YAML - Collections and Structures

YAML includes block collections which use indentation for scope. Here, each entry begins with a new line. Block sequences in collections indicate each entry with a dash and space (-). In YAML, block collections styles are not denoted by any specific indicator. Block collection in YAML can distinguished from other scalar quantities with an identification of key value pair included in them.

Mappings are the representation of key value as included in JSON structure. It is used often in multi-lingual support systems and creation of API in mobile applications. Mappings use key value pair representation with the usage of colon and space (:).


Consider an example of sequence of scalars, for example a list of ball players as shown below −

- Mark Joseph
- James Stephen
- Ken Griffey

The following example shows mapping scalars to scalars −

hr: 87
avg: 0.298
rbi: 149

The following example shows mapping scalars to sequences −

- Boston Red Sox
- Detroit Tigers
- New York Yankees

- New York Mets
- Chicago Cubs
- Atlanta Braves

Collections can be used for sequence mappings which are shown below −

name: Mark Joseph
hr: 87
avg: 0.278
name: James Stephen
hr: 63
avg: 0.288

With collections, YAML includes flow styles using explicit indicators instead of using indentation to denote space. The flow sequence in collections is written as comma separated list enclosed in square brackets. The best illustration for collection which is included in PHP frameworks like symphony.

[PHP, Perl, Python]

These collections are stored in documents. The separation of documents in YAML is denoted with three hyphens or dashes (---). The end of document is marked with three dots (…).

The separation of documents in YAML is denoted by three dashes (---). The end of document is represented with three dots (…).

The document representation is referred as structure format which is mentioned below −

# Ranking of 1998 home runs
- Mark Joseph
- James Stephen
- Ken Griffey 

# Team ranking
- Chicago Cubs
- St Louis Cardinals

A question mark with a combination of space indicates a complex mapping in structure. Within a block collection, a user can include structure with a dash, colon and question mark. The following example shows the mapping between sequences −

- 2001-07-23
? [ New York Yankees,Atlanta Braves ]
: [ 2001-07-02, 2001-08-12, 2001-08-14]
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