How does a package run without all the dependencies being installed on the target system?

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http://unix.stackexchange.com – I am trying to build the latest version of subversion on ubuntu 12.10 and was having some trouble completing ./configure as I seemed to be getting a never ending stream of configure: error: x not found messages. I installed apr and supplied the paths to the apr-1-config file to get rid of the first, then I installed sqlite etc. and currently I am working on configure: error: Expat not found. Prior to attempting an install of 1.7.7, I had just used apt-get install subversion which installed 1.7.5 and was working fine. My question is, why does 1.7.5 work on my machine if I didn't have sqlite, a (HowTos)