Enabling Communication via APIs for Mainframe Applications

Abstract: For decades, mainframe systems have been vital in enterprise computing, supporting essential applications across industries like banking, retail, and healthcare. To harness these legacy applications and facilitate their reuse, there is increasing interest in using Application Programming Interfaces (APIs) to expose their data and functionalities, enabling the creation of new applications. However, identifying and exposing APIs for various business use cases presents significant challenges, including understanding legacy code, separating dependent components, introducing new artifacts, and making changes without disrupting functionality or compromising key Service Level Agreements (SLAs) like Turnaround Time (TAT). We address these challenges by proposing a novel framework for creating APIs for legacy mainframe applications. Our approach involves identifying APIs by compiling artifacts such as transactions, screens, control flow blocks, inter-microservice calls, business rules, and data accesses. We use static analyses like liveness and reaching definitions to traverse the code and automatically compute API signatures, which include request/response fields. To evaluate our framework, we conducted a qualitative survey with nine mainframe developers, averaging 15 years of experience. This survey helped identify candidate APIs and estimate development time for coding these APIs on a public mainframe application, GENAPP, and two industry mainframe applications. The results showed that our framework effectively identified more candidate APIs and reduced implementation time. The API signature computation is integrated into IBM Watsonx Code Assistant for Z Refactoring Assistant. We verified the correctness of the identified APIs by executing them on an IBM Z mainframe system, demonstrating the practical viability of our approach.