In this chapter, we present an application scenario that corresponds to an example of service alliances to show the usefulness of Dejima architecture in practice. We first explain that database collaboration is desired to develop several kinds of service alliances. Next, we propose a mediator alliance model for database collaboration in ridesharing alliances as a specific example. We then explain how we realize this model using the Dejima architecture and present a demonstration of its implementation. As a further discussion, we explore the feasibility of the other two alliance models, that is, alliances without mediators and hierarchical alliances.