Parallel jobs use data sets to manage data within a job. You can think of each link in a job as carrying a data set. The Data Set stage allows you to store data being operated on in a persistent form which can then be used by other WebSphere DataStage jobs. Data sets are operating system files each referred to by a control file which by convention has the suffix .ds. Using data sets wisely can be key to good performance in a set of linked jobs. You can also manage data sets independently of a job using the Data Set Management utility available from the WebSphere DataStage Designer or Director In datset dat is stored in some encrypted format ie. we can view the data through view data facility available in datastage but it cant be viewed in Linux or back end system. In sequential file data can be viewed any where. Extraction of data from the datset is much more faster than the sequential file.