Broad, long-term financial, and economic datasets are a scarce resource, particularly in the European context. In this paper, we present an approach for an extensible data model that is adaptable to future changes in technologies and sources. This model may constitute a basis for digitised and structured long-term historical datasets. The data model covers the specific peculiarities of historical financial and economic data and is flexible enough to reach out for data of different types (quantitative as well as qualitative) from different historical sources, hence, achieving extensibility. Furthermore, based on historical German firm and stock market data, we discuss a relational implementation of this approach.