SOAP extensibility relates to the use of intermediaries and SOAP headers to add features to a Web service that is invoked using SOAP messaging. Give an example of an extension and howan intermediary and header would be used to implement it.

What will be an ideal response?

SlowHawk might introduce a frequent flyer feature to enhance its business. Previously, a client simply invoked the operation reserveOp to make a reservation. The operation’s parameters might include the client’s name and address and the date and number of the flight. Assuming billing is handled separately by an intermediary fulfilling the role “billing”, the client’s credit card information would be passed in a header block whose role attribute has value “billing”.
In the newsystem reserveOp is to be invoked in exactly the same way, but a new intermediary is introduced to handle frequent flyers. Clients wishing to use frequent flyer miles include a newheader block whose role attribute has value “freqf”. The
block contains data items such as account number and PIN. Messages are routed through the newintermediary prior to arriving at the billing intermediary. The new intermediary scans the header looking for frequent flyer blocks. If no such block is
present the message is simply passed on to the next intermediary and reserveOp is invoked as before. If the intermediary finds such a block, it deletes it, looks up the client’s account balance and determines if sufficient frequent flyer miles are present. If the answer is yes, it decrements the balance by the appropriate amount and either deletes the header addressed to the billing intermediary or inserts a newheader
addressed to that intermediary indicating that the client’s credit card should not be charged. (In the latter case changes must be made at the billing node to accommodate the newfeature.) In either case the final destination is ignorant of the fact the the
frequent flyer feature has been added.