The data model design in Fig. Ten relational tables are used in this database. The table can be linked to each other with the parameters labelled along the connection lines. This index provides access to the table's data in an alternate order. Although access time via this type of index is not as good as by using the cluster index, nonclustered indexes allow the user to look at the table's data in more than one way.
Composite indexes are helpful when two or more columns are best searched as a unit.
We also list the byte size in the end of each table. A total of 1 Kbytes is estimated for each set of table data. For a typical observation track, the observing time is about 8 hrs. Assuming 300 observing days each year, only about 1 Mbyte table data will be produced for the database per year if no text files of scientific proposals are considered to be stored in Sybase. Optionally, we could also store the text files of scientific proposal into Sybase.