Wikidata is a great platform for collecting information, and the high quality work of many authors yields very reliable information.

Still, a challenge for users of Wikidata is that there is no way to see whether *all* data on a certain topic is in Wikidata.

For instance, it is easy to see that Malia and Sasha are children of Obama, but there is no way to specify that these are all his children.

More generally, Wikidata stores many facts, but it stores no information about which topic it contains all facts.

Today we are happy to share with you a prototype that allows to add and manage such completeness information,

and would be happy to get your feedback on how useful you consider this tool, or where you see space for improvements.

With our prototype, called COOL-WD (Completeness Tool for Wikidata), one can:

1. See completeness statements for Wikidata facts

2. Add, remove, aggregate and filter completeness statements

3. See how completeness statements allow conclusions about the completeness of SPARQL queries over Wikidata.

COOL-WD is available at http://cool-wd.inf.unibz.it/ and a 3-min demo video can be found at http://cool-wd.inf.unibz.it/coolwd-hd.mp4

It employs various libraries, most importantly GWT, Apache Jena, SQLite and the Wikidata API.

The formal background and description of the tool including an indexing technique for completeness statements

have been accepted as a research paper at ICWE 2016 (http://icwe2016.inf.usi.ch/) available to download at: http://bit.ly/1VOsRCH

Below are some naive ideas of how completeness could be useful to users:

> Use Case 1: Rido is a geographer who would like to contribute to Wikidata about the administrative divisions of regions.

He cares so much about data quality, especially data completeness, and is collaborating with Simon, another geographer.

However, when completing data on Wikidata, there is currently no way to mark which data is complete.

Rido and Simon must make these notes about completeness manually in, say, a Google Doc.

Worse still, the effort from Rido and Simon to complete data could not be appreciated by Wikidata users since to the users’ eyes,

there is no difference between complete data and incomplete data on Wikidata.

Demo: Wikidata is complete for all administrative divisions of Saxony (http://cool-wd.inf.unibz.it/?p=Q1202)

> Use Case 2: Jen is a developer of a moviegoer application. She usually integrates data between multiple sources including Wikidata.

If some movies on Wikidata have completeness statements, she might optimize her application

to not search in other data sources for those movies.

Demo: So, when her app is asking on COOL-WD at http://cool-wd.inf.unibz.it/?p=query

for cast and screenwriters of the movie Before Sunset (http://cool-wd.inf.unibz.it/?p=Q652186):

SELECT * WHERE { wd:Q652186 wdt:P161 ?c . wd:Q652186 wdt:P58 ?s }

Her app gets not only query answers but also the completeness information of her query.

We are looking forward to your feedback!

Best,

Fariz, Simon, Rido, and Werner

Free University of Bozen-Bolzano, Italy