Musing on abstraction

Angelo Hulshout · October 23, 2005

The following is a musing on the concept of abstraction - I’ll be refining it over time…

A short while ago, I was involved in the creation of a product roadmap, and budget discussions for the first year of implementing that roadmap. A discussion that kept recurring in different settings during this process focussed on a concept that been at the center of dicussions on software engineering for years:


In another discussion around the same time, on Operating System Abstraction Layers and Hardware Abstraction Layers (OSAL and HAL), the same topic popped up, showing another set of examples of how people talk about, think about and use abstraction. This triggered me to write the following short text about one of the most dangerous concepts in software engineering…

Abstraction is one of the tools of the software architect - next to generalisation, composition, and others. Within the architect’s toolbox, abstraction is one of the most dangerous tools. It’s about as dangerous as generalisation, but at least generalisation has some sort of negative sound to it that warns people to apply it with a bit of care. Abstraction doesn’t have that sound to it, instead it is mostly seen as a way to simplify things and make it easier to reason about certain problems.

As we know, dictionaries tend to describe the same word in different ways, but most definitions of abstraction in our context as software and system engineers can be translated into something like ‘removing unnecessary detail in order to create an understandable view of a problem’.

First of all, this way of regarding abstraction is correct, but while it is intended to be applied in design of an architecture, it is often applied in discussions around the design process. A good example of this I found in the roadmapping and budget discussions, where management wanted to get initial effort estimation for development of a new subsystem. The date set for that product was set about two years in the future and initial feasibility studies had not started at the time. As a result there were just as many opinions on how to design the system as there were people involved in the estimation discussions. The only way out in such a situation - given that management does not take ‘no estimation’ for an answer - is by involuntarily applying abstraction. The subsystem is subdivided into chunks, called hardware and software and rough estimations based on functionality implemented in each of these are made up and discussed.

A lot of things get lost in this process - including attention for the system architecture, and it’s spin-off, such as such as selection of a useable (embedded) operating system.

When estimating software development efforts, engineers assume an operating system to be present, so the selection and evaluation process - which does take time and money - is not made part of the estimation. Luckily we noticed this, but the risk of oversight is evident, given that an operating system was in use for existing products (hey, it’s there, so why bother selecting another one).

On reconsidering this - about a month after the initial posting, I must add that there’s another factor that is not helping us here. At estimation meetings in the organisation I’m talking about, there’s usually about 6 engineers involved in estimations, but often none of them brings or creates a few design figures as input for the meeting. Everything is done from the top of people’s heads.

Another example comes from an architecting assessment a longer while ago. A company developed a product consisting of two carts, both involving a number of electronical, mechanical and software parts. At some point, with cost reduction on the bill of materials in mind, the software architect came up with the idea to run all software, except for some communications related stuff, on one processor, in one of the carts. Effectively, this meant that one cart would get a better processor, and the other one would get a simple microcontroller - with a slight reduction of material cost as a result. Since the two carts were designed only for end user logistics purposes, and the two were only used in conjunction, this looked workable.

What was not taken into account, because it was abstracted away, was the fact that the product also had to be assembled and tested before delivery. This was done at the manufacturing site, where the following problem occurred: one cart was assembled in about half the time as the other one. Because only one of them ran all software, both carts were needed for delivery testing. Because of the difference in assembly time, a queue of carts developed at the test center. This resulted in costly changes to the assembly lines, and less manufacturing throughput.

Combined with the fact that the simple microcontroller was not powerful enough, the anticipated material cost reduction turned out to be an over-all cost increase. One could argue that this is not a matter of abstraction, but of not taking into account the full scale of the problem. In a way, I think this is still a form of abstraction, because abstraction leads to simplification, and in this case, oversimplification of the problem statement.

Because of these examples, and a few others, I more and more getting to the conclusion that we should be very careful when applying abstraction in our work. Abstraction introduces the risk of oversimplification, and oversimplification makes us miss the important details.

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