When you need to pass configuration data to an application, **there are many file formats available**, some more well-known than others. **There is no perfect format, the goal is always to have a format that is both complete, very readable and easy to pick up**, but the specifics of each ecosystem mean that each of them is relevant. The goal of this article is to **introduce you to and familiarize you with formats you may not necessarily know**, which is why the same dataset will be used as an example each time. ## INI Format **This is a format made mostly of key-value pairs but with the possibility of separating them into sections.** It is mainly used in the Microsoft environment (under the .ini extension), but a large part of the configuration files on Linux are represented by a simplified key-value format. ``` ;List of all endpoints [request] id=request protocol=https domain=example.com uri=/request, description="Request enpoint" [search] id=search protocol=https domain=google.com uri=/search, description="Search enpoint" ``` The INI format is unusual because, compared to the other formats in this list, **it is the only one to be "informal" as it is not defined by a strict specification.** ## CSV Format The CSV format is a format originally designed to represent two-dimensional tables, **widely used to export data present in spreadsheets (such as Excel).** **This format is very simple and its explicit name (comma-separated values) describes very well how it works.** Comments are not meant to appear in a CSV file, only values, and commas! ``` id, protocol, domain, uri, description request, https, example.com, /request, Request endpoint search, https, google.com, /search, Search enpoint ``` ## XML Format This format is very present in the Java ecosystem, but also on the web (less and less). **While XML is verbose, it has the advantage of being very explicit, and above all it is the only format that provides in its specification a validation technology** for the file's structure with DTD! ``` https example.com /request Request endpoint https google.com /search Search endpoint ``` ## JSON Format If you've done Javascript, then you know what the JSON format is. **Actually called "JavaScript Object Notation" it is used throughout the entire Javascript ecosystem**, NodeJS and is taking up more and more space on the web in general. ``` [{ "id": "request", "protocol": "https", "domain":"example.com" "uri":"/request", "description":"Request enpoint" }, { "id":"search", "protocol":"https" "domain":"google.com" "uri":"/search", "description":"Search enpoint" }] ``` **The JSON format is also used by some NoSQL databases** to store data and build queries, as is the case with [MongoDB](https://www.mongodb.com/) for example. ## YAML Format YAML (whose name is a recursive acronym for "YAML Ain't Markup Language") is a format that pits **ease of reading against a certain complexity of writing due to the many data types, the mandatory space indentation, etc...** **The data types and structures added to YAML 1.2 notably make it a "superset" of JSON** with the arrival of lists "\[...\]" and maps "{...}", so it is possible to describe complex data architectures. ``` ---# List of all endpoints - request: protocol: https domain: example.com uri: /request description: Request enpoint - search: protocol: https domain: google.com uri: /search description: Search enpoint ``` ## TOML Format This format, an acronym for "Tom's Obvious, Minimal Language" is **a newcomer (it has existed since 2013, but version 1.0 dates from January 2021) and combines the good sides of several of the formats mentioned above.** For now, the uses of this format remain rather few, but it is used, for example, for configuring the [Cargo](https://doc.rust-lang.org/cargo/index.html) tool, Rust's package manager. ``` #List of all endpoints [endpoints] [endpoint.request] protocol="https" domain="example.com" uri="/request", description="Request enpoint" [endpoint.search] protocol=https domain=google.com uri=/search, description="Search enpoint" ``` **TOML offers a complex but readable and easily editable structure**, has comments, indentation but optional, and remains much easier to implement than YAML given its lighter specification.