# Developer Guide

## Document Information

### Copyright Notice

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This document is released under the [Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license](https://creativecommons.org/licenses/by-sa/4.0/).

### Status

This document is in draft.

### Author / contact

[Joris Scharp](mailto:joris@headease.nl)\
[Headease B.V.](https://www.headease.nl/)

## Important differences with Koppeltaal 1.3.x

| Concept                | **KT 1.3.x**                                | KT 2.0                   |
| ---------------------- | ------------------------------------------- | ------------------------ |
| **FHIR Exchange**      | Messaging                                   | RESTful API              |
| **Content Validation** | Separate service                            | Built-in                 |
| **Authorisation**      | None - application has access to everything | On resource & CRUD-level |

### FHIR Exchange

By using the (FHIR) RESTful API exchange there is a single source of truth. Koppeltaal 1.x acted as a message broker, giving each participant the responsibility to keep all data up-to-date.

Another big advantage is that Koppeltaal 2.0 works with small messages. So no self-contained bundles. This saves a lot of data being transferred over the line and the chance of 409 Conflicts are considerably reduced.

### Content Validation

Previously, a separate service could be used to check whether the content of a `Bundle` is valid. However, this validation was not enforced by the Koppeltaal server.

Koppeltaal 2.0 uses [profiles](https://simplifier.net/Koppeltaalv2.0/~resources?fhirVersion=R4). A profile indicates exactly what the rules are per [Resource](https://www.hl7.org/fhir/r4/resourcelist.html). The Koppeltaal server can enforce profiles by validating that the Resources adhere to the profile.

### **Authorisation**

Applications connect to the Koppeltaal server. Within "Domeinbeheer" (Domain Management), roles are assigned to the applications. A role can contain multiple CRUD permissions per Resource. With Koppeltaal 2.0, you are only allowed to work with resources to which you are entitled. With Koppeltaal 1.x, applications can see everything that they are subscribed to within a Domain.

{% hint style="warning" %}
Note: Resources are managed at application level Koppeltaal 2.0.

The golden rule is that the application **itself** determines which resources are accessible at user level within the application.
{% endhint %}

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