The verb "allows" can never take an infinitive as its direct object.
adu creates a database containing disk usage statistics of a given
-directory. It allows to query that database to quickly retrieve usage
-patterns of subdirectories containing files owned by a given user.
+directory. This database can be queried to quickly retrieve, for
+example, the number and the size of all files in a subdirectory owned
+by a given user.
Four different output modes are available: global list, global summary,
user list and user summary. The format of the output may be customized