OmniClass is, in simple terms, a standard for organizing all construction information. The concept for OmniClass is derived from internationally-accepted standards that have been developed by the International Organization for Standardization (ISO) and the International Construction Information Society (ICIS) subcommittees and workgroups from the early-1990s to the present.
ISO Technical Committee 59, Subcommittee 13, Working Group 2 (TC59/SC13/WG2) drafted a standard for a classification framework (ISO 12006-2, more information below) based on traditional classification but also recognized an alternative "object oriented" approach, which had to be explored further.

ISO TC59/SC13/WG6 developed an electronic framework (ISO/PAS 12006-3, more information below) for the tagging and managing of objects and their attributes.

These standards, ISO 12006-2: Organization of Information about Construction Works - Part 2: Framework for Classification of Information, and ISO/PAS (Publicly Available Specification) 12006-3: Organization of Information about Construction Works - Part 3: Framework for Object-oriented Information, define methods of organizing the information associated with construction and affiliated industries, and also promote a standard object-modeling definition for concepts addressed. Of these two standards, ISO 12006-2 has more immediate impact on OmniClass, and the OCCS Development Committee has closely adhered to this standard in establishing and defining the tables that make up OmniClass.

The Construction Industry Project Information Committee (CPIC) of the UK which was formed to create Uniclass has, to date, exploited this standard most successfully by publishing a usable version of Uniclass in 1997. It is anticipated that the UK authors will assess OmniClass as they work to update to that publication.

In addition to the application of ISO 12006-2 in Uniclass, the object-oriented framework standardized by ISO/PAS 12006-3 has been adopted by ICIS members in their Lexicon program, and both standards are followed by groups in several other countries that are developing similar classification standards, including Norway, Netherlands, UK, and others, in concert with the Nordic chapter of the International Alliance for Interoperability (IAI), and the Japan Construction Information Center (JACIC) which is currently working to develop the Japanese Construction Classification System (JCCS), modeled in part on OmniClass.

The OmniClass Construction Classification System (OCCS) Development Committee believes that following these ISO standards will promote the ability to map between localized classification systems developed worldwide. It is the Committee’s hope that organizations in other countries pursuing initiatives similar to OmniClass will also strive to be ISO-compatible, thereby enabling smoother exchange of information between them.

As stated by ISO in the text of ISO 12006-2, “Provided that each country uses this framework of tables and follows the definitions given in this standard, it will be possible for standardization to develop table by table in a flexible way. For example Country A and Country B could have a common classification table of e.g. elements, but different classification tables for work results without experiencing difficulties of ‘fit’ at the juncture.

ISO 12006-2: Organization of Information about Construction Works - Part 2: Framework for Classification of Information: This standard provides a basic structure of information about construction that is grouped into three primary categories composing the process model: construction resources, construction processes and construction results. These are then divided into fifteen suggested “Tables” for organizing construction information. The OmniClass Tables correspond to this arrangement of information:

The fifteen tables of OmniClass also map to the suggested tables in Section 4 of ISO 12006-2 (shown in italics) in the following way:

OmniClass Table 11: Construction Entities by Function
4.2 Construction entities (by function or user activity)
4.3 Construction complexes (by function or user activity)
4.6 Facilities (construction complexes, construction entities and spaces by function or user activity)

OmniClass Table 12: Construction Entities by Form
4.1 Construction entities (by form)

OmniClass Table 13: Spaces by Function
4.5 Spaces (by function or user activity)

OmniClass Table 14: Spaces by Form
4.4 Spaces (by degree of enclosure)

OmniClass Table 21: Elements (Table 21 includes Designed Elements)
4.7 Elements (by characteristic predominating function of the construction entity)
4.8 Designed elements (element by type of work)

OmniClass Table 22: Work Results
4.9 Work results (by type of work)

OmniClass Table 23: Products
4.13 Construction products (by function)

OmniClass Table 31: Phases
4.11 Construction entity life cycle stages (by overall character of processes during the stage)
4.12 Project stages (by overall character of processes during the stage)

OmniClass Table 32: Services
4.10 Management processes (by type of process)

OmniClass Table 33: Disciplines
4.15 Construction agents (by discipline)

(OmniClass Table 33 and Table 34 are both drawn from different facets of Table 4.15, which then can be combined for classification)

OmniClass Table 34: Organizational Roles
4.15 Construction agents (by discipline)

OmniClass Table 35: Tools
4.14 Construction aids (by function)

OmniClass Table 36: Information
4.16 Construction information (by type of medium)

OmniClass Table 41: Materials
4.17 Properties and characteristics (by type)

OmniClass Table 49: Properties
4.17 Properties and characteristics (by type)

ISO/PAS 12006-3: Organization of information about construction works - Part 3: Framework for object-oriented information implements the basic approach of ISO 12006-2 but uses the entries on these tables as the defining points (or characteristics) for object-oriented information organization. The ‘object-oriented’ approach describes the characteristics of things without imparting a grouping preference or hierarchical order.

In the object-oriented approach, the object is central, acting as a basis for characteristics or properties that describe it. An object thus described can then be grouped with similar objects using a classification arrangement like OmniClass. The framework established by ISO/PAS 12006-3 will enable computers to store and relate information in an object-oriented manner, while OmniClass Tables provide humans with a variety of viewpoints to that data, and a useful approach to establishing relationships between objects.

From the Foreword to ISO/PAS 12006-3: “While ISO 12006-2 is a standard that reflects many years of refinement of classification systems, ISO/PAS 12006-3 represents not so much new thinking, but a new implementation of established information modeling practice using a new ISO process which aims to bring new work of this kind into use as quickly as possible.”

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