Databases &/or binary data

[David Jaquay <djaquay@dejazzd.com>]

Forgive this very simple set of questions, but I'm just getting started 
with Scheme & PLTScheme.

I'm wanting to write an application, similar in nature, I suppose, to 
SimCity, but dealing with railroads.  (Like Railroad Tycoon, but not a 
game.)  I've been playing with (and really enjoy, actually) the GUI classes 
in MrEd, and have a pretty good handle on how to deal with writing my own 
objects (using mzscheme objects).

But at runtime, rather than be limited to available memory, I'd like to 
persist various objects to a random-access store, and it's not a clear to 
me how I'd do that in MrEd.

1) Looking at the PLT Scheme Libraries & Extensions page, I see that I can 
get ODBC connectivity, but I'd rather not require application users to 
install and maintain a separate database process.

2) I'm not averse to writing my own simple b+tree implementation, but I'm 
still a bit fuzzy on how that'd work given Scheme's I/O routines.

3) I found write-image-to-file & read-image-from-file, which look like 
simple ways to save program state, but don't do much for keeping other 
things on disk during program execution.

4) I've seen discussion on this list regarding C/C++ code being mixed with 
MrEd, although I'd rather stick with pure Scheme, (unless that winds up not 
being practical for this type of usage).

What are typical ways for solving this type of problem in Scheme and/or 
MrEd?  Thanks very much in advance for your assistance.

Regards,
Dave