Abstract
Software as a Service (SaaS) is a paradigm that provides end users or clients easy and seamless access to various applications, using the Internet without requiring any infrastructure or related software. To virtualize the access to applications and functionalities, SaaS providers use the cloud-computing environment to rent resources, thereby reducing both the capital and operational expenditure. SaaS uses the cloud-computing infrastructure to distribute applications to many users, irrespective of their location or infrastructure capacity. This one-to-many model with centralized control has the potential to transform the behavior of traditional IT architecture, its pricing, partnering, and management. With the emergence of SaaS as a delivery system, the whole software environment is moving toward a producer-consumer system, where both are distributed globally. We point out the motivation for accepting the new technologies, such as to reduce the expense, energy consumption, maintenance, etc. We also point out the challenges and risks associated with the paradigm shift. The present study categorically presents state-of-the-art research on the security issues of collaborative SaaS cloud computing and integrating service-level-agreement and quality-of-service-related issues of SaaS in cloud-computing environments.

Key words: Software engineering; software-as-a-service; cloud computing; service-level agreement; quality of service, security