  Time periods are frequently used to specify time in metadata and retrieval.
However, it is not easy to describe and retrieve information about periods,
because the temporal ranges represented by periods are often ambiguous. This is
because these temporal ranges do not have fixed beginning and end points. To
solve this problem, basic logics to describe and process uncertain time
intervals were developed in this study. An uncertain time interval is
represented as a set of time intervals that indicate states when the uncertain
time interval is determined. Based on this concept, a logic to retrieve
uncertain time intervals satisfying a given condition was established, and it
was revealed that retrieval results belong to three states: reliable,
impossible, and possible matches. Additionally, to describe data about
uncertain periods, an ontology (the HuTime Ontology) was constructed based on
the logic. This ontology is characterized by the fact that uncertain time
intervals can be defined recursively. It is expected that more data about time
periods will be created and released using the result of this study.
