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Классификация моделей данных, реализованных в современных СУБД
Table 1 - Principal distinctions between data model classes
Comparing element | Graph models | Set-oriented models | Map based models |
Data structure type of an item | Record | Tuple | Value |
Links between data items | Explicit | Implicit (set operations) | Not supported |
Data integrity rules | Supported | Supported | Not supported (*) |
Access to a data item | Explicit path (trajectory) | Implicit (set operations) | Explicit (by key) |
Storing of data items | Ordered | Not ordered | Ordered |
Output of data items | Ordered | Not ordered (**) | Not ordered |
* – may be partially supported when introducing constraints on values and types; ** – an ordered set can be produced with some specific operations; for example, ORDER BY in SQL but the storage does not respect any item order