Software Architecture

Metaphors in Software Engineering

One metaphor frequently used in the field of software development is the metaphor of software architecture. The architecture of a software system consists, like the architecture of building,  of the main structures of the systems.

For a software system, the term “structure” could mean structures that are logical or conceptual. They don’t necessary match with tangible system boundaries. But the term “structure” does mean that the metaphor is biased towards expressing the static aspects of the software system.

Unlike buildings, software systems have also dynamic aspects. Information flows in a software system, and systems communicate with each others. Therefore, other metaphors can be useful to explain the nature of software systems.

Here are a few that I find interesting.

A city

As said, the architecture metaphor is limited in that if focuses too much on the statics. The city metaphor is in this regard better, since it evoques simulateously static structures (roads, bridges, buildings) but also dynamic aspects (traffic flow, people living in the city). Good city planning deals with both. The metaphor can be used for a software system, but also for collections of software systems.

Enterprise architecture is the field of IT that addresses IT strategy at the enterprise level. The city metaphor is a good own for the enterprise architectture. Changes of IT strategy (for instance, moving to the cloud) impact many systems and take years to be achieved. They significantly and durably change the way software system are built for the enterprise. If Hausmann’s renovations gave a new face to Paris, moving to the cloud will give a new face to the IT of your enterprise. 

A garden

The architecture metaphor is also limited in that it conveys the impression that a software is built once, and then never changes. It may be true for a building, but isn’t for software systems. According to the laws of software evolution, a software system must constantly be maintained and adapted to the needs of their users, or it will become useless. As software systems are developped and grow, they tend to accumulate inconsistencies that must be actively removed. This is much like a garden, which must be constantly maintained, and bad weeds, which must be removed. 

It’s possible to convey something similar with the architecture metaphor too, since building suffer wear and tear. We speak sometimes of architecture erosion, to denote the degrading quality of the architecture. By the way, buildings do change over time, sometimes quite significantly.

A book

Software is expressed using programming languages and its source code consists of text. A software system can thus be compared to a book, albeit a very special one. You can’t read it linearly and everything is interlinked. But there is a sense of style in a given code base, and code can be more or less elegant. There is something arful to programming. Given that developpers spend a lot more time reading code than writing code, taking care of software as text makes sense. With development approaches like literate programming, developpers a supposed to write the source code like a story to explain their thoughts. It didn’t catch on, but still worth a look.

A living organism

A running software system can also be compared to a living organism: it needs energy to run and do something useful. In some way, functions of the runtime, like memory management or thread scheduling, can been seen as some form of metabolism. Interestingly, some software systems like blockchains are explicitly designed to have an inefficient metabolism and consume large amount of energy. A running software system has a health too, which indicates how well the system works. Millions of things can go wrong during run time, degrading its health and behavior. For instance a memory leak will over time degrade the performance of the system until it simply dies.  Some components of a software system have at run time multiple instances. A failure of one component doesn’t break the whole system, just like we can live with one kidney. A running software systems can be compromised by a hostile inputs, the equivalent of a pathogen. The immune system of a running software consists of mechanisms like SQL sanitization, managed memory, safe pointers, etc. which aim at making software more robust. Usually software systems do not reproduce, though. Except for software viruses.

An asset

The IT has long been seen as a cost center, detached from business units that are profit centers. With digitalization, the perception is changing. Software is the enabler for the business, and go hand in hand with it. It is an asset and generates value. But with software, more code doesn’t mean more returns. More code means more maintenance, and only some feature of the system might actually deliver value.

There are of course more metaphors. Just have a look at the links below. The city, the garden, and the book metaphor are somewhat popular. The metaphor with living organisms is surprisingly uncommon. The asset metaphor isn’t really a metaphor- more like a mindset. The architecture metaphor is sometimes critiqued, but if we assume that software development is an eingeering discipline, it’s the only metaphor that resonates with engineers. So it’s unlikely to change.

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Software Architecture

Do You Need an Architect?

Architects do typically three things: they own, they coordinate, and they mentor.

As an owner, the architect maintains the integrity of the system at a high level. He designs the foundations, identifies tradeoffs, decides on essential changes.

As a coordinator, the architect facilitates work and optimizes the exchange of information. He connects people, gather information, and plan activities.

As a mentor, the architect provides the intellectual background to understand the system, work autonomously, and improve. He explains concepts and rationale, teaches best practices, and suggests improvements.

It’s a people and technical job.

Which kind of architect you need depend on the project and the team. If the team has enough expertise, they don’t need a mentor. If the team goes well along, they don’t need a coordinator. If the team shares the same view of the system, they can own it collectively.

So maybe you don’t need an architect.

The distinction between architecture and engineering is anyway very blurry. An architect doesn’t do something fundamentally different than an engineer. The three traits exist in every team member. Architects are simply mentoring, coordinating and owning at a different level of scale and responsabilty. Some companies (like Google and Amazon) don’t have architects. They only have engineers with different levels of seniority.

And if you think that coding vs. not coding is a fundamental difference in the job, it’s not. Both architects and engineers are doing software design.

The more happens organically through self-organisation in the team, the better. But self-organisation is hard and it frequently fails. If mentoring, coordination or ownership do not happen as they should, you’re in trouble. Identifying clear responsabilities might help.

So maybe you will need an architect after all.

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