1. A system for accessing data in an information source, the system comprising: a metadata repository configured to store a first type of the metadata element that includes physical metadata elements defining a one-to-one relationship data stored in a plurality of information sources, and a second type of metadata element that includes logical metadata elements that are linked to one or more of the physical metadata elements in a one-to-many relationship; and a server communicably coupled to the metadata repository, wherein the server is operable to: convert a query request for one or more of the logical metadata elements to a source-specific query request corresponding to at least one of the information sources by referencing the two types of metadata elements; and generate a query plan to retrieve data from the information sources referenced by the source-specific query request, wherein at least one of a join operation and a sort operation of the query plan are performed by one or more of the information sources if they have a capability to perform the operation as determined based on data maintained by the server regarding capabilities of the information sources.