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2.MetaData
MetaData fully describes all parts of QVD file.
Logically we can divide MetaData into
- general information about the table (dates, filename, software version, etc.)
- technical information about the table (name, number of rows, rows table offset, bit index width, etc)
- technical information about each table column (name, number of unique values, symbol table offset, etc)
MetaData are represented as XML (utf-8 text) enclosed into "QvdTableHeader" tags. There might be several "white space symbols" between MetaData section and binary section, they should be ignored. White symbols which I found were:
- 0: zero byte
- \n: line break
- \r: carriage return
Most important metadata elements are described in the following sections. Metadata examples are included in examples directory: XML files there contain metadata section of corresponding QVD file.
Metadata here and below is described in the form "tag: meaning". There are no metadata sections as such (except for columns section - it is surrounded by tags, see below).
Tags of interest in general section:
CreatorDoc: name of QVW file which script has produced this QVD (might be empty...)
CreateUTCTime: creation timestamp
QVBuildNo: QlikView build version
Comments: table comments (usually empty)
Lineage: script statements which produced this QVD (this should be switched on in QlikView settings otherwise will be empty). When not empty provides a lot of information about the table!
TableName: name of the source relational table
RecordByteSize: size of the row in the rows table (in bytes)
NoOfRecords: number of records in the source table and in the rows table
Offset: offset of the rows table (from the beginning of the binary section)
Length: length of the rows table in bytes
Columns metadata are contained in "Fields" array, each column is enclosed into "QvdFieldHeader" tag. Each column has following important tags:
FieldName: name of the column in the source table
Offset: offset of the symbol table (from the beginning of the binary section, first symbol table will have offset 0)
NoOfSymbols: number of unique column values
Length: length of the symbol table in bytes
BitOffset, BitWidth, Bias: are related to the rows table and are described in rows page.
There are other tags in the columns metedata (like Type, Fmt, etc.) - none of them can be used in the data extraction process. So I can say nothing about their meaning.