IFC4 Officially Released
After over 6 years of development and over 1100 issues being resolved, on 12. March 2013 buildingSMART international has finally released the new generation of IFC schemas – IFC4. It will now be the basis of future work of establishing new open BIM enabled work flows by defining new IFC4 based model view definitions. The official IFC4 release includes both the IFC4 EXPRESS schema to support current STEP-based IFC exchanges, and the ifcXML4 XSD schema to support new simple ifcXML transactions.
Visit the full announcement at http://www.buildingsmart-tech.org/news/ifc4-officially-released
A recent article regarding the significant improvements to the IFC4 schema was included in the Spring edition of JBIM (Journal of Building Information Modelling) by Tim Chipman is deputy leader of buildingSMART International’s Model Support Group.
IFC4: Evolving BIM By Tim Chipman
Tim Chipman is deputy leader of buildingSMART International’s Model Support Group and develops software at Constructivity.
JBIM (Journal of Building Information Modelling) is an official publication of the National BIM Standard (NBIMS) and the National Institute of Building Sciences (NIBS)
In recent years, the Industry Foundation Classes (IFC) standard for building information modelling (BIM) has seen widespread adoption, supported by approximately 150 registered software applications.
This article describes the next evolution across software applications. The goal of IFC has always been to describe how building information can be leveraged across applications within and across vertical industries, supporting the vast array of disciplines encountered in the building industry. To be useful across such a large ecosystem, such standards must capture necessary detail to describe how a building is to be built, along with the many non-physical aspects describing who is doing what, when, how and why.
Meanwhile, many downstream applications are only concerned with subsets of this information. Another aspect to address is the format of information, which must accommodate changing technology and diverse platforms, such as phones, tablets, desktops and servers.
For basic applications, XML provides ease of integration; compact formats such as STEP Physical Format (SPF) are more practical for representing buildings in detail; spread sheets such as Excel provide access to a wide range of users without custom software; and databases of various forms may support collaboration among concurrent users.
Meanwhile, as more applications adopt IFC, customers have asked for deeper integration to capture more detailed information across applications in a consistent way. To support this growing usage, IFC has evolved with initiatives on multiple fronts.
Data model: A number of enhancements have been introduced in IFC4, with a focus on system-wide improvements while maintaining backward compatibility.
Parametric design: While buildings are ultimately made of discrete components, during the design process it is often desirable to use higher-level representations reflecting the design intent, so that changes can be made in one place, where the composition and layout of components, can be automatically updated to reflect the change.
IFC4 introduces the concept of material profiles, where axis-based components, such as beams, pipes and ducts, can be described by paths and cross-sections of materials, along with offsets relative to the axis and end points. Similarly, a concept of material constituents has been introduced where components, such as doors and windows, can have various parts (for example, framing and glazing) designed by geometric aspects and corresponding materials. Material layers allow flat components, such as slabs and walls, to be described by material thicknesses and boundaries with offsets.
Geometry: IFC4 expands geometry to support more complex shapes as well as simplified geometry. Complex shapes may be exactly described using Non-Uniform Rational B-Spline (NURBS) curves and surfaces. Simplified shapes may be described using tessellated surfaces with compact lists of vertices and triangles, providing the closest mapping to GPUs and more efficient processing as may be suitable for mobile applications.
Libraries: IFC4 supports capturing templates of products, processes, resources and property sets. These files can be referenced by other IFC files that include instances of such templates.
Ports: Ports provide the capability for MEP elements to connect through pipes, ducts or wires. IFC4 extends the capability for defining ports at product templates and standardizes ports on objects according to product type. For example, a water heater may have ports for gas or electricity as input, cold water in and hot water out. This enables products from different manufacturers to be intelligently connected according to system type and connection geometry.
Processes: IFC4 expands the process model to support scheduling of tasks, procedures and events, with expanded detail as found in leading scheduling applications and 4D simulations. Process templates allow common processes to be captured in libraries and re-used.
Resources: IFC4 expands the resource model to track costs and environmental impacts of materials, labour, equipment and other project resources with expanded detail. Resource templates allow common resources to be captured in libraries and re-used.
Constraints: The constraint model has been formalized so that requirements may be directly validated on any object attribute, either directly or along a graph of objects and collections. For example, a requirement may indicate that the height of a space must exceed a certain length. Constraints may also be used to indicate mapping of data to external files, conflicts when multiple versions of a model are merged, formulas based on calculations from other attributes and tables of values that apply for parametric modelling.
Documentation: Published as ISO 16739, the documentation for IFC had to undergo rigorous adaptation to meet requirements for formatting and content. At the same time, documentation was expanded to provide real usage examples for hundreds of product types, while eliminating redundancy by organizing common concepts in a central place. Documentation is now multi-lingual, with translations in five languages as of this writing.
Definitions: IFC, along with hundreds of other engineering standards, is defined using the EXPRESS data definition language, where the rich semantics allow virtually any other schema representation to be derived. The IFC4 documentation now includes a simplified XSD-based representation for all data types, enabling XML to be used in a more compact form with better readability.
Diagrams: Instance diagrams are now included for all data types. Because building Journal of Building Information Modelling components in the real-world have a vast number of relationships (for example, how connected, where placed, when constructed, who is responsible and what changed). Relationships must also be captured in data model, where diagrams make it more clear how the various objects interact.
Examples: Sometimes it is easier for software developers to understand new concepts by seeing tangible examples rather than sifting through definitions. The IFC4 documentation now includes a comprehensive set of examples in various domains including: architectural; structural; mechanical, electrical and plumbing scheduling; and estimating.
Model views: While the IFC specification defines how to represent BIM electronically, it does not indicate what should be included for particular scenarios. The concept of a model view definition (MVD) has evolved to fulfil this role, describing exactly what information must be included for a handover, such as for a building maintenance request.
Contracts may be written to require information at a particular stage using the referenced model view, where submissions may be electronically validated and enforced.
mvdXML: In parallel with IFC4, the MVD approach has been formalized so that requirements may be defined in a way that is computer-interpretable, yet human-readable in resulting documentation, using a format called “mvdXML.” MVDs may also define mapping formats for translating information into general-purpose applications such as spread sheets. The electronic encoding of MVDs now also makes it possible for a new class of software applications to adapt data to conform to the MVD without prior knowledge.
Tools: buildingSMART International has provided a new tool called ifcDOC for authoring model view definitions and producing resulting schemas, documentation and diagrams. “is same tool is used for generating IFC documentation, the Construction Operations Building information exchange (COBie) specification and a growing population of MVDs.
To take advantage of new BIM capabilities and much-improved software interoperability, visit www.buildingsmart-tech.org to find the growing list of applications supporting IFC4.
The National BIM Standard and the National Institute of Building Sciences are pleased to announce the continuation of our relationship with Matrix Group Publishing in the production of the Journal of Building Information Modeling, an essential information source on business, standards and technical issues related to BIM. http://www.wbdg.org/references/jbim.php
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