This study attempts to apply UML concepts to design UML diagrams that reflect the functional processes within the Client Tracking System (CTS) of a community service organisation. This paper represents Part I of a case study of the UML model for designing the CTS at the Learning Enrichment Foundation (LEF) in Toronto, Canada by Tran (2007). It investigates the task of constructing the design elements for CTS that can be used to manage the client information within LEF. Specifically, this paper investigates the system requirements in association with business and user needs, and use case diagrams of CTS. Furthermore, this investigation represents the UML model of the existing CTS at LEF. Through a study of how the CTS has been structured and how it operates, we may learn lessons that may be useful in other community networks serving significant immigrant communities.