Скачать презентацию Vocabulary languages in searching Connection indexing searching Скачать презентацию Vocabulary languages in searching Connection indexing searching

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Vocabulary & languages in searching Connection: indexing searching © Tefko Saracevic 1 Vocabulary & languages in searching Connection: indexing searching © Tefko Saracevic 1

Basic assertion Indexing and searching: inexorably connected – you cannot search that was not Basic assertion Indexing and searching: inexorably connected – you cannot search that was not first indexed in some manner or other – indexing of documents or objects is done in order to be searchable • there are many ways to do indexing – to index one needs an indexing language • there are many indexing languages – even taking every word in a document is an indexing language Knowing searching is knowing indexing © Tefko Saracevic 2

General definitions Vocabulary [Encarta Dictionary] “ 1. words known LANGUAGE - all the words General definitions Vocabulary [Encarta Dictionary] “ 1. words known LANGUAGE - all the words used by or known to a particular person or group, or contained in a language as a whole” Language “ 1. speech of group the speech of a country, region, or group of people, including its diction, syntax, and grammar 2. system of communication a system of communication with its own set of conventions or special words” © Tefko Saracevic 3

From general to specific • These general definitions are valid for application in indexing From general to specific • These general definitions are valid for application in indexing & searching to define – – – index terms indexing vocabulary indexing language search terms search vocabulary query (request, search) language © Tefko Saracevic 4

Specific Index term a word or phrase that denotes (describes) a concept & connotes Specific Index term a word or phrase that denotes (describes) a concept & connotes (implies) a class index term “table” describes a and implies many kinds of tables: for which, if desired, we may have more specific index terms © Tefko Saracevic 5

Specific. . . Indexing vocabulary a set of index terms used in a domain Specific. . . Indexing vocabulary a set of index terms used in a domain or for a set of documents or objects • it could be even a single document or object e. g. a book Indexing language an indexing vocabulary together with rules – syntax, grammar – for their application and use © Tefko Saracevic 6

Specific. . . Search terms a counterpart to index terms, also denoting a concept Specific. . . Search terms a counterpart to index terms, also denoting a concept and connoting a class for a search Search vocabulary a set of search terms in a domain or available in a systems Query language a search vocabulary together with rules for their use in searching © Tefko Saracevic 7

More “An index language is the language used to describe documents and requests. The More “An index language is the language used to describe documents and requests. The elements of the index language are index terms, which may be derived from the text of the document to be described, or may be arrived at independently. The vocabulary of an index language may be controlled or uncontrolled. ” (van Rijsbergen, 1979) © Tefko Saracevic 8

Controlled vocabulary • Predetermined – indicating what terms to be used in indexing – Controlled vocabulary • Predetermined – indicating what terms to be used in indexing – may show definition of and relations between terms • examples: thesaurus, subject heading list, classification • Also indicates terms that may be selected for searching • An indexing AND a searching tool • Human constructed – and costly to construct and use © Tefko Saracevic 9

Uncontrolled vocabulary • Derived from documents – nowadays automatically • using various ways or Uncontrolled vocabulary • Derived from documents – nowadays automatically • using various ways or algorithms – constant issue: which way is “better” • Used to construct inverted indexes • a concordance, such as of the Bible, indicating place and position of each word mentioned in the text is an inverted index • monks used to do it in 12 th century, computers do it today • Inverted indexes are used for free text searching © Tefko Saracevic 10

Controlled vs. free text searching • Endless source of debate & controversy • But, Controlled vs. free text searching • Endless source of debate & controversy • But, each has its place for given circumstance & retrieval goal • Each has strengths & weaknesses • can you list or find a list comparing them? • Users mostly use free text searching • Professional searchers use both as warranted • As option: KNOW THY CONTROLLED VOCABULARY © Tefko Saracevic 11

Inverted indexes Useful to know how they function to understand search & retrieval. Steps: Inverted indexes Useful to know how they function to understand search & retrieval. Steps: 1. Each document is indexed – every word in a document is taken as index term with exception of stop words – position in text is noted 2. Indexes for all documents are merged • index terms are arranged alphabetically in the bowel of the system • under each index term are document numbers in which it appears & position in text for that document © Tefko Saracevic 12

So, when you search for digital AND libraries: 1. computer takes all documents under So, when you search for digital AND libraries: 1. computer takes all documents under digital 2. and all documents under libraries 3. compares to “see” which documents have both terms and then 4. provides you the list of those documents in a default format or you may choose a format • This is also called “coordinate indexing” – coordination is done at time of searching © Tefko Saracevic 13

Variation: when you search for digital (WITH) libraries or “digital libraries” i. e as Variation: when you search for digital (WITH) libraries or “digital libraries” i. e as a phrase 1. computer goes through the same steps as before but then also 2. “looks” for documents where digital is positioned right before libraries • remember: computer “knows” position of each term in each document, each sentence • So searching for a phrase is a form of searching of terms connected with AND but in a given sequence © Tefko Saracevic 14

Example of inverted file Doc # Text 1 Slow brown truck arrived 2 Shipment Example of inverted file Doc # Text 1 Slow brown truck arrived 2 Shipment of brownies damaged in a fire 3 Delivery of brownies arrived in a slow truck 4 Shipment of brownies arrived in a truck For simplicity documents have one sentence. Stop words: “a, ” “of, ” “in. ” Search for slow AND truck gets as results documents 1 and 3 since both contain slow and truck Search for slow (w) truck retrieves only document 3 in which slow is 7 th and truck is 8 th, they are right next to each other. Doc 1 has both words, but not next to each other thus not retrieved © Tefko Saracevic Inverted index Term Position in doc number arrived (1: 4), (3: 4), (4: 4) brown (1: 2) brownies (2: 3), (3: 3), (4: 3) damaged (2: 4) delivery (3: 1) fire (2: 7) shipment (2: 1), (4: 1) slow (1: 1), (3: 7) truck (1: 3), (3: 8), (4: 7) 15

Thesaurus • Good old Peter Mark Roget had a most useful idea & did Thesaurus • Good old Peter Mark Roget had a most useful idea & did a great job • Following this idea thesaurus became THE major tool for controlled vocabulary in information retrieval (IR) – starting in 1950’s & to this day many IR thesauri have been developed – all have a similar structure & function – but they are difficult & costly to construct © Tefko Saracevic 16

What is a thesaurus? “For writers, it is a tool like Roget’s one with What is a thesaurus? “For writers, it is a tool like Roget’s one with words grouped and classified to help select the best word to convey a specific nuance of meaning. For indexers and searchers, it is an information storage and retrieval tool: a listing of words and phrases authorized for use in an indexing system, together with relationships, variants and synonyms, and aids to navigation through thesaurus. ” (Milstead, 2000) © Tefko Saracevic 17

more… “A thesaurus to an information scientist is a controlled set of the terms more… “A thesaurus to an information scientist is a controlled set of the terms used to index information in a database, and therefore also to search for information in that database so the same concepts are represented by the same term. ” (Batty, 1998) © Tefko Saracevic 18

Basic thesaurus components • For each entry thesaurus has a classification grid: – Descriptor Basic thesaurus components • For each entry thesaurus has a classification grid: – Descriptor (DE) – an index term that has • • • Scope note (SN) – context in which used Broader terms (BT) – higher in a hierarchy Narrower terms (NT) – lower in a hierarchy Related terms (RT) – other connected descriptors Used for (UF) – synonyms that are not descriptors – Note: not all of these may be present for every descriptor • A searcher or indexer can use these as a guide for selection/rejection & for browsing to get ideas © Tefko Saracevic 19

Examples of thesauri • Thesauri have been constructed for great many domains, from A Examples of thesauri • Thesauri have been constructed for great many domains, from A to Z – here are some lists • international & multilingual thesauri • online thesauri • among them ERIC Thesaurus (we use it for example) – BUT: different thesauri may and do treat the same descriptor (index term) differently • having different, more or fewer narrower, broader, related terms • thus it is dangerous to use them interchangeably © Tefko Saracevic 20

Standard structure With variations on theme, thesauri have similar conceptual structure to guide searcher Standard structure With variations on theme, thesauri have similar conceptual structure to guide searcher or indexer: Broader terms - BT Related terms - RT Descriptor - DE Used for - UF Synonyms Scope note - SN Narrower terms - NT Note: Every descriptor doesn't have to have all of these © Tefko Saracevic 21

Same thesaurus but … • Examples of ERIC (Educational Resources Information Center) thesaurus as Same thesaurus but … • Examples of ERIC (Educational Resources Information Center) thesaurus as used differently in different systems: 1. ERIC own system 2. ERIC file on DIALOG (begin 1) 3. ERIC file on OVID (accessible through RUL) • • Notice how each uses thesaurus displays & search in its own way, but principles still the same Oh well… © Tefko Saracevic 22

ERIC online thesaurus on ERIC • Allows for – searching for words that are ERIC online thesaurus on ERIC • Allows for – searching for words that are included in descriptors by category or all categories – browsing alphabetically – browsing in one of about 40 categories • Search for library in all categories found 76 descriptors that have “library” included • Out of these selected library education © Tefko Saracevic 23

ERIC online thesaurus on ERIC descriptor library education © Tefko Saracevic 24 ERIC online thesaurus on ERIC descriptor library education © Tefko Saracevic 24

ERIC thesaurus on DIALOG • In a convoluted way ERIC thesaurus (and other ones) ERIC thesaurus on DIALOG • In a convoluted way ERIC thesaurus (and other ones) can be displayed on DIALOG (and other vendors, such as OVID) • How? – begin in file 1 – ERIC – then expand a desired term – here we used term library – you will see under R that certain terms have related terms – meaning that these are thesaurus entries – then expand on one of those to see related terms – then you can browse & choose which ones to use in search • And here are Print Screens of the process © Tefko Saracevic 25

going … Expand library © Tefko Saracevic 26 going … Expand library © Tefko Saracevic 26

RT indicates related terms going … 45237 items have library This one has 14 RT indicates related terms going … 45237 items have library This one has 14 related terms © Tefko Saracevic 27

going … We now chose descriptor LIBRARY ADMINISTRATION and expand on that one Neat going … We now chose descriptor LIBRARY ADMINISTRATION and expand on that one Neat trick: You can expand on expand & get related terms © Tefko Saracevic 28

These are now R terms of various type going … 14 related terms for These are now R terms of various type going … 14 related terms for this one are listed Can expand on this one to see other RT You can also select any of these to search © Tefko Saracevic 29

going … We have now selected r 10 – library expenditures © Tefko Saracevic going … We have now selected r 10 – library expenditures © Tefko Saracevic 30

going … And this is what we got Now we can view some items going … And this is what we got Now we can view some items in a chosen format or we can further modify this search - add refine, … © Tefko Saracevic 31

gone This is one of the items we got Descripto rs with * are gone This is one of the items we got Descripto rs with * are major Descripto rs used for this item al on iti dd ex A nd i s erm t © Tefko Saracevic 32

ERIC thesaurus on OVID (accessed through RUL) For library ask to map as thesauru ERIC thesaurus on OVID (accessed through RUL) For library ask to map as thesauru s term © Tefko Saracevic 33

going … There are more down there but we choose this one to expand going … There are more down there but we choose this one to expand © Tefko Saracevic 34

going … Entries for descriptor Electronic Libraries Continue to search for AND © Tefko going … Entries for descriptor Electronic Libraries Continue to search for AND © Tefko Saracevic 35

going … Retrieved & ready to display © Tefko Saracevic 36 going … Retrieved & ready to display © Tefko Saracevic 36

gone © Tefko Saracevic Choose format you want for this item 37 gone © Tefko Saracevic Choose format you want for this item 37

Relevance feedback • Method for using information in items judged relevant to further refine Relevance feedback • Method for using information in items judged relevant to further refine or change the search – e. g. in relevant items we can browse titles, descriptors, identifiers, abstracts … to get leads for further search terms & tactics • in some advanced systems this may be done automatically © Tefko Saracevic 38

Query expansion • Method for adding, modifying, changing search terms in query – to Query expansion • Method for adding, modifying, changing search terms in query – to broaden, narrow, focus, change … terms • Many sources can be used – relevance feedback, thesauri, dictionaries, textbooks, documents, catalogs, & people: users, colleagues, your own mind & experience • Some systems suggest terms for query expansion © Tefko Saracevic 39

Conclusion • At the base of all searching are – – terms vocabularies languages Conclusion • At the base of all searching are – – terms vocabularies languages but a variety exists • In reality in searching there is no completely controlled or uncontrolled vocabulary – matter of degree – & most importantly, matter of mastery © Tefko Saracevic 40

symbolically; controlled & free vocabulary © Tefko Saracevic 41 symbolically; controlled & free vocabulary © Tefko Saracevic 41

thank you! © Tefko Saracevic 42 thank you! © Tefko Saracevic 42