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Below is some explanation about QVD & QVW:
QlikView Data files are know as QVDs; which are used to extract and store data into and from QlikView. This means that whichever table you read, from whichever database, you can store it in the QVD format before or after any transformations you perform on the table.
The special characteristics of this file type are:
• It contains only one logical table.
• It uses a special algorithm to compress the data, achieving compression rates of up to 90 percent, depending on the fields cardinality of the underlying data.
• When reading a QVD table file in QlikView, the loading speed is anywhere from 10 to 100 times faster than when loading from a database. When the table file is being read without applying any transformations, QlikView performs an optimized load (super-fast mode).
One of the main advantages of using QVD files is that, once you have a QVD on your disk, the table can be exploited by more than one QlikView application. This reduces the load on the database server, and optimizes QlikView resources and development time. This process is called QVD staging, The QVD file will also be particularly useful when dealing with Incremental Load scenarios.
QlikView Documents files are know as QVWs; which are used to generate QVDs, prepare Data Model and build visualizations. We can load one QVW file into another QVW file (Binary Load). This will save time and cost required to prepare the similar data model once again.
Characteristics of this file type are:
• Load Data from Excel, CSV, Flat Files, RDMS etc. systems.
• Place to write a QlikView script.
Hope this will be helpful.
Reference: QlikView 11 for Developers