Friday, June 01, 2018

Thinking about Software Architecture & Design : Part 11

It is said that there are really only seven basic storylines and that all stories can either fit inside them or be decomposed into some combination of the basic seven. There is the rags-to-riches story. The voyage and return story. The overcoming the monster story...and so on.

I suspect that something similar applies to Software Architecture & Design. When I was a much younger practitioner in this field, I remember a very active field with new methodologies/paradigms coming along on a regular basis. Thinkers such as Yourdon, de Marco, Jackson, Booch, Hoare, Dijkstra, Hohpe distilled the essence of most of the core architecture patterns we know of today.

In more recent years, attention appears to have moved away from the discovery/creation of new architecture patterns and architecture methodologies towards concerns closer to the construction aspects of software. There is an increasing emphasis on two way flows in the creation of architectures– or perhaps circular flows would be a better description. i.e. iterating backwards from, for example user stories, to the abstractions required to support the user stories. Then perhaps a forward iteration refactoring the abstractions to get coverage of the required user stories with less “moving parts” as discussed before.

There has also been a marked trend towards embracing the volatility of the IT landscape in the form of proceeding to software build phases with “good enough” architectures and the conscious decision to factor-in the possibility of needing complete architecture re-writes in ever short time spans.

I suspect this is an area where real world physical architecture and software architecture fundamentally differ and the analogy breaks down. In the physical world, once the location of the highway is laid down and construction begins, a cascade of difficult-to-reverse events starts to occur in parallel with the construction of the highway. Housing estates and commercial areas pop up close to the highway. Urban infrastructure plans – perhaps looking decades into the future – are created predicated on the route of the highway and so on.

In software, there are often similar amount of knock-on effects to architecture changes but when these items are themselves primarily software, rearranging everything based on a architecture is more manageable. Still likely a significant challenge, but more doable because software is, well “softer” than real world concrete, bricks and mortar.

My overall sense of where software architecture is today is that it revolves around the question : “how can we make it easier to fundamentally change the architecture in the future?” The fierce competitive landscape for software has combined with cloud computing to fuel this burning question.

Creating software solutions with very short (i.e. weeks) time horizons before they change again is now possible and increasingly commonplace. The concept of version number is becoming obsolete. Today's software solution may or may not be the same as the one you interacted with yesterday and it may, in fact, be based on an utterly different architecture under the hood than it was yesterday. Modern communications infrastructure, OS/device app stores, auto-updating applications, thin clients...all combine to create a very fluid environment for modern day software architectures to work in.

Are there new software patterns still emerging since the days of data flow and ER diagrams and OOAD? Are we just re-combining the seven basic architectures in a new meta-architecture which is concerned with architecture change rather than architecture itself? Sometimes I think so.

I also find myself wondering where we go next if that is the case. I can see one possible end point for this. An end-point which I find tantalizing and surprising in equal measure. My training in software architecture – the formal parts and the decades of informal training since then – have been based on the idea that the fundamental job of the software architect is to create a digital model – a white box – of some part of the real world, such that the model meets a set of expectations in terms of its interaction with its users (which may, be other digital models).

In modern day computing, this idea of the white box has an emerging alternative which I think of as the black box. If a machine could somehow be instructed to create the model that goes inside the box – based purely on an expression of its required interactions with the rest of the world – then you basically have the only architecture you will ever need for creating what goes into these boxes. The architecture that makes all the other architectures unnecessary if you like.

How could such a thing be constructed? A machine learning approach, based on lots and lots of input/output data? A quantum computing approach which tries an infinity of possible Turing machine configurations, all in parallel? Even if this is not possible today, could it be possible in the near future? Would the fact that boxes constructed this way would be necessarily black – beyond human comprehension at the control flow level – be a problem? Would the fact that we can never formally prove the behavior of the box be a problem? Perhaps not as much as might be initially thought, given the known limitations of formal proof methods for traditionally constructed systems. After all, we cannot even tell if a process will halt, regardless of how much access we have to its internal logic. Also, society seems to be in the process of inuring itself to the unexplainability of machine learning – that genie is already out of the bottle. I have written elsewhere (in the "what is law?" series - that we have the same “black box” problem with human decision making anyway).

To get to such a world, we would need much better mechanism for formal specification. Perhaps the next generation of software architects will be focused on patterns for expressing the desired behavior of the box, not models for how the behavior itself can be achieved. A very knotty problem indeed but, if it can be achieved, radical re-arrangements of systems in the future could start and effective stop with updating the black box specification with no traditional analysis/design/ construct/test/deploy cycle at all.

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