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 have 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}).
72 * System File Record Structure::
73 * File Header Record::
75 * Value Labels Records::
77 * Machine Integer Info Record::
78 * Machine Floating-Point Info Record::
79 * Multiple Response Sets Records::
80 * Extra Product Info Record::
81 * Variable Display Parameter Record::
82 * Long Variable Names Record::
83 * Very Long String Record::
84 * Character Encoding Record::
85 * Long String Value Labels Record::
86 * Long String Missing Values Record::
87 * Data File and Variable Attributes Records::
88 * Extended Number of Cases Record::
89 * Other Informational Records::
90 * Dictionary Termination Record::
92 * Encrypted System Files::
95 @node System File Record Structure
96 @section System File Record Structure
98 System files are divided into records with the following format:
105 This header does not identify the length of the @code{data} or any
106 information about what it contains, so the system file reader must
107 understand the format of @code{data} based on @code{type}. However,
108 records with type 7, called @dfn{extension records}, have a stricter
116 char data[size * count];
120 @item int32 rec_type;
121 Record type. Always set to 7.
124 Record subtype. This value identifies a particular kind of extension
128 The size of each piece of data that follows the header, in bytes.
129 Known extension records use 1, 4, or 8, for @code{char}, @code{int32},
130 and @code{flt64} format data, respectively.
133 The number of pieces of data that follow the header.
135 @item char data[size * count];
136 Data, whose format and interpretation depend on the subtype.
139 An extension record contains exactly @code{size * count} bytes of
140 data, which allows a reader that does not understand an extension
141 record to skip it. Extension records provide only nonessential
142 information, so this allows for files written by newer software to
143 preserve backward compatibility with older or less capable readers.
145 Records in a system file must appear in the following order:
155 All pairs of value labels records and value label variables records,
159 Document record, if present.
162 Extension (type 7) records, in ascending numerical order of their
166 Dictionary termination record.
172 We advise authors of programs that read system files to tolerate
173 format variations. Various kinds of misformatting and corruption have
174 been observed in system files written by SPSS and other software
175 alike. In particular, because extension records provide nonessential
176 information, it is generally better to ignore an extension record
177 entirely than to refuse to read a system file.
179 The following sections describe the known kinds of records.
181 @node File Header Record
182 @section File Header Record
184 A system file begins with the file header, with the following format:
190 int32 nominal_case_size;
195 char creation_date[9];
196 char creation_time[8];
202 @item char rec_type[4];
203 Record type code, either @samp{$FL2} for system files with
204 uncompressed data or data compressed with simple bytecode compression,
205 or @samp{$FL3} for system files with ZLIB compressed data.
207 This is truly a character field that uses the character encoding as
208 other strings. Thus, in a file with an ASCII-based character encoding
209 this field contains @code{24 46 4c 32} or @code{24 46 4c 33}, and in a
210 file with an EBCDIC-based encoding this field contains @code{5b c6 d3
211 f2}. (No EBCDIC-based ZLIB-compressed files have been observed.)
213 @item char prod_name[60];
214 Product identification string. This always begins with the characters
215 @samp{@@(#) SPSS DATA FILE}. PSPP uses the remaining characters to
216 give its version and the operating system name; for example, @samp{GNU
217 pspp 0.1.4 - sparc-sun-solaris2.5.2}. The string is truncated if it
218 would be longer than 60 characters; otherwise it is padded on the right
222 @item int32 layout_code;
223 Normally set to 2, although a few system files have been spotted in
224 the wild with a value of 3 here. PSPP use this value to determine the
225 file's integer endianness (@pxref{System File Format}).
227 @item int32 nominal_case_size;
228 Number of data elements per case. This is the number of variables,
229 except that long string variables add extra data elements (one for every
230 8 characters after the first 8). However, string variables do not
231 contribute to this value beyond the first 255 bytes. Further, system
232 files written by some systems set this value to -1. In general, it is
233 unsafe for systems reading system files to rely upon this value.
235 @item int32 compression;
236 Set to 0 if the data in the file is not compressed, 1 if the data is
237 compressed with simple bytecode compression, 2 if the data is ZLIB
238 compressed. This field has value 2 if and only if @code{rec_type} is
241 @item int32 weight_index;
242 If one of the variables in the data set is used as a weighting
243 variable, set to the dictionary index of that variable, plus 1
244 (@pxref{Dictionary Index}). Otherwise, set to 0.
247 Set to the number of cases in the file if it is known, or -1 otherwise.
249 In the general case it is not possible to determine the number of cases
250 that will be output to a system file at the time that the header is
251 written. The way that this is dealt with is by writing the entire
252 system file, including the header, then seeking back to the beginning of
253 the file and writing just the @code{ncases} field. For files in which
254 this is not valid, the seek operation fails. In this case,
255 @code{ncases} remains -1.
259 Compression bias, ordinarily set to 100. Only integers between
260 @code{1 - bias} and @code{251 - bias} can be compressed.
262 By assuming that its value is 100, PSPP uses @code{bias} to determine
263 the file's floating-point format and endianness (@pxref{System File
264 Format}). If the compression bias is not 100, PSPP cannot auto-detect
265 the floating-point format and assumes that it is IEEE 754 format with
266 the same endianness as the system file's integers, which is correct
267 for all known system files.
269 @item char creation_date[9];
270 Date of creation of the system file, in @samp{dd mmm yy}
271 format, with the month as standard English abbreviations, using an
272 initial capital letter and following with lowercase. If the date is not
273 available then this field is arbitrarily set to @samp{01 Jan 70}.
275 @item char creation_time[8];
276 Time of creation of the system file, in @samp{hh:mm:ss}
277 format and using 24-hour time. If the time is not available then this
278 field is arbitrarily set to @samp{00:00:00}.
280 @item char file_label[64];
281 File label declared by the user, if any (@pxref{FILE LABEL,,,pspp,
282 PSPP Users Guide}). Padded on the right with spaces.
284 A product that identifies itself as @code{VOXCO INTERVIEWER 4.3} uses
285 CR-only line ends in this field, rather than the more usual LF-only or
288 @item char padding[3];
289 Ignored padding bytes to make the structure a multiple of 32 bits in
290 length. Set to zeros.
293 @node Variable Record
294 @section Variable Record
296 There must be one variable record for each numeric variable and each
297 string variable with width 8 bytes or less. String variables wider
298 than 8 bytes have one variable record for each 8 bytes, rounding up.
299 The first variable record for a long string specifies the variable's
300 correct dictionary information. Subsequent variable records for a
301 long string are filled with dummy information: a type of -1, no
302 variable label or missing values, print and write formats that are
303 ignored, and an empty string as name. A few system files have been
304 encountered that include a variable label on dummy variable records,
305 so readers should take care to parse dummy variable records in the
306 same way as other variable records.
308 @anchor{Dictionary Index}
309 The @dfn{dictionary index} of a variable is its offset in the set of
310 variable records, including dummy variable records for long string
311 variables. The first variable record has a dictionary index of 0, the
312 second has a dictionary index of 1, and so on.
314 The system file format does not directly support string variables
315 wider than 255 bytes. Such very long string variables are represented
316 by a number of narrower string variables. @xref{Very Long String
317 Record}, for details.
319 A system file should contain at least one variable and thus at least
320 one variable record, but system files have been observed in the wild
321 without any variables (thus, no data either).
327 int32 n_missing_values;
332 /* @r{Present only if @code{has_var_label} is 1.} */
336 /* @r{Present only if @code{n_missing_values} is nonzero}. */
337 flt64 missing_values[];
341 @item int32 rec_type;
342 Record type code. Always set to 2.
345 Variable type code. Set to 0 for a numeric variable. For a short
346 string variable or the first part of a long string variable, this is set
347 to the width of the string. For the second and subsequent parts of a
348 long string variable, set to -1, and the remaining fields in the
349 structure are ignored.
351 @item int32 has_var_label;
352 If this variable has a variable label, set to 1; otherwise, set to 0.
354 @item int32 n_missing_values;
355 If the variable has no missing values, set to 0. If the variable has
356 one, two, or three discrete missing values, set to 1, 2, or 3,
357 respectively. If the variable has a range for missing variables, set to
358 -2; if the variable has a range for missing variables plus a single
359 discrete value, set to -3.
361 A long string variable always has the value 0 here. A separate record
362 indicates missing values for long string variables (@pxref{Long String
363 Missing Values Record}).
366 Print format for this variable. See below.
369 Write format for this variable. See below.
372 Variable name. The variable name must begin with a capital letter or
373 the at-sign (@samp{@@}). Subsequent characters may also be digits, octothorpes
374 (@samp{#}), dollar signs (@samp{$}), underscores (@samp{_}), or full
375 stops (@samp{.}). The variable name is padded on the right with spaces.
377 The @samp{name} fields should be unique within a system file. System
378 files written by SPSS that contain very long string variables with
379 similar names sometimes contain duplicate names that are later
380 eliminated by resolving the very long string names (@pxref{Very Long
381 String Record}). PSPP handles duplicates by assigning them new,
384 @item int32 label_len;
385 This field is present only if @code{has_var_label} is set to 1. It is
386 set to the length, in characters, of the variable label. The
387 documented maximum length varies from 120 to 255 based on SPSS
388 version, but some files have been seen with longer labels. PSPP
389 accepts labels of any length.
392 This field is present only if @code{has_var_label} is set to 1. It has
393 length @code{label_len}, rounded up to the nearest multiple of 32 bits.
394 The first @code{label_len} characters are the variable's variable label.
396 @item flt64 missing_values[];
397 This field is present only if @code{n_missing_values} is nonzero. It
398 has the same number of 8-byte elements as the absolute value of
399 @code{n_missing_values}. Each element is interpreted as a number for
400 numeric variables (with HIGHEST and LOWEST indicated as described in
401 the chapter introduction). For string variables of width less than 8
402 bytes, elements are right-padded with spaces; for string variables
403 wider than 8 bytes, only the first 8 bytes of each missing value are
404 specified, with the remainder implicitly all spaces.
406 For discrete missing values, each element represents one missing
407 value. When a range is present, the first element denotes the minimum
408 value in the range, and the second element denotes the maximum value
409 in the range. When a range plus a value are present, the third
410 element denotes the additional discrete missing value.
413 @anchor{System File Output Formats}
414 The @code{print} and @code{write} members of sysfile_variable are output
415 formats coded into @code{int32} types. The least-significant byte
416 of the @code{int32} represents the number of decimal places, and the
417 next two bytes in order of increasing significance represent field width
418 and format type, respectively. The most-significant byte is not
419 used and should be set to zero.
421 Format types are defined as follows:
424 @multitable {Value} {@code{DATETIME}}
510 A few system files have been observed in the wild with invalid
511 @code{write} fields, in particular with value 0. Readers should
512 probably treat invalid @code{print} or @code{write} fields as some
515 @node Value Labels Records
516 @section Value Labels Records
518 The value label records documented in this section are used for
519 numeric and short string variables only. Long string variables may
520 have value labels, but their value labels are recorded using a
521 different record type (@pxref{Long String Value Labels Record}).
523 The value label record has the following format:
529 /* @r{Repeated @code{label_cnt} times}. */
536 @item int32 rec_type;
537 Record type. Always set to 3.
539 @item int32 label_count;
540 Number of value labels present in this record.
543 The remaining fields are repeated @code{count} times. Each
544 repetition specifies one value label.
548 A numeric value or a short string value padded as necessary to 8 bytes
549 in length. Its type and width cannot be determined until the
550 following value label variables record (see below) is read.
552 @item char label_len;
553 The label's length, in bytes. The documented maximum length varies
554 from 60 to 120 based on SPSS version. PSPP supports value labels up
558 @code{label_len} bytes of the actual label, followed by up to 7 bytes
559 of padding to bring @code{label} and @code{label_len} together to a
560 multiple of 8 bytes in length.
563 The value label record is always immediately followed by a value label
564 variables record with the following format:
573 @item int32 rec_type;
574 Record type. Always set to 4.
576 @item int32 var_count;
577 Number of variables that the associated value labels from the value
578 label record are to be applied.
581 A list of dictionary indexes of variables to which to apply the value
582 labels (@pxref{Dictionary Index}). There are @code{var_count}
585 String variables wider than 8 bytes may not be specified in this list.
588 @node Document Record
589 @section Document Record
591 The document record, if present, has the following format:
600 @item int32 rec_type;
601 Record type. Always set to 6.
604 Number of lines of documents present.
606 @item char lines[][80];
607 Document lines. The number of elements is defined by @code{n_lines}.
608 Lines shorter than 80 characters are padded on the right with spaces.
611 @node Machine Integer Info Record
612 @section Machine Integer Info Record
614 The integer info record, if present, has the following format:
626 int32 version_revision;
628 int32 floating_point_rep;
629 int32 compression_code;
631 int32 character_code;
635 @item int32 rec_type;
636 Record type. Always set to 7.
639 Record subtype. Always set to 3.
642 Size of each piece of data in the data part, in bytes. Always set to 4.
645 Number of pieces of data in the data part. Always set to 8.
647 @item int32 version_major;
648 PSPP major version number. In version @var{x}.@var{y}.@var{z}, this
651 @item int32 version_minor;
652 PSPP minor version number. In version @var{x}.@var{y}.@var{z}, this
655 @item int32 version_revision;
656 PSPP version revision number. In version @var{x}.@var{y}.@var{z},
659 @item int32 machine_code;
660 Machine code. PSPP always set this field to value to -1, but other
663 @item int32 floating_point_rep;
664 Floating point representation code. For IEEE 754 systems this is 1.
665 IBM 370 sets this to 2, and DEC VAX E to 3.
667 @item int32 compression_code;
668 Compression code. Always set to 1, regardless of whether or how the
671 @item int32 endianness;
672 Machine endianness. 1 indicates big-endian, 2 indicates little-endian.
674 @item int32 character_code;
675 @anchor{character-code} Character code. The following values have
676 been actually observed in system files:
686 The @code{windows-1250} code page for Central European and Eastern
690 The @code{windows-1252} code page for Western European languages.
699 The following additional values are known to be defined:
709 Other Windows code page numbers are known to be generally valid.
711 Old versions of SPSS for Unix and Windows always wrote value 2 in this
712 field, regardless of the encoding in use. Newer versions also write
713 the character encoding as a string (see @ref{Character Encoding
717 @node Machine Floating-Point Info Record
718 @section Machine Floating-Point Info Record
720 The floating-point info record, if present, has the following format:
736 @item int32 rec_type;
737 Record type. Always set to 7.
740 Record subtype. Always set to 4.
743 Size of each piece of data in the data part, in bytes. Always set to 8.
746 Number of pieces of data in the data part. Always set to 3.
749 @itemx flt64 highest;
751 The system missing value, the value used for HIGHEST in missing
752 values, and the value used for LOWEST in missing values, respectively.
753 @xref{System File Format}, for more information.
755 The SPSSWriter library in PHP, which identifies itself as @code{FOM
756 SPSS 1.0.0} in the file header record @code{prod_name} field, writes
757 unexpected values to these fields, but it uses the same values
758 consistently throughout the rest of the file.
761 @node Multiple Response Sets Records
762 @section Multiple Response Sets Records
764 The system file format has two different types of records that
765 represent multiple response sets (@pxref{MRSETS,,,pspp, PSPP Users
766 Guide}). The first type of record describes multiple response sets
767 that can be understood by SPSS before version 14. The second type of
768 record, with a closely related format, is used for multiple dichotomy
769 sets that use the CATEGORYLABELS=COUNTEDVALUES feature added in
779 /* @r{Exactly @code{count} bytes of data.} */
784 @item int32 rec_type;
785 Record type. Always set to 7.
788 Record subtype. Set to 7 for records that describe multiple response
789 sets understood by SPSS before version 14, or to 19 for records that
790 describe dichotomy sets that use the CATEGORYLABELS=COUNTEDVALUES
791 feature added in version 14.
794 The size of each element in the @code{mrsets} member. Always set to 1.
797 The total number of bytes in @code{mrsets}.
800 Zero or more line feeds (byte 0x0a), followed by a series of multiple
801 response sets, each of which consists of the following:
805 The set's name (an identifier that begins with @samp{$}), in mixed
806 upper and lower case.
809 An equals sign (@samp{=}).
812 @samp{C} for a multiple category set, @samp{D} for a multiple
813 dichotomy set with CATEGORYLABELS=VARLABELS, or @samp{E} for a
814 multiple dichotomy set with CATEGORYLABELS=COUNTEDVALUES.
817 For a multiple dichotomy set with CATEGORYLABELS=COUNTEDVALUES, a
818 space, followed by a number expressed as decimal digits, followed by a
819 space. If LABELSOURCE=VARLABEL was specified on MRSETS, then the
820 number is 11; otherwise it is 1.@footnote{This part of the format may
821 not be fully understood, because only a single example of each
822 possibility has been examined.}
825 For either kind of multiple dichotomy set, the counted value, as a
826 positive integer count specified as decimal digits, followed by a
827 space, followed by as many string bytes as specified in the count. If
828 the set contains numeric variables, the string consists of the counted
829 integer value expressed as decimal digits. If the set contains string
830 variables, the string contains the counted string value. Either way,
831 the string may be padded on the right with spaces (older versions of
832 SPSS seem to always pad to a width of 8 bytes; newer versions don't).
838 The multiple response set's label, using the same format as for the
839 counted value for multiple dichotomy sets. A string of length 0 means
840 that the set does not have a label. A string of length 0 is also
841 written if LABELSOURCE=VARLABEL was specified.
847 The short names of the variables in the set, converted to lowercase,
848 each separated from the previous by a single space.
850 Even though a multiple response set must have at least two variables,
851 some system files contain multiple response sets with no variables or
852 one variable. The source and meaning of these multiple response sets is
853 unknown. (Perhaps they arise from creating a multiple response set
854 then deleting all the variables that it contains?)
857 One line feed (byte 0x0a). Sometimes multiple, even hundreds, of line
862 Example: Given appropriate variable definitions, consider the
863 following MRSETS command:
866 MRSETS /MCGROUP NAME=$a LABEL='my mcgroup' VARIABLES=a b c
867 /MDGROUP NAME=$b VARIABLES=g e f d VALUE=55
868 /MDGROUP NAME=$c LABEL='mdgroup #2' VARIABLES=h i j VALUE='Yes'
869 /MDGROUP NAME=$d LABEL='third mdgroup' CATEGORYLABELS=COUNTEDVALUES
870 VARIABLES=k l m VALUE=34
871 /MDGROUP NAME=$e CATEGORYLABELS=COUNTEDVALUES LABELSOURCE=VARLABEL
872 VARIABLES=n o p VALUE='choice'.
875 The above would generate the following multiple response set record of
879 $a=C 10 my mcgroup a b c
881 $c=D3 Yes 10 mdgroup #2 h i j
884 It would also generate the following multiple response set record with
888 $d=E 1 2 34 13 third mdgroup k l m
889 $e=E 11 6 choice 0 n o p
892 @node Extra Product Info Record
893 @section Extra Product Info Record
895 This optional record appears to contain a text string that describes
896 the program that wrote the file and the source of the data. (This is
897 redundant with the file label and product info found in the file
907 /* @r{Exactly @code{count} bytes of data.} */
912 @item int32 rec_type;
913 Record type. Always set to 7.
916 Record subtype. Always set to 10.
919 The size of each element in the @code{info} member. Always set to 1.
922 The total number of bytes in @code{info}.
925 A text string. A product that identifies itself as @code{VOXCO
926 INTERVIEWER 4.3} uses CR-only line ends in this field, rather than the
927 more usual LF-only or CR LF line ends.
930 @node Variable Display Parameter Record
931 @section Variable Display Parameter Record
933 The variable display parameter record, if present, has the following
943 /* @r{Repeated @code{count} times}. */
945 int32 width; /* @r{Not always present.} */
950 @item int32 rec_type;
951 Record type. Always set to 7.
954 Record subtype. Always set to 11.
957 The size of @code{int32}. Always set to 4.
960 The number of sets of variable display parameters (ordinarily the
961 number of variables in the dictionary), times 2 or 3.
964 The remaining members are repeated @code{count} times, in the same
965 order as the variable records. No element corresponds to variable
966 records that continue long string variables. The meanings of these
967 members are as follows:
971 The measurement type of the variable:
981 SPSS sometimes writes a @code{measure} of 0. PSPP interprets this as
985 The width of the display column for the variable in characters.
987 This field is present if @var{count} is 3 times the number of
988 variables in the dictionary. It is omitted if @var{count} is 2 times
989 the number of variables.
991 @item int32 alignment;
992 The alignment of the variable for display purposes:
1004 @node Long Variable Names Record
1005 @section Long Variable Names Record
1007 If present, the long variable names record has the following format:
1016 /* @r{Exactly @code{count} bytes of data.} */
1017 char var_name_pairs[];
1021 @item int32 rec_type;
1022 Record type. Always set to 7.
1024 @item int32 subtype;
1025 Record subtype. Always set to 13.
1028 The size of each element in the @code{var_name_pairs} member. Always set to 1.
1031 The total number of bytes in @code{var_name_pairs}.
1033 @item char var_name_pairs[];
1034 A list of @var{key}--@var{value} tuples, where @var{key} is the name
1035 of a variable, and @var{value} is its long variable name.
1036 The @var{key} field is at most 8 bytes long and must match the
1037 name of a variable which appears in the variable record (@pxref{Variable
1039 The @var{value} field is at most 64 bytes long.
1040 The @var{key} and @var{value} fields are separated by a @samp{=} byte.
1041 Each tuple is separated by a byte whose value is 09. There is no
1042 trailing separator following the last tuple.
1043 The total length is @code{count} bytes.
1046 @node Very Long String Record
1047 @section Very Long String Record
1049 Old versions of SPSS limited string variables to a width of 255 bytes.
1050 For backward compatibility with these older versions, the system file
1051 format represents a string longer than 255 bytes, called a @dfn{very
1052 long string}, as a collection of strings no longer than 255 bytes
1053 each. The strings concatenated to make a very long string are called
1054 its @dfn{segments}; for consistency, variables other than very long
1055 strings are considered to have a single segment.
1057 A very long string with a width of @var{w} has @var{n} =
1058 (@var{w} + 251) / 252 segments, that is, one segment for every
1059 252 bytes of width, rounding up. It would be logical, then, for each
1060 of the segments except the last to have a width of 252 and the last
1061 segment to have the remainder, but this is not the case. In fact,
1062 each segment except the last has a width of 255 bytes. The last
1063 segment has width @var{w} - (@var{n} - 1) * 252; some versions
1064 of SPSS make it slightly wider, but not wide enough to make the last
1065 segment require another 8 bytes of data.
1067 Data is packed tightly into segments of a very long string, 255 bytes
1068 per segment. Because 255 bytes of segment data are allocated for
1069 every 252 bytes of the very long string's width (approximately), some
1070 unused space is left over at the end of the allocated segments. Data
1071 in unused space is ignored.
1073 Example: Consider a very long string of width 20,000. Such a very
1074 long string has 20,000 / 252 = 80 (rounding up) segments. The first
1075 79 segments have width 255; the last segment has width 20,000 - 79 *
1076 252 = 92 or slightly wider (up to 96 bytes, the next multiple of 8).
1077 The very long string's data is actually stored in the 19,890 bytes in
1078 the first 78 segments, plus the first 110 bytes of the 79th segment
1079 (19,890 + 110 = 20,000). The remaining 145 bytes of the 79th segment
1080 and all 92 bytes of the 80th segment are unused.
1082 The very long string record explains how to stitch together segments
1083 to obtain very long string data. For each of the very long string
1084 variables in the dictionary, it specifies the name of its first
1085 segment's variable and the very long string variable's actual width.
1086 The remaining segments immediately follow the named variable in the
1087 system file's dictionary.
1089 The very long string record, which is present only if the system file
1090 contains very long string variables, has the following format:
1099 /* @r{Exactly @code{count} bytes of data.} */
1100 char string_lengths[];
1104 @item int32 rec_type;
1105 Record type. Always set to 7.
1107 @item int32 subtype;
1108 Record subtype. Always set to 14.
1111 The size of each element in the @code{string_lengths} member. Always set to 1.
1114 The total number of bytes in @code{string_lengths}.
1116 @item char string_lengths[];
1117 A list of @var{key}--@var{value} tuples, where @var{key} is the name
1118 of a variable, and @var{value} is its length.
1119 The @var{key} field is at most 8 bytes long and must match the
1120 name of a variable which appears in the variable record (@pxref{Variable
1122 The @var{value} field is exactly 5 bytes long. It is a zero-padded,
1123 ASCII-encoded string that is the length of the variable.
1124 The @var{key} and @var{value} fields are separated by a @samp{=} byte.
1125 Tuples are delimited by a two-byte sequence @{00, 09@}.
1126 After the last tuple, there may be a single byte 00, or @{00, 09@}.
1127 The total length is @code{count} bytes.
1130 @node Character Encoding Record
1131 @section Character Encoding Record
1133 This record, if present, indicates the character encoding for string data,
1134 long variable names, variable labels, value labels and other strings in the
1144 /* @r{Exactly @code{count} bytes of data.} */
1149 @item int32 rec_type;
1150 Record type. Always set to 7.
1152 @item int32 subtype;
1153 Record subtype. Always set to 20.
1156 The size of each element in the @code{encoding} member. Always set to 1.
1159 The total number of bytes in @code{encoding}.
1161 @item char encoding[];
1162 The name of the character encoding. Normally this will be an official
1163 IANA character set name or alias.
1164 See @url{http://www.iana.org/assignments/character-sets}.
1165 Character set names are not case-sensitive, but SPSS appears to write
1166 them in all-uppercase.
1169 This record is not present in files generated by older software. See
1170 also the @code{character_code} field in the machine integer info
1171 record (@pxref{character-code}).
1173 When the character encoding record and the machine integer info record
1174 are both present, all system files observed in practice indicate the
1175 same character encoding, e.g.@: 1252 as @code{character_code} and
1176 @code{windows-1252} as @code{encoding}, 65001 and @code{UTF-8}, etc.
1178 If, for testing purposes, a file is crafted with different
1179 @code{character_code} and @code{encoding}, it seems that
1180 @code{character_code} controls the encoding for all strings in the
1181 system file before the dictionary termination record, including
1182 strings in data (e.g.@: string missing values), and @code{encoding}
1183 controls the encoding for strings following the dictionary termination
1186 @node Long String Value Labels Record
1187 @section Long String Value Labels Record
1189 This record, if present, specifies value labels for long string
1199 /* @r{Repeated up to exactly @code{count} bytes.} */
1204 long_string_label labels[];
1208 @item int32 rec_type;
1209 Record type. Always set to 7.
1211 @item int32 subtype;
1212 Record subtype. Always set to 21.
1218 The number of bytes following the header until the next header.
1220 @item int32 var_name_len;
1221 @itemx char var_name[];
1222 The number of bytes in the name of the variable that has long string
1223 value labels, plus the variable name itself, which consists of exactly
1224 @code{var_name_len} bytes. The variable name is not padded to any
1225 particular boundary, nor is it null-terminated.
1227 @item int32 var_width;
1228 The width of the variable, in bytes, which will be between 9 and
1231 @item int32 n_labels;
1232 @itemx long_string_label labels[];
1233 The long string labels themselves. The @code{labels} array contains
1234 exactly @code{n_labels} elements, each of which has the following
1245 @item int32 value_len;
1246 @itemx char value[];
1247 The string value being labeled. @code{value_len} is the number of
1248 bytes in @code{value}; it is equal to @code{var_width}. The
1249 @code{value} array is not padded or null-terminated.
1251 @item int32 label_len;
1252 @itemx char label[];
1253 The label for the string value. @code{label_len}, which must be
1254 between 0 and 120, is the number of bytes in @code{label}. The
1255 @code{label} array is not padded or null-terminated.
1259 @node Long String Missing Values Record
1260 @section Long String Missing Values Record
1262 This record, if present, specifies missing values for long string
1272 /* @r{Repeated up to exactly @code{count} bytes.} */
1275 char n_missing_values;
1276 long_string_missing_value values[];
1280 @item int32 rec_type;
1281 Record type. Always set to 7.
1283 @item int32 subtype;
1284 Record subtype. Always set to 22.
1290 The number of bytes following the header until the next header.
1292 @item int32 var_name_len;
1293 @itemx char var_name[];
1294 The number of bytes in the name of the long string variable that has
1295 missing values, plus the variable name itself, which consists of
1296 exactly @code{var_name_len} bytes. The variable name is not padded to
1297 any particular boundary, nor is it null-terminated.
1299 @item char n_missing_values;
1300 The number of missing values, either 1, 2, or 3. (This is, unusually,
1301 a single byte instead of a 32-bit number.)
1303 @item long_string_missing_value values[];
1304 The missing values themselves. This array contains exactly
1305 @code{n_missing_values} elements, each of which has the following
1314 @item int32 value_len;
1315 The length of the missing value string, in bytes. This value should
1316 be 8, because long string variables are at least 8 bytes wide (by
1317 definition), only the first 8 bytes of a long string variable's
1318 missing values are allowed to be non-spaces, and any spaces within the
1319 first 8 bytes are included in the missing value here.
1322 The missing value string, exactly @code{value_len} bytes, without
1323 any padding or null terminator.
1327 @node Data File and Variable Attributes Records
1328 @section Data File and Variable Attributes Records
1330 The data file and variable attributes records represent custom
1331 attributes for the system file or for individual variables in the
1332 system file, as defined on the DATAFILE ATTRIBUTE (@pxref{DATAFILE
1333 ATTRIBUTE,,,pspp, PSPP Users Guide}) and VARIABLE ATTRIBUTE commands
1334 (@pxref{VARIABLE ATTRIBUTE,,,pspp, PSPP Users Guide}), respectively.
1343 /* @r{Exactly @code{count} bytes of data.} */
1348 @item int32 rec_type;
1349 Record type. Always set to 7.
1351 @item int32 subtype;
1352 Record subtype. Always set to 17 for a data file attribute record or
1353 to 18 for a variable attributes record.
1356 The size of each element in the @code{attributes} member. Always set to 1.
1359 The total number of bytes in @code{attributes}.
1361 @item char attributes[];
1362 The attributes, in a text-based format.
1364 In record type 17, this field contains a single attribute set. An
1365 attribute set is a sequence of one or more attributes concatenated
1366 together. Each attribute consists of a name, which has the same
1367 syntax as a variable name, followed by, inside parentheses, a sequence
1368 of one or more values. Each value consists of a string enclosed in
1369 single quotes (@code{'}) followed by a line feed (byte 0x0a). A value
1370 may contain single quote characters, which are not themselves escaped
1371 or quoted or required to be present in pairs. There is no apparent
1372 way to embed a line feed in a value. There is no distinction between
1373 an attribute with a single value and an attribute array with one
1376 In record type 18, this field contains a sequence of one or more
1377 variable attribute sets. If more than one variable attribute set is
1378 present, each one after the first is delimited from the previous by
1379 @code{/}. Each variable attribute set consists of a long
1381 followed by @code{:}, followed by an attribute set with the same
1382 syntax as on record type 17.
1384 The total length is @code{count} bytes.
1389 A system file produced with the following VARIABLE ATTRIBUTE commands
1393 VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=fred[1]('23') fred[2]('34').
1394 VARIABLE ATTRIBUTE VARIABLES=dummy ATTRIBUTE=bert('123').
1398 will contain a variable attribute record with the following contents:
1401 0000 07 00 00 00 12 00 00 00 01 00 00 00 22 00 00 00 |............"...|
1402 0010 64 75 6d 6d 79 3a 66 72 65 64 28 27 32 33 27 0a |dummy:fred('23'.|
1403 0020 27 33 34 27 0a 29 62 65 72 74 28 27 31 32 33 27 |'34'.)bert('123'|
1411 @node Variable Roles
1412 @subsection Variable Roles
1414 A variable's role is represented as an attribute named @code{$@@Role}.
1415 This attribute has a single element whose values and their meanings
1420 Input. This, the default, is the most common role.
1433 @node Extended Number of Cases Record
1434 @section Extended Number of Cases Record
1436 The file header record expresses the number of cases in the system
1437 file as an int32 (@pxref{File Header Record}). This record allows the
1438 number of cases in the system file to be expressed as a 64-bit number.
1450 @item int32 rec_type;
1451 Record type. Always set to 7.
1453 @item int32 subtype;
1454 Record subtype. Always set to 16.
1457 Size of each element. Always set to 8.
1460 Number of pieces of data in the data part. Alway set to 2.
1462 @item int64 unknown;
1463 Meaning unknown. Always set to 1.
1465 @item int64 ncases64;
1466 Number of cases in the file as a 64-bit integer. Presumably this
1467 could be -1 to indicate that the number of cases is unknown, for the
1468 same reason as @code{ncases} in the file header record, but this has
1469 not been observed in the wild.
1472 @node Other Informational Records
1473 @section Other Informational Records
1475 This chapter documents many specific types of extension records are
1476 documented here, but others are known to exist. PSPP ignores unknown
1477 extension records when reading system files.
1479 The following extension record subtypes have also been observed, with
1480 the following believed meanings:
1484 A set of grouped variables (according to Aapi H@"am@"al@"ainen).
1487 Date info, probably related to USE (according to Aapi H@"am@"al@"ainen).
1490 A UUID in the format described in RFC 4122. Only two examples
1491 observed, both written by SPSS 13, and in each case the UUID contained
1492 both upper and lower case.
1495 XML that describes how data in the file should be displayed on-screen.
1498 @node Dictionary Termination Record
1499 @section Dictionary Termination Record
1501 The dictionary termination record separates all other records from the
1510 @item int32 rec_type;
1511 Record type. Always set to 999.
1514 Ignored padding. Should be set to 0.
1518 @section Data Record
1520 The data record must follow all other records in the system file.
1521 Every system file must have a data record that specifies data for at
1522 least one case. The format of the data record varies depending on the
1523 value of @code{compression} in the file header record:
1526 @item 0: no compression
1527 Data is arranged as a series of 8-byte elements.
1528 Each element corresponds to
1529 the variable declared in the respective variable record (@pxref{Variable
1530 Record}). Numeric values are given in @code{flt64} format; string
1531 values are literal characters string, padded on the right when
1532 necessary to fill out 8-byte units.
1534 @item 1: bytecode compression
1536 of the data record is divided into a series of 1-byte command
1537 codes. These codes have meanings as described below:
1541 Ignored. If the program writing the system file accumulates compressed
1542 data in blocks of fixed length, 0 bytes can be used to pad out extra
1543 bytes remaining at the end of a fixed-size block.
1547 value @var{code} - @var{bias}, where
1548 @var{code} is the value of the compression code and @var{bias} is the
1549 variable @code{bias} from the file header. For example,
1550 code 105 with bias 100.0 (the normal value) indicates a numeric variable
1552 One file has been seen written by SPSS 14 that contained such a code
1553 in a @emph{string} field with the value 0 (after the bias is
1554 subtracted) as a way of encoding null bytes.
1557 End of file. This code may or may not appear at the end of the data
1558 stream. PSPP always outputs this code but its use is not required.
1561 A numeric or string value that is not
1562 compressible. The value is stored in the 8 bytes following the
1563 current block of command bytes. If this value appears twice in a block
1564 of command bytes, then it indicates the second group of 8 bytes following the
1565 command bytes, and so on.
1568 An 8-byte string value that is all spaces.
1571 The system-missing value.
1574 The end of the 8-byte group of bytecodes is followed by any 8-byte
1575 blocks of non-compressible values indicated by code 253. After that
1576 follows another 8-byte group of bytecodes, then those bytecodes'
1577 non-compressible values. The pattern repeats to the end of the file
1578 or a code with value 252.
1580 @item 2: ZLIB compression
1581 The data record consists of the following, in order:
1585 ZLIB data header, 24 bytes long.
1588 One or more variable-length blocks of ZLIB compressed data.
1591 ZLIB data trailer, with a 24-byte fixed header plus an additional 24
1592 bytes for each preceding ZLIB compressed data block.
1595 The ZLIB data header has the following format:
1604 @item int64 zheader_ofs;
1605 The offset, in bytes, of the beginning of this structure within the
1608 @item int64 ztrailer_ofs;
1609 The offset, in bytes, of the first byte of the ZLIB data trailer.
1611 @item int64 ztrailer_len;
1612 The number of bytes in the ZLIB data trailer. This and the previous
1613 field sum to the size of the system file in bytes.
1616 The data header is followed by @code{(ztrailer_ofs - 24) / 24} ZLIB
1617 compressed data blocks. Each ZLIB compressed data block begins with a
1618 ZLIB header as specified in RFC@tie{}1950, e.g.@: hex bytes @code{78
1619 01} (the only header yet observed in practice). Each block
1620 decompresses to a fixed number of bytes (in practice only
1621 @code{0x3ff000}-byte blocks have been observed), except that the last
1622 block of data may be shorter. The last ZLIB compressed data block
1623 gends just before offset @code{ztrailer_ofs}.
1625 The result of ZLIB decompression is bytecode compressed data as
1626 described above for compression format 1.
1628 The ZLIB data trailer begins with the following 24-byte fixed header:
1638 @item int64 int_bias;
1639 The compression bias as a negative integer, e.g.@: if @code{bias} in
1640 the file header record is 100.0, then @code{int_bias} is @minus{}100
1641 (this is the only value yet observed in practice).
1644 Always observed to be zero.
1646 @item int32 block_size;
1647 The number of bytes in each ZLIB compressed data block, except
1648 possibly the last, following decompression. Only @code{0x3ff000} has
1649 been observed so far.
1651 @item int32 n_blocks;
1652 The number of ZLIB compressed data blocks, always exactly
1653 @code{(ztrailer_ofs - 24) / 24}.
1656 The fixed header is followed by @code{n_blocks} 24-byte ZLIB data
1657 block descriptors, each of which describes the compressed data block
1658 corresponding to its offset. Each block descriptor has the following
1662 int64 uncompressed_ofs;
1663 int64 compressed_ofs;
1664 int32 uncompressed_size;
1665 int32 compressed_size;
1669 @item int64 uncompressed_ofs;
1670 The offset, in bytes, that this block of data would have in a similar
1671 system file that uses compression format 1. This is
1672 @code{zheader_ofs} in the first block descriptor, and in each
1673 succeeding block descriptor it is the sum of the previous desciptor's
1674 @code{uncompressed_ofs} and @code{uncompressed_size}.
1676 @item int64 compressed_ofs;
1677 The offset, in bytes, of the actual beginning of this compressed data
1678 block. This is @code{zheader_ofs + 24} in the first block descriptor,
1679 and in each succeeding block descriptor it is the sum of the previous
1680 descriptor's @code{compressed_ofs} and @code{compressed_size}. The
1681 final block descriptor's @code{compressed_ofs} and
1682 @code{compressed_size} sum to @code{ztrailer_ofs}.
1684 @item int32 uncompressed_size;
1685 The number of bytes in this data block, after decompression. This is
1686 @code{block_size} in every data block except the last, which may be
1689 @item int32 compressed_size;
1690 The number of bytes in this data block, as stored compressed in this
1695 @setfilename ignored
1697 @node Encrypted System Files
1698 @section Encrypted System Files
1700 SPSS 21 and later support an encrypted system file format.
1703 The SPSS encrypted file format is poorly designed. It is much cheaper
1704 and faster to decrypt a file encrypted this way than if a well
1705 designed alternative were used. If you must use this format, use a
1706 10-byte randomly generated password.
1709 @subheading Encrypted File Format
1711 Encrypted system files begin with the following 36-byte fixed header:
1714 0000 1c 00 00 00 00 00 00 00 45 4e 43 52 59 50 54 45 |........ENCRYPTE|
1715 0010 44 53 41 56 15 00 00 00 00 00 00 00 00 00 00 00 |DSAV............|
1716 0020 00 00 00 00 |....|
1719 Following the fixed header is a complete system file in the usual
1720 format, except that each 16-byte block is encrypted with AES-256 in
1721 ECB mode. The AES-256 key is derived from a password in the following
1726 Start from the literal password typed by the user. Truncate it to at
1727 most 10 bytes, then append (between 1 and 22) null bytes until there
1728 are exactly 32 bytes. Call this @var{password}.
1731 Let @var{constant} be the following 73-byte constant:
1734 0000 00 00 00 01 35 27 13 cc 53 a7 78 89 87 53 22 11
1735 0010 d6 5b 31 58 dc fe 2e 7e 94 da 2f 00 cc 15 71 80
1736 0020 0a 6c 63 53 00 38 c3 38 ac 22 f3 63 62 0e ce 85
1737 0030 3f b8 07 4c 4e 2b 77 c7 21 f5 1a 80 1d 67 fb e1
1738 0040 e1 83 07 d8 0d 00 00 01 00
1742 Compute CMAC-AES-256(@var{password}, @var{constant}). Call the
1743 16-byte result @var{cmac}.
1746 The 32-byte AES-256 key is @var{cmac} || @var{cmac}, that is,
1747 @var{cmac} repeated twice.
1750 @subsubheading Example
1752 Consider the password @samp{pspp}. @var{password} is:
1755 0000 70 73 70 70 00 00 00 00 00 00 00 00 00 00 00 00 |pspp............|
1756 0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
1763 0000 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1770 0000 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1771 0010 3e da 09 8e 66 04 d4 fd f9 63 0c 2c a8 6f b0 45
1774 @subheading Password Encoding
1776 SPSS also supports what it calls ``encrypted passwords.'' These are
1777 not encrypted. They are encoded with a simple, fixed scheme. An
1778 encoded password is always a multiple of 2 characters long, and never
1779 longer than 20 characters. The characters in an encoded password are
1780 always in the graphic ASCII range 33 through 126. Each successive
1781 pair of characters in the password encodes a single byte in the
1784 Use the following algorithm to decode a pair of characters:
1788 Let @var{a} be the ASCII code of the first character, and @var{b} be
1789 the ASCII code of the second character.
1792 Let @var{ah} be the most significant 4 bits of @var{a}. Find the line
1793 in the table below that has @var{ah} on the left side. The right side
1794 of the line is a set of possible values for the most significant 4
1795 bits of the decoded byte.
1798 @t{2 } @result{} @t{2367}
1799 @t{3 } @result{} @t{0145}
1800 @t{47} @result{} @t{89cd}
1801 @t{56} @result{} @t{abef}
1805 Let @var{bh} be the most significant 4 bits of @var{b}. Find the line
1806 in the second table below that has @var{bh} on the left side. The
1807 right side of the line is a set of possible values for the most
1808 significant 4 bits of the decoded byte. Together with the results of
1809 the previous step, only a single possibility is left.
1812 @t{2 } @result{} @t{139b}
1813 @t{3 } @result{} @t{028a}
1814 @t{47} @result{} @t{46ce}
1815 @t{56} @result{} @t{57df}
1819 Let @var{al} be the least significant 4 bits of @var{a}. Find the
1820 line in the table below that has @var{al} on the left side. The right
1821 side of the line is a set of possible values for the least significant
1822 4 bits of the decoded byte.
1825 @t{03cf} @result{} @t{0145}
1826 @t{12de} @result{} @t{2367}
1827 @t{478b} @result{} @t{89cd}
1828 @t{569a} @result{} @t{abef}
1832 Let @var{bl} be the least significant 4 bits of @var{b}. Find the
1833 line in the table below that has @var{bl} on the left side. The right
1834 side of the line is a set of possible values for the least significant
1835 4 bits of the decoded byte. Together with the results of the previous
1836 step, only a single possibility is left.
1839 @t{03cf} @result{} @t{028a}
1840 @t{12de} @result{} @t{139b}
1841 @t{478b} @result{} @t{46ce}
1842 @t{569a} @result{} @t{57df}
1846 @subsubheading Example
1848 Consider the encoded character pair @samp{-|}. @var{a} is
1849 0x2d and @var{b} is 0x7c, so @var{ah} is 2, @var{bh} is 7, @var{al} is
1850 0xd, and @var{bl} is 0xc. @var{ah} means that the most significant
1851 four bits of the decoded character is 2, 3, 6, or 7, and @var{bh}
1852 means that they are 4, 6, 0xc, or 0xe. The single possibility in
1853 common is 6, so the most significant four bits are 6. Similarly,
1854 @var{al} means that the least significant four bits are 2, 3, 6, or 7,
1855 and @var{bl} means they are 0, 2, 8, or 0xa, so the least significant
1856 four bits are 2. The decoded character is therefore 0x62, the letter