Information Hierarchy

The information in a BIS repository is arranged in a hierarchy that is governed by rules. Some of the rules are explicitly defined by the schemas, and other rules require the applications that are creating data to follow standards.

The hierarchies in BIS repositories are intended to facilitate both human and software comprehension of the data.

Hierarchy Constructs

As was explained in Model Fundamentals, there are only three mechanisms available in BIS to create a hierarchy:

  • A Model can contain Elements
  • An Element can own child Elements
  • An Element can be modeled by (broken down into more detail by) a SubModel

Each of these three mechanism is intended to be used in specific circumstances which are explained in this chapter.

Model Contains Elements

A Model is a container for Elements. Models are a way to subdivide and organize the overall repository. Each Element is contained by exactly 1 Model as defined by the ModelContainsElements relationship.

Element Owns Child Elements

An Element can own child Elements. This is useful for modeling assembly relationships or for modeling cases where one Element exclusively controls the lifetime of other Elements. An Element can have 0 or 1 parent Elements as defined by the ElementOwnsChildElements relationship. An Element without a parent is considered a top-level Element. An Element with a parent is considered a child Element. These hierarchies can go N levels deep, which means that an Element can be both a parent and a child.

Model Models Element

A Model is more detail about an Element from a higher level in the information hierarchy. A Model is about exactly 1 Element as defined by the ModelModelsElement relationship. From the Model's perspective, this higher-level Element is known as the modeled element. From the Element's perspective, the lower-level Model is knows as the SubModel. The SubModel term is just a way to refer to a relative position in the information hierarchy. There is no special class for a SubModel, only the standard Model subclasses.

For example, a DrawingModel breaks down a Drawing Element and contains the DrawingGraphic Elements that are the details of the overall drawing.

Top of the World

The top of the information hierarchy is strictly controlled and is very similar in all BIS repositories. Its contents are explained in Top of the World

Example Information Hierarchy

Information Hierarchy

Next: Physical Models and Elements

Last Updated: 06 December, 2018