***** File TABLFORM.TXT                                                       
                                                                              
                                                                              
                        Table Data Descriptions                               
                                                                              
                                                                              
     The International Halley Watch agreed early in the project that all data 
would be submitted from the individual Disciplines to the Lead Center using   
the FITS format (Wells et al., 1981).  When the decision was made to          
distribute this information on CD-ROM, it was determined that the data had to 
have even broader accessibility.  For this reason the original FITS files,    
with contiguous headers and data, were split into separate files              
distinguishable by their filename extensions (.HDR for headers).  The file    
sizes were preserved as multiples of 2880 bytes, allowing the original FITS   
byte stream to be recovered by concatenating the appropriate header and       
datafile.  PDS labels were constructed to allow definition of the datafiles   
for the Planetary Data System.   For each datafile there must always be an    
associated FITS header.                                                       
                                                                              
     The convention for naming files on the IHW CD-ROMs was proposed by the   
Lead Center and NASA/Goddard Space Flight Center (GSFC) personnel to include a
unique data qualifier for the data.  Specifically, a set of subnet codes was  
established to enable identification of the IHW Discipline/subdiscipline from 
the filename itself.  A CD-ROM running number and file extension complete the 
filename.  A short list of this convention for tables follows:                
                                                                              
                                                                              
  PDS Object              FITS      Discipline        N   Subnet    File Ext  
 (description)         NAXIS =                             Code               
____________________________________________________________________________  
                                                                              
table (filter)             0,2      IR Studies        4  IRFT        .tab     
table (photometry)         0,2      IR    "              IRPH        .tab     
table (polarimetry)        0,2      IR    "              IRPOL       .tab     
table (broad band)         0,2      Photometry Polar  5  PMAG        .tab     
table (narrow band)        0,2          "                PFLX        .tab     
table (polarization)       0,2          "                PPOL        .tab     
table (Stokes parameters)  0,2          "                PSTOKE      .tab     
table (magnitude)          0,2      Amateur           8  AMV         .tab     
table (radar)              0,2      Meteor            9  MSNRDR      .tab     
table (visual)             0,2          "                MSNVIS      .tab     
____________________________________________________________________________  
                                                                              
                                                                              
A table linking the subnet codes above and the subdiscipline names is given in
Section 5 ('Filenaming Conventions') of the file HALGUIDE.TXT.                
                                                                              
     The file extensions follow suggestions by the Planetary Data System      
(SPIDS v1.1; Martin et al., 1988) for tabular and image data.  In addition,   
for IHW FITS, the original headers and data were split into separate files,   
with filename extensions as listed below.                                     
                                                                              
                                                                              
                 .HDR - FITS header records                                   
                 .LBL - detached PDS stream format                            
                 .TAB - table data records as ASCII                           
                                                                              
                                                                              
    These PDS labels are metadata (as headers describing data submitted to the
archive). There has been no effort to duplicate the documentation contained in
the full FITS headers because the PDS and FITS headers for a given data file  
differ only in the filename extension.  Instead we have attempted to use the  
power of the PDS label syntax to fully describe the data structures and thus  
gain access to software by that group. Standards for the Preparation and      
Interchange of Data Sets, Martin, T. Z., et al, Document D-4683, Jet          
Propulsion Laboratory, California Institute of Technology, Pasadena, CA       
document version 1.1 was the primary reference to the Object Description      
Language (ODL) necessary to create the PDS labels.   (We acknowledge R. Borgen
and M. Martin, PDS-CN, JPL, for assisting the IHW through version 2.0 of the  
ODL implementation for SPECTRUM.)   The basic PDS descriptors such as         
SFDU_LABEL, RECORD_TYPE, RECORD_BYTES, and FILE_RECORDS are explained in the  
SPIDS document. The RECORD_TYPE for all data files is FIXED_LENGTH.   The PDS 
labels have been formed as fixed length (78 byte) plus an embedded CR and LF. 
                                                                              
   In creating the TABLE descriptions we have found a good correspondence     
between the FITS and PDS syntax.   For tables, the value of NAXIS2= ROWS,     
TFIELDS=COLUMNS, and NAXIS1=ROW_BYTES; in both cases, the default FORMAT is   
ASCII.   We have attempted to describe the values in each column as a direct  
translation of the FITS header file; the data itself follows the FITS record  
format, i.e., ASCII characters with no delimiters and padded to multiples of  
2880 bytes.   The FITS data structure are currently supported by public domain
software that will be distributed with the Archive.                           
                                                                              
                                                                              
                                                                              
                                                                              
REFERENCES                                                                    
                                                                              
Martin, T.Z., Martin, M.D., Davis, R.L., Mehlman, R., Braun, M., Johnson      
M.: October 3, 1988, Standards for the Preparation and Interchange of         
Data Sets, Version 1.1, JPL D-4683.                                           
                                                                              
Wells, D.C., Greisen, E.W., and Harten, R.H.: 1981, Astron. Astrophys.        
Suppl. Ser. 44, 363.