Files come in a variety of formats. Even a file that appears to be simple text is often a UTF-8 encoding of Unicode characters. When we're processing data to extract intelligence, we need to look at three tiers of representation:
Physical Format: We might have a text file encoded in UTF-8, or we might have a GZIP file, which is a compressed version of the text file. Across these different physical formats, we can find a common structure. In the case of log files, the common structure is a line of text which represents a single event.
Logical Layout: After we've extracted data from the physical form, we often find that the order of the fields is slightly different or some optional fields are missing. The trick of using named groups in a regular expression gives us a way to handle variations in the logical layouts by using different regular expressions depending on the details of the layout.
Conceptual Content: This is the data we were looking for, represented...