apt algorithm for determining which packages to upgrade???

[hanasaki <hanasaki@hanaden.com>]

apt algorithm for determining which packages to upgrade???

Any docs out there on the algorithm apt uses to determine what to 
upgrade in a "upgrade" or "dist-upgrade"?

does it parse the Packages.gz files each time?
does it build a db/rdbms out of the Packages.gz that apt-get gets?

how are the and/or and version >=, > ... consumed, recursively? to 
determine requested packageA needs packageB and C and B needs D and 
maybe even D conflicts with A?

thanks.