new rc.d style & ordering

I've read the paper at http://www.mewburn.net/luke/talks/auug-2003/ and 
there's a subject not clear to me yet:

What about services such as apache, which may or may not depend on services 
such as databases, if they are installed? For example: If I run apache with 
php and mysql, I want mysql to be started before apache. But there are users 
who don't require mysql, so putting a hard dependancy (with REQUIRE keyword) 
in apache.sh isn't an option (and similary with other databases and 
services, such as postgresql, ldap, etc.). Maybe there's a 
REQUIRE-IF-INSTALLED functionality I'm missing (though I think that would be 
a bad idea)?

(Also, in the above example, mysql is actually a dependancy of PHP which 
runs as a module in apache, but apache can require mysql by itself (as 
authentication database) - what then?).

I'm asking this in attempt to figure out what is needed to convert startup 
scripts such as apache.sh to new-style rc.d.

-- 
Every sufficiently advanced magic is indistinguishable from technology
    - Arthur C Anticlarke