1. A system integration apparatus for managing, in response to a query command, a plurality of distributed heterogeneous data sources and a central data model configured to contain at least one of entities and attributes that are at least one of mapped and translated from the data sources, and for determining a desired query result corresponding to the command, each of the data sources having data that can flow into said apparatus, said apparatus comprising: a relationship and navigation data repository configured to contain relationship templates defining relationships among the data from the data sources, said relationship templates defining said relationships among both data within individual ones of the sources and data in different ones of the sources, said relationship and navigation data repository being configured to interface with the central data model; and an integration engine coupled to said relationship and navigation data repository, said integration engine being configured to: receive the query command, determine which of the plurality of data sources and which of said templates the query command applies to, so as to identify pertinent data sources and pertinent templates; and calculate the desired query result, responsive to the query command, based on the pertinent data sources and said pertinent templates.