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Earlier quoted context omitted.
It's code that's been developed and it's been running for decades, I'm afraid.
developed in java and running for decades? how long has the language been around?
2) treat each app as a black box, understand the major data flows involved (which data sources is it interacting with? is it doing reads or writes? which tables)
3) treat each app as a black box, and try to understand the interactions between each app and any external components (other apps, web services, etc)
4) identify the overall architecture, determine the class hierarchy for each app, identify the major classes and functionality
By this stage you should be ready for a rewrite. At no point do you need to go into the code in any great depth.
But before you start just pray to Omnissiah (http://warhammer40k.wikia.com/wiki/Machine_God).
Your question sounds like something that someone with either no real experience and/or no experience of an object-oriented language would ask.
100 million lines is a lot of code. Why do you need to "parse it to extra the AST"? That's crazy.
Do you have the original design documents and architectural documentation? If you do, read it.
What type of application has 100 million loc's? Windows 7 has 40 million lines of codes so I'm wondering why type of application/software it is.
I bet the core java code the team actually wrote is 2 orders of magnitude smaller.
With a codebase like that, it's better to look at it through the users' eyes, rather than trying to reverse engineer the business from the code. Things that look like bugs in the code may actually be features for the users, or may have been absorbed so long ago that they've fundamentally changed the nature of the business. You don't need to understand the whole codebase. It will take years. Best to focus on what the…
The size of the thing and the way we thought we were going to work is quite different.
For instance, suppose we produce AST for all the routines/pieces of logic/you_name_it we wanted to then find similar patterns or clusters that would give us hint to then work on a "pareto-like" way.
As already stated it's not ONE project, it's an old (but still running), poorly-documented codebase produce in decades around this big firm we work for.
What type of application has 100 million loc's? Windows 7 has 40 million lines of codes so I'm wondering why type of application/software it is.
I have a quite strong feeling that certain complex automated systems within financial services / insurances domain could reach those LOC levels. Including all the frontend side, internal backend logic, possible web services, internal tools, tests, tens to hundreds of interfaces to different kinds of external services, report generation, libraries, etc.
Just curious: what application needs 100M lines of anything?
It's not just one application. It's many of them.
Since a rewrite is in the card (hopefully) there is something wrong with the entire system.
* Identify where the applications interact with each other.
* Identify the most problematic applications.
* Rewrite those (starting with the smallest) while trying to keep the interfaces between applications constant.
And involve end users as much as possible.
Earlier quoted context omitted.
How does that stop you from making a callgraph? (On the off chance that you don't know what that is: http://en.wikipedia.org/wiki/Call_graph )
It doesn't. I was just answering about the code generator thing you mentioned.