Implicit Queries for Email

Vitor R. Carvalho

(Joint work with Joshua Goodman, at Microsoft Research)

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Search + Email

Email is the number 1 activity on the internet Fast, easy and cheap

Search is number 2 Highly lucrative (billion market – targeted ads)

Why not put them together? Make users happy Make more money

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Implicit Queries for Email

Find good search keywords in email messages 1 Click (or less) for users to do search

Lots of possible User Interfaces Add hyperlinks to words in message List keywords in a sidebar Perform search automatically; show results (Gmail)

Closely related to finding keywords for advertising

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Main Contributions

1) Extract Keyphrases Similar to Information

Extraction Several features

2) Rank/Display Maxent probability

estimates

3) Select/Filter Restrict to MSN Query

Logs (7.5 million entries)

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Email Dataset

20 Hotmail volunteers (not MS employees) Spam, “subs” and “wanted” folders 6 human annotators labeled 1143 msgs according to

the following instructions:

These are mail messages from real Hotmail users. Imagine that you were the recipient of each message. If your email program were to automatically perform a query to a search engine like MSN Search or Google for you, what wordsor phrases would you want the engine to search for?

In some messages, there may be no words worth searching for. In others, there may be several. When possible, the words or phrases should actually occur in the messages you annotate.

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TF-IDF baseline

Extract all possible keyphrases from email (up to 5 tokens)

Rank keyphrases by TF-IDF scores

TF = term frequency: number of times each keyphrase occurs in the email message

IDF = 1/DF = number of documents the keyphrase occurs in corpus

Top1 – percentage of “ranked-1st keyphrases” that were labeled as relevant

Top10 – number of keyphrases in the top-10 rank that were labeled as relevant, normalized by the total number of relevant keyphrases (no message had more than 10 relevant keyphrases)

Keyphrases TF-IDF

Port Angeles 0.450

Lake Crescent 0.120

Atlanta 0.090

Mt. Baker 0.045

… …

Top-1(%)

Top-10(%)

TF-IDF 4.87 9.86

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First Improvement:

Constrain Results to Query Log File

Query log file: top 7.5 million queries to MSN Search

Only return keyphrases from an email if they occur in the query log file Faster – only process

keyphrases in message that occur in the query log file.

Creates some errors Removes some errors – such as

“occur in the” Works better!

Top-1(%)

Top-10(%)

TF-IDF 4.87 9.86

TF-IDF with query log restriction

10.86 30.56

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Adding More Features1) Query Log Frequency

Frequency and log(frequency) of keyphrase

2) Capitalization Word capitalized before/after, # capitalized initials in phrase,

# capitalized letters in phrase, etc

3) Phrase Length Number of characters and number of tokens

4) TF + IDF based features TF, IDF, from Body and from Subject

5) Punctuation and Alphanumeric Punct before/after, has no alpha, has numbers only, etc

6) Email Specific Has FW: in subject, has RE: in subject

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Maximum Entropy Learner (a.k.a. Logistic Regression)

Computes

y is 1 if keyphrase is relevant is the feature vector (previous slide features) Weight vector w learned using a type of

Generalized Iterative Scaling alg. (SCGIS).

Rank and cutoff based on probability estimate

exp( | )

1 exp

x wP y x

x w

x

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Rank and cutoff based on probability

Keyphrases

Port Angeles Lake Crescent Olympic National Park Atlanta Mt. Baker Hurricane Ridge Marymere Fall Beaches on the west coast

Probability

0.121

0.105

0.034

0.031

0.022

0.012

0.0090.004

Cutoff = 10%

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Performance AnalysisTop-1 Top-10

TF-IDF (one single feature and no query log restriction) 4.87 9.86

TF-IDF (one single feature) 10.86 30.56

Baseline → 2 features: TF and IDF 11.33 32.03

Baseline + Query Frequency 23.13* 41.82*

Baseline + Phrase Length 12.81 33.25

Baseline + Capitalization 21.43* 44.71*

Baseline + Punctuation 13.47 33.02

Baseline + Email Specific 11.34 32.03

Baseline + Alphanumeric 11.66 32.65

Baseline + All Features 33.55* 55.26*

10-fold cross-validation on the 1143 email messages

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Performance Analysis

Implicit Feedback Performance

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Top 1 Score Top 10 Score

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Using Other Learning Algorithms

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Opportunities for Future Work

1. Relax the Query Log restriction

2. Use real advertisement data

3. Use feedback from users (user can be annoyed, etc)

4. Use personalization (age, gender, place, etc)

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Conclusions

Implicit Query task → finding good search keywords Use of large query log from MSN Search Maxent to combine features and output probabilities

– ranking and display cutoff Most meaningful features are associated with query

frequency and capitalization

Results several times better than baseline TF-IDF (top 1 and top 10 scores)

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Thank you