qvd and qvw are files
qvd is a like a table in a database but in QlkView proprietary format
useful for fast load of data (incremental load) in Qlik and/or for non trivial data architecture (2/3n layer)
qvw is
- nothing when you create it
- script, to load and transform data from source (database, web, ftp, qvd too as qvd is a table); like an etl
- in memory database: after you execute the script, usually you have your qlik db in memory
- user interface (charts) built on the in memory database
