Add cacheDuration of 6 hours to export preview aggregate

See ukf/ukf-meta#112.

mdx/uk/README.md

@@ -28,9 +28,10 @@ before being included in the `export` version consumed by interfederation partne
 
 ### Export Preview Aggregate vs. Export Aggregate
 
-Status (2017-12-05):
+Status (2020-04-22):
 
-* These aggregates are currently identical.
+* The `export-preview` aggregate includes a `cacheDuration` attribute with a
+  value of six hours.
 
 ## Production Maturity Pipeline
 
@@ -59,12 +60,16 @@ when it appeared in the fallback aggregate, which would be too late to take corr
 
 ### Test Aggregate vs. Production Aggregate
 
-Status (2017-12-05):
+Status (2020-04-22):
 
 * The `test` aggregate does not include the `<UKFederationMember>` label (`ukf-meta#34`).
 
 * The `test` aggregate does not include the entity-level copy of the scopes for an
-  identity provider (`ukf-meta#49`) 
+  identity provider (`ukf-meta#49`).
+
+* The `test` aggregate includes a `cacheDuration` attribute with a
+  value of six hours.
+
 
 ### `cds-all` Aggregate vs. Production Aggregate
 

mdx/uk/generate.xml

@@ -854,6 +854,7 @@
                 <ref bean="assembleAggregate"/>
                 <ref bean="stripEntityScopes"/>
                 <ref bean="stripEmptyExtensions"/>
+                <bean parent="mda.SetCacheDurationStage" p:cacheDuration="PT6H"/>
                 <ref bean="uk_finaliseExport"/>
 
                 <bean id="uk_normaliseExportPreview" parent="mda.XSLTransformationStage"