1. A machine-based method comprising: reducing usage of memory in a computer by reducing a volume of data that needs to be held in the memory to perform a data analysis associated with a context that affects the identity of the items of data to be held in the memory, the items of data being drawn from larger volumes of items of data of two or more data sources that are at least partially stored other than in the memory, the reducing of the volume of items of data comprising selecting, a set of object classes having associations with a particular process within an object model in accordance with the data analysis to be performed on data of the two or more data sources, excluding from the set of object classes at least one object class not having the associations, the associations of the object classes with the particular process being based on relationships between the object classes, the relationships being identified based on relevances of the relationships to the context associated with the data analysis to be performed; producing an object representation of the items of data of the two or more data sources to be held in the memory based on a mapping of data formats of the data sources to the object classes, at least two of the data sources having different data formats, the producing of the object representation including: (A) mapping first data of a first data source of the two or more data sources to instances of objects of the selected object classes; and (B) mapping second data of a second data source of the two or more data sources to instances of objects of the selected object classes, producing mapped data from the data sources, the mapped data being available in the instances of the objects of the object classes and comparable as between the data sources in the object representation based on mapping (A) and mapping (B), and holding the mapped data as the reduced volume of data in the memory while the data analysis is performed.