What is a flat file?
A flat file is a collection of data stored in a two-dimensional database in which similar yet discrete strings of information are stored as records in a table. The columns of the table represent one dimension of the database, while each row is a separate record.
The information stored in a flat file is generally alphanumeric with little or no additional formatting. The structure of a flat file is based on a uniform format as defined by the type and character lengths described by the columns.
One of the most prominent flat file examples is a comma-separated values (CSV) file. A CSV file is one in which table data is gathered in lines of American Standard Code for Information Interchange (ASCII) text with the value from each table cell separated by a comma and each row represented by a new line. Columns and rows are typically delimited by tabs or commas, such as in CSV files. A flat file database comprises a single table.
Types of flat files
While the term "flat file" is most often used to describe a flat-file database, it can also refer to other types of files that don't resemble databases at all. There is some ambiguity about whether control characters such as line breaks can be included in a flat file.
In any event, many call a Microsoft Word document that has been saved as text only a flat file. The resulting file contains records -- lines of text of a certain uniform length -- but no formatting information, for example, about title or subtitle sizes and positions or information that a program could use to create a table of contents for the text file.
In its broadest sense, "flat file" may refer to any text file that has minimal or no formatting besides the use of the ASCII character set.
What are the key characteristics of a flat-file database?
A flat-file database is a simple two-dimensional repository of like data. The data is arranged in rows -- or records -- across columns or fields. Each row contains the same type of information as the other rows in the flat file; that information is defined by the columns which describe the type of data and sets a limit on the number of characters allowed to represent the field information.
As noted, columns are separated by a single ASCII control character such as a tab (keyboard sequence is Alt + 09) or a comma (Alt + 44). Each row is delineated by a carriage return (Alt + 13).
A flat-file database has no predetermined limit for the number of rows it might contain. The size of a flat-file database may be limited by the host computer's operating system (OS) or its file management system. If a database application is used to create the flat-file database, that application may apply limits to the number of rows, column lengths and overall file size.
There are two basic tools for manipulating the information in a flat-file database: column sorting and search. Some applications, such as spreadsheets that allow creation of flat-file databases, may provide additional, more sophisticated data manipulation tools. Sorting allows a user to arrange the data in an ascending or descending alphanumeric order based on the contents of one column; search will find specific strings of text or numerals throughout the flat-file database.
One important additional tool is the ability to create an index of the flat-file database. Indexing effectively presorts the records in the file based on the contents of one column, and can greatly speed up the process of searching for specific data.
What is a flat-file database used for?
Although they provide relatively rudimentary means of storing, manipulating and accessing data, flat files are still widely used for a number of contemporary applications. Flat-file databases are still very useful as easy-to-create and easy-to-maintain date files for commonly accessed information such as name and address files, and membership lists or class rosters. Spreadsheet applications such as Excel or Google Sheets can be used to create and manipulate flat-file databases.
But flat files are also widely used in internet of things (IoT) and data warehouse/data lake environments. For those applications, a flat-file database's simplicity is advantageous as a low overhead, easy-to-access way to store voluminous information that needs to be preserved in its native state.
Another application for flat-file databases is in the management of object-oriented storage systems. Object storage is commonly used by cloud storage services because it can accommodate massive volumes of data. The data stored on object systems is managed by a non-hierarchical flat-file database that retains basic information about the data, such as the file names and where they are stored on media.
Flat file database vs. relational database
A flat file is sometimes referred to as a relational database, but the two types of databases are significantly different in both form and function.
A flat file consists of a single table of data. It allows the user to specify data attributes, such as columns and data types table by table, and stores those attributes separate from applications. This type of file is commonly used to import data in data warehousing projects.
In relational databases, flat file is sometimes used as a synonym for a "relation." A relational database contains multiple tables of data that relate to each other and allows the user to specify information about multiple tables and the relationships between those tables, allowing more flexibility and control over database constraints.
For example, a relational database might have one table that lists students' names, addresses and phone numbers, and a second table that holds the students' names, their current scholastic year and their major areas of study. In a relational database, the two separate tables can be associated with each other via their common field, student name.
This process essentially joins the two tables together so that relevant information can be located and drawn from the two distinct tables simultaneously, such as students' names, their majors and their phone numbers.
To gain the same effect with a flat-file database, all of the information would have to be contained in a single file or separate flat-file databases would have to include some redundant information.
As such, relational databases are more sophisticated and can be expansive, encompassing dozens (or more) of separate tables. A relational database application must have knowledge of how the data is organized within multiple files. And specialized tools, such as structured query language (SQL), have to be used to associate the various tables and to find and extract data.