Time-Cost Tradeoffs for Composed Services

Time and cost are crucial criteria in Service Level Agreements. Frequently, the time when and how long a service can be provided or used and the cost for utilizing a service are related and hence users are confronted with a trade-off between time and cost. Besides the fundamental direct and indirect proportional relationship between time and cost, composed services might also have more complex non-monotonic relationships. We introduce a novel way of expressing the trade-offs between time and cost in form of TC-Maps as a set of piece-wise linear functions. For calculating the duration, cost and their relation for service compositions, we introduce specific operations used in a bottom-up procedure resulting in an overall TC-Map. The proposed structure allows us to derive the minimum cost of a composed service given a duration limit, or for analyzing possible durations for a provided budget. TC-Maps offer the basis for optimizing the utilization of composed services according to user preferences, resources and objectives.