Apt database is binary, textual or other format?
How other programs can access it?
2. Is possible download data from sites
in machine convenient form?
1. Text. (See below.)
2. Yes, you can download the .deb files from either of those locations. As memory serves, the links to download the .deb may not always be hyperlinks. It's easy to wget said links as the URL is there.
Now, concerning your first question, have some light reading: