The compression attribute determines how a field is compressed/decompressed when writing to/reading from the database. Fixed compression is effectively no compression at all; the field is stored/retrieved without any compression or decompression. Variable compression means that the data will be compressed when written to the database and decompressed (to match the view definition) when read from the database. The filler character and justification determine which character is stripped /added from the record and from which end.

V-type compression will compress multiple adjacent blanks into a single blank. This can occur anywhere within the field. Note that this process is irreversible. Decompression will only add blanks at one end of the field.

The decompression will add the filler character to the field to pad it to the necessary length.

The compression logic will remove the filler character from either the left or right end of the field (depending on justification), until no more filler characters are left or the field is empty. The decompression will add the filler character to the field to pad it to the necessary length (as specified in the view). If the field is left justified, the truncation/padding occurs on the right. If the field is right justified, the truncation/padding occurs on the left side of the field.

Four data types are supported:

Text	Character data
Binary	Binary (unstructured) data
Integer	1, 2, 3 or 4 byte unsigned integers
Numeric	Fields containing printable numeric digits ’0’ to ’9’, and ’a’ to ’z’ (when using base 36)

The Integer and Numeric data types support base conversion. Ie. the view may request a base which differs from the base of the stored data. Base conversion is only possible for bases 2 through 36.

A customized format definition has the following syntax.

format=( [predefined fmt,] format specifier, ...)

You may base your definition on a predefined format and override certain attributes, or fully define a new custom format using format specifiers.

The

format specifier

is one of the following:

Fixed	fixed compression
Text	text data
Ljust	left justification
Rjust	right justification
Filler(<char>)	filler character
Base(nn)	base nn

Here is an example of a field definition with explicit format:

Attributes, (Base(2), Filler(0)), 16

This will format a numeric field into 16 characters in base 2 (binary base). Each position will be either ’zero’ or ’one’ and leading zeroes (the filler) will extend the value on the left if it is shorter that 16 characters. If we want the value as four hexadecimal digits instead then we should use this format:

Attributes, (Base(16), Filler(0)), 4

Which is the same as the short form (in the table above):

Attributes, X, 4