Tag Archives: legacy code

Legacy Code: How To Reverse-Engineer

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1. Introduction

In a previous post I came to the conclusion that reverse-engineering might be needed the most by new team members working in an already established project.

This covers the scenario when knowledge is not widespread and there is little time to get “the full picture” of what’s going on before being asked to be a contributive member of the team.

The only possibility is to go through the code and try to understand what the team has come up with over the lifetime of the project. Of course, experienced and /or talented programmers could be able read and understand the code fast, but they would still need to rebuild all the discussions with the customers, if they want to understand what the system is supposed to do. For the latter, some diagrams can definitely help.

In principle, reverse-engineering should be used to bring source code into a Model Driven Development process and, for this reason, it should be necessary only once. However, I have seen the process applied either just once to create some diagrams and produce some kind of documentation, or by having someone doing it regularly from the source code, just to maintain the diagrams in sync with the code. I normally call the output of the latter case UML “pictures” or “paintings“and not “diagrams“, because they are not used to communicate among stakeholders before or during development, but probably only for some contractual clause.

Instead, I’ll identify some clear objectives that, depending on the size of the project, can be achieved relatively quickly. We are going to use our tools

  1. to identify all the entities defined in the source code to implement the system
  2. to model the most important relations between the defined entities.

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Legacy Code: How Can Model Driven Development Help?

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This post tries to summarize my professional experience with legacy code and define the scope where MDD can help with it.

In recent years there has been a debate about how to define legacy code. I am probably not qualified to attempt any formal definition, but I am going to give one that corresponds to my experience.

Legacy code is that type of source code you are required to work with when you join a team of an already long-running project and you, like most of the team, don’t have a clue, not only about what the code does, but also about what the software is supposed to do. In a high percentage of cases you are immediately told by senior team members that the documentation is out-of-date, if available at all.

Very soon, new requirements, or, worse, “bugs” to deal with start to arrive.

Should they come either from a newly agreed set of requirements, or a formal test procedure, or from a phone call of an angry customer, the situation is the same, the new member is hardly in the position to deal with the requests with the necessary confidence. Add to that the pressure from the Project Manager that sees a red bar about bugs growing up in some spreadsheet and the life of the new member may become immediately very miserable indeed.

I am sure many of us have been there and you know what I mean.

Luckily, Model Driven Development can help in these situations. It’s not a panacea, also because it can have different levels of acceptance in different teams, but it’s the process that I have used every time as soon as I am given access to the source-control system of a project, with a very satisfying success rate.

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