There is value on a simple solution, but most software systems are way too complex. It need not be this way, especially in these days of high computing power, but first we must recognize the value of simplicity.
You need not take my word on the importance of simplicity. It's value has been recognized already:
"If you can't explain it to a six year old, you don't understand it yourself."
Leonardo Da Vinci:
"Simplicity is the ultimate sophistication."
Antoine de Saint-Exupery:
Perfection (in design) is achieved not when there is nothing more to add, but rather when there is nothing more to take away
A brief history
When I started programmming seriously about twenty years ago, most software systems were relatively small (aside from huge mainframe systems which were invisible) stand-alone applications. Concurrency was a non-issue back then and most of my effort was spent on making things efficient in terms of CPU and memory (time and space for the theorists).
Much has changed - a modern CPU is now multithreaded and extremely powerful, internet is everywhere and the applications are now integrated to other systems in almost real-time. The problem and solution domains have become so complex that no single person can completely master everything.
The way we approach programming has not changed to balance this. The languages have more abstractions and there are wonderful libraries. There's the agile movement and all that, but none of these really adresses the design part of software design.
Taming the complexity of the problem domain
A rich and complex problem domain leads to complex (data) model that is hard to understand unless you do something about it. The best designers know this.
Software creativity 2.0, chapter 11.2. Creativity And Software Design: The Missing Link
Great designers have a strong predilection for simplicity. Great designers have no fear of complexity.
According the traditional teachings of the relational database posse leaders, one should aim for normalization above all else. This is what they say:
A standard piece of database design guidance is that the designer should create a fully normalized design; selective denormalization can subsequently be performed for performance reasons.
Horse hockey. A normal form database design is just a tradeoff that maximizes correctness and minimizes space disregarding almost everything else. Not mentioning other worthy goals such as making the database user's work (the programmer) easy is absurd. A fully normalized database with 500+ tables takes considerable effort to understand, design or use. Been there, done that, not going there again.
Regardless of normal form, there is the important realization that "All models are wrong. some are useful". While George Box was not talking about data models, this is sound advice everywhere. There are always rare marginal cases that would be hopelessly messy to handle. Just cut them out of the algorithms or approximate them - that's what (software) design is about.
Simple is not easy
Niklaus "Pascal" Wirth has something to say about the difficulties:
Increasingly, people seem to misinterpret complexity as sophistication, which is baffling --- the incomprehensible should cause suspicion rather than admiration.
The belief that complex systems require armies of designers and programmers is wrong. A system that is not understood in its entirety, or at least to a significant degree of detail by a single individual, should probably not be built.
A primary cause of complexity is that software vendors uncritically adopt almost any feature that users want.
Especially the last point is important. Explicitly creating a Minimum Viable Product is one agile tactic to restrict feature creep. This is not a technical issue at all!
Mastering the solution domain
The solution domain is where we usually live as developers. It is our territory where we should be in control and any complexity is therefore unavoidable and a necessary evil. But is this actually true?
The battle about which language is "best" seems everlasting, though the argued languages change. As a programmer I think Paul Graham's Blub paradox is spot on and we are certainly not using the best tools available.
But as an architect, I have to balance the technical merits over the practical issues. Perhaps a Java solution is inferior, in a theoretical sense, to some Haskell code or Scala turbocharged with some macro magic, but what would it mean to choose the "better"?
Development of a Haskell based solution would not be easy unless the whole team consists of some very peculiar people. Mortals will not find it easy to understand Haskell or Scala macros. Even if they do, are they able to take advantage of everything the language has to offer?
I'm not saying we should stick with what we have, but languages do not write software. People do.
Modularity is your best friend
Always aim for modular pieces with a single clear responsibility. This applies to all levels - a method, a class, a module, a software system. I could say more, but others have already written a lot about this.
"Software systems are unique compared to physical systems. Their architectures can grow incrementally, IF we maintain the proper separation of concerns."
If my memory serves me correct, this was written in 1991 in Crafting a Compiler with C:
"Indeed, it is becoming increasingly clear, that for modern programs correctness rather than speed is the paramount concern."
There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.
Composability is the future
Modularity is prequisite for, but does not guarantee composability. There is no universal definition for either, but I will give two examples.
Maven is not composable and it's hardcoded expectations may cause severe headache. I came to same conclusions as Neal Ford some time ago. There is modularity in Maven, but in a limited sense.
On the other hand, parser combinators are by definition composable. Tutorial on Scala parser combinators provides a practical tutorial on Scala. This is an extremely powerful approach to parsing compared to the traditional approach where the programmer writes the lexer and parser descriptions in a specific DSL and generates the implementation for a lexer and parser.
Tempting the dark side is
Even if you do everything to keep things simple, there are other stakeholders. Here are three essential lessons how people can create a complex mess inadvertently:
It is probably best to avoid architectural astronauts.
It is good to question oneself occasionally. When in doubt, remember the gloves.
There is the Light side too
Unix is, despite it's shortcomings, a good example of modularity and composability. Exposing sockets as files, providing pipes to glue things together etc. provides an extremely powerful platform to build upon.
At the system integration level, ESB, SOA, REST etc. are all aiming at the same goal. Is it better to have twenty software systems integrated together or just one? I will take the former structure any day, but some people prefer the latter.
In the UK, a project to replace many healthcare systems with a big "do-it-all" system was canceled in 2011. See NHS project cancelled, money wasted for reference. The new approach proposed by the ICT industry is very different. Industry proposes that the new NHS system should be modular.
It is very hard to steer a big monolith to a new course when the requirements change, as they inevitably will. Much better if you:
- Create small modular pieces and let the system grow incrementally.
- Compose bigger pieces from the smaller ones.
- Specify and enforce boundaries. (This forms the "architecture" of the design.)
- Focus on the most important things first. (Prioritize the backlog in agile-speak.)
Easier said than done!