SemTech 2011 Semantic Search tutorial

Editor's Notes

1. Search is a form of content aggregation
2. - In recent years we have witnessed tremendous interest and substantial economic exploitation of search technologies, both at web and enterprise scale. In this regard, technologies for Information Retrieval (IR) can be distinguished from solutions in the field of Database (DB) and Knowledge-based Expert Systems (KB). Whereas IR applications support the retrieval of documents (document retrieval), DB and KB systems deliver more precise answers (data retrieval). The technical differences between these two paradigms can be broken down into three main dimensions, i.e. the representation of the user need (query model), the underlying resources (data model) and the matching technique. The representation of user need and resource content in current IR systems is still almost exclusively achieved by the lightweight syntax-centric models such as the predominant keyword paradigm (i.e. keyword queries matched against bag-of-words document representation). While these systems have shown to work well for topical search, i.e. retrieve documents based on a topic, they usually fail to address more complex information needs. Using more expressive models for the representation of the user need, and leveraging the structure and semantics inherent in the data, DB and KB systems allow for complex queries, and for the retrieval of concrete answers that precisely match them.
3. Semantic search can be seen as a retrieval paradigm Centered on the use of semanticsIncorporates the semantics entailed by the query and (or) the resources into the matching process, it essentially performs semantic search.
4. Another trend resulting from this convergence of textual, structured and semantic data is the need for hybrid semantic search systems. Whilestandard IR focuses on the retrieval of documents, the DB and KB systems are built for data retrieval. As opposed to these types of systems, hybrid search systems manage the different types of data in a holistic way, and support the retrieval of answers that are integrated units of information, possibly assembled from different types of data. In such a system, there is not only a convergence at the
5. Close to the topic of keyword-search in databases, except knowledge-bases have a schema-oblivious designDifferent papers assume vastly different query needs even on the same type of data
6. >> >> Intro Session: motivation, overview etc.: 10 min >> >>1)Representation of the Search Space (M) 45>> >>2)Offline Preprocessing: Crawling and Indexing (P) 60>> >>3)Query Processing (T) 4)Matching (T) 90>> >>5)Ranking 60 >> >>6)Result Presentation (45)>> >>7)Evaluation (45)>> >>Demo Session (30)>> >> Wrap-up Session (10)
7. Approximate many results  need rankingRanking also needed in the case where qp is complete and sound, but queries and data representation so imprecise such that we have to deal with too many results
8. Miss structural information in textsHyperlinksLinguistic structurePositional information
9. - Real world objects
10. SELECT Returns all, or a subset of, the variables bound in a query pattern match. CONSTRUCT Returns an RDF graph constructed by substituting variables in a set of triple templates. ASK Returns a boolean indicating whether a query pattern matches or not. DESCRIBE Returns an RDF graph that describes the resources found. Graph patterns are defined recursively. A graph pattern may have zero or more optional graph patterns, and any part of a query pattern may have an optional part. In this example, there are two optional graph patterns.Section 6 introduces the ability to make portions of a query optional; Section 7 introduces the ability to express the disjunction of alternative graph patterns; and Section 8 introduces the ability to constrain portions of a query to particular source graphs. Section 8 also presents SPARQL's mechanism for defining the source graphs for a query.Basic graph patterns allow applications to make queries where the entire query pattern must match for there to be a solution. For every solution of a query containing only group graph patterns with at least one basic graph pattern, every variable is bound to an RDF Term in a solution. However, regular, complete structures cannot be assumed in all RDF graphs. It is useful to be able to have queries that allow information to be added to the solution where the information is available, but do not reject the solution because some part of the query pattern does not match. Optional matching provides this facility: if the optional part does not match, it creates no bindings but does not eliminate the solution.The UNION pattern combines graph patterns; each alternative possibility can contain more than one triple pattern:SPARQL provides a means of combining graph patterns so that one of several alternative graph patterns may match. If more than one of the alternatives matches, all the possible pattern solutions are found.
11. Web data: Text+ Linked Data+ Semi-structured RDF+ Hybrid datathat can be conceived as forming data graphsHear abour bob and alice all the time (in computer science literatures), want to find out more… build Semantic Web search engine. To address complex information needs by exploiting Web data:- Query as a set of constrains Match structured data Match text
12. - Less than 5 percent of IR papers deal with query processing and the aspect of efficiency
13. Partitioning has impact on performance!)Blocking: iterator-based approachesNon-blocking: good for streaming, good we cannot wait for some parts of the results to be completely worked-offLink data: cannot wait for sources, (some are slower then other) thus better to push data into query processing as the they come instead of pulling data and wait (busy waiting)Top-k:
14. -phrase patterns (e.g., “X is the capital of Y”) for large scale extraction. Such simple patterns, when coupled with the richness and redundancy of theWeb, can be very useful in scraping millions or even billions of facts from the Web.- patterns: Matched when keywords or data types Xi appear in sequence. Matched if all keywords/data types/patterns appear within an m-words window.For extraction: relation patternsFor text search: entity patterns -When not assuming that all relevant data can be extracted such matching against text still needed: Hybrid search
15. Given some materialized indexes  no joins at all Given sorted inputs  sorted merge join
16. Given some materialized indexes  no joins at all Given sorted inputs  sorted merge joinjoin
17. Every task is a challenge of itself, some more some less well elaboratedThere are separate challenges for every problems
18. >> >> Intro Session: motivation, overview etc.: 10 min >> >>1)Representation of the Search Space (M) 45>> >>2)Offline Preprocessing: Crawling and Indexing (P) 60>> >>3)Query Processing (T) 4)Matching (T) 90>> >>5)Ranking 60 >> >>6)Result Presentation (45)>> >>7)Evaluation (45)>> >>Demo Session (30)>> >> Wrap-up Session (10)
19. Approximate many results  need rankingRanking also needed in the case where qp is complete and sound, but queries and data representation so imprecise such that we have to deal with too many results
20. Web data: Text+ Linked Data+ Semi-structured RDF+ Hybrid datathat can be conceived as forming data graphsHear abour bob and alice all the time (in computer science literatures), want to find out more… build Semantic Web search engine. To address complex information needs by exploiting Web data:- Query as a set of constrains Match structured data Match text
21. Syntactic works vs.works at Semantic works vs. employ
22. text which contains a large mentions of “Berlin” is likely to be about “Berlin”i is more likely to be the correct interpretation of K when terms in K co-occur in a large number of context (bag of words) associated with i“Berlin and apartment” more often co-occur in the geographic location context/topic than in the context of people“Berlin and apartment” more often co-occur in the geographic location context/topic than in the context of people