Increasing volumes of data are generated from a variety of industries, organizations and people. Such data is now seen as a key business asset, since analysing it allows business decision makers to make choices with confidence. This data is often “big data” - a data of such volume, velocity and variety that conventional processing techniques are not suitable. We research the specific challenge of variety, where data comprises a number of incompatible formats. Semantic technology, or the use of ontologies, is seen as a core approach to resolving this challenge and aligning the data generated from heterogeneous data sources. This paper lays down the issues which should be addressed and reviews the work which has been done in the area of integrating structured and unstructured data sources, with a special focus on the financial domain. We then chart a research plan in the area following Design Science research.