9. An apparatus comprising: one or more processors; memory; a request receiving unit stored in the memory and executable by the one or more processors configured to receive a request for querying data stored in at least two databases based at least in part on a business model, the business model comprising one or more business elements; a conversion unit stored in the memory and executable by the one or more processors configured to generate a uniform query that masks a difference among the at least two different databases by converting the query request into one or more execution modes that match with the at least two databases based at least in part on a conversion rule from the business model to a storage model, the storage model comprising attribute information of the at least two databases and the conversion rule comprising a corresponding relationship between the one or more business elements and one or more attributes in the at least two databases; and a database access unit stored in the memory and executable by the one or more processors configured to access the at least two databases according to the one or more execution modes, the database access unit further configured to, upon determining that an amount of concurrent accesses to one of the at least two different databases according to the one or more execution modes exceeds a predetermined amount: delay a subsequent access to the one of the at least two different databases, or access a backup database, if available, of the one of the at least two different databases, the backup database having less concurrent accesses than the one of the at least two different databases.
10. The apparatus of claim 9 , wherein the business model describes business scenarios through a metadata format.