The Data access layer in any application has the responsibility to access the data from underlying data repositories based on the access patterns expected. Here we can broadly categorize the data access layer to be performing either a pull or a push of data with respect to the serving layer.

At a high level, a data push refers to outflow of the data from the serving layer wherein the data is pushed out to other systems by the serving layer.

A Data Pull however refers to outflow of the data from the serving layer wherein the external systems pull the data from the serving layer, if the data is in the available format and the serving layer supports the expected data definition and protocols for data exchange.