in connection less architecture connection to the database
need  not be persist till the end of the process.after
fetching the data form database it is pushed in database
object called  dataset and connection object need not to be
persist and its closed. and the data will be available from
the dataset.


data reader - ADO.NET DataReader to retrieve a read-only,
forward-only stream of data from a database. Using the
DataReader can increase application performance and reduce
system overhead because only one row at a time is ever in
memory.Connection to the database is maintained till the
end.it is simply like an ado object.it contains only one
table at a time.it is much  faster than dataset.


dataset - is used to hold the data from the database along
with their relation. it is connection less object.it also
persist the value which  are retrieved form the database.
it is a bit bulky object.it gives both forward and backward
access to data. it uses XML.it can consist more than one
table.we have atrribtes for the dataset 


dataset
    datatable
       datarow
        datacolumn

an adapter object is used to fill the data from the   database.

dataadapter - dataadapter is a database object which
used  to fill the dataset object with data from the database.

above exp. is excellent for connection less and connection 
oriented.
data adapter performs almost five steps
1- open(create)connection
2- fatch the data
3- generate xml file of data
4- fill xml data file into the dataset by fill()method
5- closed the connection.