Portage is missing some important information about packages.
The purpose of this database is to easily answer questions:
- What ebuilds provide file foobar (or /path/to/foobar)?
- What files ebuild foobar provides?

The database should contain the following information:
ename		name of each ebuild
eversion	version of each ebuild
eused		USE-flags that were in effect while package was installed
		and used by the package (IUSE)
fpath		path to each file
fname		name of each file

Structure of the database could be:
PK = primary key (unique, indexed, notnull)
FK = foreing key
R = reference, can return multiple rows
notnull = value can not be missing


TABLE ename
column		type
---------------------
id		int, PK
name		string, unique, indexed, notnull


TABLE eversion
column		type
---------------------
id		int, PK
version		string, unique, indexed, notnull


TABLE useflags
column		type
---------------------
id		int, PK
flag		string, unique, indexed, notnull


TABLE flaglist
column		type
---------------------
id		int, PK
setid		int, indexed, notnull
flagid		R(useflags.id), notnull


TABLE fpath
column		type
---------------------
id		int, PK
path		string, unique, indexed, notnull


TABLE fname
column		type
---------------------
id		int, PK
name		string, unique, indexed, notnull


TABLE filelist
column		type
---------------------
id		int, PK
setid		int, indexed, notnull
pathid		FK(fpath.id), notnull
nameid		FK(fname.id), indexed, notnull


TABLE main
column		type
---------------------
id		int, PK
name		FK(ename.id), notnull
version		FK(eversion.id), notnull
flags		R(flaglist.setid)
files		R(filelist.setid), indexed



Referencing goes like this:

main -+-> ename
      +-> eversion
      +-> flaglist -+-> useflags
      |             | ...
      |
      `-> filelist -+-> fpath, fname
                    | ...

A row in table 'main' is a version of an ebuild installed with
given USE-flags. Only those USE-flags that the ebuild really uses
should be listed.
According to 'filelist.setid' list of 'fpath, fname' pairs can be
retrieved.

This structure solves the task given.

Database design by Pekka "PQ" Paalanen