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Core Schema Notation Interoperability Specification

STATUS: v1.0 BETA, stable release planned for 2025-02.

Summary​

Core schema notation interoperability (short: CSN Interop) is a powerful and flexible format used to describe entity and service models in the wider SAP and BTP ecosystem. CSN files are JSON-based and provide comprehensive metadata about entities and their structure, relationships, and other aspects of the model.

A CSN Interop file can look like this (extracted from ./examples/airline.json):

{
  "csnInteropEffective": "1.0",
  "$version": "2.0",
  "meta": {
    "document": {
      "version": "1.2.3",
      "doc": "This is a minimal CSN example document."
    }
  },
  "definitions": {
    "AirlineService": {
      "kind": "service",
      "doc": "This is describing the service that exposes the CDS entities through an API."
    },
    "AirlineService.Airline": {
      "kind": "entity",
      "doc": "Human readable description of the entity, in **markdown**.",
      "@EndUserText.label": "Airline",
      "@ObjectModel.modelingPattern": {
        "#": "ANALYTICAL_DIMENSION"
      },
      "elements": {
        "AirlineID": {
          "doc": "Human readable description of the element, in **markdown**.",
          "key": true,
          "type": "cds.UUID"
} } } } }

To get a first overview, read the informal Primer. The actual specification is described mostly in the formal interface documentation, also described in JSON Schema.

What is CSN Interop Effective?​

For now, we describe the CSN Interoperability Effective exchange format.

CSN​

Core Schema Notation (CSN, pronounced as "Season") is a JSON based serialization format for Core Data Services (CDS) models that can be used to describe domain, data and service models (and more) on a conceptual level, with rich semantics and annotations.

The Cloud Application Programming Model (CAP) is one platform to create CDS models and it is the first to productize CSN and provide a good documentation on CSN.

Interoperability​

CSN is well-suited as data format to exchange information about data models (a.k.a. metadata integration) between different systems or even technology stacks such as CAP and ABAP. Thus, it is a key ingredient to support data integration between such systems and technologies.

As a consequence, there is a variety of syntax in CSN that can be specific to the source technology that might be incompatible with some consuming technology stacks. To mitigate such incompatibilities, a certain set of well-defined manipulations of the CSN syntax (so-called feature dimensions) can be used to create a more compatible flavor, i.e. a more interoperable description of CDS models.

This specification aims to specify an interoperable flavor of CSN with the following goals in mind:

  • Overall ecosystem agreement on supported features and annotations.
  • Importing / exporting data and API model metadata across different tech stacks and products.
  • Simplify the format for the consumers, so it is explicit and easy to parse / understand (see effective).

This includes:

  • The core specification, which is a subset of regular CSN.
  • Interoperable annotation vocabularies, only describe what is relevant for the wider ecosystem.
  • Defined mappings, how CSN maps to other data type systems and can be serialized in APIs and data formats.

Effective​

Right now, this spec describes only the effective feature dimension.

Effective means that the format is "denormalized", and optimized towards easy consumption by machines, with the tradeoff of more verbosity and duplicated information.

Information reuse concepts like aspects have already been resolved, applied and cleaned up. What the consumer gets, is a document that does not require further post-processing / logic to be interpreted correctly. This is a tradeoff, prioritizing easy consumption over convenient creation.

Intended Audience​

  • Developers and Architects that either need to export or import CSN across different technology stacks.
  • End consumers that need to understand CSN Interop as a metadata description format for resources they want to integrate with (e.g. APIs and Events).

Contact​

CONTACT: Create a GitHub PR or issue.

CONTRIBUTORS: Andreas Balzar, Michael Belenki, Timo Bergmann, Daniel Buchmann, Timm Falter, Daniel Hutzel, Steffen Weinstock, Simon Heimler, Sandra Bracholdt, Raluca Gruber, ...