Dibyendu Majumdar wrote:
3. Following two questions are related to the
org.apache.derby.iapi.services.monitor package.
a) Is my understanding correct that each module must know what other
module it depends upon and try to boot the required module? Thus, the
Monitor system does not inject dependencies, each module needs to find
any modules it depends upon?
Modules explicitly boot other modules that they need. E.g. the database
module boots (through the monitor) an access factory and a dictionary
(system catalog) (and others). The module doesn't care about the
implementation of the modules it requires, just that they work in the
configured environment.
So there is no automatic dependency injection.
b) Is a Service a synonym for a database instance on disk?
Yes, but service is wider than that. A service is a collection of
modules working together to provide a set of functionality (a service).
A service can be non-persistent or persistent. A persistent service is
one who's configuration is derived from a service.properties file,
though there's no requirement that there is any persistent data or that
the service.properties file is actually a file on disk (or even a file).
A database instance on disk is an instance of a persistent service, the
jdbc driver is an instance of a non-persistent service.
This covers some of it at a high level:
http://db.apache.org/derby/binaries/ApacheDerbyInternals_1_1.pdf
HTH,
Dan.
