Distributed Systems

Problem Description
Using a client-server architecture, design and implement a multi-threaded server that allows concurrent
clients to search the meaning(s) of a word, add a new word, and remove an existing word.
This assignment has been designed to demonstrate the use of two fundamental technologies that have
been discussed during the lectures:
Hence, the assignment must make an EXPLICIT use of the two above. By explicit, we mean that in your
application, sockets and threads must be the lowest level of abstraction for network communication and
The system will follow a client-server architecture in which multiple clients can connect to a
(single) multi-threaded server and perform operations concurrently.
The multi-threaded server may implement a thread-per-request, thread-per-connection, or
worker pool architecture. This is a design decision for you to make.
All communication will take place via sockets. These sockets can be either TCP or UDP, however,
keep in mind that all communication between clients and server is required to be reliable.
You are responsible for designing your own message exchange protocol. Some data formats
that you may use include XML, JSON, Java Object Serialization, or you may choose to design
your own.
Failure Model
All communication between components has to be reliable. If you are using TCP, then the
reliability guarantees offered by the protocol are sufficient. If you decide to use UDP, then you
have to implement an infrastructure that offers reliable communication over UDP. For those of
you with previous experience using TCP, using UDP may be a rewarding challenge. 

It is expected that, on both the server and the client side, errors (by means of exception
handling) are properly managed. The errors include the following:
Input from the console for what concerns the parameters passed as command line.
Network communication (address not reachable, bad data…).
I/O to and from disk (cannot find the dictionary file, error reading the file, etc…).
Other errors you might come up with.
The application will be tested and validated against all these errors.
Functional Requirements
Query the meaning(s) of a given word
The client should implement a function that is used to query the dictionary with the following
minimum (additional input/output parameters can be used as required) input and output:
Input: Word to search
Output: Meaning(s) of the word
Error: The client should clearly indicate if the word was not found or if an error occurred. In
case of an error, a suitable description of the error should be given to the user.
Add a new word
Add a new word and one or more of its meanings to the dictionary. For the word to be added
successfully it should not exist already in the dictionary. Also, attempting to add a word without
an associated meaning should result in an error. A new word added by one client should be
visible to all other clients of the dictionary server. The minimum input and output parameters
are as follows:
Input: Word to add, meaning(s)
Output: Status of the operation (e.g., success, duplicate)
Error: The user should be informed if any errors occurred while performing the operation.
Remove an existing word
Remove a word and all of its associated meanings from the dictionary. A word deleted by one
client should not be visible to any of the clients of the dictionary server. If the word does not
exist in the dictionary then no action should be taken. The minimum input and output
parameters are as follows:
Input: Word to remove

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