[SOLVED] 程序代写代做代考 python Java scheme algorithm information retrieval data structure RMIT

RMIT
Computer Science & IT, School of Science

ISYS 1078 / 1079 — Information Retrieval

Assignment 1: Indexing

Due: Midday, 29/3/2017 (week 5)

This assignment is worth 20% of your overall mark.

Introduction

In this assignment, you will implement an inverted index and use it to store term occurrence
information. You will need to design and implement appropriate data structures, write your
data to disk, and be able to read it back.

This assignment is intended to give you practical programming experience for implementing
core information retrieval functionality, and to deepen your understanding of the inverted
index data structure.

The “Information Retrieval” blackboard contains further announcements and a discussion
board for this assignment. Please be sure to check these on a regular basis – it is your
responsibility to stay informed with regards to any announcements or changes. Login
through https://learninghub.rmit.edu.au.

Assignment Teams

This assignment should be carried out in groups of two. It is up to you to form a team.
Please choose your team carefully, as you will need to work with the same person on
Assignment 2, which builds on Assignment 1.

Once you have decided on your team, you should register using the form at:
https://goo.gl/forms/CRqcyuMtRXXTGlkq2

(Note: If you are a postgraduate student and have strong reasons for needing to complete
the assignment individually, you may apply to do so by sending an email to the lecturer,
explaining your reasons. However, bear in mind that the requirements and available marks
will be the same as for pairs, so you are strongly advised to work in a team.)

Teaching Servers

Three CSIT teaching servers are available for your use:
(titan|saturn|jupiter).csit.rmit.edu.au. You can log in to these machines
using ssh, for example:

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% ssh [email protected]

where s1234567 is your student number. These servers host the document collection
and other data for the assignments in this course. You are encouraged to develop your
code on these machines. If you choose to develop your code elsewhere, it is your re-
sponsibility to ensure that your assignment submission can be compiled and executed on
(titan|saturn|jupiter).csit.rmit.edu.au, as this is where your code will be run for
marking purposes.

Important: You are required to make regular backups of all of your work. This is good
practice, no matter where you are developing your assignment solutions.

Plagiarism

RMIT University takes plagiarism very seriously. All assignments will be checked with
plagiarism-detection software; any student found to have plagiarised will be subject to
disciplinary action as described in the course guide. Plagiarism includes submitting code
that is not your own or submitting text that is not your own. Allowing others to copy
your work is also plagiarism. All plagiarism will be penalised; there are no exceptions
and no excuses. For further information, please see the Academic Integrity information at
http://www1.rmit.edu.au/academicintegrity.

General Requirements

This section contains information about the general requirements that your assignment
must meet. Please read all requirements carefully before you start.

• You must implement your programs in Java, C, C++, PHP, or Python. Your pro-
grams should be well written, using good coding style and including appropriate use
of comments. Your markers will look at your source code, and coding style may form
part of the assessment of this assignment.

• The submitted programs must be your own code. You should not use existing external
libraries that implement advanced data structures. Where libraries (or in the case
of scripting languages, built-in features beyond simple low-level data types) are used
for data structures such as hash tables, they must be clearly attributed, and it is
up to you to demonstrate a clear understanding of how the library is implemented
in the discussion in your assignment report.

• Your programs may be developed on any machine, but must compile and run on the
course machines, (titan|saturn|jupiter).csit.rmit.edu.au. If your submission
does not compile and run on these machines, it will not be marked.

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• You must include a plain text file called “README.txt” with your submission.
This file should include the name and student ID of all team members at the
top. It needs to clearly explain how to compile and run your programs on
(titan|saturn|jupiter).csit.rmit.edu.au. The clarity of the instructions and
useability of your programs may form part of the assessment of this assignment.

• Paths should not be hard-coded.

• Where your programs need to create auxiliary files, these should be stored in the
current working directory.

• Parts of this assignment will include a written report, this may be in plain text or
PDF format.

• Please ensure that your submission follows the file naming rules specified in the tasks
below. File names are case sensitive, i.e. if it is specified that the file name is
gryphon, then that is exactly the file name you should submit; Gryphon, GRYPHON,
griffin, and anything else but gryphon will be rejected.

Programming Tasks

Have a look at the file /KDrive/SEH/SCSIT/Students/Courses/ISYS1078/2017/a1/latimes
on (titan|saturn|jupiter).csit.rmit.edu.au. It is part of the TREC TIPSTER test
collection, and consists of various articles from the LA Times newspaper.

Here is an example of the markup format:

LA010189-0001

…

…

…

…

The article headline.

…

The text content of the document.

Individual documents are wrapped in …tags. These indicate the begin-
ning and end of each individual document in the collection file.

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The …tags contain a unique identifier for the document. You will
need to keep track of this to refer to documents in the collection.

The …and …tags contains the text
content of the document. This is the actual content of the document that you will need to
index.

Your task is to write two programs. The first will index the collection, gather appropriate
term distribution statistics, and write the index data to disk. The second program will load
the index data, accept text terms as input, and return the appropriate term distribution
statistics for each term.

1 Indexing

Your indexing program must be called index and accept a number of optional command-
line arguments. The invocation specification should be:

% ./index [-p](or equivalent invocation in another programming language) where the optional flag -p
will print the terms being indexed, and the mandatory argumentis the
collection to be indexed. These are described in more detail below.

Note that your implementations must be efficient, making use of appropriate algorithms
and data structures. This will be part of the assessment criteria.

1.1 Parsing Module (10%)

Your first task is to parse the data, tokenising and extracting content terms, and removing
any punctuation and excess markup tags. Punctuation consists of any symbols that are
not letters or numbers. You will need to carefully consider issues of token normalisation
(for example, how to deal with acronyms and hyphenated words).

All content terms should be case-folded to lower-case as they are indexed.

Your program must be called index, and should accept an optional command-line argument
-p. This flag indicates that your program should print all content terms, in the same order
as in the original document, to the standard output stream, stdout. If the flag is not
specified, your program should produce no output to standard out. An example of how
your program might be run is as follows:

% ./index -p /KDrive/SEH/SCSIT/Students/Courses/ISYS1078/2017/a1/latimes

(or equivalent invocation). As your parser encounters each new document, you will need
to assign an ordinal number as a document identifier. These can be assigned sequentially

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(i.e. the first document is 0, the second is 1, and so on). This is how the documents will
be referred to in the inverted list information (see below).

You also need to track the unique document identifier specified in the tags, and
how these map to the integer identifiers that you assign. Your program should therefore
always write an output file to disk, called map, which contains this mapping information.
Auxiliary files such as this must be written to the current working directory.

1.2 Stopping Module (10%)

Stopping is the process of excluding words that have grammatical functions, but contain no
meaning themselves, from consideration during indexing. Examples of such stopwords are
the, of, and and. A stoplist is available on (titan|saturn|jupiter).csit.rmit.edu.au
at /KDrive/SEH/SCSIT/Students/Courses/ISYS1078/2017/a1/stoplist.

Extend your program index with a module to stop the input terms. Your program should
accept an optional command-line argument, -s , where stoplist is a file of
stopwords that are to be excluded from indexing. An example of how your program should
be invoked is:

% ./index [-s ] [-p]Note that the -p option must still be available; when it is specified, your program should
print all content terms that are not stopwords to the standard output stream.

An efficient lookup structure to store the content of the file is a hash table.
It is up to you to choose a suitable hash function for text strings. You will be asked to
explain your implementation in the report (see below).

1.3 Indexing Module (20%)

Extend your program index to build an inverted index. The inverted index needs to
store term occurrence information for all content terms that occur in the file that is being
indexed. For each term t, you need to store:

• The document frequency, ft, a count of the number of documents in the collection in
which term t occurs.

• An inverted list for term t, which consists of postings of the form

< d, fd,t >

where:

– d is the document in which t occurs

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– fd,t is the within-document frequency, a count of how often t occurs in document
d

For example, if the term insomnia occurs in two documents in the collection, twice in
document 10, and three times in document 23, then the inverted list would be:

insomnia: 2 <10, 2> <23, 3>

Note: the punctuation symbols are only used to make the list human-readable. The
actual internal representation of the inverted list would just store a sequence of integers,
represented appropriately, for example 2 10 2 23 3. Your stored lists must not include
the extra punctuation between items. See the lecture notes for further details on the
inverted index and inverted lists.

You can assume that you will be working with collections that are small enough to fit in
main memory.

When your index program has finished constructing the inverted lists for each unique term
that occurs in the collection, the data should be written to disk. Your program should
write three data files:

1. lexicon, containing each unique term that occurs in the collection and a “pointer”
to the inverted list for that term

2. invlists, which contains the inverted list information, consisting only of numerical
data

3. map, which contains the mapping information from document id numbers (as used in
the inverted lists) to the actual document names

These files must be written to the current working directory.

Since the lexicon and inverted lists are stored separately, your lexicon file will need to
include information about the file offset position in invlists where the inverted list for
the corresponding term occurs. Your program should not simply read the invlists file
sequentially from the start each time it is accessed.

It is up to you to design the particulars of the implementation. However, please read the
next section on Querying carefully first, as this is likely to have implications for how you
store your data. You will be asked to explain your implementation in a report (see below).

2 Querying (20%)

Write a program called search that loads your index data, and searches it to retrieve the
inverted lists for particular terms. An example of how your program should be invoked is:

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% ./search