SDB_Extend - Object space extents

Object space extents are collections (global database variables), which allow storing instances on object space (or database) level in an ODABA database. Extents are properties of object spaces and exist outside any data type definition. Extents are associated with a complex data type, which might refer to VOID type for untyped extents or to the base type for weak-typed extents. As any collection, extents may define one or more indexes, but must have an identifying key index (main index).

There is always exact one extent, which does not have super-sets, which is called root extent. Usually, the root extent contains all global instances of a given type and is the owner of the object instances.

Extents are special collections (SDB_Reference). Collections may be defined as persistent or transient collections, which is described in detail in "Reference collections".