HTW Berlin Fachbereich 4 Internationaler Bachelor Studiengang Internationale Medieninformatik (Bachelor) Informatik 3 Winter Term 2021/22
	Info 3: Informatik III Modern Software Engineering

SOLID

We don't have much Christmas vacation, so I thought I would do a "read up on your own time" lecture on SOLID today (although then I miss telling some of my stories, but I'll fit them in here somehow).

Software development is not a game of Jenga!

The SOLID principles of object-oriented programming are

• Single-responsibility principle
• Uncle Bob's post from 8 May 2014, but similarly described by Tom DeMarco (1979) and Meilir Page-Jones (1988) as cohesion.
  

• Hackernoon with a short excursion into the history of programming in Medium. I have had the supreme pleasure of meeting Dave Parnas on a number of occasions, he taught in Darmstadt for some years. He quit the "Star Wars / SDI initiative" of Ronald Reagan by observing (correctly) that you can't actually test software that is designed to prevent a nuclear attack. Are you going to have Russia shoot a few missiles at New York and hope you can intercept them? We only disagree heartily on whether there should be a professional engineering certificate issued to software engineers - he insists it is necessary, I say it can't be done because SW development moves too fast.
  

• Open-closed principle
• A chapter from Uncle Bob's Engineering Notebook hosted on someone's public Google drive.
  
• Bertrand Meyer was the originator of this in 1988, says Hackernoon@Medium.
  
  
• Liskov substitution principle
• Barbara Liskov was one of the first women to be awarded a PhD in computer science (Stanford, 1968). Her research group at MIT, the Programming Methodology group developed what we know today as object-oriented programming with her ideas of inheritance. She was awarded the Turing Award from the ACM in 2009 for her work on data abstraction. I had the extreme pleasure of being her dinner partner at the GI yearly conference in Braunschweig. She noted that men often scoff at her being a Turing award winner, because "that's how we program, that's nothing special." She still takes pride in her work having been so useful to programming.
• Subtypes must be substitutable for their base types: “What is wanted here is something like the following substitution property; If for each object s of type S there is an object t of type T such that for all programs P defined in terms of T, the behavior of P is unchanged when s is substituted for t then S is a subtype of T.”
• Barbara Liskov. 1987. Keynote address - data abstraction and hierarchy. SIGPLAN Not. 23, 5 (May 1988), 17–34. DOI:https://doi.org/10.1145/62139.62141
• Thorben Janssen. 2018. SOLID Design Principles Explained: The Liskov Substitution Principle with Code Examples
  
  
• Interface segregation principle
• No client should be forced to depend on methods it does not use.
  
• David Hayden. 2007. Interface-Segregation Principle (ISP) - Principles of Object-Oriented Class Design
  
  
• Dependency inversion principle
• Decouple modules - high-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend on details.
  
• Uncle Bob's chapter
  
  
  

The Viking Code School has a great overview of all five concepts, look especially at the bakery and drill examples!

Yes, there will be a question on the exam about SOLID.