+@c PSPP - a program for statistical analysis.
+@c Copyright (C) 2019 Free Software Foundation, Inc.
+@c Permission is granted to copy, distribute and/or modify this document
+@c under the terms of the GNU Free Documentation License, Version 1.3
+@c or any later version published by the Free Software Foundation;
+@c with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+@c A copy of the license is included in the section entitled "GNU
+@c Free Documentation License".
+@c
+
@node System File Format
@appendix System File Format
the format of a system file.
System files use four data types: 8-bit characters, 32-bit integers,
-64-bit integers,
+64-bit integers,
and 64-bit floating points, called here @code{char}, @code{int32},
@code{int64}, and
@code{flt64}, respectively. Data is not necessarily aligned on a word
int32 rec_type;
int32 label_count;
-/* @r{Repeated @code{label_cnt} times}. */
+/* @r{Repeated @code{n_label} times}. */
char value[8];
char label_len;
char label[];
@table @code
@item int32 measure;
-The measurement type of the variable:
+The measurement level of the variable:
@table @asis
+@item 0
+Unknown
@item 1
-Nominal Scale
+Nominal
@item 2
-Ordinal Scale
+Ordinal
@item 3
-Continuous Scale
+Scale
@end table
-SPSS sometimes writes a @code{measure} of 0. PSPP interprets this as
-nominal scale.
+An ``unknown'' @code{measure} of 0 means that the variable was created
+in some way that doesn't make the measurement level clear, e.g.@: with
+a @code{COMPUTE} transformation. PSPP sets the measurement level the
+first time it reads the data using the rules documented in
+@ref{Measurement Level,,,pspp, PSPP Users Guide}, so this should
+rarely appear.
@item int32 width;
The width of the display column for the variable in characters.
@table @asis
@item 5
-A set of grouped variables (according to Aapi H@"am@"al@"ainen).
+A named variable set for use in the GUI (according to Aapi
+H@"am@"al@"ainen).
@item 6
Date info, probably related to USE (according to Aapi H@"am@"al@"ainen).
field sum to the size of the system file in bytes.
@end table
-The data header is followed by @code{(ztrailer_ofs - 24) / 24} ZLIB
+The data header is followed by @code{(ztrailer_len - 24) / 24} ZLIB
compressed data blocks. Each ZLIB compressed data block begins with a
ZLIB header as specified in RFC@tie{}1950, e.g.@: hex bytes @code{78
01} (the only header yet observed in practice). Each block
@item int32 n_blocks;
The number of ZLIB compressed data blocks, always exactly
-@code{(ztrailer_ofs - 24) / 24}.
+@code{(ztrailer_len - 24) / 24}.
@end table
The fixed header is followed by @code{n_blocks} 24-byte ZLIB data