EXTENSION can be described as a completion feature of the matched value rather than a normalization. It adds elements surrounding the original matched data to the final output value.
Its action is based on the concept of "extension", which in turn is linked to the
SCOPE statement (the part of the rule's syntax in which the portion of text to which a rule applies is specified).
EXTENSION option reads what the
SCOPE statement (found at the beginning of the rule) contains and returns the portion of text containing the value matched by an attribute as defined in the
SCOPE statement. In this way,
EXTENSION dynamically reproduces what the options
SECTION do without having to choose the extension beforehand.
The syntax for extraction rules is:
The syntax for tagging rules is:
This option is useful in cases where it's necessary to expand the output revolving around a matched element, to include exactly what the extension of the rule is; whereas the options
SECTION allow the extension of the rule to be different from the transformation option.
Consider the following example:
@Subject[TYPE(NPH) + ROLE(SUBJECT)]|[EXTENSION]
The purpose of this rule is to extract people's names (
TYPE (NPH)), only if the names identified are the subjects of a clause (
+ ROLE (SUBJECT)). If this condition is verified, the
EXTENSION transformation option will ensure that every extracted value will be expanded to the defined extension in the
SCOPE statement of the rule, in this case, a clause.
Consider the extraction output if the rule above is run against the following sample sentence:
My sister Louise Letterman loves dogs and her husband loves cats.
The text contains one value matching the sample rule: Louise Letterman. Louise Letterman is recognized as both a person's name and as the subject in the first clause of the sentence, so it causes the rule to trigger while the
EXTENSION transformation determines the extraction of the extension defined in the
SCOPE statement of the rule, the clause to which the person's name belongs, which is My sister Louise Letterman loves dogs.
If the rule's scope is changed to
PHRASE and the transformation remains unchanged, the extraction will become the phrase that contains the person's name: My sister Louise Letterman.