layout: true <footer> <span class="icon github"> <svg version="1.1" class="github-icon-svg" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 16 16" enable-background="new 0 0 16 16" xml:space="preserve"> <path fill-rule="evenodd" clip-rule="evenodd" fill="#C2C2C2" d="M7.999,0.431c-4.285,0-7.76,3.474-7.76,7.761c0,3.428,2.223,6.337,5.307,7.363c0.388,0.071,0.53-0.168,0.53-0.374c0-0.184-0.007-0.672-0.01-1.32c-2.159,0.469-2.614-1.04-2.614-1.04c-0.353-0.896-0.862-1.135-0.862-1.135c-0.705-0.481,0.053-0.472,0.053-0.472c0.779,0.055,1.189,0.8,1.189,0.8c0.692,1.186,1.816,0.843,2.258,0.645c0.071-0.502,0.271-0.843,0.493-1.037C4.86,11.425,3.049,10.76,3.049,7.786c0-0.847,0.302-1.54,0.799-2.082C3.768,5.507,3.501,4.718,3.924,3.65c0,0,0.652-0.209,2.134,0.796C6.677,4.273,7.34,4.187,8,4.184c0.659,0.003,1.323,0.089,1.943,0.261c1.482-1.004,2.132-0.796,2.132-0.796c0.423,1.068,0.157,1.857,0.077,2.054c0.497,0.542,0.798,1.235,0.798,2.082c0,2.981-1.814,3.637-3.543,3.829c0.279,0.24,0.527,0.713,0.527,1.437c0,1.037-0.01,1.874-0.01,2.129c0,0.208,0.14,0.449,0.534,0.373c3.081-1.028,5.302-3.935,5.302-7.362C15.76,3.906,12.285,0.431,7.999,0.431z"/> </svg> </span> <a href="https://github.com/sikoried"><span class="username">sikoried</span></a> </footer> --- .skip[ # Softwarearchitektur ] .skip[ Prof. Dr.-Ing. Korbinian Riedhammer ] --- # Introduction - Software Architecture: mandatory class for CS majors - materials - https://ohm-softa.github.io - Github organization: https://github.com/ohm-softa (BIO) - ...in English! ☺ - slides, lecture notes, assignments (with READMEs) - class: Montays at **11.30a** in HQ.007, starting Oct 2 (updated Oct 1) - tutorials: - Mondays at *9.45a* in HQ.406, starting Oct 19. - Thursdays at *9.45* in HW.209, starting Oct 23. - _nota bene: assignments typically take longer than 90'!_ ??? https://github.com/gnab/remark/wiki/Formatting Materialien auf Englisch, Vorlesung aber auf Deutsch. Github orga ist closed/BIO--by invitation only Office hours: Übungen können die meisten nicht in 90' Programmieren. --- # Credits (Leistungsnachweis) - written exam (90') at the end of the term - you may bring three (3) pages notes (stapled and signed) - you must sign up for the exam - theoretical and coding questions --- # Review (what you should know by now!) ## Prozedurale Programmierung - imperative programming - constants, variables, expressions, functions, I/O - basic data structures (fields, arrays, lists) - pointers ☺ ## Objektorientierte Programmierung - OOP, classes and objects (and references! ☺) - basic data structures (lists, maps, etc.) - interfaces and inheritance - errors, exceptions and how to deal with them --- # Agenda for Software Architecture See https://ohm-softa.github.io/ (Syllabus) - modularity and component based development - UML, mostly class, component and sequence diagrams - programming patterns: idioms, design, architecture - assignments: tools and toolkits Assignments are one week "behind". --- # About this Class ### I'd like you to become better programmers ### Some slides, but mostly hands-on live coding (plus lecture notes!) .skip[ All examples are found in the `/examples/` directory of the [site's repository](https://github.com/ohm-softa/ohm-softa.github.io/tree/master/examples). ] --- # A note on (programming) languages - class materials are in English (so is most of the internet/SO) - examples are (mostly) in Java... - ...but translate to C#, C++, Python, Scala, etc. - we'll focus on the concept, not the language --- # Software Architecture ...is a craft. - takes practice - takes patience - takes diligence - takes experience --- # A word on GPT .center[  ] - Yes, GPT will produce correct code for most of the common programming problems - Yes, you should use GPT. - The point is: you need to understand what the use case requires, and then find the right coding concept. --- # Don't be that guy... .center[  ] .right[ <https://xkcd.com/292/> ] --- # Speaking of `goto` ## Why would you use `goto`? ## Is it possible in C#? ## Is it possible in Java? ??? c#: yes, emulate while, break outer loops Java: no; but break out of outer loops with labelled loops and labeled break/continue --- .center[ <img src="/assets/xkcd844-good-code.png" width="45%"> ] .right[ <https://xkcd.com/844/> ] --- # Agenda today 1. What is software architecture? 2. What is abstraction? 3. What is decomposition? 4. Clean Code 5. Tools --- # Software Architecture Thoughts? --- # Software Architecture ## Complexity - Ideal: linear process (analysis, draft, implementation, test, maintenance) - Constrained by: features, budget, time - Real world: somethings changes along the way... ## Architecture - Result of the software development process - Components, systems, subsystems, etc. - V-model, agile, ..., typically recurrent at some stage --- # Abstraction Thoughts? --- # Abstraction ## high level → low level - drive to the airport - → go straight, right, straight, left, ... - →→ clutch, brake, ignition, put in drive, ... .skip[ - reduce complexity by removing details - goal: model a system from a specific point of view ] ??? see: H. Stachowiak: Allgemeine Modelltheorie, Springer Verlag, 1973 --- # Abstraction ## Example: programming - hardware instructions - assembler (low-level) - c, fortran, java (high-level) - code generators --- # Decomposition Thoughts? --- # Stepwise Refinement > [...] a sequence of design decisions concerning the decomposition of a task into subtasks and of data into data structures N. Wirth, "[Program Development by Stepwise Refinement](https://dl.acm.org/citation.cfm?id=362577)", Comm. ACM, 1971 → break problem down in simpler problems until solvable --- # Functional Decomposition - Thoughts follow the process - Bottom-up/top-down ### Example: Withdraw cash at ATM - insert debit card - enter pin - select amount - process cash - ... --- # Object Oriented Decomposition > it is almost always incorrect to begin the decomposition of a system into modules on the basis of a flowchart. We propose instead that one begins with a list of difficult design decisions or design decisions which are likely to change. Each module is then designed to hide such a decision from the others. Since, in most cases, design decisions transcend time of execution, modules will not correspond to steps in the processing. D.L. Parnas, "[On the Criteria used in Decomposing Systems into Modules](https://dl.acm.org/citation.cfm?id=361623)", Comm. ACM, 1972 ### Modularization and Encapsulation > Every module [...] is characterized by its knowledge of a design decision which it hides from all others. Its interface or definition was chosen to reveal as little as possible about its inner workings. → Coherence and loose/tight coupling ??? probably one of the reasons OOP became so popular... --- # Some Guidelines for Good (OO) Architecture ## High Cohesion, Low Coupling There should be high cohesion within classes and packages, but low coupling between objects and across packages. ## Law of Demeter In simple words: "Each unit should have only limited knowledge about other units: only units "closely" related to the current unit.". K. Liebherr, I. Holland and A. Riel: "[Object-oriented programming: an objective sense of style](https://dl.acm.org/citation.cfm?id=62113)", Proc. OOPSLA, 1988 ## High Fan-In, Low Fan-Out --- # A Bit of "Historic" Context - early days of programming (pre 60s!) focused on procedures - the 1970s layed the ground work (see previously cited papers!) - 1970: Smalltalk (Xerox PARC; object oriented language) - 1973: ML (U Edinburgh; functional language) - 90s and 2000s: OOP widely taught as "gold standard", FP often considered "academic" - 2010s and onwards: heavy parallelization reintroduced FP (almost hype!) - "old" languages introduce functional elements (Java, C++, ...) - Scala - Actor frameworks, e.g. Akka --- # Clean Code <http://www.netlib.org/clapack/cblas/dgemm.c> --- # Clean Code - Choose good naming conventions - Methods should be short, concise and with few paramters - Comments only where needed; rewrite bad code - Java conventions? - [Google Java Format](https://github.com/google/google-java-format) - [Elasticsearch](https://github.com/elastic/elasticsearch/blob/master/CONTRIBUTING.md#contributing-to-the-elasticsearch-codebase) - Please read "Clean Code" by Prof. Tavakoli (`Teams > General > Files`) --- # Tools - Your preferred search engine - Your preferred interactive generative information system*) - [Stack Overflow](https://stackoverflow.com/questions/tagged/java) - [Java documentation](https://docs.oracle.com/javase/11/docs/) - JetBrains [IntelliJ](https://www.jetbrains.com/idea/), Community Edition (free!*) - [Git version control](https://git-scm.com/) *) Mind you: assignments are not mandatory — copying a solution typically has zero benefit