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01s-intro.html
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---
layout: presentation
title: Introduction
permalink: /01s-intro/
---
layout: true
<footer>
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<a href="https://github.com/sikoried"><span class="username">sikoried</span></a>
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---
.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: Fridays at 11.30a **(HW.303)** (updated Mar 18)
- tutorials:
- Tuesdays at *9.45a* in HQ.306, starting Mar 21.
- Thursdays at *9.45a* on Zoom (until May), Starting Mar 23.
- Fridays at *9.45a* in HQ.406, starting Mar 24.
- _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 kann man 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!)
## Programmieren 1 (now: Prozedurale Programmierung)
- imperative programming
- constants, variables, expressions, functions, I/O
- basic data structures (fields, arrays, lists)
- pointers ☺
## Programmieren 2 (now: 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
---
# 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