We study the basic operation of set union in the global model of differential privacy. In this problem, we are given a universe $U$ of items, possibly of infinite size, and a database $D$ of users. Each user $i$ contributes a subset $W_i \subseteq U$ of items. We want an ($\epsilon$,$\delta$)-differentially private Algorithm which outputs a subset $S \subset \cup_i W_i$ such that the size of $S$ is as large as possible. The problem arises in countless real world applications, and is particularly ubiquitous in natural language processing (NLP) applications. For example, discovering words, sentences, $n$-grams etc., from private text data belonging to users is an instance of the set union problem. In this paper we design new algorithms for this problem that significantly outperform the best known algorithms.

Vertex is a Wrapper Induction system developed at Yahoo! for extracting structured records from template-based Web pages. To operate at Web scale, Vertex employs a host of novel algorithms for (1) Grouping similar structured pages in a Web site, (2) Picking the appropriate sample pages for wrapper inference, (3) Learning XPath-based extraction rules that are robust to variations in site structure, (4) Detecting site changes by monitoring sample pages, and (5) Optimizing editorial costs by reusing rules, etc. The system is deployed in production and currently extracts more than 250 million records from more than 200 Web sites. To the best of our knowledge, Vertex is the first system to do high-precision information extraction at Web scale.

We propose a novel extraction approach that exploits content redundancy on the web to extract structured data from template-based web sites. We start by populating a seed database with records extracted from a few initial sites. We then identify values within the pages of each new site that match attribute values contained in the seed set of records. To filter out noisy attribute value matches, we exploit the fact that attribute values occur at fixed positions within template-based sites. We develop an efficient Apriori-style algorithm to systematically enumerate attribute position configurations with sufficient matching values across pages. Finally, we conduct an extensive experimental study with real-life web data to demonstrate the effectiveness of our extraction approach.

We propose a novel extraction approach that exploits content redundancy on the web to extract structured data from template-based web sites. We start by populating a seed database with records extracted from a few initial sites. We then identify values within the pages of each new site that match attribute values contained in the seed set of records. To match attribute values with diverse representations across sites, we define a new similarity metric that leverages the templatized structure of attribute content. Specifically, our metric discovers the matching pattern between attribute values from two sites, and uses this to ignore extraneous portions of attribute values when computing similarity scores. Further, to filter out noisy attribute value matches, we exploit the fact that attribute values occur at fixed positions within template-based sites. We develop an efficient Apriori-style algorithm to systematically enumerate attribute position configurations with sufficient matching values across pages. Finally, we conduct an extensive experimental study with real-life web data to demonstrate the effectiveness of our extraction approach.