Vocabulary

&

languages in searching Connection: indexing searching

© Tefko Saracevic 1

Basic assertion

Indexing and searching: inexorably connected

– you cannot search that 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 Language [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” “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 & 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 (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 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 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 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 – 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 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, 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: 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

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

”

before but then also i.e as a phrase 1. computer goes through the same steps as 2. “looks” for documents where

digital

positioned right before

libraries

is • 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

2 3 4

Doc #

1

Text

Slow brown truck arrived Shipment of brownies damaged in a fire Delivery of brownies arrived in a slow truck Shipment of brownies arrived in a truck For simplicity documents have one sentence.

Stop words: “a,” “of,” “in.” Search for

slow

both contain AND

slow truck

gets as results documents 1 and 3 since 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

Term

arrived brown brownies damaged delivery fire shipment slow truck Inverted index

Position in doc number

(1:4), (3:4), (4:4) (1:2) (2:3), (3:3), (4:3) (2:4) (3:1) (2:7) (2:1), (4:1) (1:1), (3:7) (1:3), (3:8), (4:7) © Tefko Saracevic 15

Thesaurus

• Good old (IR) 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 – 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 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 ) © Tefko Saracevic 17

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 (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 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 the theme, thesauri have similar conceptual structure to guide searcher or indexer: Broader terms - BT Related terms - RT

Descriptor - DE

Scope note - SN Used for - UF Synonyms 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 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 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 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

© Tefko Saracevic Expand

library

going …

26

RT indicates related terms 45237 items have

library

This one has 14 related terms

going …

© Tefko Saracevic 27

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 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

going …

29

going …

We have now selected r10 –

library expenditures

© Tefko Saracevic 30

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

Descriptors used for this item © Tefko Saracevic

gone

This is one of the items we got 32

© Tefko Saracevic

ERIC thesaurus on OVID (accessed through RUL)

For library ask to map as thesaurus term 33

© Tefko Saracevic

going …

There are more down there but we choose this one to expand 34

going …

© Tefko Saracevic Entries for descriptor

Electronic Libraries

Continue to search for AND 35

© Tefko Saracevic

going …

Retrieved & ready to display 36

© Tefko Saracevic

gone

Choose format you want for this item 37

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 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 –

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

© Tefko Saracevic

thank you!

42