Before revision:  However, if the time series database is heterogeneous  accuracy may degenerate, so that on the way towards fully automatic forecasting methods in this space, a notion of similarity between the time series needs to be built into the methods.
After revision:  However, if the time series database is heterogeneous , accuracy may degenerate, so that on the way towards fully automatic forecasting methods in this space, a notion of similarity between the time series needs to be built into the methods.