"External formatter URI" is a predefined property provided by Semantic MediaWiki to specify an external resource with a placeholder. The URI is expected to contain a placeholder that will be adjusted with an external identifier value to form a valid resource reference. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.
The database is currently locked to new entries and other modifications, probably for routine database maintenance, after which it will be back to normal.
The system administrator who locked it offered this explanation: The wiki is under maintenance. Das Wiki wird derzeit gewartet.
