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5.2 Portable File Structure

Every portable file consists of the following records, in sequence:

• File header.
• Version and date info.
• Product identification.
• Author identification (optional).
• Subproduct identification (optional).
• Variable count.
• Case weight variable (optional).
• Variables. Each variable record may optionally be followed by a missing value record and a variable label record.
• Value labels (optional).
• Documents (optional).
• Data.

Most records are identified by a single-character tag code. The file header and version info record do not have a tag.

Other than these single-character codes, there are three types of fields in a portable file: floating-point, integer, and string. Floating-point fields have the following format:

• Zero or more leading spaces.
• Optional asterisk (‘*’), which indicates a missing value. The asterisk must be followed by a single character, generally a period (‘.’), but it appears that other characters may also be possible. This completes the specification of a missing value.
• Optional minus sign (‘-’) to indicate a negative number.
• A whole number, consisting of one or more base-30 digits: ‘0’ through ‘9’ plus capital letters ‘A’ through ‘T’.
• Optional fraction, consisting of a radix point (‘.’) followed by one or more base-30 digits.
• Optional exponent, consisting of a plus or minus sign (‘+’ or ‘-’) followed by one or more base-30 digits.
• A forward slash (‘/’).

Integer fields take a form identical to floating-point fields, but they may not contain a fraction.

String fields take the form of an integer field having value n, followed by exactly n characters, which are the string content.