# Ifc Core Ifcx Architecture > 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. - Skill: `impertio-studio/ifc-core-ifcx-architecture` (Agent Skill, multi-file: 4 files) - Install (CLI): `npx skillmds@latest add impertio-studio/ifc-core-ifcx-architecture` - Raw SKILL.md: https://api.skillmd.com/api/skills/impertio-studio/ifc-core-ifcx-architecture/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Productivity - License: MIT - Author: Impertio-Studio (https://skillmd.com/u/impertio-studio) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/impertio-studio/ifc-core-ifcx-architecture --- # 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 *"preliminary and will be updated."* Every fact in this skill is a moving target. NEVER teach IFCx as a stable target and NEVER recommend it for a production exchange. 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. ### Official sources - IFC5 development repository : https://github.com/buildingSMART/IFC5-development - IFC5 examples FAQ : https://raw.githubusercontent.com/buildingSMART/IFC5-development/main/Examples_FAQ.md - IFC5 schema readme : https://raw.githubusercontent.com/buildingSMART/IFC5-development/main/schema/readme.md - IFCx schema host : https://ifcx.dev/ - IFCx.dev repository : https://github.com/buildingSMART/IFCx.dev ### Related skills - `ifc-core-ifc5-architecture` : the IFC5 standard generation (composition, layering, modular domain schemas, TypeSpec). - `ifc-core-version-evolution` : how IFCx relates to the released IFC versions. - `ifc-impl-library-selection` : tooling that reads IFCx, including emerging Rust tooling.