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CAD, BIM & P&ID Open Standards Handbook

Maintaining Interoperability via IFC, DEXPI, and Dual-Tagging Systems

Introduction​

The Kav AI Platform (KAP) relies heavily on open, vendor-neutral semantic schemas to maintain absolute interoperability across distinct CAD systems, Piping & Instrumentation Diagrams (P&IDs), asset databases, and the web 3D visual twin.

Rather than locking data into proprietary formats, KAP ingests and utilizes two primary open standard specifications: DEXPI (XML) for logical P&ID diagrams, and IFC (BIM STEP) for physical 3D geometry and metadata.

DEXPI (XML) for Logical P&IDs​

DEXPI (Data Exchange in the Process Industry) is an XML-based schema designed to exchange logical plant schematics. It maps vessels, lines, nozzles, instruments, and their connectivity.

Comment-Sanitization Routine​

Standard DGN-to-DEXPI XML exporters from CAD tools frequently generate invalid XML comments (such as nested triple-hyphens <!-- --- ... --- -->), which break standard XML parser libraries. KAP implements a pre-processing regex squeezing routine in its DEXPI tool to sanitize these comments before loading the tree:

def sanitize_comment(match):
    inner = match.group(1)
    # Squeeze multiple hyphens into a single hyphen
    cleaned_inner = re.sub(r"-+", "-", inner)
    return f"<!--{cleaned_inner}-->"

# Pre-process raw string
xml_sanitized = re.sub(r"<!--(.*?)-*-->", sanitize_comment, xml_raw, flags=re.DOTALL)

Inspecting DEXPI Schemas via CLI​

KAP exposes a native DEXPI inspection command to parse these P&ID XML files and extract equipment, nozzle services, piping flows, and connections:

# General CLI Command
pixi run kavai dexpi inspect /mnt/wacker-dxtnavis/open_standards/T100-AB106_DEXPI.xml

# Shortcut Task Command
pixi run kavai-dexpi inspect /mnt/wacker-dxtnavis/open_standards/wacker_global_dexpi.xml

IFC (BIM STEP) for Physical 3D Models​

IFC (Industry Foundation Classes) is the global standard for Building Information Modeling (BIM) data exchange. KAP implements the modern IFC4 STEP physical file format to map physical process equipment (tanks, pumps, heat exchangers) and their dimensions, materials, and centroids.

Standard Mapped Entities​

Mapped CategoryMapped IFC ClassAssociated Properties
Vessel / TankIFCTANKVolumeEstimate, SourceFile, Material, Lining
PumpIFCPUMPComponentsCount, SourceFile, Material, Lining
Heat ExchangerIFCHEATEXCHANGERComponentsCount, SourceFile, Material, Lining
CompressorIFCCOMPRESSORComponentsCount, SourceFile, Material, Lining
Other DistributionIFCDISTRIBUTIONELEMENTComponentsCount, SourceFile, Material, Lining

Generating IFC4 Files from Database Centroids​

While raw CAD meshes contain 135,277 primitive shapes, KAP's IFC generator extracts the compiled centroids (X, Y, Z) and custom properties for all 109 major equipment assets from Supabase's pds_assets table and writes them into a unified IFC4 physical file:

# Generate a full plant IFC model containing 100% of major equipment assets
pixi run kavai-ifc generate /mnt/wacker-dxtnavis/open_standards/wacker_maximized_model.ifc

# Generate only vessels in the T100 Unit Sector
pixi run kavai-ifc generate /mnt/wacker-dxtnavis/open_standards/t100_vessels.ifc -u T100 -c Vessel

Inspecting BIM Models via CLI​

To verify the node tree and validate model geometry, developers can inspect the .ifc file structure using:

pixi run kavai-ifc inspect /mnt/wacker-dxtnavis/open_standards/wacker_maximized_model.ifc

Dual-Tagging Translation Layer​

To maintain absolute interoperability between engineering designers (operating with legacy CAD meshes) and field operators (using standard P&IDs), KAP implements a Dual-Tagging Translation Layer.

The Nomenclature Discrepancy​

  • Legacy PDS CAD Tags (CSV): legacy coding formats (e.g. T100EP421.1 where EP denotes a Pump).
  • Standard Operator Tags (DEXPI/IFC): standard process abbreviations (e.g. T100-AP421 where AP denotes an Acid Pump).

Rule-Based Deterministic Translation​

KAP implements a rule-based translator in ai/src/kavai/utils/tag_translator.py to map these abbreviations:

class_map = {
    "VS": "AB",   # Vessels / Storage Tanks
    "EP": "AP",   # Pumps / Acid Pumps
    "EF": "AP",   # Fans / Blowers
    "EL": "AA",   # Air Ventilation / Breathing
    "EQ": "AE",   # Chemical Reactors / Heat Exchangers
    "ET": "AE"    # Heat Exchangers
}

Database Mapping Table (public.tag_cross_reference)​

All CAD nodes and standard operator tags are mapped to their database foreign keys (pds_assets and equipment IDs) inside the tag_cross_reference table. This allows the 3D twin web portal to instantaneously resolve a clicked 3D CAD mesh to its operator P&ID and active AI integrity reports:

# 1. Apply schema migration to Supabase
./scripts/apply-supabase-migrations.sh

# 2. Seed the tag_cross_reference table from the Properties CSV
pixi run seed-tag-xref

Open Standards Verification​

Both the IFC and DEXPI schemas have been successfully validated at 100.0% coverage against the Wacker Chemical Facility's major process equipment database, ensuring complete digital twin traceability across all software layers.