Spatial Composition


BIS's SpatialComposition Domain Schema allows an iModel author to cleanly express the spatial structure of a site/facility and use that structure to organize PhysicalElements and SpatialLocationElements regardless of how they are organized into separate Models.

As many levels of composition as necessary can be used when modeling the spatial structure of an infrastructure asset. SpatialCompositon defines base SpatialStructureElement classes for Region, Site, Facility, FacilityPart, and Space that are used to express the primary spatial structure of an infrastructure asset. Discipline-specific domains supply more-specialized semantics through subclasses of these base classes. Instances of these classes are organized into a hierarchy using an "Aggregates" relationship.

The following table shows a sample infrastructure asset that involves a building, a road, and a bridge at a Bus Terminal. The table lists a name for the real-world Entity along with the discipline-specific class that it maps to (with its SpatialComposition base class in parenthesis).

Entity Discipline-specific class label (SpatialComposition class)
Bus Terminal Site (Site)
-- Bus Terminal Building Building (Facility)
---- First floor Story (FacilityPart)
------ Restroom 1 Space (Space)
-- Access Road Road (Facility)
---- Southbound Roadway Roadway (FacilityPart)
------ Travel Lane Traffic Lane (FacilityPart)
---- Median Central Reserve (FacilityPart)
---- Northbound Roadway Roadway (FacilityPart)
-- Ramp Bridge (Facility)
---- Superstructure Bridge Superstructure (FacilityPart)
------ Deck Bridge Deck (FacilityPart)
---- Substructure Bridge Substructure (FacilityPart)
------ Pier Bridge Pier (FacilityPart)

SpatialComposition also defines a Zone which can be used to express some alternate spatial-based grouping.

Using the Spatial Structure to organize other Elements

Once the spatial structure is modeled, its elements can be used to organize any bis:SpatialElement (the base class for both bis:PhysicalElement and bis:SpatialLocationElement) using "Holds" and "References" relationships. "Holds" implies that the related element (or some significant part of it, like the base of an elevator shaft) is contained in the SpatialStructureElement or Zone. "References" implies some weaker relationship (e.g. the elevator shaft passes through the space). See the Element Held by Spatial Organizer section of the "Information Hierarchy" article.

The following table shows bis:SpatialElements that could be associated to the Bus Terminal example presented earlier.

Entity Spatial Structure Element Physical/Spatial Elements Relationship
Bus Terminal Site Holds Road Alignments
-- Bus Terminal Building Building Holds Grids
---- First floor Story Holds Columns, Beams, Walls, Doors
------ Restroom 1 Space Holds Sinks, Toilets
-- Access Road Road
---- Southbound Roadway Roadway Holds Pavement courses
------ Travel Lane Traffic Lane References Lane Markings
---- Median Central Reserve Holds Barriers
---- Northbound Roadway Roadway Holds Pavement courses
-- Ramp Bridge
---- Superstructure Bridge Superstructure Holds Beams
------ Deck Bridge Deck Holds Slab, Guard-rails
---- Substructure Bridge Substructure
------ Pier Bridge Pier Holds Columns, Footings, Caps

As seen in the example above, real-world infrastructure entities can be modeled using multiple parallel organizational structures, including the spatial composition hierarchy, spatial zones, physical assemblies, and partitioning of elements into models. Each modeling technique independently expresses a different aspect of meaning, enabling flexibility for schema designers and end-users.

| Next: Modeling Systems |:---

Last Updated: 21 November, 2022