REST frame- work transaction handling domain library programming language ORM file system access domain event
  52. @hschwentner In the Large

  53. @hschwentner Don’t: Build one Giant 🍔

  54. @hschwentner Do: Make it a Menu 🍟🍔🥗

  55. @hschwentner Domain-Driven Design Eric Evans

  56. @hschwentner Banking Domain bank computer Banking 3000

  57. @hschwentner Banking Subdomains Konto- Führug Kredit- wesen Wertpapier -geschäft Banking

  58. @hschwentner Big Ball of Mud Banking 3000 Big Ball of

  59. @hschwentner Strategic Design Konto- Führug Kredit- wesen Wertpapier -geschäft Banking

    3000 🍟 🍔 🥗
  60. @hschwentner Architecture Hamburger fine grained model repository interface controller use

    case service entity value object view data model repository implementation domain event model repository interface controller use case service entity value object view data model repository implementation domain event
  61. @hschwentner Example

  62. @hschwentner LeasingNinja https://leasingninja.io

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  64. https://domainstorytelling.org/book

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  66. @hschwentner FEEDBACK

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  69. @hschwentner Bibliography Buschmann, Frank, Regine Meunier, Hans Rohnert, Peter Sommerlad,

    and Michael Stal. Pattern-Oriented Software Architecture Volume 1: A System of Patterns. Hoboken, NJ: Wiley, 1996. Cockburn, Alistair. “Hexagonal Architecture.” January 4, 2005. https://alistair.cockburn.us/hexagonal-architecture/. Dijkstra, Edsger. “Go To Statement Considered Harmful.” Communications of the ACM 11, no. 3 (March 1968): 147–48. Evans, Eric. Domain-Driven Design: Tackling Complexity in the Heart of Software. Boston: Addison-Wesley, 2004. Gamma, Erich, Richard Helm, Ralph Johnson, and John Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software. Reading, MA: Addison-Wesley, 1995. Graca, Herberto. “DDD, Hexagonal, Onion, Clean, CQRS, … How I Put It All Together.”November 16, 2017. https://herbertograca.com/2017/11/16/explicit- architecture-01-ddd-hexagonal-onion-clean-cqrs-how-i-put-it-all-together/
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  71. Henning Schwentner  https://hschwentner.io  @hschwentner ✉ [email protected]