How middleware sets up multiple-account sets

Enterprise ERP, often have a number of sets of books, usually we give each set of accounts to create a database, that is, our middleware to be able to connect at the same time multiple sets of books (databases), these books and even belong to different types of databases. When the client requests the data, it passes the "set number" to get the data for the specified set of books. For a user, it is possible to query only one of the data within a set of books, but some users may be able to query the data in multiple books at the same time, then these requirements, our middleware has done for you. You can set the user's own account set, so that users can log on to query their own data sets. Middleware establishes a dedicated database connection pool for each set of books (databases).

How middleware sets up multiple-account sets