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LIS618 lecture 1 Thomas Krichel 2002-09-15. Organization homepage

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1 LIS618 lecture 1 Thomas Krichel 2002-09-15

2 Organization homepage Contents to be discussed today. Send mail to –Your name –Your secret word for grades delivery Interrupt me with as many questions as possible! Ask for breaks!

3 Proposed Organization Normal lecture Quiz at the beginning of every lecture. Main quiz next week (25% of grade) Search exercise 55% Other quizzes 10% Formal syllabus to be made early next week!

4 Search exercise find victim conduct interview about an information need experienced by the victim, write down expectations search in Dialog and on web discuss results with the victim write essay, no longer than 7 pages.

5 Structure of talk First talk about me, then about you and the course General round trip on theoretical matters. –Context of database searching –Database searching and information retrieval –The retrieval process –Information retrieval models –Retrieval performance evaluation –Query languages Logging on to Dialog Web searching exercise (if time permits)

6 About me Born 1965, in Völklingen (Germany) Studied economics and social sciences at the Universities of Toulouse, Paris, Exeter and Leiceister. PhD in theoretical macroeconomics Lecturer in Economics at the University of Surrey 1993 and 2001 Since 2001 assistant professor at the Palmer School

7 Why? During research assistantship period, (1990 to 1993) I was constantly frustrated with difficult access to scientific literature. At the same time, I discovered easy access to freely downloadable software over the Internet. I decided to work towards downloadable scientific documents. This lead to my library career (eventually).

8 Steps taken I 1993 founded the NetEc project at, later available at as well as at These are networking projects targeted to the economics community. The bulk is –Information about working papers –Downloadable working papers –Journal articles were added later

9 Steps taken II Set up RePEc, a digital library for economics research. Catalogs –Research documents –Collections of research documents –Researchers themselves –Organizations that are important to the research process Decentralized collection, model for the open archives initiative

10 Steps taken III Co-founder of Open Archives Initiative Work on the Academic Metadata Format Co-founded rclis, a RePEc clone for (Research in Computing, Library and Information Science)

11 summary There are three basic types of models in classic information retrieval. Extensions of these types are a matter of research concern and require good mathematical skills. All classic models treat document as individual pieces.

12 Database searching (DS) subset of the subject of information retrieval (IR) DS mainly thought as applicable to the set of large structured databases as opposed to do web searching for those, a general knowledge of what databases are seems useful Concentrate on textual databases

13 traditional social model user goes to a library describes problem to the librarian librarian does the search –without the user present –with the user present hands over the result to the user user fetches full-text or asks a librarian to fetch the full text.

14 economic rational for traditional model In olden days the cost of telecommunication was high. database use costs –cost of communication –cost of access time to the database the traditional model controls an upper bound on costs

15 disintermediation with access cost time gone, the traditional model is under threat there is disintermediation where the librarian looses her role but that may not be good news for information retrieval results –user knows subject matter best –librarian knows searching best

16 Web searching IR has received a lot of impetus through the web, which poses unprecedented search challenges. with more and more data appearing on the web DS may be a subject in decline, because it is primarily concerned with non- web databases

17 Main theory part Literature: "Modern Information Retrieval" by Ricardo Baeza-Yates and Berthier Ribiero-Neto Don't buy it. It is a not a good book.

18 before the IR process provider –define data that is available documents that can be used document operations document structure –index user –user need –IR system familiarity

19 the IR process query expresses user need in a query language processing of query yields retrieved documents calculation of relevance ranking examination of retrieved documents possible relevance cycle

20 main problem user is not an expert at the formulation of a query garbage in garbage out, the retrieval yields poor result ways out –design very intuitive interface –give expert guidance

21 key aid: index index term is a part of the document that has a meaning on its own (usually a noun) retrieval based on index term raises questions –semantics in query or document is lost –matching done in imprecise space of index terms predicting relevance is a central problem the IR model determines the process of relevance ranking

22 taxonomy of classic IR models Boolean, or set-theoretic –fuzzy set models –extended Boolean vector, or algebraic –generalized vector model –latent semantic indexing –neural network model probabilistic –inference network –belief network

23 basic concepts: index term an index term is a word whose semantics help to remember the document's main themes. nouns are mainly used if all words are index terms, the logical view of the document is full text

24 basic concept: weight of index term given all nouns, not all appear to have the same relevance to the text sometimes, we can have a simple measure of the importance of a term, example? more generally, for each indexing term and each document we can associate a weight with the term and the document. usually, if the document does not contain the term, its weight is zero

25 basic concept: mutual term independence Thinking of the weight of a term as a function of the document and the term only implies that it is independent of other terms. This is an important oversimplification. But it allows for fast computation. No study has shown that not assuming independence brings significant performance gain.

26 Boolean model in the Boolean model, the index weight of all index term for any document is 1 if the term appears in the document. It is 0 otherwise. This allows to combine query terms with Boolean operator AND, OR, and NOT thus powerful queries can be written

27 example: a AND (b OR NOT c) 1 2 3 4 5 6 7 a b c a b a c c b c b a

28 advantages of Boolean model supposedly easy to grasp by the user precise semantics of queries implemented in the majority of commercial systems why is it set-theoretic ?

29 problems of Boolean model sharp distinction between relevant and irrelevant documents no ranking possible users find it difficult to formulate Boolean queries

30 Thank you for your attention!

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