Filing and classification systems fall into three main types: alphabetical, numeric and alphanumeric. Each of these types of filing systems has advantages and disadvantages, depending on the information being filed and classified. In addition, you can separate each type of filing system into subgroups. An effective filing classification system uses the most logical, practical and flexible type of system for the information involved.
Alphabetical topical systems classify information according to topic, then file the topic labels in alphabetical order. Related topics are not kept together in this system. Usually this type of system is best when small amounts of information are involved. This type of filing and classification system is sometimes known as a "dictionary" system. When personal names are being filed, last names are used as the primary sorter, with first names used only in the case of identical last names.
In an "encyclopedia" filing and classification system, information is first broken down by general category, with sub-categories being placed in alphabetical order. This type of filing system is particularly useful for handling large amounts of information because users of the system don't have to keep a particular file's name in mind to find it. Instead, they can start by looking for the general category and search within it to find the specific file they need.
A subset of the encyclopedia filing and classification system is the alphabetical geographic filing system. In a geographic system, the major categories are broken down by locations. You can use any size or type of location, from countries to cities to field offices. Users of this type of system start by choosing the geographic area relevant to their search, then search alphabetically within that topic to find the specific information they seek.
Straight numeric filing and classification systems are very simple to use, since they generally start at the number one and label each file with the subsequent number. However, the use of this type of system is limited, as it often requires an index to help users find the files they seek, and high-activity files can become congested around the same numeric area.
In duplex numeric filing systems, files are given numeric labels with several sets of numbers involved. This type of filing system can handle large amounts of data. The different sets of numbers can correspond to major categories and sub-categories, paralleling the encyclopedia system of filing and classification. One drawback to such a system is that an index is required to understand what each grouping of numbers refers to. A very familiar type of duplex numeric system is the Dewey Decimal system, which most libraries use to catalog their collections.
Another subcategory of numeric filing systems are chronological systems, in which files arranged by date. Typically files are first grouped by year, then by month, then by day. Correspondence files, such as email lists, are typically organized in this fashion, with the most recent pieces of data listed first.
In alphanumeric filing systems, information is classified by category in an encyclopedic system, but using both letters and numbers to denote categories. The use of both letters and numbers allows for a much greater field of categories than does the use of numbers alone. Thus the Library of Congress filing and classification system, which is alphanumeric, allows for a greater array of categories than does the Dewey Decimal system, which is limited to ten major categories.