The File Retrieval Engine must adhere to the architecture shown in Figure $1$ and must

contain three components: AppInterface, ProcessingEngine and IndexStore.

The AppInterface component is responsible with implementing a command line interface

that the user can use to interact with the File Retrieval Engine, with interpreting indexing

and search commands submitted by the user, with forwarding the commands to the

ProcessingEngine and with printing the results of the commands on screen.

The ProcessingEngine component is responsible with running the indexing and search

commands received from the AppInterface component. In terms of indexing, the

ProcessingEngine must use multiple worker threads, that are configured at execution

time, to build an index from the files found at a specified directory. Each worker thread is

responsible with building a local index and with forwarding the local index to the

Figure $1$: File Retrieval Engine Architecture.

IndexStore in order to ultimately build a global index. In terms of search, the

ProcessingEngine must break down a search query into one or more single term queries,

must retrieve for each single term query the list of files in which the term can be found and

the number of occurrences, and must combine the list of files from each single term query

result, sort the files by occurrence and return the top $10$ files.

The IndexStore component is responsible with storing the global index and providing the

means to query the global index. More specifically, it should expose an interface to update

the global index with a local index and an interface to return the list of files and the number

of occurrences in which a term can be found.

package csc$435.$app;

import java.lang.System;

import java.util.Scanner;

public class AppInterface $\{$

private ProcessingEngine engine;

public AppInterface$($ProcessingEngine engine$)\{$

this.engine $=$ engine;

$//$ TO$-$DO implement constructor

$\}$

public void readCommands$()\{$

$//$ TO$-$DO implement the read commands method

Scanner sc $=$ new Scanner$($System$.$in$)$;

String command;

while $($true$)\{$

System.out.print$(">")$;

$//$ read from command line

command $=$ sc$.$next$()$;

$//$ if the command is quit, terminate the program

if $($command$.$compareTo$("$quit$")==0)\{$

engine.stopWorkers$()$;

break;

$\}$

$//$ if the command begins with index, index the files from the specified directory

if $($command$.$length$()>=5$ && command.substring$(0,5).$compareTo$("$index$")==0)\{$

$//$ TO$-$DO implement index operation

continue;

$\}$

$//$ if the command begins with search, search for files that matches the query

if $($command$.$length$()>=6$ && command.substring$(0,6).$compareTo$("$search$")==0)\{$

$//$ TO$-$DO implement index operation

continue;

$\}$

System.out.println$("$unrecognized command!"$)$;

$\}$

$\}$

$\}$