There are huge amounts of complex information, which needs to be filed, retrieved and referred. This is particularly true for a construction project where there can be a vast breadth and depth of information and fields of specialism which use different terminology. Classification allows us to order this information in a controlled and consistent manner, to provide a common understanding between specialisms. Fundamentally, classification means grouping things according to a common quality or characteristic. In the first place, it is necessary to define the purpose of the classification and then distinguish the properties for interest to the classification. After that, the subjects can be sorted into classes with regard to the selected properties.

A hierarchy is defined, in a series of classes or groups in successive subordination. Each characteristic is related to a subgroup of a larger group, in a process of division, according to certain characteristics. In this process of hierarchical classification, each subject should only have one place where it fits into the scheme.

Related with the fact that different people can use the same object, on different occasions, it there should be a common language and significances. Thus, a consistent terminology could enable the organisation of the objects and its characteristics, in a classification scheme, to depend on agreed definitions of terms and consistent usage.

According to the NATSPEC TECHreport TR02 (October 2021), the main benefits of classification systems in the construction industry, to facilitate the management of construction information are:

• Filing and retrieval of information about construction products, technical reference material, costs, and so on.
• Structuring the contents of individual documents in a consistent manner.
• Co-ordinating information between individual documents found in sets of documents.
• Communications and collaboration between members of a project team by providing a common language.
• Interoperability of digital systems.
• Organising BIM object libraries.
• Searching for objects or items of a similar type in models.
• Aggregating similar objects or items in models for the purposes of measurement, analysis, monitoring, and so on.
• Benchmarking measured values for assets of a similar type.
• Exchanging and integrating asset information.
• Standardising and consolidating reporting on items of interest.
• Decision making about whole-of-portfolio investments.

Some of the most important construction information classification systems are based on the principles of ISO 12006-2 Building Construction – Organization of information about Construction Works – Part 2: Framework for Classification and Part 3: Framework for Object-oriented Information. This influence is a reflection of the convergence of systems based on shared international standards, in order to trend away the separate development of incompatible national systems.

ISO 12006-2 defines a framework for the development of built environment classification systems and recommends a set of classification tables and their titles for a range of construction object classes according to particular views, e.g. buildings, construction elements and spaces. It also defines each class and shows how they are related to each other.

ISO 12006-2 does not describe a complete operational classification system. It is a framework level standard written for developers of classification systems with the aim of providing the basis for harmonising local classification systems. Several national classification systems applied the 2001 edition of the standard (Figure 55). The lessons learnt from these implementations have been applied to the 2015 edition (NATSPEC TECHreport TR02, October 2021).

The actual classification systems most relevant to construction are:

• NATSPEC, from Australia.
• Masterspec, from New Zealand.
• Cuneco Classification System (CCS), from Denmark.
• Talo (Finnish for Building) 2000 classification system, from Finland.
• CoClass, from Sweden.
• Uniclass 2015, from the United Kingdom (UK).
• OmniClass, from North America.

In a historical context, OmniClass is the result of the adoption of two systems:

• The MasterFormat, the basis of OmniClass Table 22 Work results, is the pre‑eminent means of organising commercial and institutional construction specifications, such as MasterSpec, in North America.
• The UniFormat, the basis of OmniClass Table 21 Elements (including designed elements), which provides a standard method of arranging construction information, organised around the physical parts of a facility called systems and assemblies. It is used for formatting documents on project scope, quality, cost and time, such as cost estimates or reports.

There are several differences in classifications between these systems. For instance, OmniClass lists 211 types of doors (18 in Table 21 Elements, 66 in Table 22 Work results and 127 in Table 23 Products), and the Cuneco Classification System and CoClass (ISO/IEC 81346 based) lists one type of door with the option to add many properties.

Figure 6 and 7 illustrate the differences between a typical or traditional classification (with different classification tables for different participants and purposes and specialized subtype classes incorporating more and more properties embedded in the code), and an object-oriented, generic and stable classification (with one entry class that is used all through the lifecycle, combined with an increasing number of properties).

Regarding the example of the NATSPEC TECHreport TR02 (October 2021), it is possible that all these systems are multifaceted or multi-table classification systems aligned to ISO 12006-2.

Comparing OmniClass and Uniclass 2015, they followed a similar development path in that they were both assembled from pre-existing single table systems. Both are based on ISO 12006-2, though each places them in a slightly different order and splits or combine some of them differently.

Uniclass 2015 does not match OmniClass detail in some sectors, in spite of covering buildings, civil and landscape works, transport and utilities infrastructures and processes engineering more uniformly and consistently within tables. For both systems, Excel files of tables can be readily downloaded online at no cost. OmniClass tables are also available as PDF files.

OmniClass is a multifaceted system designed within the parameters of ISO 12006-2 and ISO 12006-3 covers some sectors in detail but not others. The majority of the 15 OmniClass tables were first published in 2006 and revised some Tables in 2013.

Uniclass 2015 is a more consistent and integrated system than OmniClass, perhaps because it was created from scratch and could build on the lessons of previous systems. The internal structure of tables follows a more consistent configuration, because the basis of specialisation has been more consistently applied.

This more stable hierarchical organisation of the notation system in Uniclass 2015, allows a multifaceted classification of items across tables and makes patterns in the organisation of the system more recognisable for users. It is one of the reasons why Uniclass 2015 is updated more often and changes and extensions to the system are easier to make than in OmniClass.

The Cuneco Classification System (CCS) and CoClass have been developed in parallel and have similar tables aligned to ISO 12006-2 such as OmniClass and Uniclass. However, they diverge from these systems with the incorporation of principles derived from ISO/IEC 81346. CCS and CoClass have had a number of national predecessors – CCS was preceded by the DBK and BC/SfB systems; CoClass was preceded by the BSAB and SfB systems.

Comparing the group OmniClass/Uniclass and the group CCS/CoClass, it is possible to say that OmniClass and Uniclass 2015 represent a more established approach to classification. They will be more recognisable to most industry stakeholders. In OmniClass/Uniclass a list is found of multiple types of each element across a number of tables, with different notations in each table, by the properties assigned to them.

However, CCS and CoClass systems, after implementation, are easier to understanding. These systems list a single element and the subtypes are created by the properties assigned to them. This organization has the advantage that the initial, or root, notation for each element remains unchanged throughout a project. The details of the element are progressively defined during the design, documentation, acquisition and operational phases of a project simply by adding or modifying relevant properties, an approach that is well suited to BIM processes (NATSPEC TECHreport TR02, October 2021).

About the notation to identify and order individual items, OmniClass/Uniclass use a numerical code, generally of six digits, yet that can be extended by adding more digits after a decimal point. It reflects the hierarchical ordering of items familiar to regular users of classification systems. CCS/CoClass notations are based on the three-part Reference Designation System (RDS) described in ISO/IEC 81346, which is both human and machine-readable.

In all the cases are simply notations that consist of one, two or three relatively simple letter codes. However, more sophisticated implementations could be applied, with advanced functionalities such as making it possible to identify an individual item and its precise location/relationship to other items within a project. In these cases and for many, these notations will not be readily interpretable at first sight.

Reference:

NATSPEC TECHreport TR02 (October 2021), Information classification systems and the Australian construction industry