Web APIs can have constraints on parameters, such that not all parameters are either always required or always optional. Sometimes the presence or value of one parameter could cause another parameter to be required. Additionally, parameters could have restrictions on what kinds of values are valid. We refer to these as inter-parameter and single-parameter constraints respectively. Having a clear overview of the constraints can help API consumers to integrate without the need for additional support and with fewer integration faults.

We developed two approaches for identifying parameter constraints in complex web APIs. One approach uses online documentation to infer inter-parameter constraints, the other depends on static code analysis to extract inter- and single-parameter constraints from the control flow of the API’s source code. In our case study at several APIs at Adyen, the documentation- and code-based approach can identify 21% and 53% percent of the constraints respectively. When the constraints identified by both approaches are combined, 66% of the inter-parameter constraints can be identified. Code analysis is able to identify 78% of the single-parameter constraints.

Through the years, companies have been exploring the field of data science. The Nederlandse Spoorwegen (NS) is not an exception to this. Modern trains are equipped with sensors that measure a variety of conditions within the train. This data is being stored in their data warehouse. This data has been proven useful for detection and response times to problems, which warrants two high-level goals of the NS: punctuality and reliability. However, even with the available data, visualization and detection of location-specific problems are not yet implemented. Location-specific problems are problems that are not caused by the train, but by the infrastructure or human fault at that specific location. At the moment, most patterns in error codes are only backed up by suspicions, since these error codes are not stored in a way they are easily readable. Therefore, it is hard to find connections between multiple error codes. This document describes the created system that supports the analysis of location-specific error code patterns. With the system, the NS will be able to improve their two high-level goals and ultimately improve customer satisfaction.

For the system, a framework was made, which allows the NS to further develop and extend on data analyses. Furthermore, an extensive UI was created, allowing users to investigate found error code patterns and trace back problems to their origin. With the system, the NS is able to verify and create new hypotheses on possible problematic locations. In this document, the problem in elaborated on, multiple solutions are given of which one is chosen and thoroughly motivated, the solutions are elaborated on and, finally, some recommendations for future expansion are given.