Rules and Recommendations

The following rules and recommendations [rec.] should be honored when devising BIS names. This include Domain, Schema, Namespace, Class and Properties names as well as aliases.

NOTE: The items below are not ordered by importance but rather around related concepts.


BIS naming convention is deliberately more restrictive than EC naming: All BIS names are valid EC names but not all EC names are valid BIS names.

Description Note
Rule Only use alphanumeric characters
Rule Do not use an underbars in names Don't use underbars even if it aids readability: Use OrderLineItem not Order_LineItem
Rule Names may not start with a number E.g. 3dGeometry is not allowed
Rule Names may not differ only by case E.g. If there's already a name called Pricelist then you may not define a new one called PriceList
Rule Use PascalCase names PascalCase means words are concatenated with the first letter of each word capitalized. E.g. OrderLineItem
Rule Use United States Spelling E.g. Organization not Organisation
Rec. Use the most widely accepted and descriptive name possible Consult the current thesaurus before creating new words.
Rec. Use a single word that describes the entity E.g. Person rather than HumanBeing
Rule Don't add superfluous terms Don't use two nouns if one can equally express its meaning.

E.g. Vehicle rather than TransportationVehicle.

For relationships we can often infer the type of target from the name of the source. So, use PhysicalElementIsOfType rather than PhysicalElementIsOfPhysicalType (because the element cannot be of any type other than Physical!)
Rec. Do not add any unnecessary prefixes or suffixes to an entity Especially terms like Object, Instance, Entity, and Property.

E.g. Use Note not NoteEntity (for a class name) or NoteProperty (for a property name).
Rec. Words should be less than 30 characters
Rec. Use abbreviations and acronyms with care Use abbreviations and acronyms only where they are common and completely unambiguous. If the abbreviation/acronym is not well known, don't use it!

Try to limit the use to those that appear in the list of abbreviations and acronyms and don't use those listed in the "don't use" section.

Two letter acronyms have both letters capitalized, provided that each letter represents a different word.

E.g. UI ("User Interface") and IO ("Input/Output") because both words are capitalized, but Db because "Database" is one compound word.

Three or more letter acronyms have only the first letter in capital case.

E.g. Html or Guid

Abbreviations of a single word have only the first letter in capital case.

E.g. Id ("Identification")
Rec. Use numbers with care Avoid names such as One21 and Door2Door

A well-known exception is for terms 1d, 2d, and 3d (dimensions). These may be used to form new terms provided they don't break the rule stating that Names may not start with a number.

E.g.Acceptable names are Spatial1d, Model2d
Rec. Use special words with care. Specifically, make sure that the semantic meaning of the special term is well understood._

E.g.List, Item, Set, etc...

See list of special terms

If it isn't an Aspect, don't put Aspect in the name.
Rule Do not use New, Old, Tmp, or Temp What seems "new" when you do it will become "old" when you make the next change.
Rec. Avoid the use of 'Base' in class names E.g. use RasterModel instead of RasterBaseModel
Rec. Avoid using the organization's name If prefixes are needed, give preference to the domain rather than the organization.

E.g. Use TransportElement rather than ExorElement
Rec. Avoid using product names E.g. Avoid prefixes like eB, OpenPlant, STAAD, Dgn, ConnectedProject
Rec. Avoid domain names in the term E.g. PlanningElement, ConceptualElement, PlantElement, PlantArea, and Area
Rec. Avoid using version numbers or generation names E.g. V8iFile
Rec. Favor instances over definitions I.e. if you need to distinguish between an Entity Definition and an Entity Instance and there are no suitable words that can distinguish them, suffix the definition rather than the instance: user will work with instance more often than definitions_

E.g. Use AttributeDefinition for the definition and Attribute for the value.

Note: The ECProperty is an example where this recommendation is not being followed. There are no plans to change that - Sorry.

ECSchema / BIS Domain Names

Description Note
Rule All EcSchema/BIS Domain Names must be registered with BIS workgroup to avoid conflicts.
This includes the aliases.
E.g. BisCore (schema name) and bis

See list of BIS Schemas
Rule BIS Schema aliases must be in lowercase
Rule BIS Schema aliases must be less than 7 characters long


Description Note
Rule Use singular form E.g. File not Files
Rule When combining terms, arrange them in increasing order of significance E.g. CableCar, AnalogWaterMeter

Exceptions: 2d and 3d because names can't start with numerals
Rec. Names of direct or indirect specializations of bis:ElementAspect should end with Aspect.
Rec. Do not use prepositions such as Of, With, On, An, In, From, etc...

Property (including “Navigation” Properties)

Description Note
Rule Use the plural form of the name when the attribute is a collection, otherwise use the singular form. Document.AddedBy (a document can be added by a single person) but can have many notes, so Document.Notes
Rec. Try to create attributes with the same name as their underlying type Document.Lock is of type Lock

Exception: When the entity has more than on attribute of that type, or when it aids in readability: Document.AddedBy instead of Document.Person
Rec. Don't include the primitive datatype (int, string) with the name Exception: Dates. Since Date is both a data type and a more meaningful noun, something like DateAdded would be acceptable but NoteBlob would not be.
Rule Don't include the attribute owner name in the attribute name E.g. Document.Id not Document.DocumentId and Person.Name not Person.PersonName
Rule Prefix Boolean names with Is, Has, Can, May E.g. IsUnderChange, HasOtherRevision, MayChange
Rule When the field represents a bit mask, use the plural form of the word E.g. StateHints, HasFlags
Rule For NavigationProperties, prefer to use the name of the related ECClass as the property name If further qualification is needed, consider prefixing words from the role label.


Relationship naming rules are difficult because of competing concerns. It is important for relationship class names to be clear and unambiguous so that the purpose and constraints of the relationship can be understood. However, it is also important to be cognizant of the number of characters in the relationship class name since that is what a developer or power user will have to type in when using ECSQL. Names that are too long are frustrating, but vague names are also frustrating. The rules and recommendations below try to balance these concerns:

Description Note
Rule Use Source-Verb-Target E.g. ElementOwnsUniqueAspects, OrganizationSellsProducts

In most cases, the "source/target" will simply be the name of the object. In those cases, the addition of an adjective can be helpful: Child in ElementOwnsChildElements
Rule Fully specify the source constraint
In general, use the full class name of the source constraint for the source portion of the relationship name. In some cases, the suffix of the source constraint class name can be dropped if it doesn't help with understanding the purpose of the relationship.
E.g. "PhysicalElementIsOfType", "PhysicalSystemServicesElements"
Rule Try to use a specific action-oriented verb
Verbs like aggregates, holds, groups, represents, services are more action-oriented while verbs like has or relates to are more passive and don't identify the purpose of the relationship.
E.g. "DrawingGraphicRepresentsElement", "PhysicalElementServicesElements"
Rule Use verbs that are consistent with relationship strength - Owns, Contains, or Aggregates implies embedding
- Represents or Groups implies referencing

See list of relationship strengths
Rule Shorten the target portion if possible
Use the role within the relationship or a shortened form of the target constraint class.
E.g. "PhysicalElementIsOfType"

In this case, fully specifying the target constraint of PhysicalType would make the relationship class name longer without adding much clarity since the source constraint gives a strong hint as to the target constraint.
Rule The relationship name should indicate the multiplicity
The source is always singular and the target indicates multiplicity.
E.g. ElementOwnsChildElements (1:N), ElementHasLinks (N:N), PhysicalElementIsOfType (N:1)
Rule Don't use conjunctions
Do not use a singular noun or verb, even if it clearly defines a relationship. Always use noun-verb-noun
E.g. Don't use Marriage or ManAndWoman; use PersonIsMarriedToPerson

Last Updated: 15 June, 2021