Wow, this post got a lot more attention than I thought it would. Most of it was along the same lines, so I’ll answer it here.
Anyone suggesting, SQLite, Excel, Access, Esent, Embedded RavenDB, Munin, Embedded FireBird, MS SQL CE, DB4O or anything like it – that isn’t the purpose of the question. I am not trying to figure out if the candidate knows about embedded databases.
Performance isn’t much of a concern, we expect up to several thousands entries per phonebook, but not beyond that, and speed should be in the human response time range (hundreds of milliseconds).
I rejected JSON / XML file formats because I wanted to make the task harder than just using the built-in Linq API and serializing to a file.
Out of this question, I want actual code that I can try out, not just some high level design. I estimate that if you know what you are doing, this should take less than half an hour. At high school, I think it took about two hours, and that was in unmanaged land.
Some people questioned what is the purpose of this question, under what scenarios is it valid, etc.
Put simply, it is valid because it tests a wide range of topics in a candidate abilities. I don’t feel that I need to go into world building to setup a scenario for an interview question.
He spells out the requirements for a basic database engine with indexing. It's a multifaceted problem that can expose a lot about a candidate in their solution. Are concerns separated logically? How is performance addressed against disk I/O? How is code correctness validated (e.g. testing)? To submit a project that just wraps another database is disingenuous. He's looking for people that can solve problems head-on, not just pass the buck.
Exactly. More to the point, it forces a candidate to actually do a fairly complex task that still can be done in a short amount of time. It shows me how they think, whatever they have any idea how computers actually work. If you can’t complete this task, you don’t understand basic file IO. That means that you might be a great front end developer, but I need someone who can do more than that.