A user at a client machine can customize components of a database search performed at a server. The user does this by sending executable code to the database server. Software code runs as middleware on the database server machine to communicate between the database server and the client and performs the functions of supplying the client with vital information required for generating code which will be used for customizing various processes of the database retrieval session. Typically, the server comprises a set of database servers and the middleware runs on each database server machine to communicate between the database servers and the client. The middleware provides a virtual machine on which the user-supplied code written in a virtual machine language is executed, giving a uniform interface across the set of database servers on which the same user-supplied code will be executed ensuring that the user-supplied code executes under database server specified access privileges.