The Industry Foundation Classes (IFC) is a CAD data exchange data schema intended for description of architectural, building and construction industry data.
It is a platform-neutral, open data schema specification that is not controlled by a single vendor or group of vendors. It is an object-based data schema with a data model developed by buildingSMART (formerly the International Alliance for Interoperability, IAI) to facilitate interoperability in the architecture, engineering and construction (AEC) industry, and is a commonly used collaboration format in Building information modeling (BIM) based projects. The IFC model specification is open and available.[1] It is registered by ISO and is an official International Standard ISO 16739-1:2024.
Because of its focus on interoperability the Danish government in 2010 made the use of IFC format(s) compulsory for publicly aided building projects.[2] In 2017 the Finnish state-owned facility management company Senate Properties started to demand use of IFC compatible software and BIM in all their projects.[3] Also the Norwegian Government, Health and Defense client organisations require use of IFC BIM in all projects as well as many municipalities, private clients, contractors and designers have integrated IFC BIM in their business.[citation needed]. The popularity of the IFC data schema in construction has continued to grow, primarily for the purpose of exchanging geometry.
The IFC initiative began in 1994, when Autodesk formed an industry consortium to advise the company on the development of a set of C++ classes that could support integrated application development. Twelve US companies joined the consortium. These companies included AT&T, HOK Architects, Honeywell, Carrier, Tishman and Butler Manufacturing.[4] Initially named the Industry Alliance for Interoperability, the Alliance opened membership to all interested parties in September, 1995 and changed its name in 1997 to the International Alliance for Interoperability. The new Alliance was reconstituted as a non-profit industry-led organization, with the goal of publishing the Industry Foundation Class (IFC) as a neutral AEC product model responding to the AEC building lifecycle. A further name change occurred in 2005, and the IFC specification is now developed and maintained by buildingSMART.
IFC Specifications
The following IFC Specification versions are available[5]
IFC defines multiple file formats that may be used, supporting various encodings of the same underlying data.[7]
IFC-SPF is a text format defined by ISO 10303-21 ("STEP-File"), where each line typically consists of a single object record, and having file extension ".ifc". This is the most widely used IFC format, having the advantage of compact size yet readable text.
IFC-XML is an XML format defined by ISO 10303-28 ("STEP-XML"), having file extension ".ifcXML". This format is suitable for interoperability with XML tools and exchanging partial building models. Due to the large size of typical building models, this format is less common in practice.
IFC-ZIP is a ZIP compressed format consisting of an embedded IFC-SPF file or IFC-XML file and having file extension ".ifcZIP".
IFC-Turtle (Terse RDF Triple Language) is a textual semantic data format that uses RDF and is expressed in the ifcOWL ontology.
IFC-RDF is a XML-based semantic data format that uses RDF and is expressed in the ifcOWL ontology.
ifcJSON uses JSON, a modern format often used by web applications.
ifcHDF uses HDF and is based on the ISO 10303-26 standard for STEP data representation in HDF.
IFC-SPF is in ASCII format which, while human-readable, suffers from common ASCII file issues, in that file-sizes are bloated, files must be read sequentially from start to finish, mid-file extraction is not possible, files are slow to parse, and definitions are non-hierarchical.[8] In addition to ifcXML and ifcZIP, modern data formats include RDF/XML or Turtle (using the ifcOWL ontology), ifcJSON (JavaScript Object Notation, broadly available) and ifcHDF5 (Hierarchical Data Format v5, binary).[8] In 2020, buildingSmart had two JSON projects underway: ifcJSON v4 (a direct mapping from EXPRESS-based IFC v4) and ifcJSON v5, plus a research project experimenting with turning IFC into a binary format.[8]
Architecture
IFC defines an EXPRESS based entity-relationship model consisting of several hundred entities organized into an object-based inheritance hierarchy. Examples of entities include building elements such as IfcWall, geometry such as IfcExtrudedAreaSolid, and basic constructs such as IfcCartesianPoint.[9]
At the most abstract level, IFC divides all entities into rooted and non-rooted entities. Rooted entities derive from IfcRoot and have a concept of identity (having a GUID), along with attributes for name, description, and revision control. Non-rooted entities do not have identity and instances only exist if referenced from a rooted instance directly or indirectly. IfcRoot is subdivided into three abstract concepts: object definitions, relationships, and property sets:
IfcObjectDefinition captures tangible object occurrences and types
IfcRelationship captures relationships among objects
IfcPropertyDefinition captures dynamically extensible properties about objects.
IfcObjectDefinition
IfcObjectDefinition is split into object occurrences and object types. IfcObject captures object occurrences such as a product installation having serial number and physical placement. IfcTypeObject captures type definitions (or templates) such as a product type having a particular model number and common shape. Occurrences and types are further subdivided into six fundamental concepts: actors ("who"), controls ("why"), groups ("what"), products ("where"), processes ("when"), and resources ("how").
IfcActor represents people or organizations.
IfcControl represents rules controlling time, cost, or scope such as work orders.
IfcGroup represents collections of objects for particular purpose such as electrical circuits.
IfcProduct represents occurrences in space such as physical building elements and spatial locations.
IfcProcess represents occurrences in time such as tasks, events, and procedures.
IfcResource represents usage of something with limited availability such as materials, labor, and equipment.
IfcRelationship
IfcRelationship captures relationships among objects. There are five fundamental relationship types: composition, assignment, connectivity, association, and definition.
IfcRelDecomposes captures a whole-part relationship having exclusive containment such as subdividing a building into floors and rooms or a wall into studs and sheathing.
IfcRelAssigns captures assignment relationships where one object consumes the services of another object, such as a labor resource assigned to a task, or a task assigned to a building element.
IfcRelConnects indicates connectivity between objects such as a floor slab connected to a beam or a pipe connected to a sink.
IfcRelAssociates indicates external references for an object such as an external IFC library file where an object is defined.
IfcRelDefines indicates an instance-of relationship such as a pipe segment being of a particular type.
IfcPropertyDefinition
IfcPropertyDefinition captures dynamically extensible property sets. A property set contains one or more properties which may be a single value (e.g. string, number, unit measurement), a bounded value (having minimum and maximum), an enumeration, a list of values, a table of values, or a data structure. While IFC defines several hundred property sets for specific types, custom property sets may be defined by application vendors or end users.
IfcPropertySet represents a set of properties attached to an object occurrence or object type.
IfcPropertySetTemplate [IFC2x4] captures definitions of properties and their data types.
Products
IfcProduct is the base class for all physical objects and is subdivided into spatial elements, physical elements, structural analysis items, and other concepts. Products may have associated materials, shape representations, and placement in space. Spatial elements include IfcSite, IfcBuilding, IfcBuildingStorey, and IfcSpace. Physical building elements include IfcWall, IfcBeam, IfcDoor, IfcWindow, IfcStair, etc. Distribution elements (HVAC, electrical, plumbing) have a concept of ports where elements may have specific connections for various services, and connected together using cables, pipes, or ducts to form a system. Various connectivity relationships are used for building elements such as walls having openings filled by doors or windows.
Materials may be defined for products as a whole, or as layers, profiles, or constituents for specified parts.
IfcMaterial indicates a specific material, with optional properties (e.g. mechanical, thermal) and styles (e.g. colors, textures).
IfcMaterialLayerSet captures a list of layers, each indicating a material of a specified thickness.
IfcMaterialProfileSet [IFC2x4] captures a set of profiles, each indicating a material of a specified cross-section.
IfcMaterialConstituentSet [IFC2x4] captures a set of constituents, each indicating a material used at a named shape aspect.
Representations may be defined for explicit 3D shape, and optionally as parametric constraints. Each representation is identified by IfcShapeRepresentation with a well-known name.
'Body' indicates a 3D shape which may be represented by B-rep, NURBS, Constructive Solid Geometry (CSG), or swept profiles. It may be defined directly or derived by applying material definitions to other representations.
'Axis' indicates a path for linear elements (e.g. wall, beam, pipe) for which material profiles or layers are aligned.
'FootPrint' indicates a boundary for planar elements (e.g. slab, staircase) for which material layers are bounded.
'Profile' indicates a side profile for opening elements (e.g. door, window) for which material constituents are bounded.
'SurveyPoints' indicates a set of points for surface elements (e.g. site) for describing contours.
Placement may indicate position, vertical angle, and horizontal angle.
IfcLocalPlacement indicates placement relative to an enclosing element hierarchy.
IfcGridPlacement indicates placement relative to a grid with user-defined axes.
Quantities may be defined for take-off purposes such as Gross Area, Gross Volume, Gross Weight, Net Weight, etc. IFC defines various quantities specific to each element type and the method of calculation according to geometry and relationships.
Processes
IfcProcess is the base class for processes and is subdivided into tasks, events, and procedures. Processes may have durations and be scheduled to occur at specific time periods. Processes may be sequenced such that a successor task may start after a predecessor task finishes, following the Critical Path Method. Processes may be nested into sub-processes for summary roll-up. Processes may be assigned to products indicating the output produced by the work performed.
Resources
IfcResource is the base class for resources and is subdivided into materials, labor, equipment, subcontracts, crews, and more. Resources may have various costs and calendars of availability. Resources may be nested into sub-resources for granular allocation. Resources may be assigned to processes indicating tasks performed on behalf of a resource.
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.
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. The World Wide Web Consortium's XML 1.0 Specification of 1998 and several other related specifications—all of them free open standards—define XML.
The Resource Description Framework (RDF) is a method to describe and exchange graph data. It was originally designed as a data model for metadata by the World Wide Web Consortium (W3C). It provides a variety of syntax notations and data serialization formats, of which the most widely used is Turtle.
XSD, a recommendation of the World Wide Web Consortium (W3C), specifies how to formally describe the elements in an Extensible Markup Language (XML) document. It can be used by programmers to verify each piece of item content in a document, to assure it adheres to the description of the element it is placed in.
The Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. Key to GML's utility is its ability to integrate all forms of geographic information, including not only conventional "vector" or discrete objects, but coverages and sensor data.
JSON is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and arrays. It is a commonly used data format with diverse uses in electronic data interchange, including that of web applications with servers.
RDF Schema (Resource Description Framework Schema, variously abbreviated as RDFS, RDF(S), RDF-S, or RDF/S) is a set of classes with certain properties using the RDF extensible knowledge representation data model, providing basic elements for the description of ontologies. It uses various forms of RDF vocabularies, intended to structure RDF resources. RDF and RDFS can be saved in a triplestore, then one can extract some knowledge from them using a query language, like SPARQL.
NIEMOpen, frequently referred to as NIEM, originated as an XML-based information exchange framework from the United States, but has transitioned to an OASISOpen Project. This initiative formalizes NIEM's designation as an official standard in national and international policy and procurement. NIEMOpen's Project Governing Board recently approved the first standard under this new project; the Conformance Targets Attribute Specification (CTAS) Version 3.0. A full collection of NIEMOpen standards are anticipated by end of year 2024.
XOXO for web syndication is an XML microformat for outlines built on top of XHTML. Developed by several authors as an attempt to reuse XHTML building blocks instead of inventing unnecessary new XML elements/attributes, XOXO is based on existing conventions for publishing outlines, lists, and blogrolls on the Web.
In the macOS, iOS, NeXTSTEP, and GNUstep programming frameworks, property list files are files that store serialized objects. Property list files use the filename extension .plist, and thus are often referred to as p-list files.
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within Web documents. The Resource Description Framework (RDF) data-model mapping enables its use for embedding RDF subject-predicate-object expressions within XHTML documents. It also enables the extraction of RDF model triples by compliant user agents.
In RDF, a blank node is a node in an RDF graph representing a resource for which a URI or literal is not given. The resource represented by a blank node is also called an anonymous resource. According to the RDF standard a blank node can only be used as subject or object of an RDF triple.
The Open Packaging Conventions (OPC) is a container-file technology initially created by Microsoft to store a combination of XML and non-XML files that together form a single entity such as an Open XML Paper Specification (OpenXPS) document. OPC-based file formats combine the advantages of leaving the independent file entities embedded in the document intact and resulting in much smaller files compared to normal use of XML.
The FAO geopolitical ontology is an ontology developed by the Food and Agriculture Organization of the United Nations (FAO) to describe, manage and exchange data related to geopolitical entities such as countries, territories, regions and other similar areas.
The Office Open XML file formats are a set of file formats that can be used to represent electronic office documents. There are formats for word processing documents, spreadsheets and presentations as well as specific formats for material such as mathematical formulas, graphics, bibliographies etc.
In computing, Open Data Protocol (OData) is an open protocol that allows the creation and consumption of queryable and interoperable Web service APIs in a standard way. Microsoft initiated OData in 2007. Versions 1.0, 2.0, and 3.0 are released under the Microsoft Open Specification Promise. Version 4.0 was standardized at OASIS, with a release in March 2014. In April 2015 OASIS submitted OData v4 and OData JSON Format v4 to ISO/IEC JTC 1 for approval as an international standard. In December 2016, ISO/IEC published OData 4.0 Core as ISO/IEC 20802-1:2016 and the OData JSON Format as ISO/IEC 20802-2:2016.
The Open Geospatial Consortium (OGC), an international voluntary consensus standards organization for geospatial content and location-based services, sensor web and Internet of Things, GIS data processing and data sharing. It originated in 1994 and involves more than 500 commercial, governmental, nonprofit and research organizations in a consensus process encouraging development and implementation of open standards.
Construction Operations Building Information Exchange (COBie) is a United States-originated specification relating to managed asset information including space and equipment. It is closely associated with building information modeling (BIM) approaches to design, construction, and management of built assets.
NGSI-LD is an information model and API for publishing, querying and subscribing to context information. It is meant to facilitate the open exchange and sharing of structured information between different stakeholders. It is used across application domains such as smart cities, smart industry, smart agriculture, and more generally for the Internet of things, cyber-physical systems, systems of systems and digital twins.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
