In this paper, we describe our implemented approach for the usage and exploitation of declarative mappings for the publication of open transport data from transport authorities and operators into an ontology based on Transmodel. This allows a homogeneous representation of transport data across EU transport-related organisations and minimises the need to understand ad-hoc heterogeneous representation formats for transport data as currently published by them. We show how we create and use RML mappings for the speci c case of transforming GTFS data into a Transmodel-based ontology. In the future, such data may be further transformed into other formats such as NeTEx.
RML
to provide data about transport infrastructure, but also for route planning, but also by other route planners, such as Navita.io and OpenTripPlanner.
To achieve this homogeneity, there are several options that may be followed:
{ Transport authorities and operators may agree on using the same data
format and hence publish according to such data format. They know well the
type of data that they handle, the quality properties on such data, etc., so
they should be able to provide this data easily. To some extent, this is what
is happening currently with GTFS, and what should happen in the near
future in the European Union with NeTex, according to directive 2010/40/EU
and regulation 2017/1926 (MMTIS).
{ 3rd parties (as well as operators and authorities themselves) may be able to
create transformation rules that allow transforming the original data sources
into other generally-agreed formats, republishing such transformed data
either in the original data portals, if allowed to do so, or in other servers.
Transformations may be done programmatically (that is, with ad-hoc code)
or declaratively (using mappings in existing languages like R2RML [
In this paper, we present our work on ensuring that declarative mappings can be used for the purpose of transforming transport data published by transport authorities and operators into a homogeneous representation based on Transmodel (the reference data model for public transport at European level, which will be further described in section 2). This data can then be further transformed into NeTEx so as to comply with the EU regulations for the publication of transport-related data in National Access Points. 2
In its drive to foster interoperability across Europe, the EU is requiring each Member State to allow access to transportation data via a National Access Point (NAP). According to the EU Regulation 2017/1926, all transportation authorities, transport operators and infrastructure managers must provide static and dynamic data in speci c data formats (e.g., NeTEx, SIRI). - the EU Regulation applies to di erent transportation modes, including air, train, road vehicle, bus, ferry, metro, tram, shuttlebus, car-sharing, car-pooling and bike-sharing.
Transmodel is the European Reference Data Model for Public Transport. It provides a conceptual model of common public transport concepts and data structures that can be used to build many di erent kinds of public transport information system such as timetabling, fares, operational management, realtime data, journey planning. It is divided into eight di erent sections or Parts: Common Concepts (CC), Public Transport Network Topology (NT), Network Description (ND), Operations Monitoring & Control (OM), Fare Management (FM), Passenger Information (PI), Driver Management (DM), Management Information & Statistics (MI).
These parts or sections are usually developed by di erent standards or speci c data formats. One of the most relevant implementations is NeTEx, which covers partially some features of the parts CC, NT, ND, FM and PI. NeTEx releases the 2017/1926 EU Regulation (May 2017) where the European Commission recognized NeTEx as a strategic standard for the cross-border exchange of data. The rst step must be taken before December 2019 when every European country must provide data available in NeTEx format at National Access Points to allow EU-wide multi-modal travel information services.
The General Transit Feed Speci cation (GTFS) is a de-facto standard for representing public transport data, a collection of at least ve required, two optional required and up to fteen CSV les (with extension .txt and preferably encoded as UTF-8) contained within a compressed le to describe a transit scheduled operations system. The aim of GTFS is providing at least trip-planning functionality. It de nes the headers and a set of rules that must be taken into account when the dataset is created. Each le, as well as its headers, can be mandatory or optional and they have relations among them. The speci cation supports the representation of several public transport features such as trips, routes, stops, times, fares or calendar.
In order to provide a better GTFS to NeTEx conversion and further full data
interoperability, we start to build up a Transmodel Ontology. The development is
released in a github repository3 where every material generated is upload about
the di erent activities carried out during the development (i.e., use cases, user
stories, glossary of terms, etc.). Based on the Transmodel base URI proposed by
the CEN Transmodel working group model4 and its documentation5 we develop
the corresponding ontology following the NeOn methodology[
Table 1. Example of relation among GTFS properties and Transmodel Ontology
GTFS Agency name Agency url
Transmodel (Ontology) https://w3id.org/transmodel/terms#authorityName https://w3id.org/transmodel/terms#authorityUrl Agency timeZone https://w3id.org/transmodel/terms#authorityTimezone Agency lang
https://w3id.org/transmodel/terms#authorityLang 3
The Open NEtwork of public Transport application (ONETT)6 uses Semantic Web technologies to perform a systematic knowledge graph generation in the
transport domain. More in detail, ONETT applies the concept of Ontology Based
Data Access (OBDA) [
In this speci c case, we create a general mapping between the full speci
cation of GTFS7 and ontology based Transmodel using the RML speci cation
in its YARRRML [
These steps are a black box for the transport authorities that want to obtain the knowledge graph from their GTFS feeds. Using the web application the user only has to upload the compressed feed or provide a URL and ONETT
generates automatically the corresponding knowledge graph. With this approach, we provide a useful tool to generate National Access Point complaint data from a de-facto standard and very popular data format in a systematic manner.
The availability of homogeneous transport data from worldwide transport authorities and operators gives us the possibility of creating new types of applications related to transport (trip planners, fare calculators, ticket recommenders, etc.) that can be deployed easily in di erent regions or cities. In this paper, we have shown our approach to create such homogeneous transport data based on declarative mappings that can be used to generate transport knowledge graphs for any region or city in the world that is currently publishing data in GTFS. The mappings allow transforming GTFS data into RDF according to a TransModelbased ontology. Such data can be queried in a homogeneous manner so that the aforementioned applications can be created more easily.
This work is partially supported by EIT Digital under Grant Agreement \No. EIT/ EIT DIGITAL/SGA2019/1 through action: SNAP" and by the Spanish Ministerio de Economa, Industria y Competitividad and EU FEDER funds under DATOS 4.0: RETOS Y SOLUCIONES - UPM Spanish national project (TIN2016-78011-C4-4-R) and by an FPI grant (BES-2017-082511). Thank you to our open Summer of code 20199 students: Luis Pozo, Pablo Castellanos, Marta Retana.