PDF documents
PDF documents are another case where the internal text representation can vary widely from the visible presentation in PDF readers. Some issues that can arise:
•Text sequences can appear out of order on the same page depending on how the page was composed.
•Text can appear doubled or can have spacing inserted into or removed from the internal representation to assist some specific visual presentation.
In general, PDF documents generated via print drivers are far more susceptible to these issues than PDF documents generated directly using Acrobat and other such composing tools. However, because of the nature of PDF itself, even they are not immune.
Boolean query expressions
You can combine words, fuzzy words, and word sequences using Boolean (logical) operators AND, OR, and NOT (these must be uppercase). The following table describes Boolean operators, where exp, exp1, and exp2 represents a word, fuzzy word, word sequence, or other Boolean query expression.
Table 14 Boolean query expressions
Syntax | Matches |
|
|
NOT exp |
|
alternative syntax: - exp | all documents that do not match exp |
alternative syntax: ! exp |
|
|
|
exp1 OR exp2 | all documents that match either exp1 or exp2 |
|
|
exp1 AND exp2 |
|
alternative syntax: exp1 && exp2 | all documents that match both exp1 and exp2 |
alternative syntax: exp1exp2 |
|
|
|
NOTE:
The second alternative syntax for AND indicates that AND is the default connective in query expressions. You do not need to supply AND explicitly. It is assumed if neither AND nor OR is used explicitly. For example, the query peace quiet is equivalent to the query peace AND quiet.
A NOT expression must be combined, using AND or OR, with another expression other than NOT. A query cannot consist solely of negative criteria.
NOT quiet | illegal |
|
|
(NOT quiet) AND (NOT blue) | illegal |
|
|
NOT quiet AND blue | legal |
|
|
NOT quiet OR nois* | legal |
|
|
You must provide the proper number of arguments for a Boolean operator or an error message results: one argument for NOT (- or !), two arguments for AND (&& ) and OR. For example, the following queries result in an error message.
•alpha NOT: Missing argument for NOT
•AND alpha: Missing argument for AND
User Guide | 43 |
