We use external ID's to store other intergrated systems IDs in.
Such as an Oracle ID, then the middle ware will query this number on, lets say the account in SFDC to detemine if it exsist to possible perfore an update or push over contract info, if this ID is not found it will then create the account along with the contract. Tons of uses, typically used when interagrating external systems as far as I know.
you may refer : http://blog.jeffdouglas.com/2010/05/07/using-exernal-id-fields-in-salesforce/ for details
We use external ID's to store other intergrated systems IDs in.
Such as an Oracle ID, then the middle ware will query this number on, lets say the account in SFDC to detemine if it exsist to possible perfore an update or push over contract info, if this ID is not found it will then create the account along with the contract. Tons of uses, typically used when interagrating external systems as far as I know.
PB
There are many helps are available some useful links as below
http://salesforce.stackexchange.com/questions/1259/how-do-you-use-an-external-id-in-the-import-wizard-to-import-child-objects-of-a
http://na14.salesforce.com/help/doc/en/faq_import_general_what_is_an_external.htm
http://blog.jeffdouglas.com/2010/05/07/using-exernal-id-fields-in-salesforce/