***** File LBLFORM.TXT                                                        
                                                                              
                          PDS Label Descriptions                              
                                                                              
                                                                              
     The International Halley Watch agreed early on in the project that       
all data would be submitted from the individual disciplines to the Lead       
Center using the FITS format.  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. The         
original FITS byte stream could then be recovered by concatenating the        
appropriate header and data files.   PDS labels were constructed to allow     
definition of the data files for the Planetary Data System.   For each        
original data input there must always be a PDS detached label with the        
extension .LBL.                                                               
                                                                              
     The convention for naming files on the CD-ROM was proposed by the        
IHW Lead Center to include a unique data qualifier for the data.   A          
specific set of rules was established to identify the net and subnet for      
each discipline (given by a letter code).  A CD-ROM running number relates    
the information contained in the various indices to the files containing      
the actual data.  A short list of this convention by discipline and           
subnet (or experiment) is given below:                                        
                                                                              
  PDS Object              FITS      Discipline       Letter    File Ext       
 (description)         NAXIS =                         Code                   
                                                                              
text                       1        Astrometry         ASTR        .lbl       
fits_label (no data)       0        IR Studies         IRIM        .lbl       
table (filter)             0,2      IR    "            IRFT        .lbl       
table(photometry)          0,2      IR    "            IRPH        .lbl       
table(polarimetry)         0,2      IR    "            IRPOL       .lbl       
spectrum                   2        IR    "            IRSP        .lbl       
image                      2        IR    "            IRIM        .lbl       
fits_label (no data)       0        Large Scale Phen   LSPN        .lbl       
image(compress)            0,1      Large     "        LSPN        .lbl       
image(browse)              2        Large     "        LSPN        .lbl       
image                      2        Near Nucleus       NNSN        .lbl       
table (broad band)         0,2      Photometry Polar   PMAG        .lbl       
table (narrow band)        0,2          "              PFLX        .lbl       
table (polarization)       0,2          "              PPOL        .lbl       
fits_label (no data)       0        Radio Studies      RSCN,SL     .lbl       
spectrum                   1            "              RSOH        .lbl       
spectrum(multiple)         2            "              RSOH        .lbl       
image(multiple)            3            "              RSOC        .lbl       
spectrum                   1        Spectroscopy       SPEC        .lbl       
image                      2            "              SPEC        .lbl       
fits_label (no data)       0        Amateur            AMDR,PG     .lbl       
table (magnitude)          0,2          "              AMV         .lbl       
                                                                              
Note that the Subnet coding (explained in the Filenaming Conventions)         
is one way to distinguish file extension and content.                         
                                                                              
     The file extensions follow suggestions by the Planetary Data System      
(SPIDS v1.1) 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.                                                   
                                                                              
                 .LBL - detached PDS stream format                            
                                                                              
    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 thankfully acknowledge the help of M. Martin,    
JPL, for assisting the IHW through version 1.1 of the ODL that allows         
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) with an embedded CR and LF.