collection

Collections are sets of structured (complex data type) instances or individual objects. Collections appear as local or global collections. Collections may contain instances of the same type or instances of different types.

According to ODMG there is a distinction between bag, set and list. No one of these collection types, however, supports ordered collections, that allow duplicated. Thus, ODABA considers the attributes ordered and unique as property of the index, rather than property of the collection. i.e. a collection may have at the same time an index allowing duplicates and another, which does not.

ODABA supports reference and instance collections. Reference collections allow sharing instances between several collections. Usually, collections in ODABA are considered as reference collections. Only some special cases handle instance collections as kind of dynamic array.

• Collections are either instance or reference collections.

• Collections are either typed, untyped or weak-typed collections.
• Collections are either global or local collections