Hashing involves taking a block of data and, through the use of a one-way operation, producing a fixed-size value that can be used for comparison with other data. It is used primarily for protecting data and allowing for rapid comparison when matching data values such as passwords. Labels involve looking for header information or other categorizations of data to determine its type and possible classifications. Metadata involves looking at information attributes of the data, such as creator, application, type, and so on, in determining classification. Content analysis involves examining the actual data itself for its composition and classification level.