Efficient Live Public Transport Data Sharing for Route Planning on the Web Julián, Rojas Meléndez, Dylan, Van Assche, Harm, Delva, Pieter, Colpaert, and Ruben, Verborgh In Proceedings of the 20th International Conference on Web Engineering Accepted
Web-based information services transformed how we interact with public transport. Discovering alternatives to reach destinations and obtaining live updates about them is necessary to optimize journeys and improve the quality of travellers’ experience. However, keeping travellers updated with opportune information is demanding. Traditional Web APIs for live public transport data follow a polling approach and allocate all data processing on either data providers, lowering data accessibility, or data consumers, increasing the costs of innovative solutions. Moreover, data processing load increases further because previously obtained route plans are fully recalculated when live updates occur. In between solutions sharing processing load between clients and servers, and alternative Web API architectures were not thoroughly investigated yet. We study performance trade-offs of polling and push-based Web architectures to efficiently publish and consume live public transport data. We implement (i) alternative architectures that allow sharing data processing load between clients and servers, and evaluate their performance following polling- and push-based approaches; (ii) a rollback mechanism that extends the Connection Scan Algorithm to avoid unnecessary full route plan recalculations upon live updates. Evaluations show polling as a more efficient alternative on CPU and RAM but hint towards push-based alternatives when bandwidth is a concern. Clients update route plan results 8–10 times faster with our rollback approach. Smarter API design combining polling and push-based Web interfaces for live public transport data reduces the intrinsic costs of data sharing by equitably distributing the processing load between clients and servers. Future work can investigate more complex multimodal transport scenarios.
Publiceren van updates over openbaarvervoersdata Dylan, Van Assche 2019
Publishing real time public transport data can be a heavy task for Open Data publishers (RPC APIs) and consumers (data dumps). With Linked Connections we try to find a compromise between both worlds. Since Linked Connections is not optimised for real time data yet, we investigate how the Linked Connections server can publish real time data in a cost-efficient way. At the same time, we examine how we can optimise the algorithms to use Linked Connections on the clients. We propose a list of changes to these algorithms to reduce the processing time and computing resources. By using a separate real time resource on the Linked Connections server, only the updates to the data must be transferred. We want to reduce further the necessary resources for the client and the server for Linked Connections. We achieve this goal by modifying the Connection Scan Algorithm (CSA) and liveboard algorithms on the client. We reduced the processing time of a journey with a factor of 2 - 3 using the CSA. A liveboard could be updated 10 times faster than in the original implementation. The amount of network bandwidth is reduced by 15 % for the CSA and by 21 % for the liveboard algorithm. Based on these results, we conclude that a publish-subscribe approach (Server-Sent-Events) is more efficient than a polling approach (HTTP polling) for real time Open Data. Using a real time resource, the efficiency of the client’s algorithms is significantly improved.