Use when you encounter an .ifcx file, need to explain the IFCx JSON encoding of the next-generation IFC, or must decide whether IFCx applies to a task. Prevents treating IFCx as a finalised production format, confusing IFCx (the format) with IFC5 (the standard generation), expecting STEP syntax inside an .ifcx file, and over-claiming an RDF or USD lineage that is not verified. Covers the .ifcx JSON file format, the node-and-attribute composition graph with inheritance and children, the "schema.org for IFC" direction, the JSON Schema published at ifcx.dev under the @org/path namespace, and the relationship between IFC5 and IFCx. Keywords: IFCx, .ifcx, IFC5 format, next generation IFC, IFCx JSON, ifcx.dev, schema.org for IFC, composition graph, layering, inheritance, TypeSpec schema, what is an ifcx file, how do I open an ifcx file, IFCx vs IFC5, is IFCx ready, ifcx file will not open, JSON IFC format, IFCx schema namespace, in development.
Use when you encounter an .ifcx file, need to explain the IFCx JSON encoding of the next-generation IFC, or must decide whether IFCx applies to a task. Prevents treating IFCx as a finalised production format, confusing IFCx (the format) with IFC5 (the standard generation), expecting STEP syntax inside an .ifcx file, and over-claiming an RDF or USD lineage that is not verified. Covers the .ifcx JSON file format, the node-and-attribute composition graph with inheritance and children, the "schema.org for IFC" direction, the JSON Schema published at ifcx.dev under the @org/path namespace, and the relationship between IFC5 and IFCx. Keywords: IFCx, .ifcx, IFC5 format, next generation IFC, IFCx JSON, ifcx.dev, schema.org for IFC, composition graph, layering, inheritance, TypeSpec schema, what is an ifcx file, how do I open an ifcx file, IFCx vs IFC5, is IFCx ready, ifcx file will not open, JSON IFC format, IFCx schema namespace, in development.
license
MIT
compatibility
Designed for Claude Code. Requires IFC IFCx.
metadata
{"author":"OpenAEC-Foundation","version":"1.0"}
IFC Core : IFCx Architecture
IN DEVELOPMENT : subject to change. IFCx is not a released or ratified
specification. It is developed in the public buildingSMART/IFC5-development
repository, whose own examples are explicitly labelled Every fact in this skill is a moving target. NEVER teach IFCx as a
stable target and NEVER recommend it for a production exchange.
"preliminary and will be
updated."
IFCx is the JSON data encoding of the IFC5 generation : the .ifcx file format
and its ifcx.dev schema host. This skill explains what an .ifcx file is, how
its composition graph works, and how IFCx relates to IFC5. It is the format-side
counterpart to ifc-core-ifc5-architecture, which covers the IFC5 standard.
Quick Reference
What IFCx is
IFCx is the JSON data encoding of the IFC5 generation. An IFCx file is, in
the words of the IFC5 examples, "a JSON file, shared as .ifcx."
The file extension is .ifcx.
IFCx data is organised into objects delimited by { and } that "hold
the data." These objects can be shared across multiple files, or within one
file.
Objects can refer to children and can inherit : "This is how you
construct a tree." IFCx is a node-and-attribute composition graph.
A consumer does NOT read a pre-resolved model : "An implementation needs to
compose the scene from the available data."
The JSON Schema for IFCx is published at
https://ifcx.dev/@standards.buildingsmart.org/ifc/.
The schema source is written in TypeSpec (.tsp files); the JSON Schema
is generated from that TypeSpec source.
ifcx.dev carries the tagline "The schema.org for IFC", signalling a
web-native, semantic, graph-shaped data direction.
What IFCx is NOT
IFCx is NOT a STEP format. The IFC5 examples state plainly : "There will
not be STEP syntax in IFC 5." An .ifcx file has no ISO-10303-21
wrapper, no HEADER section, and no FILE_SCHEMA clause.
IFCx is NOT finalised. The specification is in development; schema,
objects, and structure will change before any release.
IFCx is NOT the same thing as IFC5. IFC5 is the standard generation; IFCx
is its file format. See the decision tree below.
IFCx is NOT confirmed to be RDF or JSON-LD. The graph shape is verified;
the specific linked-data serialisation is not. See the labelling pattern.
IFC5 versus IFCx
Term
What it names
IFC5
The next-generation standard : the composition semantics, the modular domain schemas, the layering model.
IFCx
The next-generation data format : the .ifcx JSON encoding and the ifcx.dev JSON-Schema host.
ALWAYS use "IFC5" for the conceptual standard and "IFCx" / .ifcx for the
concrete file format. NEVER treat the two terms as interchangeable : they are
routinely conflated and the distinction is the point of having two skills.
Decision Trees
Is IFCx the right target for this task?
Is this a production exchange another tool must reliably consume?
|
+-- YES --> NEVER use IFCx. It is in development and not finalised.
| Target a released IFC version : IFC2x3 TC1, IFC4 ADD2 TC1,
| or IFC4.3 ADD2 (STEP / ifcXML / ifcJSON). See
| ifc-core-version-evolution.
|
+-- NO, this is research or prototyping against the IFC5-development repo
--> IFCx is acceptable, WITH the explicit caveat that the .ifcx
structure and schema will change before release.
Which term applies : IFC5 or IFCx?
What is being described?
|
+-- The composition / layering model, modular domain schemas, the
| standard generation as a concept
| --> "IFC5". See ifc-core-ifc5-architecture.
|
+-- A concrete .ifcx file, the JSON encoding, the ifcx.dev schema host
--> "IFCx". This skill.
How to approach an .ifcx file
You have a file with the .ifcx extension.
|
+-- Parse it as JSON. It is a JSON document, not a STEP file.
| NEVER look for ISO-10303-21 / HEADER / FILE_SCHEMA : they are absent.
|
+-- Read the data objects ({ ... }) and their child / inherit references.
|
+-- Compose the scene : resolve the composition tree yourself. The file
| is not a pre-resolved graph.
|
+-- Validate against the JSON Schema at
ifcx.dev/@standards.buildingsmart.org/ifc/ , accepting that the
schema is a development version.
Patterns
Pattern : Treat IFCx as in-development at all times
ALWAYS state "IFCx is in development, subject to change" whenever IFCx is
referenced. The IFC5-development examples are explicitly "preliminary and will
be updated."
NEVER present an .ifcx structure, key name, or object shape as stable.
NEVER recommend IFCx for a real project deliverable.
NEVER compare an IFCx detail to a released IFC version as if both were fixed :
one side of that comparison is unfinished.
For a production exchange, route to ifc-core-version-evolution and target a
released version.
Pattern : Distinguish IFCx (format) from IFC5 (standard)
IFC5 and IFCx are developed together but name different things. ALWAYS keep them
separate :
"IFC5" is the standard generation : composition, layering, inheritance
semantics, modular domain schemas. Architecture detail lives in
ifc-core-ifc5-architecture.
"IFCx" is the data format : the .ifcx JSON files and the ifcx.dev
schema host.
NEVER write "the IFC5 file" when you mean an .ifcx file, and NEVER write "the
IFCx standard" when you mean the IFC5 generation. When a statement is about
bytes on disk, it is IFCx; when it is about the model concept, it is IFC5.
Pattern : Read the node-and-attribute composition graph
An .ifcx file is a JSON document of data objects. ALWAYS read it as a
composition graph, not as a flat instance list :
Data objects are delimited by { and } and "hold the data."
An object can reference children and can inherit from another object.
Together these construct a tree.
Objects can be shared across multiple files, or reused within one file.
The consuming application composes the scene from the available data : it
resolves the child and inheritance references itself.
ALWAYS resolve the composition before interpreting a final value : a property
may be defined on an inherited object or contributed by a layer, not stated
inline. NEVER assume a single object carries the fully resolved state.
This composition / layering model is the IFC5 mechanic; for the multi-author
layering detail (the non-destructive add-firerating example), see
ifc-core-ifc5-architecture.
Pattern : Expect no STEP syntax in an .ifcx file
ALWAYS parse an .ifcx file as JSON. The IFC5 examples state : "There will not
be STEP syntax in IFC 5."
An .ifcx file has NO ISO-10303-21; wrapper, NO HEADER section, NO
FILE_DESCRIPTION / FILE_NAME / FILE_SCHEMA, and NO #id=ENTITY(...)
instance lines.
NEVER apply STEP Physical File parsing logic to an .ifcx file.
If an IFC5 example contains an originalStepInstance field, that field exists
ONLY to show the relation to the original .ifc SPFF file in the example set.
It is an example artefact, NOT a structural requirement of IFCx. NEVER treat
originalStepInstance as a mandatory IFCx field.
In the IFC5 example set, .ifcx JSON files are paired with .ifc STEP files in
IFC4 / IFC4.3 format purely for demonstration.
Pattern : Resolve the IFCx schema from the @org/path namespace
The IFCx JSON Schema is published at
https://ifcx.dev/@standards.buildingsmart.org/ifc/.
The @organization/path form is a package-registry / linked-data style
addressing scheme : the @standards.buildingsmart.org segment identifies
the publishing organisation, and the path segment identifies the schema.
ifcx.dev is published via GitHub Pages from the
https://github.com/buildingSMART/IFCx.dev repository.
The schema is authored in TypeSpec (.tsp source files); the JSON Schema
served at ifcx.dev is generated from that TypeSpec source. TypeSpec
replaces EXPRESS as the schema definition language for this generation.
ALWAYS treat the ifcx.dev schema as a development artefact : it is generated
from evolving TypeSpec source and changes with the IFC5-development work.
Pattern : Label graph-data and schema.org claims carefully
ifcx.dev carries the tagline "The schema.org for IFC", and the IFCx mechanics
(named objects with attributes, inheritance, composition, cross-file sharing,
external references to bSDD) are consistent with a web-native, graph-shaped data
direction.
ALWAYS describe what is verified : JSON encoding, node-and-attribute
objects, composition, inheritance, external references.
NEVER assert that IFCx is RDF or uses JSON-LD : the specific
linked-data serialisation is not verified against an official source.
NEVER assert a USD (Universal Scene Description) dependency : the composition
mechanic is verified, a USD lineage is not. State the mechanic, not the
lineage.
When asked about the "schema.org for IFC" tagline, ALWAYS present it as a stated
direction, NEVER as an implemented, finalised technology choice.
Reference Links
references/methods.md : the IFCx fact sheet : verified properties of the
.ifcx format, the schema-publication namespace, the TypeSpec toolchain, the
IFC5-versus-IFCx split, and the verified-versus-unverified boundary.
references/examples.md : worked scenarios : recognising an .ifcx file,
reading the composition graph, the IFC5-versus-IFCx wording test, deciding
whether IFCx applies.
references/anti-patterns.md : the IFCx mistakes this skill prevents, each
with the reason it fails.
