Data stream and Data adapters are different.
Data stream is a group of components.It contains a data
source component, data row component and one or more data
filter components(optional).It selects data from the data
source and places the data into data row structure required
by the report.

Data adapter can be a data source component or a data filter
component.It retrieves data from an input source(data
base)and   creates data row.

A data stream is a group of components that provides the 
data for your report. The data stream selects data from a 
data source database and then places the data into the data 
row structure required by the report. A data stream can be 
made up of several types of components. Every data stream 
has a data source component and a data row component. 
Additional, optional components include filters, memory 
buffers, and intermediate data rows. 
A data adapter filters, retrieves, sorts, or otherwise 
processes information. The two types of data adapters are 
data sources and data filters. The relevant Actuate 
Foundation Class is AcDataAdapter.