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EEE 598: Multimedia/Qos

Best library and internet resources plus literature searching techniques for your assignment.

Search Statements - Introduction

The following techniques can be used to increase your recall.   Not all of the technqiues below can be used in every internet or library database; this listing let's you know what might be available.   Of course, it's best to check the database's help file to determine if the technique is supported. 

Search Statements: Boolean Operators AND, OR

In most traditional library databases, you need to specify how the words you input relate to one another.   All of these traditional databases understand the AND and OR operations. 

  • The AND operator is used between two concepts in which you want both to appear in a document.   The AND operation "narrows" a search making it more selective.  
    Example:   semiconductor AND silicon

  • The OR operator is used between two words to indicate you want either one or the other or both to appear in a document.  The OR operation "broadens" a search making it less selective. 
    Example:    silicon OR gallium 

  • If you use both an AND and an OR operator in the same search statement, you must "nest"  all of the OR operations using parentheses in order to retain control of how the statement is processed.    

    Databases are programmed to process nested segments first, then processes the operators that are outside of the nest.   If the searcher does not provide nests, the database will process the statment according to the "Order of Precedence"  with which it has been programmed.    In some cases the order of precedence says  to process the operators from left to right without regard to the operation being specified;  while in other cases, the programming says to always process one type of operation (for example the ANDs) before all the other operations.   

    Example - these two searches can give very different results:
    • (semiconductor OR superconductor) AND (silicon OR gallium)
    • semiconductor OR superconductor AND silicon OR gallium   

Search Statements - Boolean "NOT" Operator

Basically, the advice for the Boolean operator "NOT" (in some databases "ANDNOT") is ... do NOT use it!    The NOT operator works well for high precision searching but in high recall searching you will very likely eliminate items you want from the results. 

If you are tempted to use a NOT operator to eliminate unwanted material from a large result set - reverse your thinking.   Think of terms you DO want to see in the results set, then AND those terms into your search statement.    

Search Statements - Variant Word Forms

Words take different forms or spelling depending on their use - nouns can be singular or plural, verbs change with the tense, and there could be adjective, adverb, or gerund forms of the word as well.   (And don't forget variations in spellings between British and American English.)  For high recall results, the searcher must account for these variations.  Fortunately, most search interfaces have ways to help with this issue; unfortunately, how this is done is not consistent. 

You'll need to consult the search interfaces's/database's help file; look for a section labelled truncation, wildcards or autostemming.  These are the different ways search interfaces might handle word variation: 

  • Generally databases only allow right-hand truncation.  A special character is placed immediately after the word stem indicating that all words starting with that stem are wanted.  

    Example: manufactur*  

    The most common truncation character is the asterick "*" although the question mark "?", exclamation point "!" and dollar sign "$"  are also used. 

  • Sometimes a database may use more than one symbol for right-hand truncation.  One character may be used to specify a "no or one letter" substitution, while another is used for "unlimited number" of letters used at the end of the word stem.  The "no or one letter" substitution is useful when you want the singular and plural forms of the word but no other variation. 

  • Internal wildcards in which a letter within a word is substituted by a special character (ex. wom!n) is only supported by a few databases.  

  • Left-hand trunction is seldom supported.  This is where the special character comes first to specify you want the same sequence of letters at the end of the word but with different prefixes.

  • Some search interfaces automatically retrieve word variants or retrieve just the plural of a word entered in singular form; in these cases the searcher does not have to do anything special.  

Collective Nouns

Beware the collective noun, for it does not retrieve all that you think!

If you use a collective noun in your search statement, you will also have to do a separate search for every item covered by that collective noun.

It's very easy to forget that bibliographic databases are actually searching the sequence of letters and spaces you enter in the search box rather than whole words and the meanings behind those words.  As humans, we tend to group like things together and call the group by a name (ex.,fruit).   We know that fruit means the group of food items that includes apples, oranges, pears, bananas, watermelons, kiwi, etc.  But to the database,  "fruit" is nothing more than the letter "f" followed by the letter "r" followed by the letter "u" and so on.  What is retrieved are only those records that have f-r-u-i-t in them - you may see articles about apples and oranges in the results list but that's only because the word "fruit" is there, too.  What you won't see are articles about a specific fruit (ex. apples) in which the word "fruit' does not appear. 

 .  

Some databases have ways to help with this: 

  • If the database uses controlled vocabulary, see if there is a term for your "group" (ex. fruit).  If there is, then you don't have to search for the names of the all the different types of fruit.   

  • In subject areas in which a hierarchical classification system is used (Ex. Biology for plants and animals or Geography/Geology for locations), databases designed for those subjects may have a special feature that allows you to search an entry within the classification and retrieve every thing below that entry.   The newer patent classification systems function in this manner. 

  • Some databases are programmed to pick up alternatives names or items within a group; this is not a common practice in science and engineering bibliographic databases.   At this time the only database that can retrieve synonyms without being prompted for science and engineering terms is SciFinder, a database that covers the literature for pure and applied chemistry.  

Search Statements - Opposites Attract

When you are looking for synonyms and other terminology for your concepts, don't forget to think of the opposite.     For example, you may describe the concept as "safety" but others could think of it as "preventing accidents or fatalities".   

More examples:

  • resistance vs. conductance
  • stability vs. instability or degradation
  • remediation vs. contamination
  • regulatory compliance vs. noncompliance or self regulation

Search Statements - Adding Concepts

Having trouble with very large answer sets?   You may add another concept to your search, but only one; either use the C (comparison) concept or the O (outcome) concept but not both at once.  Putting all four PICO concepts in your search statement usually results in very little, or no, results.  

Search Statements - Full Text Coverage vs. Citation/Abstract Only

Not every database searches the full text (all the content) of documents; sometimes the database only has the citation (title, author, source) and an abstract (summary) to search through.  You may need to adjust your search stategy depending on the searchable content of the database.

For databases that do not search full text, if your original strategy seems to retrieve too few results, consider using a broader version of your concept(s).   

For example, consider this book ...

Author: Reier, Sharon.  
Title: The Bridges of New York.  
Source: Quadrant Press
Date: 1977

One of the 75 bridges discussed in this book is the Williamsburg Bridge.  If you searched Google Books (which indexes the full text of books) for Williamsburg Bridge New York, you would find this book in the results list.  This book is also in the WorldCat database, however, as only the citation information is contained in WorldCat, the search for Willamsburg Bridge New York would not retrieve the book.  

When searching in a  citation only (or citation with abstract) database, keep in mind the possibility that any or all of your concepts may be just a small part of a larger (i.e., broader) concept.  If you want highest recall results you may need to search the broader concept as well.  For the Williamsburg Bridge example, that means you would also search for bridges AND New York as well as Williamsburg Bridge.     

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