Vocabulary languages in indexing searching Connection indexing searching

Vocabulary & languages in indexing & searching Connection: indexing searching tefkos@rutgers. edu; http: //comminfo. rutgers. edu/~tefko/ © Tefko Saracevic 1

Central idea Indexing and searching: inexorably connected – you cannot search that was not first indexed in some manner or other • to be searched everything is and must be indexed somehow even if it is not called “indexed” – indexing of documents or objects is done in order to be searchable • there are great many ways to do indexing – to index one needs an indexing language • there are great many indexing languages – even taking every word in a document is an indexing language Knowing searching is knowing indexing Tefko Saracevic 2

To. C 1. 2. 3. 4. Definitions Controlled & uncontrolled vocabularies Inverted indexes Thesaurus © Tefko Saracevic 3

1. Definitions A few concepts from general to specific © Tefko Saracevic 4

Defined concepts valid for application in indexing & searching General – language – vocabulary Tefko Saracevic Specific – – – – index terms indexing vocabulary indexing language descriptors keywords search terms search vocabulary query language 5

General definitions [Encarta Dictionary] Language 1. communication with words: the human use of spoken or written words as a communication system 2. system of communication: a system of communication with its own set of conventions or special words Tefko Saracevic Vocabulary 1. words of language: all the words used in a language as a whole 2. words of subject area: the set of words associated with a subject or area of activity, or used by an individual person 6

Specific definitions Starting from the most basic concept: 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 7

More definitions. . . 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 8

Variation on Index term Descriptor Word or phrase used to identify a topic or idea. Part of a controlled vocabulary, normally listed in a thesaurus (defined later). May be used as a search term. Keyword A significant word from a text of a record which can be used as a search term in a free text search to retrieve all the records containing it – Could be assigned manually, but now done mostly automatically – key entry in automatic indexing Tefko Saracevic 9

Searching definitions Question request by a user related to user’s information need, task, problem at hand Question analysis breakdown & elaboration of concepts in a question to be translated into search terms Query question or part thereof as stated for searching according to rules of a given system © Tefko Saracevic 10

more. . . Search term a counterpart to index term, 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 11

elaboration … • Question is what user • Example: Question: asks and what you may – What are some major historical developments then have elaborated in the area of • Query is what is asked information retrieval? of computer to match – • Transformed into query what is put in for – history information searching retrieval (in Google) • Question is transformed – history AND into query information(w)retrieval (in Dialog) (plus you have to select which file(s) to search Tefko Saracevic 12

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 13

2. Controlled & uncontrolled vocabularies Approaches, tensions Tefko Saracevic 14

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 15

Example of controlled vocabularies Medical Subject Headings (Me. SH) of the National Library of Medicine • One of the largest & most comprehensive – used in indexing & searching • More than 22, 000 descriptors, with more than 106, 000 cross references © Tefko Saracevic • More than 139, 000 Supplementary Concept Records • Approximately 50 publication types (Journal Article, News, Editorial, Review, Randomized Controlled Trial, etc) • Done by indexers • But also experimenting with semi automatic indexing 16

Uncontrolled vocabulary • Derived from texts – natural language in documents – nowadays automatically • using various ways or algorithms – constantly tested: which algorithm is better? • Used to construct inverted indexes • In turn, inverted indexes are used for free text searching Tefko Saracevic 17

Comparison of vocabularies Controlled Uncontrolled or free • The idea of a controlled • The idea is to follow natural vocabulary is to reduce the language expressions as variability of expressions they occur in documents used to characterize • Could be automatic documents being indexed & – great advantage searched for – algorithms constantly changing & improving • Manual, costly, time • e. g. parsing phrases, consuming, also semi connections automatic in some systems • Prevailing in many • Dynamic – needs constant applications changing, updating © Tefko Saracevic 18

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? – this is a good search assignment • Users mostly use free text searching • Professional searchers use both as warranted – have to know when • Professional credo: KNOW THY CONTROLLED VOCABULARY so you can apply it in searching as/or when needed Tefko Saracevic 19

3. Inverted indexes Use in searching Tefko Saracevic 20

Inverted indexes & searching 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, if any – position in text is noted, even for stop words 2. Indexes for all documents are merged • index terms are arranged alphabetically in the bowel of the system, so they can be searched • under each index term are document numbers in which it appears & position in text for that document Tefko Saracevic 21

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 that have in the document both terms, no matter where • This is also called “coordinate indexing” – Tefko Saracevic coordination is done at time of searching 22

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 23

Example of searches in 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 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 For simplicity documents have one sentence. Stop words: “a” “of” “in” – but their position counted 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) 24

Everything is inverted consequences for searching • All words in all fields are inverted, no matter if – in title, full text, descriptor, author … • Thus all are searchable • In some systems (but not all) phrases are parsed & thus searchable – but in most phrases are searched as Aw. B, or “AB” Tefko Saracevic • But beware: – search for libraries as descriptor • e. g. libraries/DE in Dialog – will retrieve ALL other descriptors where libraries appear in addition to descriptor libraries itself • e. g. academic libraries, public libraries, special libraries, research libraries … – but there are search tricks to avoid that 25

4. Thesaurus A major tool for controlled vocabularies in information retrieval (IR) Tefko Saracevic 26

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 27

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 28

Thesaurus • Good old Peter Mark Roget had a most useful idea in 1890 s & did a great job • Following this idea thesaurus became THE major tool for controlled vocabulary in IR – starting in 1950’s & to this day great many IR thesauri have been developed for all kinds of subjects • including, for instance, in information science – all have a similar structure & function – but they are difficult & costly to construct & maintain Tefko Saracevic 29

Standards, software • Subject to international standards: – “Guidelines for the Construction, Format, and Management of Monolingual Controlled Vocabularies” ANSI/NISO Standard Z 39. 19 – followed by “Construction of Controlled Vocabularies. A Primer” • A number of software products are available for thesaurus construction and maintenance – e. g. as listed by American Society for Indexing © Tefko Saracevic 30

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 31 Tefko Saracevic

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 32

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 33

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 the same ERIC thesaurus displays & search in its own way, but principles still the same Oh well… Tefko Saracevic 34

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 libraries in all categories found 50 descriptors that have “library” included • Out of these selected libraries Tefko Saracevic 35

ERIC online thesaurus on ERIC descriptor libraries Descriptor Other descriptors – one could browse © Tefko Saracevic 36

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 printed screens of the process Tefko Saracevic 37

Note on command expand (E) in Dialog • Dialog (and some other systems) has a neat way to display all entries in any inverted index alphabetically – command is Expand or e – it could be done in any of the indexes – basic and additional © Tefko Saracevic For instance: e library will provide alpha list of term library in basic index & then after expanding again you can see related terms (see next) e Au=Saracevic will provide alpha list of all entries in the author additional index around that name 38

going Expand library Tefko Saracevic 39

going … RT indicates related terms 46865 items have library This one has 14 related terms Tefko Saracevic 40

going … We now chose descriptor LIBRARY ADMINISTRATION and expand on that one Neat trick: You can expand on expand & get related terms out of Eric thesaurus Tefko Saracevic 41

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 42

going … We have now selected r 15 – library services to search for documents Tefko Saracevic 43

going … And this is the no. of items we got Now we can view some items in a chosen format or we can further modify this search - add refine, … Tefko Saracevic 44

gone This is one of the items we got Descripto rs used for this item Tefko Saracevic Additional index terms 45

Start ERIC search on OVID (accessed through RUL) Start with © Tefko Saracevic 46

Automatically gets you to thesaurus This one of selected to enlarge Tefko Saracevic 47

Allows you to select thesaurus (or not) This one of selected to enlarge Tefko Saracevic 48

Then go to ERIC thesaurus on OVID (accessed through RUL) s Scr oll De or t crip © Tefko Saracevic 49

gone • • • Next go and select additional terms Or search for libraries only See no. of results Select fields and formats by making a check and happy going … suggestion: repeat this exercise Point being that the same thesaurus is handled differently by different databases Tefko Saracevic 50

Relevance feedback an important search tactic • Method for using information in items judged relevant to further refine or change the search – first you find a relevant document (or documents) – in relevant document(s) you browse titles, descriptors, identifiers, abstracts … to get leads (e. g. keywords) for further search terms & tactics – then you search for those • in some advanced systems this may be done automatically Tefko Saracevic 51

Query expansion – another important search tactic • Method for adding, modifying, changing search terms in a 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 52

Query expansion tactics • You can use the same structure for expanding query terms as in a thesaurus – think of what may be broader, narrower, related terms or synonyms to use as search terms Broader terms - BT Related terms - RT Query term Synonyms Narrower terms - NT Tefko Saracevic 53

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 54

symbolically; controlled & free vocabulary Tefko Saracevic 55

thank you! Tefko Saracevic 56