Release 1.0 metaschema adjustments (usnistgov#1065)

* Many fixes to the constraints in the OSCAL metaschemas to repair broken Metapaths.
* fixing defects in metaschema constraints
* Updating to latest Metaschema toolchain. Removed use of the "require" constraint.
* updating readme with current links

src/metaschema/oscal_control-common_metaschema.xml

@@ -73,6 +73,15 @@
                         <allowed-values target="prop[has-oscal-namespace('http://csrc.nist.gov/ns/oscal')]/@name">
             &allowed-values-control-group-property-name;
                         </allowed-values>
+                        <allowed-values target=".[@name='assessment']/prop/@name" allow-other="yes">
+                                <enum value="method">The assessment method to use. This typically appears on parts with the name "assessment".</enum>
+                        </allowed-values>
+                        <has-cardinality target=".[@name='assessment']/prop[@name='method']" min-occurs="1"/>
+                        <allowed-values target=".[@name='assessment']/prop[@name='method']/@value">
+                                <enum value="INTERVIEW">The process of holding discussions with individuals or groups of individuals within an organization to once again, facilitate assessor understanding, achieve clarification, or obtain evidence.</enum>
+                                <enum value="EXAMINE">The process of reviewing, inspecting, observing, studying, or analyzing one or more assessment objects (i.e., specifications, mechanisms, or activities).</enum>
+                                <enum value="TEST">The process of exercising one or more assessment objects (i.e., activities or mechanisms) under specified conditions to compare actual with expected behavior.</enum>
+                        </allowed-values>
                 </constraint>
                 <remarks>
                         <p>A <code>part</code> provides for logical partitioning of prose, and can be thought of as a grouping structure (e.g., section). A <code>part</code> can have child parts allowing for arbitrary nesting of prose content (e.g., statement hierarchy). A <code>part</code> can contain <code>prop</code> objects that allow for enriching prose text with structured name/value information.</p>

src/metaschema/oscal_profile_metaschema.xml

@@ -123,7 +123,7 @@
                               <formal-name>As-Is Structuring Directive</formal-name>
                               <description>An As-is element indicates that the controls should be structured in resolution as they are structured in their source catalogs. It does not contain any elements or attributes.</description>
                         </define-field>
-                        <define-assembly name="custom">
+                        <define-assembly name="custom" min-occurs="1">
                               <formal-name>Custom grouping</formal-name>
                               <description>A Custom element frames a structure for embedding represented controls in resolution.</description>
                               <model>