Skip to main content

(Software) Architecture = Policy + Mechanism

In the early 1980's Bob Kowalski made famous an interesting equation: Program = Logic + Control. The idea of that equation was that programming was essentially a combination of logic -- i.e., what you wanted done -- with algorithm -- how you wanted it done.

It is a fairly commonplace fact that any non-trivial program has a similar flavor to it: there is often a substantial amount of machinery that is used to deliver the value in the program; together with some form of policy statement/expression that governs the precise requirements for a particular execution of the program.

The larger the program, the more obvious it is that there is this layering into mechanisms and policies. For example, one could argue that a word processor's mechanisms are all the pieces need to implement text editing, formatting and so on. If the word processor supports styles, especially named styles, then these styles are a simple form of policy.

At larger scales, when considering networked applications for example, there are often formal languages used to express the different kinds of policy that apply: security policies, management policies and so on.

So, my thesis of the day is that Architecture consists of the specification of the mechanisms together with the specification of the policies that may apply.

Is this useful? Being clear about the `natural divisions' in a complex structure is the first step in making that structure tractable.

Popular posts from this blog

Minimum Viable Product

When was the last time you complained about the food in a restaurant? I thought so. Most people will complain if they are offended by the quality or service; but if the food and/or service is just underwhelming then they won't complain, they will simply not return to the restaurant. The same applies to software products, or to products of any kind. You will only get negative feedback from customers if they care enough to make the effort. In the meantime you are both losing out on opportunities and failing your core professional obligation. Minimum Viable Product speaks to a desire to make your customers design your product for you. But, to me, it represents a combination of an implicit insult and negligence. The insult is implicit in the term minimum. The image is one of laziness and contempt: just throw some mud on the wall and see if it sticks. Who cares about whether it meets a real need, or whether the customer is actually served. The negligence is more subtle but, in the end,

Comments Should be Meaningless

This is something of a counterintuitive idea: Comments should be meaningless What, I hear you ask, are you talking about? Comments should communicate to the reader! At least that is the received conventional wisdom handed does over the last few centuries (decades at least). Well, certainly, if you are programming in Assembler, or C, then yes, comments should convey meaning because the programming language cannot So, conversely, as a comment on the programming language itself, anytime the programmer feels the imperative to write a meaningful comment it is because the language is not able to convey the intent of the programmer. I have already noticed that I write far fewer comments in my Java programs than in my C programs.  That is because Java is able to capture more of my meaning and comments would be superfluous. So, if a language were able to capture all of my intentions, I would never need to write a comment. Hence the title of this blog.

In Praise of Crappy Code

Not all code needs to be perfect! This is pretty heretical thinking for a software engineer. The issue is simple: how do you go about developing software for a small fixed budget. Imagine that you have $500 to implement a solution to a problem. If you spend more than that you will never recoup the extra that you spent. This comes up a lot in systems integration scenarios and also in customization efforts. Someone wants you to 'tweak' an application that they are using; you know that no-one else would want that feature and that if you spend more than what the customer will pay you will end up losing money. From the customer's perspective, the common 'time and materials' approach to quoting for software development is a nightmare. Being able to offer a fixed price contract for a task is a big benefit for the customer. But, how much do you quote for? Too much and you scare the customer away. Too little and you lose money. This is where 'crappy code' com