Sketch of the two main entities

Author: jdvorak001

README.md

@@ -1,17 +1,21 @@
-# CERIF XXX Module
-Basic domain description of the module
+# CERIF Instruments Module
+This module contains classes and properties for modeling scientific instruments.
 
 ## Status
-(2026-03-05) Experimental.
+(2026-03-12) Work in progress.
 
 ## Overview
-
+Instruments – or more specifically [Instrument Instances](./entities/Instrument_Instance.md) – are [Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md).
+Instrument instances can have information about their [models](./entities/Instrument_Model.md): several instrument instances can share a single model information record.
 
 ## Listings
 
 ### Entities
-The XXX Module consists of the following entities:
-* [XXX entity](./entities/XXX.md) 
+The Instruments Module consists of the following entities:
+* [Resource](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Resource.md) (imported from [the CERIF Core](https://github.com/EuroCRIS/CERIF-Core))
+  * [Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md) (imported from [the CERIF Core](https://github.com/EuroCRIS/CERIF-Core))
+    * [Instrument Instance](./entities/Instrument_Instance.md) 
+    * [Instrument Model](./entities/Instrument_Model.md)
 
 ### Data Types
 * [XXX data type](./datatypes/XXX.md)

entities/Instrument_Instance.md

@@ -0,0 +1,31 @@
+# Instrument_Instance
+
+## Definition
+The scope of the entity and its meaning.<sup>[1](#fn1)</sup>
+
+## Usage notes
+An additional description to communicate the purpose of the entity.
+
+## Specialization of
+[Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md)
+
+## Attributes
+None besides those of [Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md).
+
+## Relationships
+Besides those of [Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md):
+
+<a name="rel__is-instance-of">is-instance-of</a> / [has-instance](../entities/Instrument_Model.md#user-content-rel__has-instance) : An Instrument_Instance is an instance of a particular [Instrument_Models](../entities/Instrument_Model.md).
+
+## Constraints
+Any constraints a subclass makes on its superclasses.
+
+## Illustrative Diagram
+A UML diagram showing this entity in its context if one is available.
+
+---
+## Matches
+1. Close match of [whatever](url)
+
+## References
+<a name="fn1">\[1\]</a> Source: ...

entities/Instrument_Model.md

@@ -0,0 +1,31 @@
+# Instrument_Model
+
+## Definition
+The scope of the entity and its meaning.<sup>[1](#fn1)</sup>
+
+## Usage notes
+An additional description to communicate the purpose of the entity.
+
+## Specialization of
+[Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md)
+
+## Attributes
+None besides those of [Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md).
+
+## Relationships
+Besides those of [Infrastructure](https://github.com/EuroCRIS/CERIF-Core/blob/main/entities/Infrastructure.md):
+
+<a name="rel__has-instance">has-instance</a> / [is-instance-of](../entities/Instrument_Instance.md#user-content-rel__is-instance-of) : An Instrument_Model can have any number of [Instrument_Instances](../entities/Instrument_Instance.md).
+
+## Constraints
+Any constraints a subclass makes on its superclasses.
+
+## Illustrative Diagram
+A UML diagram showing this entity in its context if one is available.
+
+---
+## Matches
+1. Close match of [whatever](url)
+
+## References
+<a name="fn1">\[1\]</a> Source: ...