QVD Symbol Tables

Each field of a QVD table has its own symbol table. It holds the distinct values of the field, called symbols. The rows of the table do not contain the values themselves but refer to a symbol by its position in the symbol table.

Structure

A symbol table is a sequence of symbols without any header, padding or separator. Its position and size within the binary part are given by the Offset and Length of the field in the header, and the number of symbols by NoOfSymbols.

Symbols are numbered from 0 in the order in which they are stored. This number is the index that the records of the index table refer to.

In all observed files:

• each value occurs only once in a symbol table,
• the symbols are stored in the order in which they first occur in the rows of the table, and
• NULL is not stored as a symbol. How NULL is represented is described on the Index table page.

Symbol types

Each symbol starts with a type byte, followed by the value. The type byte determines how the value is encoded and therefore how many bytes the symbol occupies.

Type byte	Type	Value
0x01	Integer	32-bit signed integer
0x02	Double	64-bit floating point number
0x04	String	Text, terminated by a NUL byte
0x05	Dual integer	32-bit signed integer, followed by a text terminated by a NUL byte
0x06	Dual double	64-bit floating point number, followed by a text terminated by a NUL byte

Integer

01

int32 (4 bytes)

Double

02

float64 (8 bytes)

String

04

UTF-8 text

00

Dual integer

05

int32 (4 bytes)

UTF-8 text

00

Dual double

06

float64 (8 bytes)

UTF-8 text

00

Type byte / terminatorNumber (little-endian)Text

The type of a symbol is determined by each symbol individually. A field may therefore contain symbols of different types. In the observed files, for example, a field with decimal amounts contains doubles, while whole amounts in the same field are stored as integers.

Unverified

It is not confirmed whether other type bytes, such as 0x03, occur.

Numbers

Integers are 32-bit signed integers in two’s complement. Doubles are 64-bit floating point numbers as defined by IEEE 754 (binary64). Both are stored in little-endian byte order.

Strings

Strings are encoded in UTF-8 and terminated by a single NUL byte (0x00). There is no length prefix; the end of a string is given by the terminator only.

Unverified

It is not confirmed how empty strings are stored, or whether strings can contain a NUL character.

Dual values

A dual value combines a number with a text. The number is the value used for calculations, while the text is its display representation. Dual values are used for data that has both a numeric and a textual meaning, such as dates.

For example, a date is stored as a dual integer with the number 44428 and the text 20.08.2021. In the observed files, dates are stored as the number of days since 1899-12-30, and the text is formatted according to the field’s number format.

The number and the text of a dual value are stored independently of each other.

Example

The symbol table of a field with the three values Open, In Progress and Completed consists of three strings, 30 bytes in total:

Symbol table of a string field

04 4f 70 65 6e 00                                 → symbol 0: "Open"
04 49 6e 20 50 72 6f 67 72 65 73 73 00            → symbol 1: "In Progress"
04 43 6f 6d 70 6c 65 74 65 64 00                  → symbol 2: "Completed"

The symbol table of a field with the two values 0 and 1, stored as dual integers:

Symbol table of a dual integer field

05 00 00 00 00 30 00                              → symbol 0: 0, "0"
05 01 00 00 00 31 00                              → symbol 1: 1, "1"