Yet Another Markup Language (YAML)

What is YAML :?

    YAML is a human-friendly data serialization language for all programming languages. It is commonly used for configuration files and in applications where data is being stored or transmitted. YAML targets many of the same communications applications as Extensible Markup Language but has a minimal syntax that intentionally differs from SGML.

Syntax:

·        YAML accepts the entire Unicode character set, except for some control characters, and maybe encoded in any one of UTF-8, UTF-16 or UTF-32.

·        Whitespace indentation is used for denoting structure; however, tab characters are not allowed as part of that indentation.

·        Comments begin with the number sign (#), can start anywhere on a line, and continue until the end of the line. Comments must be separated from other tokens by whitespace characters. If # characters appear inside of a string, then they are number sign (#) literals.

·        List members are denoted by a leading hyphen (-) with one member per line.

·        An associative array entry is represented using colon space in the form key: value with one entry per line. YAML requires the colon be followed by a space so that scalar values such as http://www.wikipedia.org can generally be represented without needing to be enclosed in quotes.

·        Strings (one type of scalar in YAML) are ordinarily unquoted, but may be enclosed in double-quotes ("), or single-quotes (').

·        Block scalars are delimited with indentation with optional modifiers to preserve (|) or fold (>) newlines.

·        Multiple documents within a single stream are separated by three hyphens (---).

·        Repeated nodes are initially denoted by an ampersand (&) and thereafter referenced with an asterisk (*).

·        Nodes may be labeled with a type or tag using a double exclamation mark (!!) followed by a string, which can be expanded into a URI.

·        YAML documents in a stream may be preceded by 'directives' composed of a percent sign (%) followed by a name and space-delimited parameters. Two directives are defined in YAML 1.1.

Key Feature of YAML are :

1)Indented delimiting

2)Non-hierarchical data models

3)Practical considerations

4)Security

5)Data processing and representation

YAML vs REST

Comparison with JSON

JSON syntax is a basis of YAML version 1.2, which was promulgated with the express purpose of bringing YAML "into compliance with JSON as an official subset". Though prior versions of YAML were not strictly compatible,[30] the discrepancies were rarely noticeable, and most JSON documents can be parsed by some YAML parsers such as Syck. This is because JSON's semantic structure is equivalent to the optional "inline-style" of writing YAML. While extended hierarchies can be written in inline-style like JSON, this is not a recommended YAML style except when it aids clarity.YAML has many additional features lacking in JSON, including comments, extensible data types, relational anchors, strings without quotation marks, and mapping types preserving key order.

Comparison with TOML

On the one hand, YAML is much more complex compared to TOML - the YAML specification was pointed out to have 23,449 words, while the TOML specification had only 3,339 words. On the other hand, YAML is less verbose, more DRY, syntactically less noisy, and the hierarchy of a document is obvious from the indentation.

Comparison with XML

YAML lacks the notion of tag attributes that are found in XML. Instead, YAML has extensible type declarations (including class types for objects). YAML itself does not have XML's language-defined document schema descriptors that allow, for example, a document to self-validate. However, there are several externally defined schema descriptor languages for YAML that fulfill that role. Moreover, the semantics provided by YAML's language-defined type declarations in the YAML document itself frequently relaxes the need for a validator in simple, common situations. Additionally, YAXML, which represents YAML data structures in XML, allows XML schema importers and output mechanisms like XSLT to be applied to YAML.