Editing Flat-file database (section)

==Overview==

Plain text files usually contain one [[Record (computer science)|record]] per line.<ref>{{Citation
 | last = Fowler
 | first = Glenn
 | year = 1994
 | title = cql: Flat-file database query language
 | periodical = WTEC'94: Proceedings of the USENIX Winter 1994 Technical Conference on USENIX Winter 1994 Technical Conference
 | url = http://static.usenix.org/publications/library/proceedings/sf94/full_papers/fowler.a
}}</ref>

Examples of flat files include <code>[[/etc/passwd]]</code> and <code>[[/etc/group]]</code> on [[Unix-like]] operating systems. Another example of a flat file is a name-and-address list with the fields ''Name'', ''Address'' and ''Phone Number''.

Flat files are typically either delimiter-separated or fixed-width.

=== Delimiter-separated values ===

In [[delimiter-separated values]] files, the [[field (computer science)|field]]s are separated by a character or string called the [[delimiter]].
Common variants are [[comma-separated values]] (CSV) where the delimiter is a comma, [[tab-separated values]] (TSV) where the delimiter is the tab character), space-separated values and vertical-bar-separated values (delimiter is <code>|</code>).

If the delimiter is allowed inside a field, there needs to be a way to distinguish delimiters characters or strings that are meant literally. For example, consider the sentence "If I have to, I'll do it myself.". To encode it in CSV, there needs to be a way to prevent the comma from splitting the field. Several [[Delimiter#Solutions|strategies to prevent delimiter collision]] exist.

=== Fixed-width formats ===

With fixed-width formats, each field has a fixed length with extra [[space character|spaces]] added as needed. The fixed lengths can be predefined and known ahead of time (i.e. stated in the format's specification), or parsed from a [[Header (computing)|header]].

With predefined lengths, fields are limited to a maximum length. The need for longer fields may appear sometime after the format is defined. Possible workarounds include abbreviating phrases, replacing values with links (e.g. a URI pointing to the value), and splitting a file into multiple files.

With delimiter-separated formats, determining the field boundaries requires finding the delimiters, which incurs some [[computational overhead]]. This is not needed for fixed-width formats. However, fixed-width formats can lead to unnecessarily large file sizes if fields tend to be shorter than the lengths reserved for them.

=== Declarative notation ===

Delimiters can be used alongside a notation stating the length of each field. For example, <code>5apple|9pineapple</code> specifies the length (5 and 9) of each field. This is called [[String literal#Declarative notation|declarative notation]]. It has low overhead and trivially avoids delimiter collisions, but it is brittle when edited manually.