1. (10 points) Which of the systems covered in the course readings have synchronization methods that correspond roughly to each of the following lease terms?
   • infinite term lease
   • zero term lease
   • intermediate term lease

2. (10 points) Do the file system semantics of leases (with the corresponding lease terms listed above) always map exactly onto the sharing semantics for the particular systems mentioned? If not, pick one system where the semantics are not exact and describe the differences.

3. (5 points) Is there a difference between a read lease and a write lease? How do the rules for assignment of leases apply in environments supporting both read and write?

4. (5 points) What happens when lease holders become unreachable?

1. (5 points) Which feature on Time-Warp is analogous to the ``check points'' in LFS? Why?

2. (5 points) What would be the trade-offs for the frequency of calculating those two?

3. (10 points) How are they similar and how are they different?

1. (5 points) Explain the difference between caching and replication

2. (5 points) Describe the benefit and costs of replication in distributed file systems and distributed information systems like the web.

3. (5 points) Describe the benefit and costs of caching in distributed file systems and distributed information systems like the web.

4. (5 points) What effect does the characteristics of the data in, and the users of, distributed file systems and distributed information systems like the web have on these costs and benefits?

Hoping that providing better tools to collect economic statistics will help provide more accurate information to the new Treasury Department Secretary in his bid to jump start the economy, you have been hired as a consultant to make changes to the information architecture used to collect and disseminate such information.

The goals of the system are to collect information from employers and purchasing managers, to perform statistical analysis on the data, and to issue monthly reports on inventories, prices, and employment.

Of critical concern is the security of the raw data collected since it identifies individual business. Additionally, since the numbers have significant economic impact, the integrity of the data is critical.

Finally, because of the economic impact, knowledge of the contents of a report in advance of its official release, or for that matter, even knowledge of drafts of such reports, would give individuals an unfair advantage in the stock, bond, and commodity markets and must be prevented. The reports must be issued and available to everyone simultaneously. There will be many people requesting the reports.

1. (10 points) Discuss the security requirements for such a system. Which security services are most important for which parts of the system? (note - different data will have different requirements).

2. (10 points) What steps would you take to improve the scalability of such a system? How do the steps you mention prevent bottlenecks in the dissemination and collection of information?

3. (10 points) Suggest steps that you would follow to (i) reduce the likelihood of early leaks of information and to (ii) ensure that everyone gets access to the publicly released data at precisely the same time.