Currently, any failed request to the source Wiki will result in the target Wikibase entering an error state. This behavior is the case even in non-critical situations (e.g. displaying property labels on the item page) and in situations where an edit is attempted and fails because accessing the source wiki is impossible.

Path 1 (Loading entity page - displaying federated property not possible): should display a message indicating the data is unavailable due to the failed call to source Wiki

Path 2 (while editing - looking up property data types fails): should display an error message when save is selected that indicates save failed due to failed call to source Wiki

Initial Estimations

• For a version that displays a partial entity page, with an error that explains that statements are unavailable due to the lack of connection to the source wiki: enormous (~21 SPs)
• A simpler version, where just the entity title and perhaps label in the current language is displayed, in addition to the error message (just an error page, avoids page rendering complexity and fun): 8 SPs
• While editing, displaying an error on save: 5 SPs

Technical Notes
The possibilities for the distinction between critical and non-critical requests is limited by the underlying technical solution. For simplicity's sake we initially made separate requests to fetch the properties' data types, and labels and descriptions, the latter arguably being the less critical. Now we are making efforts to minimize the number of requests to the source wiki so that these requests are combined into a single "prefetching" step. This means that handling problems on the request level would no longer be possible, but there are other means to ensure graceful degradation.