From b86eb69d63106831602d50ed60005b6b6e069fca Mon Sep 17 00:00:00 2001
From: rakhimov <ol.rakhimov@gmail.com>
Date: Mon, 8 Jan 2018 08:22:20 -0800
Subject: [PATCH] Add specification for the MEF version tag

Models can require certain minimum versions of the MEF
to be processed successfully.
The explicit version specification
helps tools gracefully handle old and new MEF version.

However, the actual format or semantics of MEF version numbers
are not yet specified.
---
 mef/model_organization.rst | 14 ++++++++++++++
 mef/schema/model.rnc       |  1 +
 2 files changed, 15 insertions(+)

diff --git a/mef/model_organization.rst b/mef/model_organization.rst
index 916b4cb..5b4f1ca 100644
--- a/mef/model_organization.rst
+++ b/mef/model_organization.rst
@@ -118,3 +118,17 @@ The Model Exchange Format introduces also eighteen constructs.
     :name: schema_model
     :caption: The RNC schema for the XML representation of a model
     :language: rnc
+
+The Model Exchange Format provides a version tag for the root XML element.
+This optional tag indicates the version of the MEF standard
+required by the model.
+To indicate the version of the model itself,
+one can use the extensible attribute system provided by the MEF.
+
+.. code-block:: xml
+
+    <opsa-mef version="2.0d">  <!-- The MEF standard version to process this file -->
+        <attributes>
+            <attribute name="version" value="1.0"/>  <!-- The model version -->
+        </attributes>
+    </opsa-mef>
diff --git a/mef/schema/model.rnc b/mef/schema/model.rnc
index 20c3a05..18178c9 100644
--- a/mef/schema/model.rnc
+++ b/mef/schema/model.rnc
@@ -1,5 +1,6 @@
 model =
   element opsa-mef {
+    attribute version { xsd:string }?,
     name?,
     label?,
     attributes?,