A Survey of Industry Data Models and Reference Data Libraries
3. Building Information Models
3.1.1 Defining organization
buildingSMART International (bSI) is a not for profit company incorporated in the UK in 1995. It has members organised in regional chapters.
The home page of building SMART international says:
buildingSMART has focused on solving industry interoperability challenges. buildingSMART is a neutral, international forum for initiating, developing, creating and adoption of open digital standards for BIM processes.
3.1.2 Objectives and scope
buildingSMART has developed a library of Industry Foundation Classes (IFCs) for the building industry. The IFCs have been standardised by ISO/TC 59/SC 13 "Organization and digitization of information about buildings and civil engineering works, including building information modelling (BIM)", and are also published as ISO 16739-1:2018 “Industry Foundation Classes (IFC) For data sharing in construction and facility management industries - Part 1: Data Schema”.
The summary page for the standards says:
buildingSMART standards cover wide range of process and information capabilities unique to the built environment industry, including:
- An industry-specific data model schema - Industry Foundation Classes [IFC]
- A methodology for defining and documenting business processes and data requirements - Information Delivery Manual [IDM]
- Data model exchange specifications - Model View Definitions [MVD]
- Model-based, software-independent communication protocols - BIM Collaboration Format [BCF]
- A standard library of general definitions of BIM objects and their attributes - buildingSMART Data Dictionary [bSDD]
The list continues to grow as stakeholders in the industry work together to identify opportunities to be more efficient and create greater value by applying standard processes and technologies where needed.
3.1.3 Structure of the model
The top of the IFC model is shown in Figure 2.
Figure 2 - Top of the IFC model
Comments on Figure 2:
- The model has an ISO 10303 flavour, with product as a top object and a reified product relationship. The production relationship object is called connect, but encompasses containment as well as connection. The model also has a formal structure with a root class.
- There is a distinction between element and spatial element, where a part of a building such as a beam or column is an element, but a building as a whole is a spatial element.
The distinction between spatial element and element is replicated in the Building Topology Ontology, LandInfra and CityGML, as follows:
spatial element (e.g. site, building, facility)
element (e.g. beam, column, wall, slab)
Building Topology Ontology
zone (e.g. site, building, space, storey)
facility part (e.g. building, railway, road)
physical element (e.g. railway element such as ballast, sleeper, switch)
site (e.g. building, tunnel, bridge)
building installation (with physical bounds such as interior and exterior wall surfaces)
The subclasses under element have partners which are “types”. Hence there is beam and beam type, column and column type, etc.. Several different beams within a building can be of the same beam type. Properties assigned to a beam type are inherited by each beam of that type.
The top level documentation follows the style of ISO 10303 (STEP), but is much simpler and clearer. There are easily understandable EXPRESS-G diagrams.
The documentation of subclasses under element is less well presented and no longer has clear EXPRESS-G diagrams. Nonetheless the UML-like diagrams are understandable.
3.1.5 Maintenance and usage
buildingSMART International is an active organization, and the latest [in August 2020] revision of the IFCs was published in April 2020.
The IFCs can be implemented in EXPRESS, XSD/XML and OWL. They are widely used within the building industry.
3.2 NBS Uniclass
3.2.1 Defining organization
NBS Enterprises Limited is a company registered in England, which is a commercialisation of the UK’s National Building Specification.
NBS Enterprises Limited maintains Uniclass-2015, which is a classification system for the construction industry.
3.2.2 Objectives and scope
The introduction to Uniclass-2015 says:
Uniclass is a consistent classification structure for all disciplines in the construction industry. It contains tables classifying items of any scale from a large facility such as a railway, down to products such as a CCTV camera in a railway station.
It’s an essential way of identifying and managing the vast amount of information that’s involved in a project, and it’s a requirement for BIM projects, as set by the BS EN ISO 19650 [Organization and digitization of information about buildings and civil engineering works, including building information modelling (BIM) — Information management using building information modelling] series of standards.
3.2.3 Structure of the model
The content of Uniclass-2015 is divided into tables as follows:
SL Spaces/ locations
EF Elements/ functions
TE Tools and Equipment
PM Project management
FI Form of information
Within each table, there are named objects arranged into hierarchies. The objects do not have definitions, although in most cases the names are self-explanatory. The objects do not have properties.
Uniclass-215 tables are published as simple EXCEL spreadsheets, from which hierarchies and codes can be easily extracted and represented in other formats.
Maintenance and usage
NBS Enterprises Limited is an active organization. The latest [in August 2020] revision of the tables was published in July 2020.
The Uniclass codes are widely used in the UK construction industry.
3.3 Brick - a uniform metadata schema for buildings
3.3.1 Defining organization
The Brick project was initiated by universities in the USA and Denmark and by IBM research. There is no organization, except an open source development community.
3.3.2 Objectives and scope
What is Brick? says:
Brick is an open-source effort to standardize semantic descriptions of the physical, logical and virtual assets in buildings and the relationships between them. Brick consists of an extensible dictionary of terms and concepts in and around buildings, a set of relationships for linking and composing concepts together, …
The schema principally addresses control systems within buildings.
3.3.3 Structure of the model
The model has two principal top classes:
within the scope of the model, this is control system equipment. There are subclasses such as HVAC, and below this air handler unit.
within the scope of the model, this is where equipment can be. There are subclasses such as room, and below this server room.
The model is concerned with how equipment items are connected and what their properties are. The properties can include set point values.
The documentation of the model is not uninteresting, because it recognises limits to what has been done. An interesting discussion concerns an air temperature sensor. This is defined as a temperature sensor that measures air. Naïve rendering in OWL, shows this as a relationship between a particular temperature sensor and the class air, which is not OWL-DL and requires punning. Actually, it is a relationship between a particular temperature sensor and the particular air at the location of the sensor.
There is some discussion of the model, but for the details the user is left to hack the TURTLE files. The definitions are sparse.
3.3.5 Maintenance and usage
This is unclear. A new version of the schema is shown, but there are no dates.
3.4 Building Topology Ontology
3.4.1 Defining organization
The W3C Linked Building Data Community Group (https://www.w3.org/community/lbd/) is an informal group under W3C. Its home page says:
This group brings together experts in the area of building information modelling (BIM) and Web of Data technologies to define existing and future use cases and requirements for linked data based applications across the life cycle of buildings.
3.4.2 Objectives and scope
The Building Topology Ontology is a Draft Community Group Report of 07 April 2020. The introduction to the ontology says:
The Building Topology Ontology (BOT) is a minimal OWL DL ontology for defining relationships between the sub-components of a building. It was suggested as an extensible baseline for use along with more domain specific ontologies following general W3C principles of encouraging reuse and keeping the schema no more complex than necessary.
3.4.3 Structure of the model
The Building Topology Ontology model is admirably simple. A UML representation of most of it is shown in Figure 3.
Figure 3 - Building Topology Ontology model
The Building Topology Ontology defines interfaces to other standards, including the IFCs and Brick. The interfaces are expressed as rdfs:subClassOf and rdfs:subPropertyOf relationships. Hence:
Building Topology Ontology to IFCs:
- ifc:IfcSite subclass of bot:Site
- ifc:IfcBuilding subclass of bot:Building
- ifc:IfcBuildingStorey subclass of bot:Storey
- ifc:IfcSpace subclass of bot:Space
- ifc:IfcElement subclass of bot:Element
Building Topology Ontology to Brick:
- brick:Building subclass of bot:Building
- brick:Space subclass of bot:Zone
- brick:Room subclass of bot:Space
- brick:Equipment subclass of bot:Element
- brick:contains subclass of bot:hasElement
- brick:hasPart sub-property of bot:hasElement
- brick:hasPart sub-property of bot:containsZone
- brick:hasPart sub-property of bot:hasSubElement
[The relationships between the properties do not look right to me. DL]
Being so simple, the documentation of the Building Topology Ontology is adequate. However, you have to load the ontology into Protégé, or similar tool, to understand it. No graphical representation of the model is provided.
3.4.5 Maintenance and usage
The Building Topology Ontology is work in progress, and the latest [in August 2020] draft is June 2020.
There is no evidence of any industrial use.
3.5 RICS data standards
3.5.1 Defining organization
Royal Institute of Chartered Surveyors (RICS)
3.5.2 Objectives and scope
The introduction to the standards on the RICS website says:
How do you manage your data?
The problem is that much of the existing data on real estate from land itself, through planning, construction, sales, leasing, letting, occupation, maintenance to end of life, is still held in fundamentally paper form albeit available in pdf format or as scans of original documents. Where data are held in more formal, structured databases or as Excel spreadsheets, a lack of common data standards and data models still makes sharing data within organisations and across the broader marketplace problematic.
Streamline your data models
In order to resolve this challenge around inconsistent, unstructured data in the profession, we've developed a suite of data standards – open data models - that complement our existing suite of written standards.
These data standards support the capture, verification and sharing of data to a common format. RICS Data Standards are already available for construction costs - International Construction Measurement Standards (ICMS) - and property measurement - International Property Measurement Standards (IPMS).
The introduction says that two further standards are in preparation:
- International Land Measurement Standard (ILMS);
- International Valuation Standard (IVS).
The RICS data standards do not make reference to either the BuildingSMART IFCs or the BRICK or Building Topology ontologies, and are a separate “island” of standardisation.
3.5.3 Structure of the model
184.108.40.206 The schemas
The International Construction Measurement Standard and the International Property Measurement Standard are each defined as XML schemas and equivalent JSON schemas. The RICS documentation is principally about the XML schemas.
The schemas are structured as follows:
ipms: entities relevant to property measurement;
icms: entities relevant solely to construction measurement;
common types: entities relevant to both;
common enums: reference data (enumerations) relevant to both.
The common enums contains both reference data defined by RICS and reference data imported from elsewhere. The XML schema file is 19,000 lines. Examples of enumerations are:
RICS defined: cost codes, building functions, report statuses; properties valid for different types of construction project;
imported: ISO country codes, currency codes, UN/CEFACT units of measure, UNICLASS categories.
The schemas for construction and property measurement are described in the following subsections.
220.127.116.11 International property measurement standard
The version guidance document for the IPMS version 2.1 says:
The International Property Measurement Standards RICS Data Standard (IPMS RICS data standard) is an XML schema enabling users to capture, denote and share IPMS measurements of buildings. It is compatible with:
- RICS property measurement (2nd edition), RICS professional statement and
- International Property Measurement Standards (IPMS): Office Buildings, Residential Buildings and Industrial Buildings.
The data standard supports the additional measurements required for IPMS: Industrial Buildings, together with the new component areas in IPMS: Industrial Buildings and those currently proposed for IPMS: Retail Buildings.
An outline of the IPMS schema is shown in Figure 3.5.1.
Figure 3.5.1 - Outline of the RICS IPMS schema
Comments on Figure 3.5.1:
1. The UML-like boxes correspond to element types in the XML schema. Many of the attributes shown are also complex elements. Attributes are shown as relationships only where they are relevant to the topology of the schema.
2. The element IPMS measurement shown here is taken from the ipms schema. There is also a type IPMS measurement in the common types schema. Many of the attributes shown here are of type IPMS measurement which in turn has attributes:
- utilisation rate;
- volume (optional);
- alternative measurements (any number);
- limited use measured area summaries (any number);
- included measured area summaries (any number);
- excluded measured area summaries (any number).
Many of these attributes are element types which have a separate area category as an attribute, which references a taxonomy of areas as follows:
- external balconies;
- internal balconies;
- covered galleries;
- accessible rooftop terraces;
- patios and decks at ground level not part of building structure;
- external vehicle parking;
- equipment yards;
- cooling equipment;
- refuse areas;
- ground level areas not fully enclosed;
- open light wells;
- upper level voids of an atrium;
- standard facilities;
- open external stairways not part of building structure;
- shared circulation areas;
- enclosed walkways or passages;
- internal catwalks;
- external catwalks;
- sheltered areas;
- internal permanent mezzanines;
- permanent mezzanines;
- temporary mezzanines;
- vehicle circulation;
- internal loading bays;
- external loading bays;
- vertical penetrations as part of common facilities;
- enclosed garages;
- unenclosed vehicle parking areas;
- staircase openings;
- staircase openings above level 0;
- balconies in exclusive use;
- verandas in exclusive use;
- loading bays;
- temporary structures;
- structures beyond the covered area;
- ancillary areas;
The XML schema is a precise and complicate document structure. The schema is limited to documentation. Hence a taxonomy, such as that for “separate areas”, is treated as a list of keywords, rather than a classification of spaces.
18.104.22.168 International construction measurement standard
The version guidance document for the ICMS version 1.1 says:
The International Construction Measurement Standards RICS Data Standard (ICMS RICS Data Standard) is an XML schema allowing users to capture, denote and share data on construction cost measurements. It is compatible with:
- RICS property measurement (2nd edition), RICS professional statement and
- International Construction Measurement Standards: Global Consistency in Presenting Construction Costs (ICMS).
The ICMS schema has elements relevant to the different types of construction project:
- road and motorway;
- waste water treatment works;
- water treatment works;
- well and borehole;
- power generating plant;
- chemical plant;
- other project type.
Figure 3.5.2 - Outline of the RICS ICMS schema - railway project
Comments on Figure 3.5.2:
- The UML-like boxes correspond to element types in the XML schema. Many of the attributes shown are also complex elements. Attributes are shown as relationships only where they are relevant to the topology of the schema.
- The project type specific elements shown - railway, railway works, railway quantities and railway functional units - have analogies for each different project type.
The project type specific elements for a building project are shown in Figure 3.5.3.
Figure 3.5.3 - Outline of the RICS ICMS schema - building project
Comments on Figure 3.5.3:
1. As for Figure 3.5.1, the element IPMS measurement shown here is taken from the ipms schema. There is also a type IPMS measurement in the common types schema. Many of the attributes shown here are of type IPMS measurement.
2. The building functional units attribute function is either a text string or one of the enumerated list:
- number of desks;
- number of occupants;
- number of bedrooms;
- number of hospital beds;
- number of hotel rooms;
- number of car parking spaces;
- number of classrooms;
- number of students;
- number of passengers;
- number of boarding gates.
The ICMS schema encodes a list of project types, and for each of these it encodes:
- the properties that define the nature of the project;
- the quantities that define the magnitude of the project.
Hence the addition of a new project type, or a change to the information that can be recorded about a project type, requires a new edition of the schema.
22.214.171.124 Assessment of the RICS schemas
The RICS schemas are meticulous in defining a precise document structure. However, they are inflexible so that any extensions to the types of property that can be measured, to building usage types, or to project types requires a revision of the schemas.
The schemas also “hard wire” data that are defined elsewhere, such as countries, currencies, or UNICLASS commodity types. This means that a revision of the schema may be required as a result of changes made by other organizations. The schemas do not take advantage of externally managed reference data libraries. The only external reference, which is decoupled from the RICS schemas, is to the OASIS xNAL (extensible Name and Address Language) schema.
The schemas do not have a physical basis, that recognises:
- there are physical objects, such as buildings, bridges etc. that have a decomposition into parts, with properties of the whole and of the parts;
- there are construction projects for physical objects;
- there are observation activities, which are carried out upon physical objects and upon construction projects and which estimate values for the properties.
The RICS schemas have little in common with the buildingSMART or INSPIRE schemas which have taken a more formal data modelling approach.
The schemas have detailed element by element documentation, which seems largely derived from comprehensive annotation within the schemas. However, there are no overview diagrams comparable with Figure 3.5.1, Figure 3.5.2, and Figure 3.5.3.
3.5.5 Maintenance and usage
In October 2019, the RICS launched the “Data standards leaders forum” to “explore the need for common data standards across the entire property lifecycle and RICS' role as a standard-setter and regulator”.
The latest version of the IPMS schema is 2.1 and the latest version of the ICMS schema is 1.1. Both were released in September 2019. The level of industrial use of these schemas is unclear.