It Will Never Work in Theory

Purposes, Concepts, Misfits, and a Redesign of Git

Posted Sep 30, 2016 by Greg Wilson

Santiago Perez De Rosso and Daniel Jackson: "Purposes, Concepts, Misfits, and a Redesign of Git", SPLASH 2016.

Git is a widely used version control system that is powerful but complicated. Its complexity may not be an inevitable consequence of its power but rather evidence of flaws in its design. To explore this hypothesis, we analyzed the design of Git using a theory that identifies concepts, purposes, and misfits. Some well-known difficulties with Git are described, and explained as misfits in which underlying concepts fail to meet their intended purpose. Based on this analysis, we designed a reworking of Git (called Gitless) that attempts to remedy these flaws. To correlate misfits with issues reported by users, we conducted a study of Stack Overflow questions. And to determine whether users experienced fewer complications using Gitless in place of Git, we conducted a small user study. Results suggest our approach can be profitable in identifying, analyzing, and fixing design problems.

This paper presents a detailed, well-founded critique of one of the most powerful, but frustrating, tools in widespread use today. A follow-up to earlier work published in 2013, it is distinguished from most other discussion of software design by three things:

It clearly describes its design paradigm, which comprises concepts (the major elements of the user's mental model of the system), purposes (which motivate the concepts), and misfits (which are instances where concepts do not satisfy purposes, or contradict one another). It lays out Git's concepts and purposes, analyzes its main features in terms of them, and uses that analysis to identify mis-matches. Crucially, it then analyzes independent discussion of Git (on Stack Overflow) to see if users are stumbling over the misfits identified in step 2.

That would count as a major contribution on its own, but the authors go further. They have designed a tool called Gitless that directly addresses the shortcomings they have identified, and the penultimate section of this paper presents a usability study that compares it to standard Git. Overall, subjects found Gitles more satisfying and less frustrating than Git, even though there was no big difference in efficiency, difficulty, or confusion. Quoting the paper, "This apparent contradiction might be due to the fact that all of the participants had used Git before but were encountering Gitless for the first time without any substantive training. Some participants (2 regular, 1 expert) commented that indeed their problems with Gitless were mostly due to their lack of practice using it."

This paper is one of the best examples I have ever seen of how software designs ought to be critiqued. It combines an explicit, coherent conceptual base, detailed analysis of a specific system, design grounded in that analysis, and an empirical check of that design. Sadly, nothing shows the actual state of our profession more clearly than the way this work has been greeted:

In some respects, this project has been a fool's errand. We picked a product that was popular and widely used so as not to be investing effort in analyzing a strawman design; we thought that its popularity would mean that a larger audience would be interested in our experiment. In sharing our research with colleagues, however, we have discovered a significant polarization. Experts, who are deeply familiar with the product, have learned its many intricacies, developed complex, customized workflows, and regularly exploit its most elaborate features, are often defensive and resistant to the suggestion that the design has flaws. In contrast, less intensive users, who have given up on understanding the product, and rely on only a handful of memorized commands, are so frustrated by their experience that an analysis like ours seems to them belaboring the obvious.

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