We created a timeline of events, such as a particular partner's need (Florida Department of Health's desire to detect outbreaks based on patient time of arrival) or a public health outbreak (SARS) and correlated each one with design and architecture decisions that influenced ESSENCE. We used these events to describe the epidemiology, technology, analytical, administrative, political, legal and monetary factors that were considered at each point. Looking historically and critically at each decision point, we analyzed the benefits and costs of each decision. These benefits and costs were described from many different points of view, including those of the developer, user, administrator and others.