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Vocabulary & languages in indexing & searching

Connection:indexing

searching

tefkos@rutgers.edu; http://comminfo.rutgers.edu/~tefko/

© Tefko Saracevic

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Central ideaIndexing and searching: inexorably connected– you cannot search that 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

ToC

1. Definitions2. Controlled & uncontrolled vocabularies3. Inverted indexes4. Thesaurus

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A few concepts from general to specific1. Definitions

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Defined concepts valid for application in indexing & searching

General– language– vocabulary

Specific– index terms– indexing vocabulary– indexing language– descriptors– keywords– search terms– search vocabulary– query language

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General definitions [Encarta Dictionary]

Language1. communication with words: the human use of spoken or written words as a communication system2. system of communication: a system of communication with its own set of conventions or special words

Vocabulary 1. words of language: all the words used in a language as a whole2. words of subject area: the set of words associated with a subject or area of activity, or used by an individual person

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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

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More definitions ...

Indexing vocabularya 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 languagean indexing vocabulary together with rules – syntax,

grammar – for their application and use

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Variation on Index term

DescriptorWord 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.

KeywordA 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

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Searching definitions

Questionrequest by a user related to user’s information need,

task, problem at hand

Question analysisbreakdown & elaboration of concepts in a question

to be translated into search terms

Queryquestion or part thereof as stated for searching

according to rules of a given system

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more ...

Search terma counterpart to index term, also denoting a

concept and connoting a class for a search

Search vocabularya set of search terms in a domain or available in a

systems

Query languagea search vocabulary together with rules for their use

in searching

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elaboration …

• Example: Question:– What are some major

historical developments in the area of information retrieval?

• Transformed into query– history information

retrieval (in Google)– history AND

information(w)retrieval (in Dialog) (plus you have to select which file(s) to search

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• Question is what user asks and what you may then have elaborated

• Query is what is asked of computer to match – what is put in for searching

• Question is transformed into query

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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)

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Approaches, tensions

2. Controlled & uncontrolled vocabularies

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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

Example of controlled vocabularies

Medical Subject Headings (MeSH) 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

• 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

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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

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Comparison of vocabularies

Controlled • The idea of a controlled

vocabulary is to reduce the variability of expressions used to characterize documents being indexed & searched for

• Manual, costly, time consuming, also semi-automatic in some systems

• Dynamic – needs constant changing, updating

Uncontrolled or free• The idea is to follow natural

language expressions as they occur in documents

• Could be automatic– great advantage– algorithms constantly

changing & improving• e.g. parsing phrases,

connections

• Prevailing in many applications

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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

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Use in searching3. Inverted indexes

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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

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So, when you search

for digital AND libraries:1. computer takes all documents under digital2. and all documents under libraries3. compares to “see” which documents have both terms and

then4. provides you the list of those documents that have in the

document both terms, no matter where • This is also called “coordinate indexing”

– coordination is done at time of searching

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Variation: when you search

for digital (WITH) libraries or“digital libraries” i.e as a phrase1. 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

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Example of searches in inverted fileDoc # 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

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)

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

Inverted index

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 7th and

truck is 8th, they are right next to each other. Doc 1 has both words, but

not next to each other thus not retrieved

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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 AwB, or “AB”

• 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

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A major tool for controlled vocabularies in information retrieval (IR)

4. Thesaurus

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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 the thesaurus.”

(Milstead, 2000)

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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)

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Thesaurus

• Good old Peter Mark Roget had a most useful idea in 1890s & 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

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Standards, software

• Subject to international standards:– “Guidelines for the Construction, Format, and

Management of Monolingual Controlled Vocabularies” ANSI/NISO Standard Z39.19

– 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

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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

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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

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Standard structureWith variations on the theme, thesauri have similar conceptual structure to guide searcher or indexer:

Note: Every descriptor doesn't have to have all of these

Descriptor - DE

Broader terms - BT

Narrower terms - NT

Related terms - RTUsed for - UF

Synonyms

Scope note - SN

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Same thesaurus but …

• Examples of ERIC (Educational Resources Information Center) thesaurus as used differently in different systems:

1. ERIC own system2. 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…

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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

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ERIC online thesaurus on ERICdescriptor libraries

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Other descriptors – one could browse

Descriptor

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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

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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

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

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going

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Expandlibrary

going …

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RT indicates related terms

46865 items have

library

This one has 14 related

terms

going …

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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

going …

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14 related terms for this one are listed

These are now R terms of

various type

Can expand on this one to see

other RT

You can also select any of

these to search

going …

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We have now selected r15 – library services to search for documents

going …

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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, …

gone

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This is one of the items

we got

Descriptors used for this item Additional

index terms

Start ERIC search on OVID (accessed through RUL)

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Start with

Automatically gets you to thesaurus

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This one of selected to

enlarge

Allows you to select thesaurus (or not)

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This one of selected to

enlarge

Then go to ERIC thesaurus on OVID (accessed through RUL)

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Scro

ll

Descriptor

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

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Point being that the same thesaurus is handled differently by different databases

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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

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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

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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

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Query term

Broader terms - BT

Narrower terms - NT

Related terms - RT Synonyms

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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

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symbolically;controlled & free vocabulary

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thank you! Tefko Saracevic