imported-from relations for usnistgov#1023.

Co-authored-by: David Waltermire <[email protected]>

README_validations.md

@@ -26,7 +26,7 @@ For OSCAL XML, this schema syntax is [XML Schema Definition (XSD)](https://www.w
 
 Each tool will have its own way to provide for validation. Bindings or configurations to link documents to schemas can be maintained either inside or outside the documents themselves; many tools offer several ways to do this.
 
-Some tools support self-contained validation functionality without full-fledged application frameworks or development environments, with tools like [`xmllint`](http://xmlsoft.org/xmllint.html) offering command-line interfaces. Similarly, you can use the [`ajv-cli`](https://github.com/ajv-validator/ajv-cli) for JSON.
+Some tools support self-contained validation functionality without full-fledged application frameworks or development environments, with tools like [`xmllint`](https://gitlab.gnome.org/GNOME/libxml2/) offering command-line interfaces. Similarly, you can use the [`ajv-cli`](https://github.com/ajv-validator/ajv-cli) for JSON.
 
 ## What does success look like?
 

src/metaschema/oscal_implementation-common_metaschema.xml

@@ -109,6 +109,7 @@
                         <!-- ========================================================================================================== -->
             &allowed-values-component_component_link-rel;
                         <enum value="uses-network">This component uses the network provided by the identified network component.</enum>
+                        <enum value="imported-from">The hyperlink identifies a URI pointing to the <code>component</code> in a <code>component-definition</code> that originally defined the <code>component</code>.</enum>
                   </allowed-values>
 
                   <allowed-values target="responsible-role/@role-id" allow-other="yes">

src/metaschema/oscal_ssp_metaschema.xml

@@ -1020,6 +1020,10 @@
       <field ref="remarks" in-xml="WITH_WRAPPER"/>
     </model>
     <constraint>
+      <allowed-values target="link/@rel" allow-other="yes">
+        <!-- TODO: More work needs to be done around link enforcement constraints and requires Metaschema work on recurse-depth-first() recursive index searching. -->
+        <enum value="imported-from">The hyperlink identifies a URI pointing to the <code>component</code> in a <code>component-definition</code> that originally defined the <code>component</code>.</enum>
+      </allowed-values>
       <allowed-values target=".//responsible-role/@role-id" allow-other="yes">
             &allowed-values-responsible-roles-operations;
             &allowed-values-responsible-roles-component-production;

xml/README.md

@@ -36,15 +36,15 @@ XML Schema based on the [XML Schema Definition Language (XSD) 1.1](https://www.w
 
 ## Validating OSCAL XML Content
 
-The OSCAL project uses [xmllint](http://xmlsoft.org/xmllint.html) to perform automated validation of all XML-based OSCAL [content](../content) provided in this repository. *xmllint* is an open source tool that can be [downloaded](http://xmlsoft.org/downloads.html), installed, and run on OSX, Linux, and Windows environments.
+The OSCAL project uses [xmllint](https://gitlab.gnome.org/GNOME/libxml2/-/tree/master) to perform automated validation of all XML-based OSCAL [content](../content) provided in this repository. *xmllint* is an open source tool that can be [downloaded](http://xmlsoft.org/downloads.html), installed, and run on OSX, Linux, and Windows environments.
 
 The following example uses **xmllint** to perform validation of an OSCAL catalog XML file.
 
 ```
 xmllint --noout --schema "oscal_catalog_schema.xsd" "catalog.xml"
 ```
 
-The [online documentation](http://xmlsoft.org/xmllint.html) for *xmllint* provides more information on the commandline arguments.
+The [online documentation](https://gitlab.gnome.org/GNOME/libxml2/) for *xmllint* provides more information on the commandline arguments.
 
 # OSCAL JSON to XML Converters