Michael's description is something like what GemStone/Smalltalk provides—each login is assigned an array of SymbolDictionary instances (a SymbolList), and compiling is in the context of a SymbolList. You can have multiple globals visible with the same name, but the first one found is used. Different code can be compiled with different instances of SymbolList, and multiple instances of SymbolList can reference the same SymbolDictionary. Security can be addressed by giving a user a SymbolList that does not reference things that should be hidden.