[WIP] Documentation for systems

docu/RosSystemModelDescription.md

@@ -1 +1,33 @@
-## TBD
+# HOW TO DESCRIBE ROS SYSTEMS USING THE LANGUAGE
+
+In our case we consider a system to be a combination of nodes running at the same time. Basically we use the typical component-based system concept, where each ROS node could be considered a component. Therefore the .rossystem file allows to describe a series of nodes and the connections that are created between them using topics, services or actions. It also allows to give values to the parameters.
+
+The structure of the system description is as shown in the following diagram:
+
+![alt text](images/system_class_diagram.jpg)
+
+
+The format of a system is as follows:
+```
+my_awesome_system:
+  processes:
+    process1:
+      nodes: [ node1 , node2 ]
+      threads: 2
+  nodes:
+    node1:
+      from: "my_awesome_pkg.awesome_node_provider" #From a .ros2 file
+      interfaces:
+        - awesome_pub: pub-> "awesome::awesome_pub" # From a .ros2 file
+      parameters:
+       - description: "awesome::awesome_param"
+         value: "Label"
+    node2:
+      from: "my_awesome_pkg.awesome_node_consumer" #From a .ros2 file
+      interfaces:
+        - awesome_sub: sub-> "awesome::awesome_sub"
+  connections:
+    -[awesome_pub, awesome_sub] # From line 10 and 17
+```
+
+