1 @node System File Format
2 @appendix System File Format
4 A system file encapsulates a set of cases and dictionary information
5 that describes how they may be interpreted. This chapter describes
6 the format of a system file.
8 System files use four data types: 8-bit characters, 32-bit integers,
10 and 64-bit floating points, called here @code{char}, @code{int32},
12 @code{flt64}, respectively. Data is not necessarily aligned on a word
13 or double-word boundary: the long variable name record (@pxref{Long
14 Variable Names Record}) and very long string records (@pxref{Very Long
15 String Record}) have arbitrary byte length and can therefore cause all
16 data coming after them in the file to be misaligned.
18 Integer data in system files may be big-endian or little-endian. A
19 reader may detect the endianness of a system file by examining
20 @code{layout_code} in the file header record
21 (@pxref{layout_code,,@code{layout_code}}).
23 Floating-point data in system files may nominally be in IEEE 754, IBM,
24 or VAX formats. A reader may detect the floating-point format in use
25 by examining @code{bias} in the file header record
26 (@pxref{bias,,@code{bias}}).
28 PSPP detects big-endian and little-endian integer formats in system
29 files and translates as necessary. PSPP also detects the
30 floating-point format in use, as well as the endianness of IEEE 754
31 floating-point numbers, and translates as needed. However, only IEEE
32 754 numbers with the same endianness as integer data in the same file
33 has actually been observed in system files, and it is likely that
34 other formats are obsolete or were never used.
36 System files use a few floating point values for special purposes:
40 The system-missing value is represented by the largest possible
41 negative number in the floating point format (@code{-DBL_MAX}).
44 HIGHEST is used as the high end of a missing value range with an
45 unbounded maximum. It is represented by the largest possible positive
46 number (@code{DBL_MAX}).
49 LOWEST is used as the low end of a missing value range with an
50 unbounded minimum. It was originally represented by the
51 second-largest negative number (in IEEE 754 format,
52 @code{0xffeffffffffffffe}). System files written by SPSS 21 and later
53 instead use the largest negative number (@code{-DBL_MAX}), the same
54 value as SYSMIS. This does not lead to ambiguity because LOWEST
55 appears in system files only in missing value ranges, which never
59 System files may use most character encodings based on an 8-bit unit.
60 UTF-16 and UTF-32, based on wider units, appear to be unacceptable.
61 @code{rec_type} in the file header record is sufficient to distinguish
62 between ASCII and EBCDIC based encodings. The best way to determine
63 the specific encoding in use is to consult the character encoding
64 record (@pxref{Character Encoding Record}), if present, and failing
65 that the @code{character_code} in the machine integer info record
66 (@pxref{Machine Integer Info Record}). The same encoding should be
67 used for the dictionary and the data in the file, although it is
68 possible to artificially synthesize files that use different encodings
69 (@pxref{Character Encoding Record}).
71 System files are divided into records, each of which begins with a
72 4-byte record type, usually regarded as an @code{int32}.
74 The records must appear in the following order:
84 All pairs of value labels records and value label variables records,
88 Document record, if present.
91 Extension (type 7) records, in ascending numerical order of their
95 Dictionary termination record.
101 Each type of record is described separately below.
104 * File Header Record::
106 * Value Labels Records::
108 * Machine Integer Info Record::
109 * Machine Floating-Point Info Record::
110 * Multiple Response Sets Records::
111 * Extra Product Info Record::
112 * Variable Display Parameter Record::
113 * Long Variable Names Record::
114 * Very Long String Record::
115 * Character Encoding Record::
116 * Long String Value Labels Record::
117 * Long String Missing Values Record::
118 * Data File and Variable Attributes Records::
119 * Extended Number of Cases Record::
120 * Miscellaneous Informational Records::
121 * Dictionary Termination Record::
123 * Encrypted System Files::
126 @node File Header Record
127 @section File Header Record
129 The file header is always the first record in the file. It has the
136 int32 nominal_case_size;
141 char creation_date[9];
142 char creation_time[8];
148 @item char rec_type[4];
149 Record type code, either @samp{$FL2} for system files with
150 uncompressed data or data compressed with simple bytecode compression,
151 or @samp{$FL3} for system files with ZLIB compressed data.
153 This is truly a character field that uses the character encoding as
154 other strings. Thus, in a file with an ASCII-based character encoding
155 this field contains @code{24 46 4c 32} or @code{24 46 4c 33}, and in a
156 file with an EBCDIC-based encoding this field contains @code{5b c6 d3
157 f2}. (No EBCDIC-based ZLIB-compressed files have been observed.)
159 @item char prod_name[60];
160 Product identification string. This always begins with the characters
161 @samp{@@(#) SPSS DATA FILE}. PSPP uses the remaining characters to
162 give its version and the operating system name; for example, @samp{GNU
163 pspp 0.1.4 - sparc-sun-solaris2.5.2}. The string is truncated if it
164 would be longer than 60 characters; otherwise it is padded on the right
168 @item int32 layout_code;
169 Normally set to 2, although a few system files have been spotted in
170 the wild with a value of 3 here. PSPP use this value to determine the
171 file's integer endianness (@pxref{System File Format}).
173 @item int32 nominal_case_size;
174 Number of data elements per case. This is the number of variables,
175 except that long string variables add extra data elements (one for every
176 8 characters after the first 8). However, string variables do not
177 contribute to this value beyond the first 255 bytes. Further, system
178 files written by some systems set this value to -1. In general, it is
179 unsafe for systems reading system files to rely upon this value.
181 @item int32 compressed;
182 Set to 0 if the data in the file is not compressed, 1 if the data is
183 compressed with simple bytecode compression, 2 if the data is ZLIB
184 compressed. This field has value 2 if and only if @code{rec_type} is
187 @item int32 weight_index;
188 If one of the variables in the data set is used as a weighting
189 variable, set to the dictionary index of that variable, plus 1
190 (@pxref{Dictionary Index}). Otherwise, set to 0.
193 Set to the number of cases in the file if it is known, or -1 otherwise.
195 In the general case it is not possible to determine the number of cases
196 that will be output to a system file at the time that the header is
197 written. The way that this is dealt with is by writing the entire
198 system file, including the header, then seeking back to the beginning of
199 the file and writing just the @code{ncases} field. For files in which
200 this is not valid, the seek operation fails. In this case,
201 @code{ncases} remains -1.
205 Compression bias, ordinarily set to 100. Only integers between
206 @code{1 - bias} and @code{251 - bias} can be compressed.
208 By assuming that its value is 100, PSPP uses @code{bias} to determine
209 the file's floating-point format and endianness (@pxref{System File
210 Format}). If the compression bias is not 100, PSPP cannot auto-detect
211 the floating-point format and assumes that it is IEEE 754 format with
212 the same endianness as the system file's integers, which is correct
213 for all known system files.
215 @item char creation_date[9];
216 Date of creation of the system file, in @samp{dd mmm yy}
217 format, with the month as standard English abbreviations, using an
218 initial capital letter and following with lowercase. If the date is not
219 available then this field is arbitrarily set to @samp{01 Jan 70}.
221 @item char creation_time[8];
222 Time of creation of the system file, in @samp{hh:mm:ss}
223 format and using 24-hour time. If the time is not available then this
224 field is arbitrarily set to @samp{00:00:00}.
226 @item char file_label[64];
227 File label declared by the user, if any (@pxref{FILE LABEL,,,pspp,
228 PSPP Users Guide}). Padded on the right with spaces.
230 A product that identifies itself as @code{VOXCO INTERVIEWER 4.3} uses
231 CR-only line ends in this field, rather than the more usual LF-only or
234 @item char padding[3];
235 Ignored padding bytes to make the structure a multiple of 32 bits in
236 length. Set to zeros.
239 @node Variable Record
240 @section Variable Record
242 There must be one variable record for each numeric variable and each
243 string variable with width 8 bytes or less. String variables wider
244 than 8 bytes have one variable record for each 8 bytes, rounding up.
245 The first variable record for a long string specifies the variable's
246 correct dictionary information. Subsequent variable records for a
247 long string are filled with dummy information: a type of -1, no
248 variable label or missing values, print and write formats that are
249 ignored, and an empty string as name. A few system files have been
250 encountered that include a variable label on dummy variable records,
251 so readers should take care to parse dummy variable records in the
252 same way as other variable records.
254 @anchor{Dictionary Index}
255 The @dfn{dictionary index} of a variable is its offset in the set of
256 variable records, including dummy variable records for long string
257 variables. The first variable record has a dictionary index of 0, the
258 second has a dictionary index of 1, and so on.
260 The system file format does not directly support string variables
261 wider than 255 bytes. Such very long string variables are represented
262 by a number of narrower string variables. @xref{Very Long String
263 Record}, for details.
269 int32 n_missing_values;
274 /* @r{Present only if @code{has_var_label} is 1.} */
278 /* @r{Present only if @code{n_missing_values} is nonzero}. */
279 flt64 missing_values[];
283 @item int32 rec_type;
284 Record type code. Always set to 2.
287 Variable type code. Set to 0 for a numeric variable. For a short
288 string variable or the first part of a long string variable, this is set
289 to the width of the string. For the second and subsequent parts of a
290 long string variable, set to -1, and the remaining fields in the
291 structure are ignored.
293 @item int32 has_var_label;
294 If this variable has a variable label, set to 1; otherwise, set to 0.
296 @item int32 n_missing_values;
297 If the variable has no missing values, set to 0. If the variable has
298 one, two, or three discrete missing values, set to 1, 2, or 3,
299 respectively. If the variable has a range for missing variables, set to
300 -2; if the variable has a range for missing variables plus a single
301 discrete value, set to -3.
303 A long string variable always has the value 0 here. A separate record
304 indicates missing values for long string variables (@pxref{Long String
305 Missing Values Record}).
308 Print format for this variable. See below.
311 Write format for this variable. See below.
314 Variable name. The variable name must begin with a capital letter or
315 the at-sign (@samp{@@}). Subsequent characters may also be digits, octothorpes
316 (@samp{#}), dollar signs (@samp{$}), underscores (@samp{_}), or full
317 stops (@samp{.}). The variable name is padded on the right with spaces.
319 @item int32 label_len;
320 This field is present only if @code{has_var_label} is set to 1. It is
321 set to the length, in characters, of the variable label. The
322 documented maximum length varies from 120 to 255 based on SPSS
323 version, but some files have been seen with longer labels. PSPP
324 accepts longer labels and truncates them to 255 bytes on input.
327 This field is present only if @code{has_var_label} is set to 1. It has
328 length @code{label_len}, rounded up to the nearest multiple of 32 bits.
329 The first @code{label_len} characters are the variable's variable label.
331 @item flt64 missing_values[];
332 This field is present only if @code{n_missing_values} is nonzero. It
333 has the same number of 8-byte elements as the absolute value of
334 @code{n_missing_values}. Each element is interpreted as a number for
335 numeric variables (with HIGHEST and LOWEST indicated as described in
336 the chapter introduction). For string variables of width less than 8
337 bytes, elements are right-padded with spaces; for string variables
338 wider than 8 bytes, only the first 8 bytes of each missing value are
339 specified, with the remainder implicitly all spaces.
341 For discrete missing values, each element represents one missing
342 value. When a range is present, the first element denotes the minimum
343 value in the range, and the second element denotes the maximum value
344 in the range. When a range plus a value are present, the third
345 element denotes the additional discrete missing value.
348 The @code{print} and @code{write} members of sysfile_variable are output
349 formats coded into @code{int32} types. The least-significant byte
350 of the @code{int32} represents the number of decimal places, and the
351 next two bytes in order of increasing significance represent field width
352 and format type, respectively. The most-significant byte is not
353 used and should be set to zero.
355 Format types are defined as follows:
358 @multitable {Value} {@code{DATETIME}}
444 A few system files have been observed in the wild with invalid
445 @code{write} fields, in particular with value 0. Readers should
446 probably treat invalid @code{print} or @code{write} fields as some
449 @node Value Labels Records
450 @section Value Labels Records
452 The value label records documented in this section are used for
453 numeric and short string variables only. Long string variables may
454 have value labels, but their value labels are recorded using a
455 different record type (@pxref{Long String Value Labels Record}).
457 The value label record has the following format:
463 /* @r{Repeated @code{label_cnt} times}. */
470 @item int32 rec_type;
471 Record type. Always set to 3.
473 @item int32 label_count;
474 Number of value labels present in this record.
477 The remaining fields are repeated @code{count} times. Each
478 repetition specifies one value label.
482 A numeric value or a short string value padded as necessary to 8 bytes
483 in length. Its type and width cannot be determined until the
484 following value label variables record (see below) is read.
486 @item char label_len;
487 The label's length, in bytes. The documented maximum length varies
488 from 60 to 120 based on SPSS version. PSPP supports value labels up
492 @code{label_len} bytes of the actual label, followed by up to 7 bytes
493 of padding to bring @code{label} and @code{label_len} together to a
494 multiple of 8 bytes in length.
497 The value label record is always immediately followed by a value label
498 variables record with the following format:
507 @item int32 rec_type;
508 Record type. Always set to 4.
510 @item int32 var_count;
511 Number of variables that the associated value labels from the value
512 label record are to be applied.
515 A list of dictionary indexes of variables to which to apply the value
516 labels (@pxref{Dictionary Index}). There are @code{var_count}
519 String variables wider than 8 bytes may not be specified in this list.
522 @node Document Record
523 @section Document Record
525 The document record, if present, has the following format:
534 @item int32 rec_type;
535 Record type. Always set to 6.
538 Number of lines of documents present.
540 @item char lines[][80];
541 Document lines. The number of elements is defined by @code{n_lines}.
542 Lines shorter than 80 characters are padded on the right with spaces.
545 @node Machine Integer Info Record
546 @section Machine Integer Info Record
548 The integer info record, if present, has the following format:
560 int32 version_revision;
562 int32 floating_point_rep;
563 int32 compression_code;
565 int32 character_code;
569 @item int32 rec_type;
570 Record type. Always set to 7.
573 Record subtype. Always set to 3.
576 Size of each piece of data in the data part, in bytes. Always set to 4.
579 Number of pieces of data in the data part. Always set to 8.
581 @item int32 version_major;
582 PSPP major version number. In version @var{x}.@var{y}.@var{z}, this
585 @item int32 version_minor;
586 PSPP minor version number. In version @var{x}.@var{y}.@var{z}, this
589 @item int32 version_revision;
590 PSPP version revision number. In version @var{x}.@var{y}.@var{z},
593 @item int32 machine_code;
594 Machine code. PSPP always set this field to value to -1, but other
597 @item int32 floating_point_rep;
598 Floating point representation code. For IEEE 754 systems this is 1.
599 IBM 370 sets this to 2, and DEC VAX E to 3.
601 @item int32 compression_code;
602 Compression code. Always set to 1, regardless of whether or how the
605 @item int32 endianness;
606 Machine endianness. 1 indicates big-endian, 2 indicates little-endian.
608 @item int32 character_code;
609 @anchor{character-code} Character code. The following values have
610 been actually observed in system files:
620 The @code{windows-1250} code page for Central European and Eastern
624 The @code{windows-1252} code page for Western European languages.
633 The following additional values are known to be defined:
643 Other Windows code page numbers are known to be generally valid.
645 Old versions of SPSS for Unix and Windows always wrote value 2 in this
646 field, regardless of the encoding in use. Newer versions also write
647 the character encoding as a string (see @ref{Character Encoding
651 @node Machine Floating-Point Info Record
652 @section Machine Floating-Point Info Record
654 The floating-point info record, if present, has the following format:
670 @item int32 rec_type;
671 Record type. Always set to 7.
674 Record subtype. Always set to 4.
677 Size of each piece of data in the data part, in bytes. Always set to 8.
680 Number of pieces of data in the data part. Always set to 3.
683 The system missing value.
686 The value used for HIGHEST in missing values.
689 The value used for LOWEST in missing values.
692 @node Multiple Response Sets Records
693 @section Multiple Response Sets Records
695 The system file format has two different types of records that
696 represent multiple response sets (@pxref{MRSETS,,,pspp, PSPP Users
697 Guide}). The first type of record describes multiple response sets
698 that can be understood by SPSS before version 14. The second type of
699 record, with a closely related format, is used for multiple dichotomy
700 sets that use the CATEGORYLABELS=COUNTEDVALUES feature added in
710 /* @r{Exactly @code{count} bytes of data.} */
715 @item int32 rec_type;
716 Record type. Always set to 7.
719 Record subtype. Set to 7 for records that describe multiple response
720 sets understood by SPSS before version 14, or to 19 for records that
721 describe dichotomy sets that use the CATEGORYLABELS=COUNTEDVALUES
722 feature added in version 14.
725 The size of each element in the @code{mrsets} member. Always set to 1.
728 The total number of bytes in @code{mrsets}.
731 A series of multiple response sets, each of which consists of the
736 The set's name (an identifier that begins with @samp{$}), in mixed
737 upper and lower case.
740 An equals sign (@samp{=}).
743 @samp{C} for a multiple category set, @samp{D} for a multiple
744 dichotomy set with CATEGORYLABELS=VARLABELS, or @samp{E} for a
745 multiple dichotomy set with CATEGORYLABELS=COUNTEDVALUES.
748 For a multiple dichotomy set with CATEGORYLABELS=COUNTEDVALUES, a
749 space, followed by a number expressed as decimal digits, followed by a
750 space. If LABELSOURCE=VARLABEL was specified on MRSETS, then the
751 number is 11; otherwise it is 1.@footnote{This part of the format may
752 not be fully understood, because only a single example of each
753 possibility has been examined.}
756 For either kind of multiple dichotomy set, the counted value, as a
757 positive integer count specified as decimal digits, followed by a
758 space, followed by as many string bytes as specified in the count. If
759 the set contains numeric variables, the string consists of the counted
760 integer value expressed as decimal digits. If the set contains string
761 variables, the string contains the counted string value. Either way,
762 the string may be padded on the right with spaces (older versions of
763 SPSS seem to always pad to a width of 8 bytes; newer versions don't).
769 The multiple response set's label, using the same format as for the
770 counted value for multiple dichotomy sets. A string of length 0 means
771 that the set does not have a label. A string of length 0 is also
772 written if LABELSOURCE=VARLABEL was specified.
778 The short names of the variables in the set, converted to lowercase,
779 each separated from the previous by a single space.
782 A line feed (byte 0x0a).
786 Example: Given appropriate variable definitions, consider the
787 following MRSETS command:
790 MRSETS /MCGROUP NAME=$a LABEL='my mcgroup' VARIABLES=a b c
791 /MDGROUP NAME=$b VARIABLES=g e f d VALUE=55
792 /MDGROUP NAME=$c LABEL='mdgroup #2' VARIABLES=h i j VALUE='Yes'
793 /MDGROUP NAME=$d LABEL='third mdgroup' CATEGORYLABELS=COUNTEDVALUES
794 VARIABLES=k l m VALUE=34
795 /MDGROUP NAME=$e CATEGORYLABELS=COUNTEDVALUES LABELSOURCE=VARLABEL
796 VARIABLES=n o p VALUE='choice'.
799 The above would generate the following multiple response set record of
803 $a=C 10 my mcgroup a b c
805 $c=D3 Yes 10 mdgroup #2 h i j
808 It would also generate the following multiple response set record with
812 $d=E 1 2 34 13 third mdgroup k l m
813 $e=E 11 6 choice 0 n o p
816 @node Extra Product Info Record
817 @section Extra Product Info Record
819 This optional record appears to contain a text string that describes
820 the program that wrote the file and the source of the data. (This is
821 redundant with the file label and product info found in the file
831 /* @r{Exactly @code{count} bytes of data.} */
836 @item int32 rec_type;
837 Record type. Always set to 7.
840 Record subtype. Always set to 10.
843 The size of each element in the @code{info} member. Always set to 1.
846 The total number of bytes in @code{info}.
849 A text string. A product that identifies itself as @code{VOXCO
850 INTERVIEWER 4.3} uses CR-only line ends in this field, rather than the
851 more usual LF-only or CR LF line ends.
854 @node Variable Display Parameter Record
855 @section Variable Display Parameter Record
857 The variable display parameter record, if present, has the following
867 /* @r{Repeated @code{count} times}. */
869 int32 width; /* @r{Not always present.} */
874 @item int32 rec_type;
875 Record type. Always set to 7.
878 Record subtype. Always set to 11.
881 The size of @code{int32}. Always set to 4.
884 The number of sets of variable display parameters (ordinarily the
885 number of variables in the dictionary), times 2 or 3.
888 The remaining members are repeated @code{count} times, in the same
889 order as the variable records. No element corresponds to variable
890 records that continue long string variables. The meanings of these
891 members are as follows:
895 The measurement type of the variable:
905 SPSS sometimes writes a @code{measure} of 0. PSPP interprets this as
909 The width of the display column for the variable in characters.
911 This field is present if @var{count} is 3 times the number of
912 variables in the dictionary. It is omitted if @var{count} is 2 times
913 the number of variables.
915 @item int32 alignment;
916 The alignment of the variable for display purposes:
928 @node Long Variable Names Record
929 @section Long Variable Names Record
931 If present, the long variable names record has the following format:
940 /* @r{Exactly @code{count} bytes of data.} */
941 char var_name_pairs[];
945 @item int32 rec_type;
946 Record type. Always set to 7.
949 Record subtype. Always set to 13.
952 The size of each element in the @code{var_name_pairs} member. Always set to 1.
955 The total number of bytes in @code{var_name_pairs}.
957 @item char var_name_pairs[];
958 A list of @var{key}--@var{value} tuples, where @var{key} is the name
959 of a variable, and @var{value} is its long variable name.
960 The @var{key} field is at most 8 bytes long and must match the
961 name of a variable which appears in the variable record (@pxref{Variable
963 The @var{value} field is at most 64 bytes long.
964 The @var{key} and @var{value} fields are separated by a @samp{=} byte.
965 Each tuple is separated by a byte whose value is 09. There is no
966 trailing separator following the last tuple.
967 The total length is @code{count} bytes.
970 @node Very Long String Record
971 @section Very Long String Record
973 Old versions of SPSS limited string variables to a width of 255 bytes.
974 For backward compatibility with these older versions, the system file
975 format represents a string longer than 255 bytes, called a @dfn{very
976 long string}, as a collection of strings no longer than 255 bytes
977 each. The strings concatenated to make a very long string are called
978 its @dfn{segments}; for consistency, variables other than very long
979 strings are considered to have a single segment.
981 A very long string with a width of @var{w} has @var{n} =
982 (@var{w} + 251) / 252 segments, that is, one segment for every
983 252 bytes of width, rounding up. It would be logical, then, for each
984 of the segments except the last to have a width of 252 and the last
985 segment to have the remainder, but this is not the case. In fact,
986 each segment except the last has a width of 255 bytes. The last
987 segment has width @var{w} - (@var{n} - 1) * 252; some versions
988 of SPSS make it slightly wider, but not wide enough to make the last
989 segment require another 8 bytes of data.
991 Data is packed tightly into segments of a very long string, 255 bytes
992 per segment. Because 255 bytes of segment data are allocated for
993 every 252 bytes of the very long string's width (approximately), some
994 unused space is left over at the end of the allocated segments. Data
995 in unused space is ignored.
997 Example: Consider a very long string of width 20,000. Such a very
998 long string has 20,000 / 252 = 80 (rounding up) segments. The first
999 79 segments have width 255; the last segment has width 20,000 - 79 *
1000 252 = 92 or slightly wider (up to 96 bytes, the next multiple of 8).
1001 The very long string's data is actually stored in the 19,890 bytes in
1002 the first 78 segments, plus the first 110 bytes of the 79th segment
1003 (19,890 + 110 = 20,000). The remaining 145 bytes of the 79th segment
1004 and all 92 bytes of the 80th segment are unused.
1006 The very long string record explains how to stitch together segments
1007 to obtain very long string data. For each of the very long string
1008 variables in the dictionary, it specifies the name of its first
1009 segment's variable and the very long string variable's actual width.
1010 The remaining segments immediately follow the named variable in the
1011 system file's dictionary.
1013 The very long string record, which is present only if the system file
1014 contains very long string variables, has the following format:
1023 /* @r{Exactly @code{count} bytes of data.} */
1024 char string_lengths[];
1028 @item int32 rec_type;
1029 Record type. Always set to 7.
1031 @item int32 subtype;
1032 Record subtype. Always set to 14.
1035 The size of each element in the @code{string_lengths} member. Always set to 1.
1038 The total number of bytes in @code{string_lengths}.
1040 @item char string_lengths[];
1041 A list of @var{key}--@var{value} tuples, where @var{key} is the name
1042 of a variable, and @var{value} is its length.
1043 The @var{key} field is at most 8 bytes long and must match the
1044 name of a variable which appears in the variable record (@pxref{Variable
1046 The @var{value} field is exactly 5 bytes long. It is a zero-padded,
1047 ASCII-encoded string that is the length of the variable.
1048 The @var{key} and @var{value} fields are separated by a @samp{=} byte.
1049 Tuples are delimited by a two-byte sequence @{00, 09@}.
1050 After the last tuple, there may be a single byte 00, or @{00, 09@}.
1051 The total length is @code{count} bytes.
1054 @node Character Encoding Record
1055 @section Character Encoding Record
1057 This record, if present, indicates the character encoding for string data,
1058 long variable names, variable labels, value labels and other strings in the
1068 /* @r{Exactly @code{count} bytes of data.} */
1073 @item int32 rec_type;
1074 Record type. Always set to 7.
1076 @item int32 subtype;
1077 Record subtype. Always set to 20.
1080 The size of each element in the @code{encoding} member. Always set to 1.
1083 The total number of bytes in @code{encoding}.
1085 @item char encoding[];
1086 The name of the character encoding. Normally this will be an official
1087 IANA character set name or alias.
1088 See @url{http://www.iana.org/assignments/character-sets}.
1089 Character set names are not case-sensitive, but SPSS appears to write
1090 them in all-uppercase.
1093 This record is not present in files generated by older software. See
1094 also the @code{character_code} field in the machine integer info
1095 record (@pxref{character-code}).
1097 When the character encoding record and the machine integer info record
1098 are both present, all system files observed in practice indicate the
1099 same character encoding, e.g.@: 1252 as @code{character_code} and
1100 @code{windows-1252} as @code{encoding}, 65001 and @code{UTF-8}, etc.
1102 If, for testing purposes, a file is crafted with different
1103 @code{character_code} and @code{encoding}, it seems that
1104 @code{character_code} controls the encoding for all strings in the
1105 system file before the dictionary termination record, including
1106 strings in data (e.g.@: string missing values), and @code{encoding}
1107 controls the encoding for strings following the dictionary termination
1110 @node Long String Value Labels Record
1111 @section Long String Value Labels Record
1113 This record, if present, specifies value labels for long string
1123 /* @r{Repeated up to exactly @code{count} bytes.} */
1128 long_string_label labels[];
1132 @item int32 rec_type;
1133 Record type. Always set to 7.
1135 @item int32 subtype;
1136 Record subtype. Always set to 21.
1142 The number of bytes following the header until the next header.
1144 @item int32 var_name_len;
1145 @itemx char var_name[];
1146 The number of bytes in the name of the variable that has long string
1147 value labels, plus the variable name itself, which consists of exactly
1148 @code{var_name_len} bytes. The variable name is not padded to any
1149 particular boundary, nor is it null-terminated.
1151 @item int32 var_width;
1152 The width of the variable, in bytes, which will be between 9 and
1155 @item int32 n_labels;
1156 @itemx long_string_label labels[];
1157 The long string labels themselves. The @code{labels} array contains
1158 exactly @code{n_labels} elements, each of which has the following
1169 @item int32 value_len;
1170 @itemx char value[];
1171 The string value being labeled. @code{value_len} is the number of
1172 bytes in @code{value}; it is equal to @code{var_width}. The
1173 @code{value} array is not padded or null-terminated.
1175 @item int32 label_len;
1176 @itemx char label[];
1177 The label for the string value. @code{label_len}, which must be
1178 between 0 and 120, is the number of bytes in @code{label}. The
1179 @code{label} array is not padded or null-terminated.
1183 @node Long String Missing Values Record
1184 @section Long String Missing Values Record
1186 This record, if present, specifies missing values for long string
1196 /* @r{Repeated up to exactly @code{count} bytes.} */
1199 char n_missing_values;
1200 long_string_missing_value values[];
1204 @item int32 rec_type;
1205 Record type. Always set to 7.
1207 @item int32 subtype;
1208 Record subtype. Always set to 22.
1214 The number of bytes following the header until the next header.
1216 @item int32 var_name_len;
1217 @itemx char var_name[];
1218 The number of bytes in the name of the long string variable that has
1219 missing values, plus the variable name itself, which consists of
1220 exactly @code{var_name_len} bytes. The variable name is not padded to
1221 any particular boundary, nor is it null-terminated.
1223 @item char n_missing_values;
1224 The number of missing values, either 1, 2, or 3. (This is, unusually,
1225 a single byte instead of a 32-bit number.)
1227 @item long_string_missing_value values[];
1228 The missing values themselves. This array contains exactly
1229 @code{n_missing_values} elements, each of which has the following
1238 @item int32 value_len;
1239 The length of the missing value string, in bytes. This value should
1240 be 8, because long string variables are at least 8 bytes wide (by
1241 definition), only the first 8 bytes of a long string variable's
1242 missing values are allowed to be non-spaces, and any spaces within the
1243 first 8 bytes are included in the missing value here.
1246 The missing value string, exactly @code{value_len} bytes, without
1247 any padding or null terminator.
1251 @node Data File and Variable Attributes Records
1252 @section Data File and Variable Attributes Records
1254 The data file and variable attributes records represent custom
1255 attributes for the system file or for individual variables in the
1256 system file, as defined on the DATAFILE ATTRIBUTE (@pxref{DATAFILE
1257 ATTRIBUTE,,,pspp, PSPP Users Guide}) and VARIABLE ATTRIBUTE commands
1258 (@pxref{VARIABLE ATTRIBUTE,,,pspp, PSPP Users Guide}), respectively.
1267 /* @r{Exactly @code{count} bytes of data.} */
1272 @item int32 rec_type;
1273 Record type. Always set to 7.
1275 @item int32 subtype;
1276 Record subtype. Always set to 17 for a data file attribute record or
1277 to 18 for a variable attributes record.
1280 The size of each element in the @code{attributes} member. Always set to 1.
1283 The total number of bytes in @code{attributes}.
1285 @item char attributes[];
1286 The attributes, in a text-based format.
1288 In record type 17, this field contains a single attribute set. An
1289 attribute set is a sequence of one or more attributes concatenated
1290 together. Each attribute consists of a name, which has the same
1291 syntax as a variable name, followed by, inside parentheses, a sequence
1292 of one or more values. Each value consists of a string enclosed in
1293 single quotes (@code{'}) followed by a line feed (byte 0x0a). A value
1294 may contain single quote characters, which are not themselves escaped
1295 or quoted or required to be present in pairs. There is no apparent
1296 way to embed a line feed in a value. There is no distinction between
1297 an attribute with a single value and an attribute array with one
1300 In record type 18, this field contains a sequence of one or more
1301 variable attribute sets. If more than one variable attribute set is
1302 present, each one after the first is delimited from the previous by
1303 @code{/}. Each variable attribute set consists of a long
1305 followed by @code{:}, followed by an attribute set with the same
1306 syntax as on record type 17.
1308 The total length is @code{count} bytes.
1313 A system file produced with the following VARIABLE ATTRIBUTE commands
1317 VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=fred[1]('23') fred[2]('34').
1318 VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=bert('123').
1322 will contain a variable attribute record with the following contents:
1325 0000 07 00 00 00 12 00 00 00 01 00 00 00 22 00 00 00 |............"...|
1326 0010 64 75 6d 6d 79 3a 66 72 65 64 28 27 32 33 27 0a |dummy:fred('23'.|
1327 0020 27 33 34 27 0a 29 62 65 72 74 28 27 31 32 33 27 |'34'.)bert('123'|
1335 @node Variable Roles
1336 @subsection Variable Roles
1338 A variable's role is represented as an attribute named @code{$@@Role}.
1339 This attribute has a single element whose values and their meanings
1344 Input. This, the default, is the most common role.
1357 @node Extended Number of Cases Record
1358 @section Extended Number of Cases Record
1360 The file header record expresses the number of cases in the system
1361 file as an int32 (@pxref{File Header Record}). This record allows the
1362 number of cases in the system file to be expressed as a 64-bit number.
1374 @item int32 rec_type;
1375 Record type. Always set to 7.
1377 @item int32 subtype;
1378 Record subtype. Always set to 16.
1381 Size of each element. Always set to 8.
1384 Number of pieces of data in the data part. Alway set to 2.
1386 @item int64 unknown;
1387 Meaning unknown. Always set to 1.
1389 @item int64 ncases64;
1390 Number of cases in the file as a 64-bit integer. Presumably this
1391 could be -1 to indicate that the number of cases is unknown, for the
1392 same reason as @code{ncases} in the file header record, but this has
1393 not been observed in the wild.
1396 @node Miscellaneous Informational Records
1397 @section Miscellaneous Informational Records
1399 Some specific types of miscellaneous informational records are
1400 documented here, but others are known to exist. PSPP ignores unknown
1401 miscellaneous informational records when reading system files.
1410 /* @r{Exactly @code{size * count} bytes of data.} */
1415 @item int32 rec_type;
1416 Record type. Always set to 7.
1418 @item int32 subtype;
1419 Record subtype. May take any value. According to Aapi
1420 H@"am@"al@"ainen, value 5 indicates a set of grouped variables and 6
1421 indicates date info (probably related to USE). Subtype 24 appears to
1422 contain XML that describes how data in the file should be displayed
1426 Size of each piece of data in the data part. Should have the value 1,
1427 4, or 8, for @code{char}, @code{int32}, and @code{flt64} format data,
1431 Number of pieces of data in the data part.
1434 Arbitrary data. There must be @code{size} times @code{count} bytes of
1438 @node Dictionary Termination Record
1439 @section Dictionary Termination Record
1441 The dictionary termination record separates all other records from the
1450 @item int32 rec_type;
1451 Record type. Always set to 999.
1454 Ignored padding. Should be set to 0.
1458 @section Data Record
1460 The data record must follow all other records in the system file.
1461 Every system file must have a data record that specifies data for at
1462 least one case. The format of the data record varies depending on the
1463 value of @code{compression} in the file header record:
1466 @item 0: no compression
1467 Data is arranged as a series of 8-byte elements.
1468 Each element corresponds to
1469 the variable declared in the respective variable record (@pxref{Variable
1470 Record}). Numeric values are given in @code{flt64} format; string
1471 values are literal characters string, padded on the right when
1472 necessary to fill out 8-byte units.
1474 @item 1: bytecode compression
1476 of the data record is divided into a series of 1-byte command
1477 codes. These codes have meanings as described below:
1481 Ignored. If the program writing the system file accumulates compressed
1482 data in blocks of fixed length, 0 bytes can be used to pad out extra
1483 bytes remaining at the end of a fixed-size block.
1487 value @var{code} - @var{bias}, where
1488 @var{code} is the value of the compression code and @var{bias} is the
1489 variable @code{bias} from the file header. For example,
1490 code 105 with bias 100.0 (the normal value) indicates a numeric variable
1492 One file has been seen written by SPSS 14 that contained such a code
1493 in a @emph{string} field with the value 0 (after the bias is
1494 subtracted) as a way of encoding null bytes.
1497 End of file. This code may or may not appear at the end of the data
1498 stream. PSPP always outputs this code but its use is not required.
1501 A numeric or string value that is not
1502 compressible. The value is stored in the 8 bytes following the
1503 current block of command bytes. If this value appears twice in a block
1504 of command bytes, then it indicates the second group of 8 bytes following the
1505 command bytes, and so on.
1508 An 8-byte string value that is all spaces.
1511 The system-missing value.
1514 The end of the 8-byte group of bytecodes is followed by any 8-byte
1515 blocks of non-compressible values indicated by code 253. After that
1516 follows another 8-byte group of bytecodes, then those bytecodes'
1517 non-compressible values. The pattern repeats to the end of the file
1518 or a code with value 252.
1520 @item 2: ZLIB compression
1521 The data record consists of the following, in order:
1525 ZLIB data header, 24 bytes long.
1528 One or more variable-length blocks of ZLIB compressed data.
1531 ZLIB data trailer, with a 24-byte fixed header plus an additional 24
1532 bytes for each preceding ZLIB compressed data block.
1535 The ZLIB data header has the following format:
1544 @item int64 zheader_ofs;
1545 The offset, in bytes, of the beginning of this structure within the
1548 @item int64 ztrailer_ofs;
1549 The offset, in bytes, of the first byte of the ZLIB data trailer.
1551 @item int64 ztrailer_len;
1552 The number of bytes in the ZLIB data trailer. This and the previous
1553 field sum to the size of the system file in bytes.
1556 The data header is followed by @code{(ztrailer_ofs - 24) / 24} ZLIB
1557 compressed data blocks. Each ZLIB compressed data block begins with a
1558 ZLIB header as specified in RFC@tie{}1950, e.g.@: hex bytes @code{78
1559 01} (the only header yet observed in practice). Each block
1560 decompresses to a fixed number of bytes (in practice only
1561 @code{0x3ff000}-byte blocks have been observed), except that the last
1562 block of data may be shorter. The last ZLIB compressed data block
1563 gends just before offset @code{ztrailer_ofs}.
1565 The result of ZLIB decompression is bytecode compressed data as
1566 described above for compression format 1.
1568 The ZLIB data trailer begins with the following 24-byte fixed header:
1578 @item int64 int_bias;
1579 The compression bias as a negative integer, e.g.@: if @code{bias} in
1580 the file header record is 100.0, then @code{int_bias} is @minus{}100
1581 (this is the only value yet observed in practice).
1584 Always observed to be zero.
1586 @item int32 block_size;
1587 The number of bytes in each ZLIB compressed data block, except
1588 possibly the last, following decompression. Only @code{0x3ff000} has
1589 been observed so far.
1591 @item int32 n_blocks;
1592 The number of ZLIB compressed data blocks, always exactly
1593 @code{(ztrailer_ofs - 24) / 24}.
1596 The fixed header is followed by @code{n_blocks} 24-byte ZLIB data
1597 block descriptors, each of which describes the compressed data block
1598 corresponding to its offset. Each block descriptor has the following
1602 int64 uncompressed_ofs;
1603 int64 compressed_ofs;
1604 int32 uncompressed_size;
1605 int32 compressed_size;
1609 @item int64 uncompressed_ofs;
1610 The offset, in bytes, that this block of data would have in a similar
1611 system file that uses compression format 1. This is
1612 @code{zheader_ofs} in the first block descriptor, and in each
1613 succeeding block descriptor it is the sum of the previous desciptor's
1614 @code{uncompressed_ofs} and @code{uncompressed_size}.
1616 @item int64 compressed_ofs;
1617 The offset, in bytes, of the actual beginning of this compressed data
1618 block. This is @code{zheader_ofs + 24} in the first block descriptor,
1619 and in each succeeding block descriptor it is the sum of the previous
1620 descriptor's @code{compressed_ofs} and @code{compressed_size}. The
1621 final block descriptor's @code{compressed_ofs} and
1622 @code{compressed_size} sum to @code{ztrailer_ofs}.
1624 @item int32 uncompressed_size;
1625 The number of bytes in this data block, after decompression. This is
1626 @code{block_size} in every data block except the last, which may be
1629 @item int32 compressed_size;
1630 The number of bytes in this data block, as stored compressed in this
1635 @setfilename ignored
1637 @node Encrypted System Files
1638 @section Encrypted System Files
1640 SPSS 21 and later support an encrypted system file format.
1643 The SPSS encrypted file format is poorly designed. It is much cheaper
1644 and faster to decrypt a file encrypted this way than if a well
1645 designed alternative were used. If you must use this format, use a
1646 10-byte randomly generated password.
1649 @subheading Encrypted File Format
1651 Encrypted system files begin with the following 36-byte fixed header:
1654 0000 1c 00 00 00 00 00 00 00 45 4e 43 52 59 50 54 45 |........ENCRYPTE|
1655 0010 44 53 41 56 15 00 00 00 00 00 00 00 00 00 00 00 |DSAV............|
1656 0020 00 00 00 00 |....|
1659 Following the fixed header is a complete system file in the usual
1660 format, except that each 16-byte block is encrypted with AES-256 in
1661 ECB mode. The AES-256 key is derived from a password in the following
1666 Start from the literal password typed by the user. Truncate it to at
1667 most 10 bytes, then append (between 1 and 22) null bytes until there
1668 are exactly 32 bytes. Call this @var{password}.
1671 Let @var{constant} be the following 73-byte constant:
1674 0000 00 00 00 01 35 27 13 cc 53 a7 78 89 87 53 22 11
1675 0010 d6 5b 31 58 dc fe 2e 7e 94 da 2f 00 cc 15 71 80
1676 0020 0a 6c 63 53 00 38 c3 38 ac 22 f3 63 62 0e ce 85
1677 0030 3f b8 07 4c 4e 2b 77 c7 21 f5 1a 80 1d 67 fb e1
1678 0040 e1 83 07 d8 0d 00 00 01 00
1682 Compute CMAC-AES-256(@var{password}, @var{constant}). Call the
1683 16-byte result @var{cmac}.
1686 The 32-byte AES-256 key is @var{cmac} || @var{cmac}, that is,
1687 @var{cmac} repeated twice.
1690 @subsubheading Example
1692 Consider the password @samp{pspp}. @var{password} is:
1695 0000 70 73 70 70 00 00 00 00 00 00 00 00 00 00 00 00 |pspp............|
1696 0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
1703 0000 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1710 0000 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1711 0010 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1714 @subheading Password Encoding
1716 SPSS also supports what it calls ``encrypted passwords.'' These are
1717 not encrypted. They are encoded with a simple, fixed scheme. An
1718 encoded password is always a multiple of 2 characters long, and never
1719 longer than 20 characters. The characters in an encoded password are
1720 always in the graphic ASCII range 33 through 126. Each successive
1721 pair of characters in the password encodes a single byte in the
1724 Use the following algorithm to decode a pair of characters:
1728 Let @var{a} be the ASCII code of the first character, and @var{b} be
1729 the ASCII code of the second character.
1732 Let @var{ah} be the most significant 4 bits of @var{a}. Find the line
1733 in the table below that has @var{ah} on the left side. The right side
1734 of the line is a set of possible values for the most significant 4
1735 bits of the decoded byte.
1738 @t{2 } @result{} @t{2367}
1739 @t{3 } @result{} @t{0145}
1740 @t{47} @result{} @t{89cd}
1741 @t{56} @result{} @t{abef}
1745 Let @var{bh} be the most significant 4 bits of @var{b}. Find the line
1746 in the second table below that has @var{bh} on the left side. The
1747 right side of the line is a set of possible values for the most
1748 significant 4 bits of the decoded byte. Together with the results of
1749 the previous step, only a single possibility is left.
1752 @t{2 } @result{} @t{139b}
1753 @t{3 } @result{} @t{028a}
1754 @t{47} @result{} @t{46ce}
1755 @t{56} @result{} @t{57df}
1759 Let @var{al} be the least significant 4 bits of @var{a}. Find the
1760 line in the table below that has @var{al} on the left side. The right
1761 side of the line is a set of possible values for the least significant
1762 4 bits of the decoded byte.
1765 @t{03cf} @result{} @t{0145}
1766 @t{12de} @result{} @t{2367}
1767 @t{478b} @result{} @t{89cd}
1768 @t{569a} @result{} @t{abef}
1772 Let @var{bl} be the least significant 4 bits of @var{b}. Find the
1773 line in the table below that has @var{bl} on the left side. The right
1774 side of the line is a set of possible values for the least significant
1775 4 bits of the decoded byte. Together with the results of the previous
1776 step, only a single possibility is left.
1779 @t{03cf} @result{} @t{028a}
1780 @t{12de} @result{} @t{139b}
1781 @t{478b} @result{} @t{46ce}
1782 @t{569a} @result{} @t{57df}
1786 @subsubheading Example
1788 Consider the encoded character pair @samp{-|}. @var{a} is
1789 0x2d and @var{b} is 0x7c, so @var{ah} is 2, @var{bh} is 7, @var{al} is
1790 0xd, and @var{bl} is 0xc. @var{ah} means that the most significant
1791 four bits of the decoded character is 2, 3, 6, or 7, and @var{bh}
1792 means that they are 4, 6, 0xc, or 0xe. The single possibility in
1793 common is 6, so the most significant four bits are 6. Similarly,
1794 @var{al} means that the least significant four bits are 2, 3, 6, or 7,
1795 and @var{bl} means they are 0, 2, 8, or 0xa, so the least significant
1796 four bits are 2. The decoded character is therefore 0x62, the letter