Editing Industry Foundation Classes (section)

===Contexts===
IfcProject encapsulates an overall project and indicates the project name, description, default units, currency, coordinate system, and other contextual information.  A valid IFC file must always include exactly one IfcProject instance, from which all other objects relate directly or indirectly.  A project may include multiple buildings, multiple participants, and/or multiple phases according to the particular use.

In addition to project-specific information, an IfcProject may also reference external projects from which shared definitions may be imported such as product types.  Each external project is encapsulated using IfcProjectLibrary [IFC2x4] along with IfcRelAssociatesLibrary and IfcLibraryInformation to identify the particular revision of the imported project library.

Projects support [[revision control]] where any IfcRoot-based entity has a unique identifier and may be marked as added, modified, deleted, or having no change.  Such capability allows multiple IFC files to be merged deterministically, ensuring data integrity without human intervention.