Since the Science Archive is based on an object-oriented database, we have classes for each object, not tables as opposed to objects in a relational database. The classes are linked to each other either by inheritance or by association . Inheritance is a way to specialize a class. Every data member of the base class is also member of the inherited class, but the inherited class may have additional data members. In the schemata below, inheritance is represented by a large empty arrowhead between the classes.
Associations link classes to one another.
Photometric Survey Objects Objects of the photometric survey are all members of the base class PhotoObj . A secondary object may be associated to more than one primary if the secondary observation is of a bad quality and could not be resolved into two or more objects. And obviously primaries can have associations to several secondary observations. Bad objects are kept only if they are member of a family, for example spiral arms of a galaxy that have been deblended. The Tag object contains the coordinates and model magnitudes of each object along with the object flags.