Overview

Introduction

The serialization format based on Web Template (WT) is a JSON representation of openEHR data instances that uses simplified field identifiers instead of canonical archetype paths. The format was originally developed by Better d.o.o. and later adopted and extended by the EHRbase open-source community. In this specification we refer to these as Simplified Formats.

Although historically different names have been used (e.g. Web Template serialization and the former “Simplified Data Template” term), in the context of this document they represent the same idea.

Prior to Release 1.1.0, the openEHR specification used the name "Simplified Data Template (SDT) specification". This has been superseded by the current "Simplified Formats specification".

The Simplified Formats have two structural variants:

  • Flat - colloquially known as the "flat format"

  • Structured - colloquially known as the "structured format"

Key characteristics include:

  • Human-readable field identifiers: Uses friendly names like temperature|magnitude instead of archetype paths like /content[openEHR-EHR-OBSERVATION.body_temperature.v1]/data[at0002]/events[at0003]/data[at0001]/items[at0004]/value|magnitude

  • JSON-based: a form of JSON representation of openEHR data

  • Context data separation: Clinical data separated from context metadata (usually under a ctx/ prefix)

  • Template-specific: Field identifiers are specific to each operational template

  • Element-value simplification: In Flat format, there is no distinction between an ELEMENT and its value

Scope

This specification covers:

  • The structure and syntax of the Flat and Structured formats

  • Field identifier generation rules

  • Context data representation

  • RM attributes handling (underscore-prefixed attributes)

  • Mapping between the Simplified Formats and canonical openEHR RM

  • Serialization and deserialization requirements

This specification does not cover:

  • Web Template itself as a resource

  • Archetype technology and associated constraints

  • Storage or indexing strategies

MIME Types

Two MIME types are defined for the Simplified Formats serialization:

  • Flat format: application/openehr.wt.flat+json

  • Structured format: application/openehr.wt.structured+json

Relationship to Other Specifications

The format relates to other openEHR specifications as follows:

  • openEHR Reference Model: serialized instances represent valid RM structures (e.g. COMPOSITION)

  • Operational Templates (OPT): field identifiers are generated from OPT definitions

  • AQL: serialized instances include AQL paths to enable query integration

  • Canonical JSON/XML: the Simplified Formats are an alternative serialization, convertible to canonical formats