we see many examples of soa when we use the web we can go to single web site and book air travelhotelsand automobiles all from single site the data for hotels is not stored on the airline computers insteadthe airline computers contact the services on the hotel computers and retrieve the hotel data and present it to the user when the user agrees to make hotel reservation using the airline sitethe airline site uses another web service on the hotel systems to actually make the reservation and when it comes time to charge your credit card for the whole transactionstill other computers become involved in the process auto rental service hotel reservation service airline reservation service api api api travel application figure service-oriented architecture service-oriented architecture has many advantagesincluding( we always maintain only one copy of data (this is particularly important for things like hotel reservations where we do not want to over-commitand ( the owners of the data can set the rules about the use of their data with these advantagesan soa system must be carefully designed to have good performance and meet the user' needs when an application makes set of services in its api available over the webwe call these web services security and api usage it is quite common that you need an api key to make use of vendor' api the general idea is that they want to know who is using their services and how much each user is using perhaps they have free and pay tiers of their services or have policy that limits the number of requests that single individual can make during particular time period sometimes once you get your api keyyou simply include the key as part of post data or perhaps as parameter on the url when calling the api