1. A computer-implemented method, comprising: an items manager receiving a set of one or more requests from a client for multiple data representation items, the data representation items representing data items in a data source; and in response to the one or more requests, the items manager performing acts comprising: generating placeholders corresponding to the data representation items; returning the placeholders to the client in response to the one or more requests; requesting the data items from the data source; receiving the data items from the data source; providing the data representation items to the client; and informing the client that the placeholders are to be replaced with the data representation items.