编辑“︁Meta object model for relational data storage”︁（章节）

=== Instance Layer ===

Based on the model layer instances can be created:

[[Image:Instance_layer.png]]

On the instance layer the actual life data is managed. Every object on the instance layer has a type on the model layer. So for example every object is an instance of exactly one class. Just as the model layers classes have attributes, objects have values. Those values are instances of the appropriate attribute. This means that there is a consistency condition: A value may only belong to an object which is an instance of a class (or subclass) to which the attribute belongs.
The same is true for links on the other side of the diagram. They are instances of association with the same set of consistency conditions.

Differences to Marauroa: In Marauroa associations (slots) don't have a target type. So that condition is not required. But the slots are ordered lists, so an additional attribute in link for the sort oder is required.