docs: add initial model-api doc

Author: nkoester

docs/global/modules/core/images/model-api.api.png

@@ -0,0 +1,45 @@
+= Model API
+:navtitle: `model-api`
+
+
+:tip-caption: 🔗 Quick Links
+[TIP]
+--
+https://api.modelix.org/2.3.0/model-api/index.html[API doc^] | https://github.com/modelix/modelix.core[Repository^] | Artifacts: https://artifacts.itemis.cloud/service/rest/repository/browse/maven-mps/org/modelix/model-api/[Nexus^] https://github.com/modelix/modelix.core/packages/1834768[GitHub Packages^]
+--
+
+== Overview
+
+The *Model API* (`model-api`) is a Kotlin component which provides a metamodel independent model API.
+This API is the shared basis and used across all modelix components.
+
+
+The `model-api` provides three distinct parts
+
+1. `org.modelix.model.api`: The untyped API to provide model access
+2. `org.modelix.model.data`: Data classes for (meta-)model serialization
+3. `org.modelix.model.area`: Model grouping and transactional access
+
+
+=== `org.modelix.model.api`
+
+The following diagram provides a meta-model of the `model-api`
+
+image::model-api.api.png[]
+
+Using the `model-api` an **untyped** access to model content is always possible.
+In case you want to use domain-specific model access, the xref:core:reference/component-model-api-gen.adoc[model-api-gen] provides a generator which generates a typed model API specializes the API provided by the `model-api`.
+
+
+=== `org.modelix.model.data`
+
+Additionally, the `model-api` provides serializable data classes to represent a meta-model.
+The following diagrams show a class diagram of the data classes for the model and meta-model.
+
+image::model-api.data.model.png[]
+
+image::model-api.data.metamodel.png[]
+
+
+//=== === `org.modelix.model.area`
+//TODO

docs/global/modules/core/images/model-api.data.metamodel.png

@@ -1,3 +1,4 @@
+* xref:core:reference/component-model-api.adoc[]
 * xref:core:reference/component-model-server.adoc[]
 * xref:core:reference/component-metamodel-export.adoc[]
 * xref:core:reference/component-model-api-gen.adoc[]