Torben Ægidius Mogensen's "Basics of Compiler Design, Chapter 4: Scopes and Symbol Tables"
Read Chapter 4 on scope of names and symbol tables.
Click http://web.archive.org/web/20120915222417/http://www.diku.dk/hjemmesider/ansatte/torbenm/Basics/basics_lulu2.pdf link to open resource.