Service-oriented architecture

Q1- Giving reasons for your answer, suggest two important types of application where you would not recommend the use of service-oriented architecture.

Answer1- 1. Embedded applications in devices where a network connection cannot be guaranteed. These are unlikely to make use of services as there is no guarantee that these services will be available when required. 2. Real-time applications with stringent deadlines, especially those with lots of user interaction e.g. computer games. In these applications, the performance overhead in coding and decoding XML messages is likely to be unacceptable. A web service is a service that is accessed using standard Internet and XML-based protocols.

Q2- Explain what is meant by a ‘compensation action’ and, using an example, show why these actions may have to be included in workflows.

Answer2- A compensation action is an action that is included in a workflow to ‘undo’ a transaction that has been completed earlier in the workflow. Compensation actions may have to be included in workflows because the success of the entire workflow may rely on all included workflows successfully completing. If some of these included workflows are successful but some aren’t, then the compensating actions have to be executed to ensure that the overall system is left in a consistent state. Compensation actions are required when dependent services, offered by different suppliers, are composed to create an integrated service. For example, say a meeting organizer has to book a room for a meeting then organize catering for the people attending the meeting. It may not be possible to do this concurrently as the numbers attending the meeting may not be known. If the room is booked but, subsequently, it transpires that no catering is available that day, then the booking must be cancelled by a compensating action.

Q3- For the example of the vacation package reservation service, design a workflow that will book ground transportation for a group of passengers arriving at an airport. They should be given the option of booking either a taxi or a hire car. You may assume that the taxi and car hire companies offer web services to make a reservation.

Answer3-