cds export (#2275)

Co-authored-by: René Jeglinsky <rene.jeglinsky@sap.com>

Author: stewsk

tools/assets/cds-export.png

@@ -468,6 +468,70 @@ To customize the diagram layout, use these settings in the _Cds > Preview_ categ
 - [Diagram: Namespaces](vscode://settings/cds.preview.diagram.namespaces)
 - [Diagram: Queries](vscode://settings/cds.preview.diagram.queries)
 
+
+## cds export <Beta />
+
+With `cds export` you create an API client package to be used
+for data exchange via CAP-level Service integration ("Calesi").
+
+Define data provider services in your CDS model that serve as an interface to your data, placing each data provider service in a separate file.
+
+For the [xflights](https://github.com/capire/xflights) sample app,
+an API that provides information about flights, airports, and airlines
+could look like this:
+
+::: code-group
+
+```cds [srv/data-service.cds]
+using { sap.capire.flights as my } from '../db/schema';
+
+@data.product @hcql @rest @odata 
+service sap.capire.flights.data {
+  @readonly entity Flights as projection on my.Flights;
+  @readonly entity Airlines as projection on my.Airlines;
+  @readonly entity Airports as projection on my.Airports;
+}
+```
+
+:::
+
+Then create an API client package for this service:
+
+```sh
+cds export srv/data-service.cds
+```
+
+The command generates the API client package into a new folder _apis/data-service_.
+
+![The screenshot is described in the accompanying text.](assets/cds-export.png) {style="filter: drop-shadow(0 2px 5px rgba(0,0,0,.40));"}
+
+The `service.csn` contains only the interface defined in the service, removing the query part of the entities and all the underlying model.
+In addition, there are i18n bundles with the localized metadata relevant
+for the interface, and a _data_ folder with test data
+that exactly matches the structure of the entities in the API.
+
+`cds export` also adds a _package.json_. The package name combines the application name (from the main _package.json_) with the file name of the data service. In our example, this results in `@capire/xflights-data-service`.
+You can change this name as appropriate.
+
+You can then publish the generated package, for example, via `npm publish`.
+
+To consume the API in another CAP application:
+1. Import the API package with `npm add`
+2. Define consumption views on the imported entities
+3. Use them in your model as if they were local entities
+4. Add custom code to access the data in the provider app via any of the offered protocols
+
+Have a look at the [xtravels](https://github.com/capire/xtravels) sample app for an
+example of using an API client package.
+
+:::warning Do not use EDMX to exchange API information
+Prefer exporting and importing API packages via `cds export` and `npm add`.
+**Do not use** EDMX (or OpenAPI) as intermediate format for exchanging API information
+between CAP applications, as you might loose information.
+:::
+
+
+
 ## cds watch
 
 Use `cds watch` to watch for changed files, restarting your Node.js server.