Lua Data Formats

wiki

Different languages have been devised for different types of data representation in text format [1]:

• [Markup languages] - XHTML [2], markdown [3]
• [Data serialization languages] - YAML [4]
• Data interchange languages (a less general form of serialization) - JSON [5]

Although markup languages have been implemented in Lua [6], the Lua syntax is not in itself that suitable as a markup language. However, it has some nice capabilities for data serialization and interchange.

A number of different data representation styles may be used in Lua:

-- JSON style
library = { books = { {name="PiL", author="roberto"},
                      {name="BLP", author="kurt,aaron"} } }

-- Lisp/s-expression style
return {'library', {'book', name="PiL", author="roberto"},
                   {'book', name="BLP", author="kurt,aaron"} }

-- Java property page / INI / Unix config style
library.books[1].name = 'PiL'
library.books[1].author = 'roberto'
library.books[2].name = 'BLP'
library.books[2].author = 'kurt,aaron'

-- XML / object constructor style
library { book {name="PiL", author="roberto"},
          book {name="BLP", author="kurt,aaron"} }

-- XML with namespaces style
local LIB = require "library"
LIB.library { LIB.book {name="PiL", author="roberto"},
              LIB.book {name="BLP", author="kurt,aaron"} }

Features of Lua:

• Fairly efficient, small library (a couple hundred KB)
• Loads entire file into memory -- not very suitable for very large data sets that must be streamed, like in SAX [7]
• Support for basic data types (including numbers, strings, and booleans), arrays, associative arrays, object constructor syntax, and assignment
• You need to do your own data validation (no XML schemas) and serialization (TableSerialization). Less extensive tools/adoption than XML/XPath/etc.
• Extensible semantics (via metamethods and function calls)
• Powerful programming capabilities
• The programming capabilities have security implementations (SandBoxes)

See Also

• [Programming in Lua: 10.1 - Data Description]
• [About Lua] - "Lua combines simple procedural syntax with powerful data description constructs based on associative arrays and extensible semantics."
• [Declarative Internal DSLs in Lua: A Game Changing Experience], by AlexanderGladysh, LogicEditor.com (Lua Workshop 2011 Talk) - discusses a good strategy for implementing declarative DSLs in Lua ([summary]).
• [The Lua Architecture] - "This rudimentary ancestor of Lua was not a script language, but a data representation language...."
• LuaList:2000-06/msg00148.html - "Lua tables vs XML"
• LuaList:2008-03/msg00101.html - "Lua x XML"
• LuaList:2003-07/msg00043.html - "Representing XML in tables"
• TableScope - solutions (and patch) to allow table constructs to enclose a scope
• LuaXml - XML parsers in Lua