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 compression;
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 The @samp{name} fields should be unique within a system file. System
320 files written by SPSS that contain very long string variables with
321 similar names sometimes contain duplicate names that are later
322 eliminated by resolving the very long string names (@pxref{Very Long
323 String Record}). PSPP handles duplicates by assigning them new,
326 @item int32 label_len;
327 This field is present only if @code{has_var_label} is set to 1. It is
328 set to the length, in characters, of the variable label. The
329 documented maximum length varies from 120 to 255 based on SPSS
330 version, but some files have been seen with longer labels. PSPP
331 accepts labels of any length.
334 This field is present only if @code{has_var_label} is set to 1. It has
335 length @code{label_len}, rounded up to the nearest multiple of 32 bits.
336 The first @code{label_len} characters are the variable's variable label.
338 @item flt64 missing_values[];
339 This field is present only if @code{n_missing_values} is nonzero. It
340 has the same number of 8-byte elements as the absolute value of
341 @code{n_missing_values}. Each element is interpreted as a number for
342 numeric variables (with HIGHEST and LOWEST indicated as described in
343 the chapter introduction). For string variables of width less than 8
344 bytes, elements are right-padded with spaces; for string variables
345 wider than 8 bytes, only the first 8 bytes of each missing value are
346 specified, with the remainder implicitly all spaces.
348 For discrete missing values, each element represents one missing
349 value. When a range is present, the first element denotes the minimum
350 value in the range, and the second element denotes the maximum value
351 in the range. When a range plus a value are present, the third
352 element denotes the additional discrete missing value.
355 @anchor{System File Output Formats}
356 The @code{print} and @code{write} members of sysfile_variable are output
357 formats coded into @code{int32} types. The least-significant byte
358 of the @code{int32} represents the number of decimal places, and the
359 next two bytes in order of increasing significance represent field width
360 and format type, respectively. The most-significant byte is not
361 used and should be set to zero.
363 Format types are defined as follows:
366 @multitable {Value} {@code{DATETIME}}
452 A few system files have been observed in the wild with invalid
453 @code{write} fields, in particular with value 0. Readers should
454 probably treat invalid @code{print} or @code{write} fields as some
457 @node Value Labels Records
458 @section Value Labels Records
460 The value label records documented in this section are used for
461 numeric and short string variables only. Long string variables may
462 have value labels, but their value labels are recorded using a
463 different record type (@pxref{Long String Value Labels Record}).
465 The value label record has the following format:
471 /* @r{Repeated @code{label_cnt} times}. */
478 @item int32 rec_type;
479 Record type. Always set to 3.
481 @item int32 label_count;
482 Number of value labels present in this record.
485 The remaining fields are repeated @code{count} times. Each
486 repetition specifies one value label.
490 A numeric value or a short string value padded as necessary to 8 bytes
491 in length. Its type and width cannot be determined until the
492 following value label variables record (see below) is read.
494 @item char label_len;
495 The label's length, in bytes. The documented maximum length varies
496 from 60 to 120 based on SPSS version. PSPP supports value labels up
500 @code{label_len} bytes of the actual label, followed by up to 7 bytes
501 of padding to bring @code{label} and @code{label_len} together to a
502 multiple of 8 bytes in length.
505 The value label record is always immediately followed by a value label
506 variables record with the following format:
515 @item int32 rec_type;
516 Record type. Always set to 4.
518 @item int32 var_count;
519 Number of variables that the associated value labels from the value
520 label record are to be applied.
523 A list of dictionary indexes of variables to which to apply the value
524 labels (@pxref{Dictionary Index}). There are @code{var_count}
527 String variables wider than 8 bytes may not be specified in this list.
530 @node Document Record
531 @section Document Record
533 The document record, if present, has the following format:
542 @item int32 rec_type;
543 Record type. Always set to 6.
546 Number of lines of documents present.
548 @item char lines[][80];
549 Document lines. The number of elements is defined by @code{n_lines}.
550 Lines shorter than 80 characters are padded on the right with spaces.
553 @node Machine Integer Info Record
554 @section Machine Integer Info Record
556 The integer info record, if present, has the following format:
568 int32 version_revision;
570 int32 floating_point_rep;
571 int32 compression_code;
573 int32 character_code;
577 @item int32 rec_type;
578 Record type. Always set to 7.
581 Record subtype. Always set to 3.
584 Size of each piece of data in the data part, in bytes. Always set to 4.
587 Number of pieces of data in the data part. Always set to 8.
589 @item int32 version_major;
590 PSPP major version number. In version @var{x}.@var{y}.@var{z}, this
593 @item int32 version_minor;
594 PSPP minor version number. In version @var{x}.@var{y}.@var{z}, this
597 @item int32 version_revision;
598 PSPP version revision number. In version @var{x}.@var{y}.@var{z},
601 @item int32 machine_code;
602 Machine code. PSPP always set this field to value to -1, but other
605 @item int32 floating_point_rep;
606 Floating point representation code. For IEEE 754 systems this is 1.
607 IBM 370 sets this to 2, and DEC VAX E to 3.
609 @item int32 compression_code;
610 Compression code. Always set to 1, regardless of whether or how the
613 @item int32 endianness;
614 Machine endianness. 1 indicates big-endian, 2 indicates little-endian.
616 @item int32 character_code;
617 @anchor{character-code} Character code. The following values have
618 been actually observed in system files:
628 The @code{windows-1250} code page for Central European and Eastern
632 The @code{windows-1252} code page for Western European languages.
641 The following additional values are known to be defined:
651 Other Windows code page numbers are known to be generally valid.
653 Old versions of SPSS for Unix and Windows always wrote value 2 in this
654 field, regardless of the encoding in use. Newer versions also write
655 the character encoding as a string (see @ref{Character Encoding
659 @node Machine Floating-Point Info Record
660 @section Machine Floating-Point Info Record
662 The floating-point info record, if present, has the following format:
678 @item int32 rec_type;
679 Record type. Always set to 7.
682 Record subtype. Always set to 4.
685 Size of each piece of data in the data part, in bytes. Always set to 8.
688 Number of pieces of data in the data part. Always set to 3.
691 The system missing value.
694 The value used for HIGHEST in missing values.
697 The value used for LOWEST in missing values.
700 @node Multiple Response Sets Records
701 @section Multiple Response Sets Records
703 The system file format has two different types of records that
704 represent multiple response sets (@pxref{MRSETS,,,pspp, PSPP Users
705 Guide}). The first type of record describes multiple response sets
706 that can be understood by SPSS before version 14. The second type of
707 record, with a closely related format, is used for multiple dichotomy
708 sets that use the CATEGORYLABELS=COUNTEDVALUES feature added in
718 /* @r{Exactly @code{count} bytes of data.} */
723 @item int32 rec_type;
724 Record type. Always set to 7.
727 Record subtype. Set to 7 for records that describe multiple response
728 sets understood by SPSS before version 14, or to 19 for records that
729 describe dichotomy sets that use the CATEGORYLABELS=COUNTEDVALUES
730 feature added in version 14.
733 The size of each element in the @code{mrsets} member. Always set to 1.
736 The total number of bytes in @code{mrsets}.
739 Zero or more line feeds (byte 0x0a), followed by a series of multiple
740 response sets, each of which consists of the following:
744 The set's name (an identifier that begins with @samp{$}), in mixed
745 upper and lower case.
748 An equals sign (@samp{=}).
751 @samp{C} for a multiple category set, @samp{D} for a multiple
752 dichotomy set with CATEGORYLABELS=VARLABELS, or @samp{E} for a
753 multiple dichotomy set with CATEGORYLABELS=COUNTEDVALUES.
756 For a multiple dichotomy set with CATEGORYLABELS=COUNTEDVALUES, a
757 space, followed by a number expressed as decimal digits, followed by a
758 space. If LABELSOURCE=VARLABEL was specified on MRSETS, then the
759 number is 11; otherwise it is 1.@footnote{This part of the format may
760 not be fully understood, because only a single example of each
761 possibility has been examined.}
764 For either kind of multiple dichotomy set, the counted value, as a
765 positive integer count specified as decimal digits, followed by a
766 space, followed by as many string bytes as specified in the count. If
767 the set contains numeric variables, the string consists of the counted
768 integer value expressed as decimal digits. If the set contains string
769 variables, the string contains the counted string value. Either way,
770 the string may be padded on the right with spaces (older versions of
771 SPSS seem to always pad to a width of 8 bytes; newer versions don't).
777 The multiple response set's label, using the same format as for the
778 counted value for multiple dichotomy sets. A string of length 0 means
779 that the set does not have a label. A string of length 0 is also
780 written if LABELSOURCE=VARLABEL was specified.
786 The short names of the variables in the set, converted to lowercase,
787 each separated from the previous by a single space.
789 Even though a multiple response set must have at least two variables,
790 some system files contain multiple response sets with no variables at
791 all. The source and meaning of these multiple response sets is
792 unknown. (Perhaps they arise from creating a multiple response set
793 then deleting all the variables that it contains?)
796 One line feed (byte 0x0a). Sometimes multiple, even hundreds, of line
801 Example: Given appropriate variable definitions, consider the
802 following MRSETS command:
805 MRSETS /MCGROUP NAME=$a LABEL='my mcgroup' VARIABLES=a b c
806 /MDGROUP NAME=$b VARIABLES=g e f d VALUE=55
807 /MDGROUP NAME=$c LABEL='mdgroup #2' VARIABLES=h i j VALUE='Yes'
808 /MDGROUP NAME=$d LABEL='third mdgroup' CATEGORYLABELS=COUNTEDVALUES
809 VARIABLES=k l m VALUE=34
810 /MDGROUP NAME=$e CATEGORYLABELS=COUNTEDVALUES LABELSOURCE=VARLABEL
811 VARIABLES=n o p VALUE='choice'.
814 The above would generate the following multiple response set record of
818 $a=C 10 my mcgroup a b c
820 $c=D3 Yes 10 mdgroup #2 h i j
823 It would also generate the following multiple response set record with
827 $d=E 1 2 34 13 third mdgroup k l m
828 $e=E 11 6 choice 0 n o p
831 @node Extra Product Info Record
832 @section Extra Product Info Record
834 This optional record appears to contain a text string that describes
835 the program that wrote the file and the source of the data. (This is
836 redundant with the file label and product info found in the file
846 /* @r{Exactly @code{count} bytes of data.} */
851 @item int32 rec_type;
852 Record type. Always set to 7.
855 Record subtype. Always set to 10.
858 The size of each element in the @code{info} member. Always set to 1.
861 The total number of bytes in @code{info}.
864 A text string. A product that identifies itself as @code{VOXCO
865 INTERVIEWER 4.3} uses CR-only line ends in this field, rather than the
866 more usual LF-only or CR LF line ends.
869 @node Variable Display Parameter Record
870 @section Variable Display Parameter Record
872 The variable display parameter record, if present, has the following
882 /* @r{Repeated @code{count} times}. */
884 int32 width; /* @r{Not always present.} */
889 @item int32 rec_type;
890 Record type. Always set to 7.
893 Record subtype. Always set to 11.
896 The size of @code{int32}. Always set to 4.
899 The number of sets of variable display parameters (ordinarily the
900 number of variables in the dictionary), times 2 or 3.
903 The remaining members are repeated @code{count} times, in the same
904 order as the variable records. No element corresponds to variable
905 records that continue long string variables. The meanings of these
906 members are as follows:
910 The measurement type of the variable:
920 SPSS sometimes writes a @code{measure} of 0. PSPP interprets this as
924 The width of the display column for the variable in characters.
926 This field is present if @var{count} is 3 times the number of
927 variables in the dictionary. It is omitted if @var{count} is 2 times
928 the number of variables.
930 @item int32 alignment;
931 The alignment of the variable for display purposes:
943 @node Long Variable Names Record
944 @section Long Variable Names Record
946 If present, the long variable names record has the following format:
955 /* @r{Exactly @code{count} bytes of data.} */
956 char var_name_pairs[];
960 @item int32 rec_type;
961 Record type. Always set to 7.
964 Record subtype. Always set to 13.
967 The size of each element in the @code{var_name_pairs} member. Always set to 1.
970 The total number of bytes in @code{var_name_pairs}.
972 @item char var_name_pairs[];
973 A list of @var{key}--@var{value} tuples, where @var{key} is the name
974 of a variable, and @var{value} is its long variable name.
975 The @var{key} field is at most 8 bytes long and must match the
976 name of a variable which appears in the variable record (@pxref{Variable
978 The @var{value} field is at most 64 bytes long.
979 The @var{key} and @var{value} fields are separated by a @samp{=} byte.
980 Each tuple is separated by a byte whose value is 09. There is no
981 trailing separator following the last tuple.
982 The total length is @code{count} bytes.
985 @node Very Long String Record
986 @section Very Long String Record
988 Old versions of SPSS limited string variables to a width of 255 bytes.
989 For backward compatibility with these older versions, the system file
990 format represents a string longer than 255 bytes, called a @dfn{very
991 long string}, as a collection of strings no longer than 255 bytes
992 each. The strings concatenated to make a very long string are called
993 its @dfn{segments}; for consistency, variables other than very long
994 strings are considered to have a single segment.
996 A very long string with a width of @var{w} has @var{n} =
997 (@var{w} + 251) / 252 segments, that is, one segment for every
998 252 bytes of width, rounding up. It would be logical, then, for each
999 of the segments except the last to have a width of 252 and the last
1000 segment to have the remainder, but this is not the case. In fact,
1001 each segment except the last has a width of 255 bytes. The last
1002 segment has width @var{w} - (@var{n} - 1) * 252; some versions
1003 of SPSS make it slightly wider, but not wide enough to make the last
1004 segment require another 8 bytes of data.
1006 Data is packed tightly into segments of a very long string, 255 bytes
1007 per segment. Because 255 bytes of segment data are allocated for
1008 every 252 bytes of the very long string's width (approximately), some
1009 unused space is left over at the end of the allocated segments. Data
1010 in unused space is ignored.
1012 Example: Consider a very long string of width 20,000. Such a very
1013 long string has 20,000 / 252 = 80 (rounding up) segments. The first
1014 79 segments have width 255; the last segment has width 20,000 - 79 *
1015 252 = 92 or slightly wider (up to 96 bytes, the next multiple of 8).
1016 The very long string's data is actually stored in the 19,890 bytes in
1017 the first 78 segments, plus the first 110 bytes of the 79th segment
1018 (19,890 + 110 = 20,000). The remaining 145 bytes of the 79th segment
1019 and all 92 bytes of the 80th segment are unused.
1021 The very long string record explains how to stitch together segments
1022 to obtain very long string data. For each of the very long string
1023 variables in the dictionary, it specifies the name of its first
1024 segment's variable and the very long string variable's actual width.
1025 The remaining segments immediately follow the named variable in the
1026 system file's dictionary.
1028 The very long string record, which is present only if the system file
1029 contains very long string variables, has the following format:
1038 /* @r{Exactly @code{count} bytes of data.} */
1039 char string_lengths[];
1043 @item int32 rec_type;
1044 Record type. Always set to 7.
1046 @item int32 subtype;
1047 Record subtype. Always set to 14.
1050 The size of each element in the @code{string_lengths} member. Always set to 1.
1053 The total number of bytes in @code{string_lengths}.
1055 @item char string_lengths[];
1056 A list of @var{key}--@var{value} tuples, where @var{key} is the name
1057 of a variable, and @var{value} is its length.
1058 The @var{key} field is at most 8 bytes long and must match the
1059 name of a variable which appears in the variable record (@pxref{Variable
1061 The @var{value} field is exactly 5 bytes long. It is a zero-padded,
1062 ASCII-encoded string that is the length of the variable.
1063 The @var{key} and @var{value} fields are separated by a @samp{=} byte.
1064 Tuples are delimited by a two-byte sequence @{00, 09@}.
1065 After the last tuple, there may be a single byte 00, or @{00, 09@}.
1066 The total length is @code{count} bytes.
1069 @node Character Encoding Record
1070 @section Character Encoding Record
1072 This record, if present, indicates the character encoding for string data,
1073 long variable names, variable labels, value labels and other strings in the
1083 /* @r{Exactly @code{count} bytes of data.} */
1088 @item int32 rec_type;
1089 Record type. Always set to 7.
1091 @item int32 subtype;
1092 Record subtype. Always set to 20.
1095 The size of each element in the @code{encoding} member. Always set to 1.
1098 The total number of bytes in @code{encoding}.
1100 @item char encoding[];
1101 The name of the character encoding. Normally this will be an official
1102 IANA character set name or alias.
1103 See @url{http://www.iana.org/assignments/character-sets}.
1104 Character set names are not case-sensitive, but SPSS appears to write
1105 them in all-uppercase.
1108 This record is not present in files generated by older software. See
1109 also the @code{character_code} field in the machine integer info
1110 record (@pxref{character-code}).
1112 When the character encoding record and the machine integer info record
1113 are both present, all system files observed in practice indicate the
1114 same character encoding, e.g.@: 1252 as @code{character_code} and
1115 @code{windows-1252} as @code{encoding}, 65001 and @code{UTF-8}, etc.
1117 If, for testing purposes, a file is crafted with different
1118 @code{character_code} and @code{encoding}, it seems that
1119 @code{character_code} controls the encoding for all strings in the
1120 system file before the dictionary termination record, including
1121 strings in data (e.g.@: string missing values), and @code{encoding}
1122 controls the encoding for strings following the dictionary termination
1125 @node Long String Value Labels Record
1126 @section Long String Value Labels Record
1128 This record, if present, specifies value labels for long string
1138 /* @r{Repeated up to exactly @code{count} bytes.} */
1143 long_string_label labels[];
1147 @item int32 rec_type;
1148 Record type. Always set to 7.
1150 @item int32 subtype;
1151 Record subtype. Always set to 21.
1157 The number of bytes following the header until the next header.
1159 @item int32 var_name_len;
1160 @itemx char var_name[];
1161 The number of bytes in the name of the variable that has long string
1162 value labels, plus the variable name itself, which consists of exactly
1163 @code{var_name_len} bytes. The variable name is not padded to any
1164 particular boundary, nor is it null-terminated.
1166 @item int32 var_width;
1167 The width of the variable, in bytes, which will be between 9 and
1170 @item int32 n_labels;
1171 @itemx long_string_label labels[];
1172 The long string labels themselves. The @code{labels} array contains
1173 exactly @code{n_labels} elements, each of which has the following
1184 @item int32 value_len;
1185 @itemx char value[];
1186 The string value being labeled. @code{value_len} is the number of
1187 bytes in @code{value}; it is equal to @code{var_width}. The
1188 @code{value} array is not padded or null-terminated.
1190 @item int32 label_len;
1191 @itemx char label[];
1192 The label for the string value. @code{label_len}, which must be
1193 between 0 and 120, is the number of bytes in @code{label}. The
1194 @code{label} array is not padded or null-terminated.
1198 @node Long String Missing Values Record
1199 @section Long String Missing Values Record
1201 This record, if present, specifies missing values for long string
1211 /* @r{Repeated up to exactly @code{count} bytes.} */
1214 char n_missing_values;
1215 long_string_missing_value values[];
1219 @item int32 rec_type;
1220 Record type. Always set to 7.
1222 @item int32 subtype;
1223 Record subtype. Always set to 22.
1229 The number of bytes following the header until the next header.
1231 @item int32 var_name_len;
1232 @itemx char var_name[];
1233 The number of bytes in the name of the long string variable that has
1234 missing values, plus the variable name itself, which consists of
1235 exactly @code{var_name_len} bytes. The variable name is not padded to
1236 any particular boundary, nor is it null-terminated.
1238 @item char n_missing_values;
1239 The number of missing values, either 1, 2, or 3. (This is, unusually,
1240 a single byte instead of a 32-bit number.)
1242 @item long_string_missing_value values[];
1243 The missing values themselves. This array contains exactly
1244 @code{n_missing_values} elements, each of which has the following
1253 @item int32 value_len;
1254 The length of the missing value string, in bytes. This value should
1255 be 8, because long string variables are at least 8 bytes wide (by
1256 definition), only the first 8 bytes of a long string variable's
1257 missing values are allowed to be non-spaces, and any spaces within the
1258 first 8 bytes are included in the missing value here.
1261 The missing value string, exactly @code{value_len} bytes, without
1262 any padding or null terminator.
1266 @node Data File and Variable Attributes Records
1267 @section Data File and Variable Attributes Records
1269 The data file and variable attributes records represent custom
1270 attributes for the system file or for individual variables in the
1271 system file, as defined on the DATAFILE ATTRIBUTE (@pxref{DATAFILE
1272 ATTRIBUTE,,,pspp, PSPP Users Guide}) and VARIABLE ATTRIBUTE commands
1273 (@pxref{VARIABLE ATTRIBUTE,,,pspp, PSPP Users Guide}), respectively.
1282 /* @r{Exactly @code{count} bytes of data.} */
1287 @item int32 rec_type;
1288 Record type. Always set to 7.
1290 @item int32 subtype;
1291 Record subtype. Always set to 17 for a data file attribute record or
1292 to 18 for a variable attributes record.
1295 The size of each element in the @code{attributes} member. Always set to 1.
1298 The total number of bytes in @code{attributes}.
1300 @item char attributes[];
1301 The attributes, in a text-based format.
1303 In record type 17, this field contains a single attribute set. An
1304 attribute set is a sequence of one or more attributes concatenated
1305 together. Each attribute consists of a name, which has the same
1306 syntax as a variable name, followed by, inside parentheses, a sequence
1307 of one or more values. Each value consists of a string enclosed in
1308 single quotes (@code{'}) followed by a line feed (byte 0x0a). A value
1309 may contain single quote characters, which are not themselves escaped
1310 or quoted or required to be present in pairs. There is no apparent
1311 way to embed a line feed in a value. There is no distinction between
1312 an attribute with a single value and an attribute array with one
1315 In record type 18, this field contains a sequence of one or more
1316 variable attribute sets. If more than one variable attribute set is
1317 present, each one after the first is delimited from the previous by
1318 @code{/}. Each variable attribute set consists of a long
1320 followed by @code{:}, followed by an attribute set with the same
1321 syntax as on record type 17.
1323 The total length is @code{count} bytes.
1328 A system file produced with the following VARIABLE ATTRIBUTE commands
1332 VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=fred[1]('23') fred[2]('34').
1333 VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=bert('123').
1337 will contain a variable attribute record with the following contents:
1340 0000 07 00 00 00 12 00 00 00 01 00 00 00 22 00 00 00 |............"...|
1341 0010 64 75 6d 6d 79 3a 66 72 65 64 28 27 32 33 27 0a |dummy:fred('23'.|
1342 0020 27 33 34 27 0a 29 62 65 72 74 28 27 31 32 33 27 |'34'.)bert('123'|
1350 @node Variable Roles
1351 @subsection Variable Roles
1353 A variable's role is represented as an attribute named @code{$@@Role}.
1354 This attribute has a single element whose values and their meanings
1359 Input. This, the default, is the most common role.
1372 @node Extended Number of Cases Record
1373 @section Extended Number of Cases Record
1375 The file header record expresses the number of cases in the system
1376 file as an int32 (@pxref{File Header Record}). This record allows the
1377 number of cases in the system file to be expressed as a 64-bit number.
1389 @item int32 rec_type;
1390 Record type. Always set to 7.
1392 @item int32 subtype;
1393 Record subtype. Always set to 16.
1396 Size of each element. Always set to 8.
1399 Number of pieces of data in the data part. Alway set to 2.
1401 @item int64 unknown;
1402 Meaning unknown. Always set to 1.
1404 @item int64 ncases64;
1405 Number of cases in the file as a 64-bit integer. Presumably this
1406 could be -1 to indicate that the number of cases is unknown, for the
1407 same reason as @code{ncases} in the file header record, but this has
1408 not been observed in the wild.
1411 @node Miscellaneous Informational Records
1412 @section Miscellaneous Informational Records
1414 Some specific types of miscellaneous informational records are
1415 documented here, but others are known to exist. PSPP ignores unknown
1416 miscellaneous informational records when reading system files.
1425 /* @r{Exactly @code{size * count} bytes of data.} */
1430 @item int32 rec_type;
1431 Record type. Always set to 7.
1433 @item int32 subtype;
1434 Record subtype. May take any value. According to Aapi
1435 H@"am@"al@"ainen, value 5 indicates a set of grouped variables and 6
1436 indicates date info (probably related to USE). Subtype 24 appears to
1437 contain XML that describes how data in the file should be displayed
1441 Size of each piece of data in the data part. Should have the value 1,
1442 4, or 8, for @code{char}, @code{int32}, and @code{flt64} format data,
1446 Number of pieces of data in the data part.
1449 Arbitrary data. There must be @code{size} times @code{count} bytes of
1453 @node Dictionary Termination Record
1454 @section Dictionary Termination Record
1456 The dictionary termination record separates all other records from the
1465 @item int32 rec_type;
1466 Record type. Always set to 999.
1469 Ignored padding. Should be set to 0.
1473 @section Data Record
1475 The data record must follow all other records in the system file.
1476 Every system file must have a data record that specifies data for at
1477 least one case. The format of the data record varies depending on the
1478 value of @code{compression} in the file header record:
1481 @item 0: no compression
1482 Data is arranged as a series of 8-byte elements.
1483 Each element corresponds to
1484 the variable declared in the respective variable record (@pxref{Variable
1485 Record}). Numeric values are given in @code{flt64} format; string
1486 values are literal characters string, padded on the right when
1487 necessary to fill out 8-byte units.
1489 @item 1: bytecode compression
1491 of the data record is divided into a series of 1-byte command
1492 codes. These codes have meanings as described below:
1496 Ignored. If the program writing the system file accumulates compressed
1497 data in blocks of fixed length, 0 bytes can be used to pad out extra
1498 bytes remaining at the end of a fixed-size block.
1502 value @var{code} - @var{bias}, where
1503 @var{code} is the value of the compression code and @var{bias} is the
1504 variable @code{bias} from the file header. For example,
1505 code 105 with bias 100.0 (the normal value) indicates a numeric variable
1507 One file has been seen written by SPSS 14 that contained such a code
1508 in a @emph{string} field with the value 0 (after the bias is
1509 subtracted) as a way of encoding null bytes.
1512 End of file. This code may or may not appear at the end of the data
1513 stream. PSPP always outputs this code but its use is not required.
1516 A numeric or string value that is not
1517 compressible. The value is stored in the 8 bytes following the
1518 current block of command bytes. If this value appears twice in a block
1519 of command bytes, then it indicates the second group of 8 bytes following the
1520 command bytes, and so on.
1523 An 8-byte string value that is all spaces.
1526 The system-missing value.
1529 The end of the 8-byte group of bytecodes is followed by any 8-byte
1530 blocks of non-compressible values indicated by code 253. After that
1531 follows another 8-byte group of bytecodes, then those bytecodes'
1532 non-compressible values. The pattern repeats to the end of the file
1533 or a code with value 252.
1535 @item 2: ZLIB compression
1536 The data record consists of the following, in order:
1540 ZLIB data header, 24 bytes long.
1543 One or more variable-length blocks of ZLIB compressed data.
1546 ZLIB data trailer, with a 24-byte fixed header plus an additional 24
1547 bytes for each preceding ZLIB compressed data block.
1550 The ZLIB data header has the following format:
1559 @item int64 zheader_ofs;
1560 The offset, in bytes, of the beginning of this structure within the
1563 @item int64 ztrailer_ofs;
1564 The offset, in bytes, of the first byte of the ZLIB data trailer.
1566 @item int64 ztrailer_len;
1567 The number of bytes in the ZLIB data trailer. This and the previous
1568 field sum to the size of the system file in bytes.
1571 The data header is followed by @code{(ztrailer_ofs - 24) / 24} ZLIB
1572 compressed data blocks. Each ZLIB compressed data block begins with a
1573 ZLIB header as specified in RFC@tie{}1950, e.g.@: hex bytes @code{78
1574 01} (the only header yet observed in practice). Each block
1575 decompresses to a fixed number of bytes (in practice only
1576 @code{0x3ff000}-byte blocks have been observed), except that the last
1577 block of data may be shorter. The last ZLIB compressed data block
1578 gends just before offset @code{ztrailer_ofs}.
1580 The result of ZLIB decompression is bytecode compressed data as
1581 described above for compression format 1.
1583 The ZLIB data trailer begins with the following 24-byte fixed header:
1593 @item int64 int_bias;
1594 The compression bias as a negative integer, e.g.@: if @code{bias} in
1595 the file header record is 100.0, then @code{int_bias} is @minus{}100
1596 (this is the only value yet observed in practice).
1599 Always observed to be zero.
1601 @item int32 block_size;
1602 The number of bytes in each ZLIB compressed data block, except
1603 possibly the last, following decompression. Only @code{0x3ff000} has
1604 been observed so far.
1606 @item int32 n_blocks;
1607 The number of ZLIB compressed data blocks, always exactly
1608 @code{(ztrailer_ofs - 24) / 24}.
1611 The fixed header is followed by @code{n_blocks} 24-byte ZLIB data
1612 block descriptors, each of which describes the compressed data block
1613 corresponding to its offset. Each block descriptor has the following
1617 int64 uncompressed_ofs;
1618 int64 compressed_ofs;
1619 int32 uncompressed_size;
1620 int32 compressed_size;
1624 @item int64 uncompressed_ofs;
1625 The offset, in bytes, that this block of data would have in a similar
1626 system file that uses compression format 1. This is
1627 @code{zheader_ofs} in the first block descriptor, and in each
1628 succeeding block descriptor it is the sum of the previous desciptor's
1629 @code{uncompressed_ofs} and @code{uncompressed_size}.
1631 @item int64 compressed_ofs;
1632 The offset, in bytes, of the actual beginning of this compressed data
1633 block. This is @code{zheader_ofs + 24} in the first block descriptor,
1634 and in each succeeding block descriptor it is the sum of the previous
1635 descriptor's @code{compressed_ofs} and @code{compressed_size}. The
1636 final block descriptor's @code{compressed_ofs} and
1637 @code{compressed_size} sum to @code{ztrailer_ofs}.
1639 @item int32 uncompressed_size;
1640 The number of bytes in this data block, after decompression. This is
1641 @code{block_size} in every data block except the last, which may be
1644 @item int32 compressed_size;
1645 The number of bytes in this data block, as stored compressed in this
1650 @setfilename ignored
1652 @node Encrypted System Files
1653 @section Encrypted System Files
1655 SPSS 21 and later support an encrypted system file format.
1658 The SPSS encrypted file format is poorly designed. It is much cheaper
1659 and faster to decrypt a file encrypted this way than if a well
1660 designed alternative were used. If you must use this format, use a
1661 10-byte randomly generated password.
1664 @subheading Encrypted File Format
1666 Encrypted system files begin with the following 36-byte fixed header:
1669 0000 1c 00 00 00 00 00 00 00 45 4e 43 52 59 50 54 45 |........ENCRYPTE|
1670 0010 44 53 41 56 15 00 00 00 00 00 00 00 00 00 00 00 |DSAV............|
1671 0020 00 00 00 00 |....|
1674 Following the fixed header is a complete system file in the usual
1675 format, except that each 16-byte block is encrypted with AES-256 in
1676 ECB mode. The AES-256 key is derived from a password in the following
1681 Start from the literal password typed by the user. Truncate it to at
1682 most 10 bytes, then append (between 1 and 22) null bytes until there
1683 are exactly 32 bytes. Call this @var{password}.
1686 Let @var{constant} be the following 73-byte constant:
1689 0000 00 00 00 01 35 27 13 cc 53 a7 78 89 87 53 22 11
1690 0010 d6 5b 31 58 dc fe 2e 7e 94 da 2f 00 cc 15 71 80
1691 0020 0a 6c 63 53 00 38 c3 38 ac 22 f3 63 62 0e ce 85
1692 0030 3f b8 07 4c 4e 2b 77 c7 21 f5 1a 80 1d 67 fb e1
1693 0040 e1 83 07 d8 0d 00 00 01 00
1697 Compute CMAC-AES-256(@var{password}, @var{constant}). Call the
1698 16-byte result @var{cmac}.
1701 The 32-byte AES-256 key is @var{cmac} || @var{cmac}, that is,
1702 @var{cmac} repeated twice.
1705 @subsubheading Example
1707 Consider the password @samp{pspp}. @var{password} is:
1710 0000 70 73 70 70 00 00 00 00 00 00 00 00 00 00 00 00 |pspp............|
1711 0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
1718 0000 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1725 0000 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1726 0010 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1729 @subheading Password Encoding
1731 SPSS also supports what it calls ``encrypted passwords.'' These are
1732 not encrypted. They are encoded with a simple, fixed scheme. An
1733 encoded password is always a multiple of 2 characters long, and never
1734 longer than 20 characters. The characters in an encoded password are
1735 always in the graphic ASCII range 33 through 126. Each successive
1736 pair of characters in the password encodes a single byte in the
1739 Use the following algorithm to decode a pair of characters:
1743 Let @var{a} be the ASCII code of the first character, and @var{b} be
1744 the ASCII code of the second character.
1747 Let @var{ah} be the most significant 4 bits of @var{a}. Find the line
1748 in the table below that has @var{ah} on the left side. The right side
1749 of the line is a set of possible values for the most significant 4
1750 bits of the decoded byte.
1753 @t{2 } @result{} @t{2367}
1754 @t{3 } @result{} @t{0145}
1755 @t{47} @result{} @t{89cd}
1756 @t{56} @result{} @t{abef}
1760 Let @var{bh} be the most significant 4 bits of @var{b}. Find the line
1761 in the second table below that has @var{bh} on the left side. The
1762 right side of the line is a set of possible values for the most
1763 significant 4 bits of the decoded byte. Together with the results of
1764 the previous step, only a single possibility is left.
1767 @t{2 } @result{} @t{139b}
1768 @t{3 } @result{} @t{028a}
1769 @t{47} @result{} @t{46ce}
1770 @t{56} @result{} @t{57df}
1774 Let @var{al} be the least significant 4 bits of @var{a}. Find the
1775 line in the table below that has @var{al} on the left side. The right
1776 side of the line is a set of possible values for the least significant
1777 4 bits of the decoded byte.
1780 @t{03cf} @result{} @t{0145}
1781 @t{12de} @result{} @t{2367}
1782 @t{478b} @result{} @t{89cd}
1783 @t{569a} @result{} @t{abef}
1787 Let @var{bl} be the least significant 4 bits of @var{b}. Find the
1788 line in the table below that has @var{bl} on the left side. The right
1789 side of the line is a set of possible values for the least significant
1790 4 bits of the decoded byte. Together with the results of the previous
1791 step, only a single possibility is left.
1794 @t{03cf} @result{} @t{028a}
1795 @t{12de} @result{} @t{139b}
1796 @t{478b} @result{} @t{46ce}
1797 @t{569a} @result{} @t{57df}
1801 @subsubheading Example
1803 Consider the encoded character pair @samp{-|}. @var{a} is
1804 0x2d and @var{b} is 0x7c, so @var{ah} is 2, @var{bh} is 7, @var{al} is
1805 0xd, and @var{bl} is 0xc. @var{ah} means that the most significant
1806 four bits of the decoded character is 2, 3, 6, or 7, and @var{bh}
1807 means that they are 4, 6, 0xc, or 0xe. The single possibility in
1808 common is 6, so the most significant four bits are 6. Similarly,
1809 @var{al} means that the least significant four bits are 2, 3, 6, or 7,
1810 and @var{bl} means they are 0, 2, 8, or 0xa, so the least significant
1811 four bits are 2. The decoded character is therefore 0x62, the letter