Each level in the structure of the data to extract with an Extractor component (see section Extractor) has an associated tagset. A scanner is just a set of tagsets that can be used inside of the same Extractor component: if we want to use tagset A and tagset B in the same Extractor, we need to have a scanner with at least both tagsets.
A tag can be seen as a regular expression that matches an HTML element appearing in the page which data is to be extracted. As its name indicates, a tagset is a group of tags. When ITPilot applies a tagset on a page, it ignores all HTML elements that do not match any tag in the set. Besides, it considers tags to act as separators between data elements so, therefore, it assumes that they cannot appear inside the value of a field to extract.
Example: suppose that an electronic bookstore shows the authors of any book by separating them with a carriage return, using a <BR> tag:
John Smith, <BR> Peter Jones
In this situation, we want to extract the name of all authors in a single field of our Extractor structure (‘John Smith, Peter Jones’); to accomplish it, the tagset used cannot include any tag that matches the <BR> tag.
On the other hand, adding more tags to a set is useful in the following situations:
- We need to make the extraction process more specific. When an Extractor extracts more data than desired, adding tags to the set might be the solution.
- We wish to extract the attribute value of an HTML element that does not match any other tag in our set. The Extractor component only allows extracting attributes from HTML elements that match tags of the set that is being used (see section Configuration of the Extractor Component).