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Publications

Publications by Thiago Sobral

2020

An Ontology-based approach to Knowledge-assisted Integration and Visualization of Urban Mobility Data

Authors
Sobral, T; Galvao, T; Borges, J;

Publication
EXPERT SYSTEMS WITH APPLICATIONS

Abstract
This paper proposes an ontology-based framework to support integration and visualization of data from Intelligent Transportation Systems. These activities may be technically demanding for transportation stakeholders, due to technical and human factors, and may hinder the use of visualization tools in practice. The existing ontologies do not provide the necessary semantics for integration of spatio-temporal data from such systems. Moreover, a formal representation of the components of visualization techniques and expert knowledge can leverage the development of visualization tools that facilitate data analysis. The proposed Visualization-oriented Urban Mobility Ontology (VUMO) provides a semantic foundation to knowledge-assisted visualization tools (KVTs). VUMO contains three facets that interrelate the characteristics of spatio-temporal mobility data, visualization techniques and expert knowledge. A built-in rule set leverages semantic technologies standards to infer which visualization techniques are compatible with analytical tasks, and to discover implicit relationships within integrated data. The annotation of expert knowledge encodes qualitative and quantitative feedback from domain experts that can be exploited by recommendation methods to automate part of the visualization workflow. Data from the city of Porto, Portugal were used to demonstrate practical applications of the ontology for each facet. As a foundational domain ontology, VUMO can be extended to meet the distinctiveness of a KVT.

2020

Automatic Generation of Spider Maps for Providing Public Transports Information

Authors
Santos, S; Dias, TG; Sobral, T;

Publication
INTELLIGENT TRANSPORT SYSTEMS

Abstract
With the continuous growth and complexity of public transport systems, it is essential that the users have access to transport maps that help them easily understand the underlying network, thus facilitating the user experience and public transports ridership. Spider Maps combine elements from geographical and schematic maps, to allow answering questions like "From where I am, where can I go?". Although these maps could be very useful for travellers, they still are mostly manually generated and not widely used. Moreover, these maps have several design constraints, which turns the automation of the generation process into a complex problem. Although optimisation techniques can be applied to support the generation process, current solutions are time expensive and require heavy computational power. This paper presents a solution to automatically generate spider maps. It proposes an algorithm that adapts current methods and generates viable spider map solutions in a short execution time. Results show successful spider maps solutions for areas in Porto city.

2021

Performance assessment of upper secondary schools in Italian regions using a circular pseudo-Malmquist index

Authors
Camanho, AS; Varriale, L; Barbosa, F; Sobral, T;

Publication
EUROPEAN JOURNAL OF OPERATIONAL RESEARCH

Abstract
This paper investigates the relationship between students' performance and the type of school attended during upper secondary education. The performance of three different types of schools (Liceo, Technical and Professional schools) in four Italian macroregions (North West, North East, Centre, South & Islands) is investigated. A benchmarking analysis of the variability in students' performance among regions (within macroregions) for cohorts of students attending Liceo is also conducted. The data was collected at the student level from the Italian Institute for the Evaluation of Education System (INVALSI), for the academic year 2017/18. Families with higher socio-economic status may self-select into Liceo, so a direct comparison with vocational schools could lead to biased conclusions regarding the impact of school type on student performance. To overcome this limitation, we used a Propensity Score Matching approach prior to the estimation of efficiency. A pseudo-Malmquist index, based on a metafrontier and satisfying the circular property, is developed. It enables comparing the location of the best-practice frontier for each type of school and the spread in the educational efficiency of the students attending each type of school. Thus, best performance of a given school type corresponds to the combined effect of these two aspects. This study is an interesting starting point to challenge the stereotypes that persist in Italy, especially concerning general and vocational studies and geographic differences in educational achievements.

2021

Knowledge-Assisted Visualization of Multi-Level Origin-Destination Flows Using Ontologies

Authors
Sobral, T; Galvao, T; Borges, J;

Publication
IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS

Abstract
Origin-destination matrices help understand the movement of people within cities. This work is built upon the premise that stakeholders, e.g. decision makers, need to analyze mobility flows from spatio-temporal perspectives that are appropriate to their context of analysis. The data retrieved from sensors and Intelligent Transportation Systems are useful for this purpose due to their lower acquisition costs and fine granularity, although it is complex to use such data in an integrated way, as they might have heterogeneous representations of spatio-temporal attributes and granularities. Most of the related works on the analysis of OD flows consider matrices with a fixed spatio-temporal aggregation level, and do not explore the intrinsic issue of data heterogeneity. Herein we report our findings on building the semantic foundation of knowledge-assisted visualization tools for analyzing OD matrices from multiple stakeholder levels. We propose a set of ontology design patterns for modeling the semantics of OD data, and the relations between the spatio-temporal constructs that stakeholders ought to choose when visualizing urban mobility flows. Our approach aims to be reusable by researchers and practitioners. We describe a practical implementation using estimated flows from smart card data from Porto, Portugal.

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