Document Overview
This is a systematic literature review (SLR) published by Taylor & Francis and written by Bokolo Anthony Jnr. Its subject is the role of Application Programming Interfaces (APIs) in enabling seamless interoperability of digital systems in smart cities, where isolated "vertical silos" often cannot exchange data because of a lack of standardized interfaces.
Context and Motivation
The review states that smart cities depend on many service providers whose systems must collaborate to deliver digital services. It notes that interoperability is a barrier to data transfer between heterogeneous systems such as mobility, energy and weather, and that prior reviews by Costin and Eastman, Noura et al., Di Martino et al., Abdelouahid et al., Andročec and Ahlgren et al. focused on narrower aspects such as IoT, open data or technical interoperability.
Methodology
The author followed the SLR guidelines of Kitchenham et al. (2009) across seven phases. Five research questions guided the work, covering the importance of interoperability, prior methods, interoperability categories, the support APIs provide, and available API management tools. The search covered databases including Google Scholar, Scopus, Web of Science and IEEE Xplore. Of 92 retrieved papers, 60 were selected as main studies after duplicate checks, title and abstract screening, inclusion criteria and a quality assessment with a threshold above 3.5 out of 7.
Key Findings on Interoperability
- Interoperability is described as important for making cities smarter, with the review noting that data silos limit the discovery and development of services.
- Interoperability is categorized into communication, data (syntactic and semantic), physical (technical, device, network and platform) and enterprise levels.
- The review states that data in digital systems is often locked or closed and cannot be reused by other systems or providers.
Role of APIs
- The document states that APIs support application-to-application communication and provide access to open, real-time and historical data for third parties.
- REST is described as the most common protocol for application services, and the review contrasts it with SOAP, which it describes as more complicated.
- A worked energy-data example illustrates HTTP POST and GET requests to a metering device and an HDFS database.
Case Scenario and Architecture
The review presents a layered architecture, modelled in ArchiMate, covering context, service, business, application and data processing, data space, technology and physical infrastructure layers. The scenario shows how service booking and payment for mobility services can occur within a single application.
API Management Tools
The review identifies fifteen API management systems, including Apigee, 3scale, Kong Enterprise, MuleSoft, Microsoft Azure and WSO2. It describes the core functions of such systems, namely gateway, publishing tools, developer portal, analytics, monetization, open source options and governance, and compares several tools in a table.
Limitations and Purpose for Urban Policy and Practice
The author states that the study relies only on secondary data from the literature and that APIs were not designed, deployed or published within it. The document says it is intended to provide practitioners and researchers with the key requirements and concepts for deploying interoperable digital systems in smart cities, and it presents this as guidance for future service interoperability research in urban environments.