is not mixed with the tested application. This separation of concern
:ref:`is a must <howto_science>` for your Modeling and Simulation (M&S)
work. When XML is too limiting, you may describe your platforms using
-directly :ref:`C++ code <platform_cpp>`
+directly :ref:`C++ code <platform_cpp>`.
Any simulated platform must contain **basic elements**, such as
:ref:`pf_tag_host`, :ref:`pf_tag_link`, :ref:`pf_tag_disk`, and similar.
SimGrid makes no assumption about the **routing of your platform**, so you must declare
-explicitly the network path taken between each pair of hosts.
+explicitly the network path taken between each pair of hosts.
This can be done through a flat list of :ref:`pf_tag_route` for each pair of hosts (routes
are symmetrical by default), or you may use the advanced concept of :ref:`networking zone <platform_routing>`
to efficiently express the routing of your platform.
Finally, you may also describe an **experimental scenario**, with qualitative (e.g., bandwidth variations representing
an external load) and qualitative (e.g., representing how some elements fail and restart over time) changes.
-The most efficient way to learn about platform description is to look at the
+Here is a minimalistic platform example, describing a zone in which routing is fully described, containing two hosts and a
+link. You need to explicitly add a :ref:`pf_tag_route` between ``host0`` and ``host1`` for this link to get used during
+communications.
+
+.. code-block:: xml
+
+ <zone id="AS5-4" routing="Full">
+ <host id="host0" speed="1Gf"/>
+ <host id="host1" speed="2Gf"/>
+ <link id="link0" bandwidth="125MBps" latency="100us"/>
+ <route src="host0" dst="host1"><link_ctn id="link0"/></route>
+ </zone>
+
+SimGrid only performs minimalistic verifications about the described platforms, to make things flexible and interesting.
+It enables weird topologies, such as a single link used for all communications in a large platform, or a link used by
+hosts from different zones, or even worse. It is also OK to not describe some routing paths. SimGrid won't complain
+unless your application tries to actually use inexistant paths. In short, it is your responsibility to write proper
+platform files, and SimGrid will not try to be smarter than you!
+
+To learn further about platform descriptions, the easiest is to look at the
:ref:`many examples <platform_examples>` included in the archive and described
in the next section. This documentation also contains some :ref:`hints and
howtos <howto>`, as well as the full :ref:`XML reference guide
