60-538: information retrievaljlu.myweb.cs.uwindsor.ca/538/538intro2018.pdfranking search results...

what is IRcourse schedulegrading scheme

60-538: Information Retrieval

September 9, 2018

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Outline

1 what is IR

2 course schedule

3 grading scheme

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Outline

1 what is IR

2 course schedule

3 grading scheme

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IR not long time ago

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now IR is mostly about search engines

there are many search engines ...

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IR is more than web search

These days we frequently think first of web search, but there aremany other cases:

digital library search

E-mail search, Searching your desktop and laptop computers

Corporate knowledge bases, local business search, expertsearch

Legal information retrieval, patent search

news search

image and video search

(micro-)blog search

product search, federated search

social search, community Q&A, question-answering

recommender systems

opinion mining

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definition of information retrieval

Information retrieval (IR) is finding material (usually documents) ofan unstructured nature (usually text) that satisfies an informationneed from within large collections (usually stored on computers).

–from IIR book.

Introduction to Information Retrieval, by C. Manning, P.Raghavan, and H. Schutze. Cambridge University Press

book website https://nlp.stanford.edu/IR-book/

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Structured vs. unstructured data

in the 90’s. todayInformation retrieval is finding material of an unstructured naturethat satisfies an information need from within large collections

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other definitions

Jaime Arguello

Information retrieval (IR) is the science and practice ofdesigning, developing, and evaluating systems that matchinformation seekers with the information they seek.

Gerard Salton, 1968:

Information retrieval is a field concerned with the structure,analysis, organization, storage, and retrieval ofinformation.

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The search task

Given a query and a corpus, find relevant items

query: user’s expression of their information need

corpus: a repository of retrievable items

relevance: satisfaction of the user’s information need

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Why is IR fascinating?

Information retrieval is an uncertain process

Query

users don’t know what they wantusers don’t know how to convey what they wantcomputers can’t elicit information like a librariancomputers can’t understand natural language text

Relevance

the search engine can only guess what is relevantthe search engine can only guess if a user is satisfiedover time, we can only guess how users adjust their short- andlong-term behavior

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classic search model

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A query is an impoverished description of the user’sinformation need

Highly ambiguous to anyone other than the user

Retrieval Model

A formal method that predicts the degree of relevance of adocument to a query

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taxonomy of IR models

Document Property

text

links

multimedia

IR models

Boolean

vector

probalistic

Semistructured text

proximal nodes

xml based

web

page rank

hubs and authorities (HITs)

Multimedia

image retrieval

audio

video

Set theoretic

fuzzy

extended boolean

set-based

algebraic

generalized vector

LSI

NN

probablistic

BM25

language models

Bayersian networks

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Boolean Retrieval Model

The user describes their information need using booleanconstraints (e.g., AND, OR, and AND NOT)

The burden is on the user to formulate a good boolean query

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Example

Which plays of Shakespeare contain the words Brutus ANDCaesar but NOT Calpurnia?

One choice: use grep command in unix.

grep all of Shakespeare’s plays for Brutus and Caesar,strip out lines containing Calpurnia

Why is that not the answer?

Slow (for large corpora)NOT Calpurnia is non-trivialOther operations (e.g., find the word Romans nearcountrymen) not feasibleRanked retrieval (best documents to return)

so we need to index the text

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what is an index

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index construction process

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Initial stages of text processing

Tokenization

Cut character sequence into word tokens

NormalizationMap text and query term to same form

You want U.S.A. and USA to match

StemmingWe may wish different forms of a root to match

authorize, authorization

Stop wordsWe may want to omit very common words (modern methodsmay not)

the, a, to, of

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postings

Multiple term entriesin a single documentare merged.

Split into Dictionaryand Postings

Doc. frequencyinformation is added.

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query processing

Consider processing the query:

Brutus AND Caesar

Locate Brutus in the Dictionary;

Retrieve its postings.

Locate Caesar in the Dictionary;

Retrieve its postings.

Merge the two postings (intersect the document sets):

brutus 1 2 4 11 31 45 173 174

caesar 1 2 4 5 6 16 57 132

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Outline

1 what is IR

2 course schedule

3 grading scheme

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tentative schedule

boolean model

text transformation

web crawling. Data cleaning (e.g. near-duplicate detection)

build a search engine using Lucene

vector space model

evaluation methods in information retrieval

link analysis and PageRank

document classification

document clustering

representation learning

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Text Book

[IIR] Introduction to Information Retrieval, by C. Manning, P.Raghavan, and H. Schutze. Cambridge University Press, 2008.

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Other reference books

SE Search Engines: Information Retrieval in Practice, by BruceCroft, Donald Metzler and Trevor Strohman.

MIR Modern Information Retrieval, by R. Baeza-Yates and B.Ribeiro-Neto. 2-nd edition 2010.

MMD Anand Rajaraman and Jeff Ullman, Mining of massivedatasets , 2013.

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IIR 02: The term vocabulary and postings lists

Phrase queries: “Stanford University”

Proximity queries: Gates near Microsoft

We need an index that captures position information forphrase queries and proximity queries.

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IIR 04: Index construction

masterassign

mapphase

reducephase

assign

parser

splits

parser

parser

inverter

postings

inverter

inverter

a-f

g-p

q-z

a-f g-p q-z

a-f g-p q-z

a-f

segmentfiles

g-p q-z

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statistic properties of text

0 1 2 3 4 5 6 7

01

23

45

67

log10 rank

log1

0 cf

Zipf’s law, heaps’ law, power law.

the mechanism: Yule process, Preferential attachment

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IIR 06: Scoring, term weighting and the vector spacemodel

Ranking search results

Boolean queries only give inclusion or exclusion of documents.For ranked retrieval, we measure the proximity between the query andeach document.One formalism for doing this: the vector space model

Key challenge in ranked retrieval: evidence accumulation for a term ina document

1 vs. 0 occurence of a query term in the document3 vs. 2 occurences of a query term in the documentUsually: more is betterBut by how much?Need a scoring function that translates frequency into score or weight

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Language models

assign a probability to a sequence of m words by means of aprobability distribution.

How to compute this joint probability:

P(its,water , is, so, transparent, that) (1)

P(w1w2 . . .wn) = ΠP(wi )? (2)

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Text classification & Naive Bayes

Text classification = assigning documents automatically topredefined classes

Examples:

CS vs. Non-CS paperspositive/negative reviewsSpams

Naive Bayes (Multinomial and Bernoulli model), Supportvector machine, feature selection, representation learning,neural networks.

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Neural network based representation learning

Answer analogical questions, e.g

Man : Woman = King :?

The answer will be Queen.An application of deep learning

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clustering

Flat clustering

Hierarchical agglomerative clustering (HAC)

Single-link and complete-link clustering

Centroid and group-average agglomerative clustering (GAAC)

Bisecting K-means

How to label clusters automatically

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HAC

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Latent Semantic Indexing

how to find semantically related documents?matrix decompositionSVD

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Crawling

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Link analysis / PageRank

which web page is more important?

who are in a community?

PageRank algorithm

graph analysis and mining. Modularity maximizationalgorithms.

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Outline

1 what is IR

2 course schedule

3 grading scheme

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marking scheme

exam 40%

project 50%

class participation 10%

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project

indexing and searching engine

CS papers

enhance the search engine by adding one or more features,such as:

semantic searchclassificationclusteringrankingpersonalizationrecommendation...

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open source search engines

Lemur

C++

used by IR researchers

compare advanced IR techniques

Lucene

Java-based

relatively simple IR techniques

Galago

Java-based

used by the book [SE] Search Engines: Information Retrievalin Practice, by Bruce Croft et al.

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60-538: information retrievaljlu.myweb.cs.uwindsor.ca/538/538intro2018.pdfranking search results...

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