What s d diff between 'sed' and 'tr' command??

Both 'sed' and 'tr' command transforms or replaces text right...though 'sed' s for stream editing i m not able to understand the difference...
can someone explain with an example??

'tr' is specially for substitution and deletion of specified characters. 'sed' can be used for lot of things. 'sed' is called stream editor.

sed,tr,awk,grep are all filters in Unix.tr is a simple filter when compared to sed.sed and awk are very powerful when compared to tr.Not just replacement, sed and awk provide other functions as well.This is my limited knowledge.

thanks...