GRASS site (or point) data is stored in a text format which supports multiple dimensions, one integer category number and multiple floating point and text attributes.
To query the categories of an existing site file, use the following modules:
s.what : Allows the user to query site list descriptions
d.what.sites : Interactively query a single site list descriptions
s.out.ascii : Converts a GRASS site list file into an ASCII listing of site locations and their descriptions
The text format of the site file allows you to manipulate site categories and attributes directly. To create a site file with the attributes you desire, you can edit a file yourself and then copy it to the site_lists directory of your mapset: cp NameOfYourSitesFile $GISDBASE/$LOCATION_NAME/$MAPSET/site_lists/. If you want to change the attribute values of a site file, copy the file to your current working directory with cp $GISDBASE/$LOCATION_NAME/$MAPSET/site_lists/NameOfYourSitesFile . and change whatever values you would like to. When finished, just copy the file back with cp NameOfYourSitesFile $GISDBASE/$LOCATION_NAME/$MAPSET/site_lists/. See the man page for s.in.ascii for details about the format.