add note with link to rml-io-registry

spec/docs/config.js

@@ -62,12 +62,16 @@ var respecConfig = {
   license: "w3c-software-doc",
   localBiblio: {
     RML: {
-        title: "RDF Mapping Language (RML)",
-        href: "https://rml.io/specs/rml/",
-        status: "Unofficial Draft",
-        publisher: "",
-        date: "",
-      },
+      title: "RDF Mapping Language (RML)",
+      href: "https://rml.io/specs/rml/",
+      status: "Unofficial Draft",
+      publisher: "",
+      date: "",
+    },
+    // TODO: update once RML-IO-Registry is published
+    "RML-IO-Registry": {
+      title: "RML-IO Registry",
+    }
   },
   otherLinks: [
     {

spec/docs/logicalSource.md

@@ -9,3 +9,7 @@ A [=logical source=] (`rml:LogicalSource`) MUST have:
 A <dfn data-lt="iteration">logical iteration</dfn> is an item in the sequence produced by the [=logical source=], on which [=expressions=] can be evaluated.
 
 A <dfn>data source</dfn> is an abstract concept that represents a source of data that can be accessed via a [=logical source=]. A [=data source=] can be a file, a database, a web service, or any other source of data.
+
+<aside class="note">
+There can be many different types of [=reference formulation=]. The known types, and the details of how a reference formulation is handled and implemented for each data format, are specified in [[RML-IO-Registry]].
+</aside>