Software use cases to elicit the software requirements analysis within the ASTRI project

The Italian National Institute for Astrophysics (INAF) is leading the Astrofisica con Specchi a Tecnologia Replicante Italiana (ASTRI) project whose main purpose is the realization of small size telescopes (SST) for the Cherenkov Telescope Array (CTA). The first goal of the ASTRI project has been the development and operation of an innovative end-to-end telescope prototype using a dual-mirror optical configuration (SST-2M) equipped with a camera based on silicon photo-multipliers and very fast read-out electronics. The ASTRI SST-2M prototype has been installed in Italy at the INAF "M.G. Fracastoro" Astronomical Station located at Serra La Nave, on Mount Etna, Sicily. This prototype will be used to test several mechanical, optical, control hardware and software solutions which will be used in the ASTRI mini-array, comprising nine telescopes proposed to be placed at the CTA southern site. The ASTRI mini-array is a collaborative and international effort led by INAF and carried out by Italy, Brazil and South-Africa. We present here the use cases, through UML (Unified Modeling Language) diagrams and text details, that describe the functional requirements of the software that will manage the ASTRI SST-2M prototype, and the lessons learned thanks to these activities. We intend to adopt the same approach for the Mini Array Software System that will manage the ASTRI miniarray operations. Use cases are of importance for the whole software life cycle; in particular they provide valuable support to the validation and verification activities. Following the iterative development approach, which breaks down the software development into smaller chunks, we have analysed the requirements, developed, and then tested the code in repeated cycles. The use case technique allowed us to formalize the problem through user stories that describe how the user procedurally interacts with the software system. Through the use cases we improved the communication among team members, fostered common agreement about system requirements, defined the normal and alternative course of events, understood better the business process, and defined the system test to ensure that the delivered software works properly. We present a summary of the ASTRI SST-2M prototype use cases, and how the lessons learned can be exploited for the ASTRI mini-array proposed for the CTA Observatory.