Week 1

Q1. A supply system and inventory system. A system where employees place order for parts and order alert prompts an employee in inventory to draw the item and send it to movement. The inventory system updates its holdings (and if holdings are low will place an order with the wholesaler). The physical part is moved to movement the system prompts the movers to ship the item to the client. The system allows the client to track the order through the system. The mover delivers the order and closes the ticket on the system. The client confirms receipt of the order. In this example all the users do not track the different systems that are involved with allowing this connectivity.

Q2. Middleware in a distributed system is software that is layered below the application layer and above the operating system layer. It allows various applications to communicate with each other it also allows applications to run on different operating systems.

Q3. Still working on it

Q4. To the user the fact that the system is distributed or not is unknown. The user isn’t aware that some of the processes s/he uses could be located a great distance away from them. If a system is able to appear to both users and applications to be one computer then the distributed system is transparent. There are 6 types of transparency: access, location, migrating, relocation, replication, concurrency, and failure. An example of failure transparency is when an application or client within the system fails but the other clients never know that there is an issue.

Q5. A big reason failure ad recovery transparency is difficult is there is no way to distinguish between a dead component and a really slow component. The example provided in the reading talks about a web server which might be processing millions of requests and is running slow. The user’s browser will timeout and report an error that the server isn’t responding. From this it’s not clear if the web server is offline or just really slow to reply.

Q6. The times where not being completely transparent is useful is when a service is located very far from the user/client. In line with examples from the reading a military example is, when we deploy networks around the world, we cannot always deploy servers and therefore a mission in Egypt only supports a few local services but the bulk of SharePoint applications and others are hosted in Canada. Therefore, the speed of the requests between the mission in Africa and Canada is slower ten if the services were provided locally. Users can expect that their connection will be slow and won’t be so angry when they have to wait a second or two to access a file.

Q7. An open distributed system is a system that offers services according to standard rules that describe the syntax and semantics of those services. Benefits that an open system provides is different develops can design products that create different systems but the different systems are interoperable because they all follow the set standard rules for syntax etc.

Q8. A scalable system is that can increase or decrease according to the requirement. The system will function in the same manner and the users do not notice if the system grows to add more users, expands to locations around the world or the amount of administrators decreases. An example is the DWAN for the military. The DWAN core servers are in Canada but there are remote servers and clients all over the world. As the military moves around DWAN nodes connect and disconnect all the time, increase the number of clients and decrease the number clients.

Q9. The techniques outlined in the reading for scalability are hide communication latencies, distribution and replication.

Q10. Within grid computing systems virtual organizations group users together to support collaboration between the different groups or businesses. To implement virtual organizations users and applications are provided rights to access data and resources. To me this would eb something like SharePoint where different units are provided rights to access SharePoint pages where they can share products/reports with other units who are also part of the virtual organization.

Q11. Transaction abortion doesn’t reset the world when the transaction results in a physical output. If a transaction resulted in something getting printed, and the printer completed the print job before the abort signal was sent then that cannot be undone or reset. 

Q12. A coordinator will ensure that the nested transactions will commit when they can and if a nested transaction aborts then the other nested transactions also abort.

Q13. We argued that distribution transparency may not be in place for pervasive systems. This statement is not true for all types of transparencies. Give an example. An example of when transparency should be in place for pervasive systems is when moving from one group to another such as a mobile phone which crosses from one access point to another there is a handover action that is transparent to the user.

Q14. Extend the list with more examples of distributed pervasive systems: mobile networks; cars/trucks/vehicles; GPS;