[Mulgara-dev] Architecture questions: connections, sessions, servers

[Gregg Reynolds]

Hi,

I've gone through a bunch of the source code related to
EmbeddedMulgaraServer but I'm still a little unclear on some issues.  The
basic process seems to be:  EmbeddedMulgaraServer launches a mulgara server,
then configures Jetty with some servlets and launches it (actually two of
it).  When a request for e.g. the sparql servlet arrives, the query is
extracted, compiled, and executed against the server.

Where I'm not clear is the relation between the "server" and the sparql
processing servlet that queries the server.  I gather the servlet must talk
to the server via an RMI connection, correct?  But it looks to me like the
sparql servlet is instantiating a server, via ServerMulgaraServlet.  I'm
afraid I don't know much about RMI, but I assume the sparql servlet must be
using some kind of proxy or stub to talk to the server over rmi; is that
close?

More generally, can anybody clarify what is meant by such terms as
"session", "connection", "factory", etc. in the source?  For example,
sometimes a variable of type SessionFactory is named sessionFactory, but the
comments indicate it is supposed to be a database.  Elsewhere an MBean is
called a database.  Sometimes "session" seems to mean HTTP session in the
servlet, other times it seems to mean a session with the database..  It's
all rather confusing, I'm afraid.

FYI I'm trying to use the conceptual categories and architectural structures
outlined in Architecture of a Database
System<http://books.google.com/books?id=aBPcm3C1avMC&printsec=frontcover&dq=architecture+of+a+database+system&source=bl&ots=jKrOGYj0Fo&sig=kIJnkzIf3wPqS8jX6dvnWtHx8iI&hl=en&ei=BlABTaHaH8SAlAf6v7yMCw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCEQ6AEwAQ#v=onepage&q&f=false>,
by Hellerstein, Stonebraker, and Hamilton.  (PDF copy available online,
search for the title), which is a terrifically clear overview of terms and
concepts many of which should in principle apply to any RDF database system.

Thanks,

-Gregg
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