SemTech 2011 Semantic Search tutorial

1. Peter Mika| Yahoo Research, Spain pmika@yahoo-inc.com Thanh Tran | Institute AIFB, KIT, Germany Tran@aifb.uni-karlsruhe.de Semantic Search TutorialIntroduction

2. About the speakers Peter Mika Semantic Search group at Yahoo! Barcelona Semantic Search, Web Object Retrieval, Natural Language Processing Tran Duc Thanh Semantic Search group at AIFB Semantic Search, Semantic Data Management, Linked Data Query Processing

3. Agenda Introduction (5 min) Semantic Web data (50 min) The RDF data model Publishing RDF Crawling and indexing RDF data Query processing (35 min) Ranking (25 min) Result presentation (15 min) Semantic Search evaluation (15 min) Demos (15 min) Questions (5 min)

4. Why Semantic Search? I. “We are at the beginning of search.“ (Marissa Mayer) Solved large classes of queries, e.g. navigational Heavy investment in computational power Remaining queries are hard, not solvable by brute force, and require a deep understanding of the world and human cognition Background knowledge and metadata can help to address poorly solved queries

5. Poorly solved information needs Ambiguous searches parishilton Long tail queries george bush (and I mean the beer brewer in Arizona) Multimedia search parishilton sexy Imprecise or overly precise searches jimhendler pictures of strong adventures people Precise searches for descriptions countries in africa 32 year old computer scientist living in barcelona reliable digital camera under 300 dollars Many of these queries would not be asked by users, who learned over time what search technology can and can not do.

6. Example: multiple interpretations

7. Why Semantic Search? II. The Semantic Web is now a reality Large amounts of data published in RDF Heterogeneous data of varying quality Users who are not skilled in writing complex queries (e.g. SPARQL) and may not be experts in the domain Searching data instead or in addition to searching documents Direct answers Novel search tasks

8. Information box with content from and links to Yahoo! Travel Example: direct answers in search Points of interest in Vienna, Austria Shopping results from Yahoo! Shopping Since Aug, 2010, ‘regular’ search results are ‘Powered by Bing’

9. Novel search tasks Aggregation of search results e.g. price comparison across websites Analysis and prediction e.g. world temperature by 2020 Semantic profiling recommendations based on particular interests Semantic log analysis understanding user behavior in terms of objects Support for complex tasks e.g. booking a vacation using a combination of services

10. Document retrieval and data retrieval Information Retrieval (IR) support the retrieval of documents (document retrieval) Representation based on lightweight syntax-centric models Work well for topical search Not so well for more complex information needs Web scale Database (DB) and Knowledge-based Systems (KB) deliver more precise answers (data retrieval) More expressive models Allow for complex queries Retrieve concrete answers that precisely match queries Not just matching and filtering, but also joins Limitations in scalability

11. Combination of document and data retrieval Documents with metadata Metadata may be embeddedinside the document I’m looking for documents that mention countries in Africa. Data retrieval Structured data, but searchable text fields I’m looking for directors, who have directed movies where the synopsis mentions dinosaurs.

12. Semantic Search Target (combination of) document and data retrieval Semantic search is a retrieval paradigm that Exploits the structure/semantics of the data or explicit background knowledge to understand user intent and the meaning of content Incorporates the intent of the query and the meaning of content into the search process (semantic models) Wide range of semantic search systems Employ different semantic models, possibly at different steps of the search process and in order to support different tasks

13. Semantic models Semantics is concerned with the meaning of the resources made available for search Various representations of meaning Linguistic models: models of relationships among words Taxonomies, thesauri, dictionaries of entity names Inference along linguistic relations, e.g. broader/narrower terms Natural language search Conceptual models: models of relationships among objects Ontologies capture entities in the world and their relationships Inference along domain-specific relations Knowledge-based search We will focus on conceptual models in this tutorial In particular, the RDF/OWL conceptual model for representing classes in a domain, and describing their instances

14. Semantic Search – a process view Knowledge Representation Semantic Models Resources Documents DocumentRepresentation

15. Semantic Search systems For data / document retrieval, semantic search systems might combine a range of techniques, ranging from statistics-based IR methods for ranking, database methods for efficient indexing and query processing, up to complex reasoning techniques for making inferences!

16. Semantic Web data

17. Semantic Web Sharing data across the Web Standard data model RDF A number of syntaxes (file formats) RDF/XML, RDFa Powerful, logic-based languages for schemas OWL, RIF Query languages and protocols HTTP, SPARQL

18. Resource Description Framework (RDF) Each resource (thing, entity) is identified by a URI Globally unique identifiers Locators of information Data is broken down into individual facts Triples of (subject, predicate, object) A set of triples (an RDF graph) is published together in an RDF document RDF document foaf:Person type example:roi name “Roi Blanco”

19. Linking resources Friend-of-a-Friend ontology Roi’s homepage type example:roi foaf:Person name “Roi Blanco” sameAs Yahoo type worksWith example:roi2 example:peter email “pmika@yahoo-inc.com”

20. Publishing RDF Linked Data Data published as RDF documents linked to other RDF documents Community effort to re-publish large public datasets (e.g. Dbpedia, open government data) RDFa Data embedded inside HTML pages Recommended for site owners by Yahoo, Google, Facebook SPARQL endpoints Triple stores (RDF databases) that can be queried through the web

21. Linked Data A web of RDF documents in parallel to the current Web often implemented as wrappers around databases or APIs The four rules of Linked Data: Use URIs to identify things. Use HTTPURIs so that these things can be referred to and looked up ("dereference") by people and user agents. Provide useful information about the thing when its URI is dereferenced, using standard formats such as RDF-XML. Include links to other, related URIs in the exposed data to improve discovery of other related information on the Web.

22. Linked Data Advantages: No change to the publishing of the HTML documents Data can be published by third party (e.g. Dbpedia) Disadvantages: Web servers need to be configured to properly handle URIs that identify concepts instead of documents Not favored by search engines Lack of use cases Crawling needs to be changed Authority is difficult to determine Tools Triple stores (Virtuoso, Oracle etc.) and front-ends (Pubby) RDB-to-RDF mappers (e.g. D2RQ, Triplify) Validators (Vapour) Linked Data browsers (many)

23. The state of Linked Data Rapidly growing community effort to (re)publish open datasets as Linked Data In particular, scientific and government datasets see linkeddata.org Less commercial interest, real usage

24. Metadata in HTML 1995: HTML meta tags 1996: Simple HTML Ontology Extensions (SHOE) 1998: RDF/XML RDF/XML in HTML RDF linked from HTML 2003: Web 2.0 Tagging Microformats Metadata in Wikipedia Machine tags in Flickr 2005: eRDF 2008: RDFa 1.0 2011: RDFa 1.1 2012: Microdata?

25. HTML meta tags <HTML> <HEAD profile="http://dublincore.org/documents/dcq-html/"> <META name="DC.author" content="Peter Mika"> <LINK rel="DC.rights copyright" href="http://www.example.org/rights.html" /> <LINK rel="meta" type="application/rdf+xml" title="FOAF" href= "http://www.cs.vu.nl/~pmika/foaf.rdf"> </HEAD> … </HTML>

26. Microformats (μf) Agreements on the way to encode certain kinds metadata in HTML Reuse of semantic-bearing HTML elements Based on existing standards Minimality Microformats exist for a limited set of objects hCard (persons and organizations) hCalendar (events) hResume hProduct hRecipe Varying degrees of support and stability hCard and rel-tag are widely supported Community centered around microformats.org Specifications and discussions are hosted there

27. Microformats: limitations No shared syntax Each microformat has a separate syntax tailored to the vocabulary No formal schemas Limited reuse, extensibility of schemas Unclear which combinations are allowed No datatypes No namespaces, unique identifiers (URIs) no interlinking mapping between instances is required Always appears in the HTML <body>

28. Example: the hCard microformat <div class="vcard"> <a class="email fn" href="mailto:jfriday@host.com">Joe Friday</a> <div class="tel">+1-919-555-7878</div> <div class="title">Area Administrator, Assistant</div> </div> <cite class="vcard"> <a class="fn url" rel="friend colleague met” href="http://meyerweb.com/"> Eric Meyer</a> </cite> wrote a post (<cite> <a href="http://meyerweb.com/eric/thoughts/2005/12/16/tax-relief/"> Tax Relief</a></cite>) about an unintentionally humorous letter he received from the <a class="fn org url" href="http://irs.gov/"> Internal Revenue Service</a> .

29. RDFa W3C standard for embedding RDF data in HTML documents A set of new HTML attributes to be used in head or body A specification of how to extract the data from these attributes RDFa is just a syntax, you have to choose a vocabulary separately RDFa 1.0 is a W3C Recommendation since October, 2008 RDFa Primer RDFa 1.1 is a small update on RDFa to make it easier to use Currently Working Draft (March 31, 2011) Updated version of the RDFa Primer (April 19, 2011) RDFa API for accessing RDFa data in a webpage in the browser from JavaScript Currently Working Draft (April 19, 2011)

30. RDFa 1.1 Changes New vocab attribute to define the default namespace for the document or subtree Profile documents to define multiple namespace prefixes The prefix attribute as a recommended replacement of xmlns You can use URIs even where only CURIEs where allowed before RDFa 1.1 is backward compatible with RDFa 1.0 RDFa 1.1 is recommended if you want to use HTML5

31. When to use RDFa Choose microformats when you find a microformat that fits your needs and supported by your consumers Microformats are first option because they are simple Yahoo supports all major microformats, see the documentation It’s a common misconception that RDFa requires XHTML or that it’s compatible with HTML5 It’s compatible with HTML4, HTML5, XHTML If you find none that perfectly fits your needs then you need RDFa Microformats have a fixed schema: you can not add your own attributes Example: a social networking site with user profiles VCard is a good candidate, but for example it doesn’t have a way to express the user’s social connections You either live without this, or go with RDFa

32. Example: Facebook’s Like and the Open Graph Protocol The ‘Like’ button provides publishers with a way to promote their content on Facebook and build communities Shows up in profiles and news feed Site owners can later reach users who have liked an object Facebook Graph API allows 3rd party developers to access the data Open Graph Protocol is an RDFa-based format that allows to describe the object that the user ‘Likes’

33. Example: Facebook’s Open Graph Protocol RDF vocabulary to be used in conjunction with RDFa Simplify the work of developers by restricting the freedom in RDFa Activities, Businesses, Groups, Organizations, People, Places, Products and Entertainment Only HTML <head> accepted <html xmlns:og="http://opengraphprotocol.org/schema/"> <head> <title>The Rock (1996)</title> <meta property="og:title" content="The Rock" /> <meta property="og:type" content="movie" /> <meta property="og:url" content="http://www.imdb.com/title/tt0117500/" /> <meta property="og:image" content="http://ia.media-imdb.com/images/rock.jpg" /> … </head> ...

34. Example: Yahoo! Enhanced Results (was: SearchMonkey) Guide for publishers to mark-up their pages for common types of objects Product, Local, News, Video, Events, Documents, Discussion, Games Using popular microformats and RDF vocabularies Copy-paste code Validator Yahoo as a consumer See later

35. Example: Google’s Rich Snippets Google accepts popular microformats and its own RDFa vocabulary Similar approach to RDFa as Facebook Validator to check if the markup is correct Google displays enhanced results based on this metadata Rich Snippets

36. RDFa on the rise 510% increase between March, 2009 and October, 2010 Percentage of URLs with embedded metadata in various formats

37. Microdata Currently under standardization at the W3C Originally part of the HTML5 spec, but now a separate document Similar to microformats, but with the extensibility of RDFa Introduce new terms using reverse domain names or full URIs HTML5 also has a number of “semantic” elements such as <time>, <video>, <article>…

38. Microdata example <div itemscope itemid=“http://www.yahoo.com/resource/person”> My name is Neil. My band is called Four Parts Water. I was born on <time itemprop="birthday" datetime="2009-05-10">May 10th 2009</time>. <img itemprop="image" src=”me.png" alt=”me”> </div

39. The state of metadata in HTML 5-10% of webpages contain some explicit metadata Depending on how you count… Too many competing approaches Too many formats: microformats vs RDFa vs Microdata When using RDFa, publishers may need to use multiple different vocabularies to satisfy everyone

40. Crawling the Semantic Web Linked Data Similar to HTML crawling, but the the crawler needs to parse RDF/XML (and others) to extract URIs to be crawled Semantic Sitemap/VOID descriptions RDFa Same as HTML crawling, but data is extracted after crawling Mika et al. Investigating the Semantic Gap through Query Log Analysis, ISWC 2010. SPARQL endpoints Endpoints are not linked, need to be discovered by other means Semantic Sitemap/VOID descriptions

41. Data fusion Ontology matching Widely studied in Semantic Web research, see e.g. list of publications at ontologymatching.org Unfortunately, not much of it is applicable in a Web context due to the quality of ontologies Entity resolution Logic-based approaches in the Semantic Web Studied as record linkage in the database literature Machine learning based approaches, focusing on attributes Graph-based approaches, see e.g. the work of Lisa Getoor are applicable to RDF data Improvements over only attribute based matching Blending Merging objects that represent the same real world entity and reconciling information from multiple sources

42. Data quality assessment and curation Heterogeneity, quality of data is an even larger issue Quality ranges from well-curated data sets (e.g. Freebase) to microformats In the worst of cases, the data becomes a graph of words Short amounts of text: prone to mistakes in data entry or extraction Example: mistake in a phone number or state code Quality assessment and data curation Quality varies from data created by experts to user-generated content Automated data validation Against known-good data or using triangulation Validation against the ontology or using probabilistic models Data validation by trained professionals or crowdsourcing Sampling data for evaluation Curation based on user feedback

43. Indexing Search requires matching and ranking Matching selects a subset of the elements to be scored The goal of indexing is to speed up matching Retrieval needs to be performed in milliseconds Without an index, retrieval would require streaming through the collection The type of index depends on the query model to support DB-style indexing IR-style indexing

44. IR-style indexing Index data as text Create virtual documents from data One virtual document per subgraph, resource or triple typically: resource Key differences to Text Retrieval RDF data is structured Minimally, queries on property values are required

45. Horizontal index structure Two fields (indices): one for terms, one for properties For each term, store the property on the same position in the property index Positions are required even without phrase queries Query engine needs to support the alignment operator ✓ Dictionary is number of unique terms + number of properties Occurrences is number of tokens * 2

46. Vertical index structure One field (index) per property Positions are not required But useful for phrase queries Query engine needs to support fields Dictionary is number of unique terms Occurrences is number of tokens ✗ Number of fields is a problem for merging, query performance

47. Indexing using MapReduce MapReduce is the perfect model for building inverted indices Map creates (term, {doc1}) pairs Reduce collects all docs for the same term: (term, {doc1, doc2…} Sub-indices are merged separately Term-partitioned indices Peter Mika. Distributed Indexing for Semantic Search, SemSearch 2010.

48. Query Processing

49. Structure Taxonomy of retrieval approaches Query processing for semantic search Types of semantic data Formalisms for querying semantic data Approaches General task: hybrid graph pattern matching Matching keyword query against text Matching structured query against structured data Matching keyword query against structured data Matching structured query against text (a hybrid case) Main tasks, challenges and opportunities

50. Taxonomy of retrieval approaches (1) Data retrieval problem A collection of resources represented by the data model G Information needs expressed as queries in Q Retrieval is the task of efficiently computing results from G that are relevant to the queries in Q Document retrieval vs. data retrieval Differences in query and data representation and matching Efficiently retrieve structured data that exactly match formal information needs expressed as structured queries Effectively rank textual results that match ambiguous NL / keyword queries to a certain degree (notions of relevance)

51. Taxonomy of retrieval approaches (2) Exact Complete Sound Query Matching <ul><li>Approximate

52. Not complete

53. Not sound

54. Ranked

55. Best effort

56. Top-k</li></ul>Data Query processing mainly focuses on efficiency of matching whereas ranking deals with degree of matching (relevance)!

57. Query processing for Semantic Search (1) The underlying collection of resources is represented by semantic data G ranging from Structured data with well defined schemas Semi-structured data with incomplete or no schemas Data that largely comprise text Hybrid / embedded data Targeted information needs Q are of varying complexity, captured using different formalisms and querying paradigms Natural language texts and keywords Form-based inputs Formal structured queries Semantic search, mainly, is the task of efficiently computing results(query processing) from G that are relevantto the queries in Q (ranking)

58. Query processing for Semantic Search (2) Keywords NL Questions Form- / facet-based Inputs Structured Queries (SPARQL) Query Matching Data OWL ontologies with rich, formal semantics Structured RDF data Semi-Structured RDF data RDF data embedded in text (RDFa)

59. Query processing for Semantic Search (3) Textual Data Keyword query on textual data (IR/document retrieval) Structured query on textual data Semantic Search target different group of users, information needs, and types of data. Query processing for semantic search is hybrid combination of techniques! Unstructured Query Structured Query Keyword query on structured data Structured query on structured data (DB/data retrieval) Structured Data

60. Types of data models (1) Textual Bag-of-words Represent documents, text in structured data,…, real-world objects (captured as structured data) Lacks “structure” in text, e.g. linguistic structure, hyperlinks, (positional information) Structure in structured data representation term (statistics) In combination with Cloud Computing technologies, promising solutions for the management of `big data' have emerged. Existing industry solutions are able to support complex queries and analytics tasks with terabytes of data. For example, using a Greenplum. combination Cloud Computing Technologies solutions management `big data' industry solutions support complex ……

61. Types of data models (2) Textual Structured Resource Description Framework (RDF) Represent real-world objects, services, applications, …. documents Resource attribute values and relationships between resources Schema Picture creator Person Bob

62. Types of data models (3) Textual Structured Hybrid RDF data embedded in text (RDFa)

63. Types of data models – RDFa (1) … <div about="/alice/posts/trouble_with_bob"> <h2 property="dc:title">The trouble with Bob</h2> <h3 property="dc:creator">Alice</h3> Bob is a good friend of mine. We went to the same university, and also shared an apartment in Berlin in 2008. The trouble with Bob is that he takes much better photos than I do: <div about="http://example.com/bob/photos/sunset.jpg"> <imgsrc="http://example.com/bob/photos/sunset.jpg" /> Beautiful Sunset by Bob. </div> </div> … adoptedfrom : http://www.w3.org/TR/xhtml-rdfa-primer/

64. Types of semantic data – RDFa (2) Bob is a good friend of mine. We went to the same university, and also shared an apartment in Berlin in 2008. The trouble with Bob is that he takes much better photos than I do: content content adoptedfrom : http://www.w3.org/TR/xhtml-rdfa-primer/

65. Types of semantic data - conclusion Semantic data in general can be conceived as a graph with text and structured data items as nodes, and edges represent different types of relationships including explicit semantic relationships and vaguely specified ones such as hyperlinks!

66. Formalisms for querying semantic data (1) Example information need “Information about a friend of Alice, who shared an apartment with her in Berlin and knows someone working at KIT.” Unstructured queries Fully-structured queries Hybrid queries: unstructured + structured

67. Formalisms for querying semantic data (2) Example information need “Information about a friend of Alice, who shared an apartment with her in Berlin and knows someone working at KIT.” Unstructured NL Keywords apartment Berlin Alice shared

68. Formalisms for querying semantic data (3) Example information need “Information about a friend of Alice, who shared an apartment with her in Berlinand knows someone working at KIT.” Unstructured Fully-structured SPARQL: BGP, filter, optional, union, select, construct, ask, describe PREFIX ns: <http://example.org/ns#> SELECT ?x WHERE { ?x ns:knows ? y. ?y ns:name “Alice”. ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT” }

69. Formalisms for querying semantic data (4) Fully-structured Unstructured Hybrid: content and structure constraints “shared apartment Berlin Alice” ?x ns:knows ? y. ?y ns:name “Alice”. ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT”

70. Formalisms for querying semantic data (5) Fully-structured Unstructured Hybrid: content and structure constraints “shared apartment Berlin Alice” ?x ns:knows ? y. ?y ns:name “Alice”. ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT”

71. Formalisms for querying semantic data - conclusion Semantic search queries can be conceived as graph patterns with nodes referring to text and structured data items, and edges referring to relationships between these items!

72. Processing hybrid graph patterns (1) Example information need “Information about a friend of Alice, who shared an apartment with her in Berlin and knows someone working at KIT.” ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT” apartment shared Berlin Alice ?y ns:name “Alice”. ?x ns:knows ? y age works 34 trouble with bob FluidOps Peter sunset.jpg Bob is a good friend of mine. We went to the same university, and also shared an apartment in Berlin in 2008. The trouble with Bob is that he takes much better photos than I do: Beautiful Sunset author title Semantic Search Germany Alice creator author creator knows year Germany 2009 Bob Thanh knows located works KIT

73. Processing hybrid graph patterns (2) Matching hybrid graph patterns against data

74. Matching keyword query against text <ul><li>Retrieve documents

75. Inverted list (inverted index)</li></ul>keyword  {<doc1, pos, score, ...>, <doc2, pos, score, ...>, ...} <ul><li>AND-semantics: top-k join</li></ul>shared Berlin Alice shared Berlin Alice D1 D1 D1 shared berlin alice = = shared

76. Matching structured query against structured data <ul><li>Retrieve data for triple patterns

77. Index on tables

78. Multiple “redundant” indexes to cover different access patterns

79. Join (conjunction of triples)

80. Blocking, e.g. linear merge join (required sorted input)

81. Non-blocking, e.g. symmetric hash-join

82. Materialized join indexes</li></ul>?x ns:knows ?y. ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT” Per1 ns:works?v ?vns:name “KIT” SP-index PO-index = = = Per1 ns:worksIns1 Ins1ns:name KIT Per1 ns:works Ins1 Ins1 ns:name KIT

83. Matching keyword query against structured data <ul><li>Retrieve keyword elements

84. Using inverted index</li></ul> keyword  {<el1, score, ...>, <el2, score, ...>,…} <ul><li>Exploration / “Join”

85. Data indexes for triple lookup

86. Materialized index (paths up to graphs)

87. Top-k Steiner tree search, top-k subgraph exploration </li></ul>Alice Bob Bob KIT Alice KIT ↔ ↔ = = Alice ns:knowsBob Inst1ns:name KIT Bobns:worksInst1

88. Matching structured query against text <ul><li>Based on offline IE (offline see Peter’s slides)

89. Based on online IE, i.e., “retrieve “ is as follows

90. Derive keywords to retrieve relevant documents

91. On-the-fly information extraction, i.e., phrase pattern matching “X title Y”

92. Retrieve extracted data for structured part

93. Retrieve documents for derived text patterns, e.g. sequence, windows, reg. exp.

94. Index

95. Inverted index for document retrieval and pattern matching

96. Join index  inverted index for storing materialized joins between keywords

97. Neighborhood indexes for phrase patterns</li></ul>?x ns:knows ?y. ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT” KIT name knows name KIT Hybrid case

98. Query processing – main tasks Retrieval Documents , data elements, triples, paths, graphs Inverted index,…, but also other indexes (B+ tree) Index documents, triples materialized join paths Join Different join implementations, efficiency depends on availability of indexes Non-blocking join good for early result reporting and for “unpredictable” linked data scenario Query Matching Data

99. Query processing – more tasks Disjunction, aggregation, grouping Join order optimization Approximate Approximate the search space Approximate the results (matching, join) Parallelization Top-k Use only some entries in the input streams to produce k results Multiple sources Federation, routing On-the-fly mapping, similarity join Hybrid Join text and data Query Matching Data

100. Query processing on the Web - research challenges and opportunities Large amount of semantic data Data inconsistent, redundant, and low quality Large amount of data embedded in text Large amount of sources Large amount of links between sources <ul><li>Optimization parallelization,

101. Approximation

102. Hybrid querying and data management

103. Federation, routing

104. Online schema mappings

105. Similarity join </li></li></ul><li>Ranking

106. Structure Problem definition Types of ambiguities Ranking paradigms Model construction Content-based Structure-based

107. Ranking – problem definition Query <ul><li>Ambiguities arise when representation is incomplete / imprecise

108. Ambiguities at the level of

109. elements (content ambiguity)

110. structure between elements (structure ambiguity)</li></ul>Matching Data Due to ambiguities in the representation of the information needs and the underlying resources, the results cannot be guaranteed to exactly match the query. Ranking is the problem of determining the degree of matching using some notions of relevance.

111. Content ambiguity ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT” apartment shared Berlin Alice ?y ns:name “Alice”. ?x ns:knows ? y age works 34 trouble with bob FluidOps Peter sunset.jpg Bob is a good friend of mine. We went to the same university, and also shared an apartment in Berlin in 2008. The trouble with Bob is that he takes much better photos than I do: Beautiful Sunset author title Semantic Search Germany Alice creator author creator knows year Germany 2009 Bob Thanh knows located works KIT What is meant by “Berlin” in the query? What is meant by “Berlin” in the data? A city with the name Berlin? a person? What is meant by “KIT” in the query? What is meant by “KIT” in the data? A research group? a university? a location?

112. Structure ambiguity ?x ns:knows ?z. ?z ns: works ?v. ?v ns:name “KIT” apartment shared Berlin Alice ?y ns:name “Alice”. ?x ns:knows ? y age works 34 trouble with bob FluidOps Peter sunset.jpg Bob is a good friend of mine. We went to the same university, and also shared an apartment in Berlin in 2008. The trouble with Bob is that he takes much better photos than I do: Beautiful Sunset author title Semantic Search Germany Alice creator author creator knows year Germany 2009 Bob Thanh knows located works KIT What is the connection between “Berlin” and “Alice”? Friend? Co-worker? What is meant by “works”? Works at? employed?

113. Ambiguity Recall: query processing is matching at the level of syntax and semantics Ambiguities arise when data or query allow for multiple interpretations, i.e. multiple matches Syntactic, e.g. works vs. works at Semantic, e.g. works vs. employ “Aboutness”, i.e., contain some elements which represent the correct interpretation Ambiguities arise when matching elements of different granularities Does icontains the interpretation for j, given some part(s) of i (syntactically/semantically) match j E.g. Berlin vs. “…we went to the same university, and also, we shared an apartment in Berlin in 2008…” Strictly speaking, ranking is performed after syntactic / semantic matching is done!

114. Features: What to use to deal with ambiguities? What is meant by “Berlin”? What is the connection between “Berlin” and “Alice”? Content features Frequencies of terms: d more likely to be “about” a query term k when d more often, mentions k (probabilistic IR) Co-occurrences: terms K that often co-occur form a contextual interpretation, i.e., topics (cluster hypothesis) Structure features Consider relevance at level of fields Linked-based popularity

115. Ranking paradigms Explicit relevance model Foundation: probability ranking principle Ranking results by the posterior probability (odds) of being observed in the relevant class: P(w|R) varies in different approaches, e.g., binary independence model, 2-poisson model, relevancemodel

116. Ranking paradigms No explicit notion of relevance: similarity between the query and the document model Vector space model (cosine similarity) Language models (KL divergence)

117. Model construction How to obtain Relevance models? Weights for query / document terms? Language models for document / queries?

118. Content-based model construction Document statistics, e.g. Term frequency Document length Collection statistics, e.g. Inverse document frequency Background language models <ul><li> An object is more likely about “Berlin”?

119. When it contains a relatively high number of mentions of the term “Berlin”

120. When the number of mentions of this term in the overall collection is relatively low</li></li></ul><li>Structure-based model construction Consider structure of objects during content-based modeling, i.e., to obtain structured content-based model Content-based model for structured objects, documents and for general tuples <ul><li> An object is more likely about “Berlin”?

121. When one of its (important) fields contains a relatively high number of mentions of the term “Berlin”</li></li></ul><li>Structure-based model construction PageRank Link analysis algorithm Measuring relative importance of nodes Link counts as a vote of support The PageRank of a node recursively depends on the number and PageRank of all nodes that link to it (incoming links) ObjectRank Types and semantics of links vary in structured data setting Authority transfer schema graph specifies connection strengths Recursively compute authority transfer data graph <ul><li> An object about “Berlin” is more important than one another?

122. When a relatively large number of objects are linked to it</li></li></ul><li>Taxonomy of ranking approaches Explicitly vs. non-explicitly relevance-based Content-based ranking Structure-based ranking Content- and-structure-based ranking

123. Result Presentation

124. Search interface Input and output functionality helping the user to formulate complex queries presenting the results in an intelligent manner Semantic Search brings improvements in Query formulation Snippet generation Adaptive and interactive presentation Presentation adapts to the kind of query and results presented Object results can be actionable, e.g. buy this product Aggregated search Grouping similar items, summarizing results in various ways Filtering (facets), possibly across different dimensions Task completion Help the user to fulfill the task by placing the query in a task context

125. Query interpretation “Snap-to-grid”: find the most likely interpretation of the query given the ontology or a summary of the data See Query Processing Display the system’s interpretation of the user query Offer one or more interpretations, possibly while the user is typing

126. Example: Freebase suggest

127. Example: TrueKnowledge Q: “How many people live in Shanghai?” I: What is the population of Shanghai (Shanghainese: Zånhae), the metropolis in eastern China and a direct-controlled municipality of the People's Republic of China? A: The population of Shanghai on November 7th 2010 is approximately 19,300,389. (Extrapolated from a population of 18,884,600 in 2008 and a population of 19,210,000 on June 6th 2010.)

128. Snippet generation using metadata Yahoo displays enriched search results for pages that contain microformat or RDFa markup using recognized ontologies Displaying data, images, video Example: GoodRelations for products Enhanced results also appear for sites from which we extract information ourselves Also used for generating facets that can be used to restrict search results by object type Example: “Shopping sites” facet for products Documentation and validator for developers http://developer.search.yahoo.com Formerly: SearchMonkey allowed developers to customize the result presentation and create new ones for any object type

129. Example: Yahoo! Enhanced Results Enhanced result with deep links, rating, address.

130. Automated snippet summarization Generate search result snippets given a query and a search result Penin et al. Snippet Generation for Semantic Web Search Engines, ASWC 2010 Search results are ontologies

131. Example: Facets in Yahoo! Search Click to restrict results to shopping sites

132. Example: Yahoo! Vertical Intent Search Related actors and movies

133. Adaptive presentation: semantic bookmarking Extract objects from pages tagged/bookmarked by a user Visualize the extracted objects Tabular display Sorting on attributes Map Tracking changes in data Alert me when the price drops below… Prototype: house search application Delicious profiles Extracting housing data from popular Spanish real-estate sites

134. Adaptive presentation: semantic bookmarking

135. Interactive presentation: Time Explorer Deliverable of the LivingKnowledge European Project Not a Yahoo product http://fbmya01.barcelonamedia.org:8080/future/ Won the HCIR 2010 challenge Tool for understanding current news stories what are the events that led to a particular situation? what are the important entities for a given topic? (people,places,dates, etc.) what entities are important at a given time? How do their relationships change? what are the predictions made of a given topic?

136. Interactive presentation: Time Explorer Technology Named Entity Recognition (persons, organizations) Temporal expression mining Inverted (sentence and document) index Forward index (archive) for retrieving relevant entities Ranking of both documents and relevant entities Display Two synchronized timelines showing relevant documents and the volume of documents Entity relationships Sentiments (future work)

137. Example: Time Explorer

138. Evaluation

139. Semantic Search evaluation at SemSearch 2010/2011 Started at SemSearch 2010 Two tasks Entity Search Queries where the user is looking for a single real world object Pound et al. Ad-hoc Object Retrieval in the Web of Data, WWW 2010. List search (new in 2011) Queries where the user is looking for a class of objects Billion Triples Challenge 2009 dataset Evaluated using Amazon’s Mechanical Turk See Halpin et al. Evaluating Ad-Hoc Object Retrieval, IWEST 2010 Prizes sponsored by Yahoo! Labs (2011)

140. Entity Search Track Entity Search retrieval of data related to a single entity Queries Selected from the Search Query Tiny Sample v1.0 dataset, provided by the Yahoo! Webscope program Real web search queries sampled from the US query log of January, 2009 Queries asked by at least three different users and with long number sequence removed (privacy reasons) 50 selected queries that name an entity explicitly (but may also provide context) Last year: same type of queries, but a mix of Microsoft and Yahoo! Logs

141. List query track List queries Queries that describe a set of entities The answer is a closed set Relatively small number of possible answers The answer is not likely to change Hand-picked but not hand-written Yahoo! Search logs Queries from the Tiny Sample v1.0 dataset Queries with clicks on Wikipedia TrueKnowledge Recent queries

142. Data set Same as Billion Triples Challenge 2009 data set Blank nodes are encoded as URIs A data set combining crawls of multiple semantic search engines doesn’t necessarily match the current state of the Web doesn’t necessarily match the coverage of any particular search engine Final dataset

143. Collecting the results Submissions via semsearch.yahoo.com NTNU, IIIT Hyderabad, DERI, U of Delaware, Daiict max. 3 submissions per team per track Pooling of results Top 20 results are evaluated Despite validation, still problems e.g. N-Triples encoded URIs, lowercased URIs Collecting triples for each result All triples where the URI is the subject Discarded URIs that didn’t appear as subject Rendering result display Values are clipped at 300 chars (last # or / for object-properties) RDF built-ins shown first Preference to English language values

144. semsearch.yahoo.com

145. Assessment with Amazon Mechanical Turk Evaluation using non-expert judges Paid $0.2 per 12 results Typically done in 1-2 minutes $6-$12 an hour Sponsored by the European SEALS project Each result is evaluated by 5 workers Workers are free to choose how many tasks they do Makes agreement difficult to compute Number of tasks completed per worker (2010)

146. Evaluation form

147. Evaluation form

148. Catching the bad guys Payment can be rejected for workers who try to game the system An explanation is commonly expected, though cheaters rarely complain We opted to mix control questions into the real results Gold-win cases that are known to be perfect Gold-loose cases that are known to be bad Metrics Avg. and std. dev on gold-win and gold-loose results Time to complete

149. Lessons learned Finding complex queries is not easy Query logs from web search engines contain simple queries Semantic Web search engines are not used by the general public Computing agreement is difficult Each judge evaluates a different number of items Result rendering is critically important The Semantic Web is not necessarily all DBpedia sub30-RES.3 40.6% DBpedia sub31-run3 93.8% Dbpedia Follow up experiments validated the Mechanical Turk approach Blanco et al. Repeatable and Reliable Search System Evaluation using Crowd-Sourcing, SIGIR2011

150. Next steps Achieve repeatability Simplify our process and publish our tools Automate as much as possible… except the Turks ;) Web site for evaluation Continuous submission? Positioning compared to other evaluation campaigns TREC Entity Track Question Answering over Linked Data SEALS campaigns Join the discussion at semsearcheval@yahoogroups.com

151. Demos

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