=Paper=
{{Paper
|id=Vol-3637/paper35
|storemode=property
|title=A Spatiotemporal Ontology for Semantic Trajectories (extended abstract)
|pdfUrl=https://ceur-ws.org/Vol-3637/paper35.pdf
|volume=Vol-3637
|authors=Yunpiao Bai,Michae Grüninger
|dblpUrl=https://dblp.org/rec/conf/jowo/BaiG23
}}
==A Spatiotemporal Ontology for Semantic Trajectories (extended abstract)==
https://ceur-ws.org/Vol-3637/paper35.pdf
A Spatiotemporal Ontology for Semantic Trajectories:
Extended Abstract
Yunpiao Bai1,* , Michael Grüninger1
1
Department of Mechanical & Industrial Engineering University of Toronto, 5 King’s College Rd, Toronto, Ontario,
M5S3G8, Canada
Abstract
A geospatial query is a question where the concept of location is necessary for formulating the answer.
In particular, we are interested in queries that can support location intelligence reasoning about the ways
in which people can possibly move through space in the urban environment. In this project, we explore
how can ontologies be used for automated reasoning to answer geospatial queries based on people’s
trajectories. In such context, a trajectory is the sequence of activities in which people participate while
moving along a path. In order to do so we need an integrated set of ontologies that cover the notions of
space-time, events, moving objects as well as the relations among them.
Keywords
spatiotemproal, semantic trajectory, ontology
1. Motivation
In urban areas, by using the Global Positioning System (GPS), moving objects like vehicles
and human can be tracked in connection with city infrastructure such as buildings and roads.
Large volumes of spatiotemporal data are collected in different fields, including transportation,
human mobility, and business transactions. Nowadays, the trend of mobility analysis has been
shifted from raw movement to semantically rich trajectories. Rather than tracks of moving
objects, trajectories are considered as spatiotemporal entities that represent the sequence of
activities in which physical objects participate while the objects are moving along a path,
such as an individuals daily activities. Therefore, in order to represent semantic trajectories
and answer queries of trajectories in natural languages, we need an integrated ontology that
covers the notion of space, time, activities and participating objects. Though there exist a
number of OWL ontologies for trajectories [1, 2, 3, 4], most of them just simply associate
spatiotemporal points or objects to space, time and event data. They provide neither explicit
axiomatizations for spatiotemporal relations nor formalisms of events or processes. Regarding
formal representations of spatiotemporal knowledge, there is considerable foundational work
on qualitative representation and reasoning about space [1, 2], as well as relationships between
physical objects and spatial regions [3, 4]. Meanwhile, temporal formalisms have also been
FOIS 2023 Early Career Symposium (ECS), held at FOIS 2023, co-located with 9th Joint Ontology Workshops (JOWO
2023), 19-20 July, 2023, Sherbrooke, Québec, Canada
*
Corresponding author.
$ wbai@mie.utoronto.ca (Y. Bai)
© 2023 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
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studied extensively together with actions and events [5]. However, to reason about a moving
object, it is not only essential to represent its location and spatial relations to other objects in
time but also changes in the spatial aspects over time. Thus, a practical concern of spatial and
temporal reasoning is to deal with the historical and spatial changes of objects and hence the
emerging need for developing spatiotemporal hybrids. There have been continuing attempts to
integrate space and time, including temporalizing spatial relations and combining space and
time as one primitive entity, such as BFO. Yet, existing approaches fail to provide a reasonable
philosophical stance of space-time treatment nor a mereotopology of spatiotemporal entities.
In addition to spatiotemporal formalisms, we also need representations of activities and their
relations to space and time. Ontologies of events or activities have been well established
such as Process Specification Language and Event Calculus; nevertheless, very little research
has formalized the relation between event and spacetime. Some previous research discussed
philosophical theories and some principles of locating events [6, 7], but none of these studies
proposed formal axioms of the relation between an activity and space-time.
2. Research Questions
What ontologies are required to represent semantic trajectories for question-answering?
3. Objectives
• Assess existing approaches to representing space-time and activities.
• Develop a set of ontologies to represent spatiotemporal entities, activities, and relations
between them.
4. Research Methodology
The research methodology follows the typical ontology design pattern driven by competency
questions, and it includes three main phases. The first phase is to develop use case scenario and
define the domain scope and requirements of the ontology. The second phase is developing the
formal axioms. The last phase is to implement and evaluate the ontologies based on the use
case scenarios. To capture the major concepts and requisites of knowledge representation on
event locations, we develop a scoping scenario comprehending the motion of moving objects
with respect to occurring activities, also called semantic trajectories.
Alice leaves her house in Riverdale and crosses the Don Valley to Leaside. She
purchases plumbing supplies at Canadian Tire (825 Eglinton Avenue East) and
bathroom tiles at the Home Depot that is nearby on Wicksteed Avenue.
In order to represent this scenario, one of the fundamental notions that we need to cover is
Alices trajectory which consists of a series of timely ordered activities at different locations,
including moving from her house from Riverdale to Leaside, purchasing plumbing supplies at
Canadian tire and bathroom tiles at the Home Depot. To further conceptualize and break down
Figure 1: The structure of semantic trajectory ontology
the trajectory, it can be treated as tracks of Alice’s movement (a moving object) plus a sequence
of activities while the object is moving along a spatial path. In that case, we need two sets of
ontologies to represent the locations of objects and locations of events respectively. In order to
represent this scenario semantically, the key questions to investigate are:
• What are the relationships among events, space and time?
• Are there distinct types of relationships between an event and space-time and an object and
space-time respectively? If so, how do these relationships relate to the mereotopologies
of objects, events, space and time?
• Motion and spatial change: when an entity moves or has spatial change, what exactly
changes?
The scenario and questions are used throughout the research to define the scope of the ontology,
to evaluate existing work on spatiotemporal and event modelling and to address the needs for
the proposed ontology. Based on these questions, we develop the architecture of the major
components that the proposed ontology should include. Figure 1 presents an overview structure
of the integrated ontology for semantic trajectories. There are two modules that we need
to represent semantic trajectories. As noted earlier, a semantic trajectory is the sequence of
activities in which physical objects participate while the objects are moving along a path. Thus,
we divide the semantic trajectory into two modules. The first one is the location of physical
objects. The fundamental trajectories are tracks of moving objects, so we need a location
ontology for the relationship between a physical object and a spatial region, which is closely
related to the mereotopology of physical objects and spatial regions. The second module is
the location of events. In this module, we need the formalization of the relation between an
activity and spacetime, and this formalization is related to two sets of ontologies: activities and
spacetime. Events and activities are usually tied to time closely, and a spatiotemporal ontology
requires integrating space and time specifications.
5. Research Results to Date
So far we have completed the work of developing a spatiotemporal ontology and the ontology
for location events. The next step is to integrate our ontology for event locations and the
ontology for physical object locations.
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