NAME

       dirfile — a filesystem based database format for time-ordered binary data

DESCRIPTION

       The  dirfile  database format is designed to provide a fast, simple format for storing and
       reading binary time-ordered data.  Dirfiles can be read using the GetData library.

       The dirfile database is centred around one or  more  time-ordered  data  streams  (a  time
       stream).   Each  time  stream  is written to disk in a separate file, in its native binary
       format.  The name of these binary files correspond to the time stream's field  name.   Two
       time  streams may have different constant sampling frequencies and mechanisms exist within
       the dirfile format to ensure these time streams remain properly sequenced in time.

       To do this, the time streams in the  dirfile  are  subdivided  into  frames.   Each  frame
       contains  an integer number of samples of each time stream.  When synchronous retrieval of
       data from more than one time stream is required, position in the dirfile can be  specified
       in frames, which will ensure synchronicity.

       The  binary  files are all located in a central directory, known as the dirfile directory.
       The dirfile as a whole may be referred to by its dirfile directory path.

       Included in the dirfile along with the time streams is the dirfile  format  specification,
       which  is  an  ASCII  text file called format located in the dirfile directory.  This file
       fully  specifies  the  dirfile's  metadata.   For   the   syntax   of   this   file,   see
       dirfile-format(5).

       Version 3 of the Dirfile Standards introduced the large dirfile extension.  This extension
       added the ability  to  distribute  the  dirfile  metadata  among  multiple  files  (called
       fragments) in addition to the format file, as well as the ability to house portions of the
       database in subdirfiles.  These subdirfiles may be fully fledged  dirfiles  in  their  own
       right,  but  may also be contained within a larger, parent dirfile.  See dirfile-format(5)
       for information on specifying these subdirfiles.

       In addition to the raw fields on disk, the dirfile format specification may  also  specify
       derived fields which are calculated from one or more raw or derived time streams.  Derived
       fields behave identically to raw fields when read via GetData.  See dirfile-format(5)  for
       a  complete  list  of  derived  field types.  Dirfiles may also contain both numerical and
       character string constant scalar fields, also further outlined in dirfile-format(5).

       Dirfiles are designed to be written to and read simultaneously. The dirfile  specification
       dictates  that  one particular raw field (specified either explicitly or implicitly by the
       format specification) is to be used as the reference field: all other  vector  fields  are
       assumed  to  have  at  least  as  many frames as the reference field has, and the size (in
       frames) of the reference field is used as the size of the dirfile as a whole.

       Version 6 of the Dirfile Standards added the ability to encode the binary files  on  disk.
       Each fragment may have its own encoding scheme. Notably this can be used to compress these
       files.  See dirfile-encoding(5) for information on encoding schemes.

   Complex Number Storage Format
       Version 7 of the Dirfile Standards added support for complex valued data.   Two  types  of
       complex valued data are supported by the Dirfile Standards:

       •   A  64-bit  complex  number  consisting  of a IEEE-754 standard 32-bit single precision
           floating point real part and a IEEE-754  standard  32-bit  single  precision  floating
           point imaginary part, and

       •   A  128-bit  complex  number  consisting of a IEEE-754 standard 64-bit double precision
           floating point real part and a IEEE-754  standard  64-bit  double  precision  floating
           point imaginary part.

       No integer-type complex numbers are supported.

       Unencoded complex numbers are stored on disk in "Fortran order", that is with the IEEE-754
       real part followed by the IEEE-754 imaginary part.  The specified endianness  of  the  two
       components follows that of purely real floating point numbers.  Endianness does not affect
       the ordering of the real and imaginary parts.   This  format  also  conforms  to  the  C99
       standard.   The latest C++ standard (C++98) does not specify a standard storage format for
       native complex numbers, but the upcoming standard, (C++0x)  is  intended  to  specify  the
       above format for compatibility with C99 (see: ISO/IEC JTC1/SC22/WG21/N1388).

       To  aid  in  using  complex  valued data, dirfile field codes may contain a representation
       suffix which specifies a norm to apply to the complex  valued  data  to  convert  it  into
       purely real data.  See dirfile-format(5).

AUTHORS

       The     dirfile     specification     was     developed     by     C.    B.    Netterfield
       <netterfield@astro.utoronto.ca>.

       The dirfile specification is now maintained by D. V. Wiebe <getdata@ketiltrout.net>.

SEE ALSO

       dirfile-encoding(5), dirfile-format(5)