Tarballs don't have a TOC and can't easily index into individual entities.
One could create a utility to make tarballs with a TOC and the ability to index while still remaining compatible with tar and gzip. Pigz is one step in the direction.
One could create a utility to make tarballs with a TOC and the ability to index while still remaining compatible with tar and gzip. Pigz is one step in the direction.
to extract a particular entity 'tar -vxf tarball.tar path_in tarball_to_entity`
edit: good points on it not being efficient for large archives, just demonstrating it is possible.
It isn't that it is possible, it is that is horribly inefficient.
Zips on other hand unify storage and compression such that one has random access to particular file, hence most modern file formats are zips with xml or json inside.