Autonomy of operations combined with decentralised management of data has given rise to a number of heterogeneous databases or information systems within an enterprise. These systems are often incompatible in structure as well as content and hence difficult to integrate. This thesis investigates the problem of heterogeneous database integration, in order to meet the increasing demand for obtaining meaningful information from multiple databases without disturbing local autonomy. In spite of heterogeneity, the unity of overall purpose within a common application domain, nevertheless, provides a degree of semantic similarity which manifests itself in the form of similar data structures and common usage patterns of existing information systems. This work introduces a conceptual integration approach that exploits the similarity in meta level information in existing systems and performs metadata mining on database objects to discover a set of concepts common to heterogeneous databases within the same application domain. The conceptual integration approach proposed here utilises the background knowledge available in database structures and usage patterns and generates a set of concepts that serve as a domain abstraction and provide a conceptual layer above existing legacy systems. This conceptual layer is further utilised by an information re-engineering framework that customises and packages information to reflect the unique needs of different user groups within the application domain. The architecture of the information re-engineering framework is based on an object-oriented model that represents the discovered concepts as customised application objects for each distinct user group.