DATASET:
The dataset is a in-memory representation of data.
DataSet is made up of a collection of DataTable objects. 
It can be considered as a local copy of the relevant 
portions of the database. 
The data is persisted in memory and the data in it can be 
manipulated and updated independent of the database. When 
the use of this dataset is finished, changes can made back 
to the central database for updating. 
The data in dataset can be loaded from any valid 
datasources like Microsoft SQL Server database, an Oracle 
database or a Microsoft Access database.
USES:
1. You normally use datasets to hold results of database 
queries, but you can also create them on the fly and 
populate them programmatically. 
2. The DataSet object has characteristics that make it 
suitable for persisting application settings: It can hold 
hierarchical data in the Tables collection, and you can use 
the WriteXml() method to save the entire dataset into an 
XML file with a simple call: 

ds.WriteXml(strFileName, 
   XmlWriteMode.WriteSchema);
3. We can seperate data layer from presentation layer by 
using class or dataset in .net 2.0.
4. The DataSet in .Net rocks, it provides so much        
functionality for free, that it makes it the prefered data 
transport mechanism between the presentation layer and the 
buisiness layer, when dealing with a pure .Net technology 
stack then DataSet's are the way to go. 
5. DataSet has some powerful XML-related capabilities. For 
example, you can serialize a DataSet into XML through its 
WriteXml() method; conversely, you can populate a DataSet 
from a properly formatted XML stream using the DataSet's 
ReadXml() method.

dataset solved a lot of handling huge amount of data.The
dataset when pointed to stored procedures can be able to
load data of many tables and can be accessed at any instant
any record.

1. datasert is connection less in memory representation of 
the data xml represention.
2. once the data load into dataset their is no need to 
maintain the live  connection.
3.once dataset is collection of any no.of datatable 
objects.the information of these table may be taken from 
diff datasource.
4.the dataset updatable
5.the data set will represent the information inthe xml 
format internally

dataset are tow types
typed dataset typeddataset and untypeddataset
typedataset is xml format
untypeddataset is textformat
dataset as any modifications create insert delete insert 
update & edit
dataset like as database