Presentation on theme: "LIS618 lecture 4 Thomas Krichel 2003-10-19. Structure Document preprocessing Practice: Nexis –document preprocessing –segment theory and practice Practice:"— Presentation transcript:
LIS618 lecture 4 Thomas Krichel
Structure Document preprocessing Practice: Nexis –document preprocessing –segment theory and practice Practice: Factiva
document preprocessing There are some operations that may be done to the documents before indexing –lexical analysis –stemming of words –elimination of stop words –selection of index terms –construction of term categorization structures we will look at those in turn in many cases, document preprocessing is not well documented by the provider. but searchers need to be aware of them…
lexical analysis divides a stream of characters into a stream of words seems easy enough but…. should we keep numbers? hyphens. compare "state-of-the-art" with "b-52" removal of punctuation, but "333B.C." casing. compare "bank" and "Bank"
stemming in general, users search for the occurrence of a term irrespective of grammar plural, gerund forms, past tense can be subject to stemming important algorithm by Porter evidence about the effect of stemming on information retrieval is mixed stemming is relatively rare these days.
elimination of stop words some words carry no meaning and should be eliminated in fact any word that appears in 80% of all documents is pretty much useless, but consider a searcher for "to be or not to be". It is better to reduce the index weight of terms that appear very frequently
index term selection In printed indexes, we use nouns only some nouns that appear heavily together can be considered to be one index term, such as "computer science" Dialog deals with this through phrase indexing. Most web engines, however, index all words, and all of the individually
thesauri a list of words and for each word, a list of related words –synonyms –broader terms –narrower terms used –to provide a consistent vocabulary for indexing and searching –to assist users with locating terms for query formulation –allow users to broaden or narrow query
use of thesauri Thesauri are limited to experimental systems, or some high-quality systems, see bin/thesaurus.pl for an example, or look at Nexis It can be confusing to users. Frequently the relationship between terms in the query is badly served by the relationships in the thesaurus. Thus thesaurus expansion of an initial query (if performed automatically) can lead to bad results.
Back to Nexis: word limits The following are always considered word limits –hyphens –slashes –parentheses –spaces
plurals Nexis indexes plural and possive as the singular. But in power search, you can use the following –PLURAL (term) only the plural of term –SINGULAR (term) only the singular of term –ALLCAPS (term) only capitals of term –NOCAPS (term) no capitals of term –CAPS (term) capitalized term only
Document preprocessing in Nexis ampersand: if it is surrounded by blanks, it treats it as "and". If it is not, it treats it as a normal character company(at&t). apostrophe: works if not followed by "s", in which case it is a possessive at-sign: used for sections in case law, ignored otherwise, e.g. in addresses: presidentwhitehouse.com
Document preprocessing in nexis colon and comma are read as a space unless adjacent characters are numbers. hyphen / and \ is read as a space percent and pound sign mean themselves and are not equivalent to anything. " ? $ ; are all ignored ® is replaced by the word "R", is replaced by the word "TM".
equivalents Nexis has a number of "equivalents" where, depending on sources, it replaces one with the other. Contrary to their claims they also work in quick search First (second, third, etc.)is 1st (2nd, 3rd, etc.) Monday (All days ex. Sunday) Mon (Tues, Weds, etc.) January (Abbreviations work) Jan (Feb, Mar, etc.) One (all numbers < 20) 1 (2, 3, etc.) and& companyco corporationcorp incorporated inc
noise and reserved words Noise words are common words –in power search, noise words are ignored, replace by space –in quick search, you can use phrases –no list of noise words Reserved words are –and –or –not used in Boolean expressions. They are not indexed.
Nexis segments Nexis does some document preprocessing for characters, discussed in a later slide. The processed document has a number field/value pairs that are called segments Not every source has every segment. I make a distinction between –native –smart-indexed segments.
some segments in legal docs CITE CLASS DATE common search for any date field FIRST-ACTION date HISTORY ISSUED-BY LAST-ACTION date NAME REFERENCES TEXT full text TITLE same as name TYPE
typical segments in news BYLINE CORRRECTION CORRECTION-DATE DATE DATELINE(not a date) GRAPHIC HEADLINE HIGHLIGHT LEAD HLEAD is HEADLINE, HIGHLIGHT, & LEAD
typical segments in news PUBLICATION name and copyright SECTION SERIES SOURCE TICKER TYPE
typical smart-indexed segments CITY COMPANY COUNTRY GEOGRAPHIC INDUSTRY KEYWORD ORGANIZATION PERSON PRODUCT SUBJECT TICKER TYPE TERMS includes all these
segment search You can place query terms and connectors in a segment and then search for it. Example: hlead((drug or substance) w/10 abuse)
using segments for news uses power search expressions, plus hlead (expression) ? headline (expression) company (expression) for a company byline (expression) for the author show (expression) for a television show transcript expression is a Boolean expression or simple keyword.
power search for legal data uses power search expressions, plus name (expression) for the name of a party cite (expression) for a citation expression for case law title (expression) for the title of a law article expression is a Boolean expression or simple keyword
Search forms There are special forms for –News –Company reports –Market indicators –Portfolio –News and quotes about companies
Personal news alert do a search then click on track in personal news to get to a screen where you can enter –periodicity –what documents to be sent –subject This works for real estate for me.
Real time news This uses a different query language –terms are implicitly ANDed –explicit AND and OR allowed –phrases have to be put in quotes –* starts for any number of characters, not just one as in power search –parenthesis can be used I have poor experience with this.
Summary on Nexis Nexis has a rich set of resources. It can be searched by inexperienced, but likely to get poor result. Clever learning about its features can get you quite far, however, the features are not well documented online. There is not enough detail.
Factiva Nexis is news with legal "stuff". Factiva is news with business "stuff". It will only work with Microsoft Internet Explorer! This violates the most important rule of web site design. It is because the use asp technology. A bad choice!
Login to factiva We have a public account that will serve up to 30 users concurrently up to –user id: mls003 –password: transcripts –name space: 16 https://global.factiva.com/factivalogin/login. asp has the login Sessions time out after 30 minutes.
More on Factiva has –downloadable brochures –case studies –white papers –product tour I looked the broshure "Inside-Out". Well written, ordered copies.
Free text search similar to nexis power search operators "and" "or" "not" "w/i", "near/n" where n is a number. /f/n requires the preceding expression to be in the first n words in the full text. "same" stands for same paragraph "atleastn" requires at least n occurences. "wc" is a word count, use and then a number, e.g. wc<1000.
but as well You can add codes from indexing terms. Note that the + shows that there is more. When you press the triangle the code is dropped into the text box.