SDL (Simple Declarative Language)

SDL version supported: 1.3
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Getting Started with SDL4R

To get the Ruby Gem:

    gem install sdl4r

Then, you can start reading SDL documents:

    require 'pathname'
    require 'sdl4r'

    root = SDL4R::read("my_directory/my_config.sdl"))
    puts root.attribute("port")

Or you can create SDL documents with the API:

    require 'fileutils'
    require 'sdl4r'

    root ="root") do
        new_child("server") do
            set_attribute("port", 1234)
    end"my_directory/my_config.sdl", "w") { |io|

which will write the following in your file:

    server port=1234

SDL Documents

SDL documents are made up of Tags. A Tag contains

For the SDL code:

  size 4
  smoker false

Assuming this code is in a file called values.sdl, the values can be read using the following code (ignoring exceptions):

  root ="root").read("values.sdl"))
  size = root.child("size").value
  smoker = root.child("smoker").value

A tag is basically a data structure with a list of values, a map of attributes, and (if it has a body) child tags. In the example above, the values.sdl file is read into a tag called “root”. It has two children (tags) called “size” and “smoker”. Both these children have one value, no attributes, and no bodies.

SDL is often used for simple key-value mappings. To simplify things Tag has the methods value and value= which operate on the first element in the values list. Also notice SDL understands types which are determined using type inference.

The example above used the simple format common in property files:

  name value

The full SDL tag format is:

  namespace:name value_list attribute_list {

where value_list is zero or more space separated SDL literals and attribute_list is zero or more space separated (namespace:)key=value pairs. The name, namespace, and keys are SDL identifiers. Values are SDL literals. Namespace is optional for both tag names and attributes. Tag bodies are also optional. SDL identifiers begin with a unicode letter or an underscore (_) followed by zero or more unicode letters, numbers, underscores (_), dashes (-) and periods (.).

Tags without bodies are terminated by a new line character (\n) and may be continue onto the next line by placing a backslash (\) at the end of the line. Tags may be nested to an arbitrary depth. SDL ignores all other white space characters between tokens. Although nested blocks are indented by convention, tabs have no significance in the language.

Anonymous Tags

SDL also supports anonymous tags which are assigned the name “content”. An anonymous tag starts with a literal and is followed by zero or more additional literals and zero or more attributes. The examples section below demonstrates the use of anonymous tags.

    greetings {
       "hello" language="English"

    # If we have a handle on the "greetings" tag we can access the
    # anonymous child tag by calling
    #    Tag child1 = greetingTag.child("content");

String literals

There are two ways to write String literals.

Starting and ending with double quotes (“)

Double quotes, backslash characters (\), and new lines (\n) within this type of String literal must be escaped like so:

  file "C:\\folder\\file.txt"
  say "I said \"something\""

This type of String literal can be continued on the next line by placing a backslash (\) at the end of the line like so:

  line "this is a \
    long string of text"

White space before the first character in the second line will be ignored.

Starting and ending with a backquote (`)

This type of string literal can only be ended with a second backquote (`). It is not necessary (or possible) to escape any type of character within a backquote string literal. This type of literal can also span lines. All white spaces are preserved including new lines.


  file `C:\folder\file.txt`
  say `I said "something"`
  regex `\w+\.suite\(\)`
  long_line `This is
      a long line
      fee fi fo fum`

Note: SDL interprets new lines in `` String literals as a single new line character (\n) regarless of the platform.

Binary literals

Binary literals use base64 characters enclosed in square brackets ([]). The binary literal type can also span lines. White space is ignored.


  key [sdf789GSfsb2+3324sf2] name="my key"
  image [
  upload from="" data=[

Date and Time Literals

SDL supports date, time span, and date/time literals. Date and Date/Time literals use a 24 hour clock (0-23). If a timezone is not specified, the default locale’s timezone will be used.


Literal Types

SDL 1.0 has thirteen literal types (parenthesis indicate optional components)

  1. string (unicode) - examples: "hello" or `aloha`
  2. character (unicode) - example: '/' Note: \uXXXX style unicode escapes are not supported (or needed because sdl files are UTF8)
  3. integer (32 bits signed) - example: 123
  4. long integer (64 bits signed) - examples: 123L or 123l
  5. float (32 bits signed) - examples 123.43F 123.43f
  6. double float (64 bits signed) - example: 123.43 or 123.43d or 123.43D
  7. decimal (128+ bits signed) - example: 123.44BD or 123.44bd
  8. boolean - examples: true or false or on or off
  9. date yyyy/mm/dd - example 2005/12/05
  10. date time yyyy/mm/dd hh:mm(:ss)(.xxx)(-ZONE) example - 2005/12/05 05:21:23.532-JST notes: uses a 24 hour clock (0-23), only hours and minutes are mandatory
  11. time span using the format (d:)hh:mm:ss(.xxx) notes: if the day component is included it must be suffixed with a lower case ‘d’ examples
        12:14:42 # (12 hours, 14 minutes, 42 seconds)
        00:09:12 # (9 minutes, 12 seconds)
        00:00:01.023 # (1 second, 23 milliseconds)
        23d:05:21:23.532 # (23 days, 5 hours, 21 minutes, 23 seconds, 532 milliseconds)
  12. binary [base64] example - [sdf789GSfsb2+3324sf2]
  13. null

Timezones must be specified using a valid time zone ID (ex. America/Los_Angeles), three letter abbreviation (ex. HST), or GMT(/-)hh(:mm) formatted custom timezone (ex. GMT02 or GMT+02:30)

These types are designed to be portable across Java, .NET, and other popular platforms.

SDL Comments

SDL supports four comment types.

  1. // single line comments identicle to those used in Java, C, etc. // style
    comments can occur anywhere in a line.  All text after // up to the new line
    will be ignored.
  2. # property style comments.  They work the same way as //
  3. -- separator comments useful for visually dividing content.  They work the same way as //
  4. Slash star (/*) style multiline comments.  These begin with a slash
    star and end with a star slash.  Everything in between is ignored.


An example SDL file:

    # a tag having only a name

    # three tags acting as name value pairs
    first_name "Akiko"
    last_name "Johnson"
    height 68

    # a tag with a value list
    person "Akiko" "Johnson" 68

    # a tag with attributes
    person first_name="Akiko" last_name="Johnson" height=68

    # a tag with values and attributes
    person "Akiko" "Johnson" height=60

    # a tag with attributes using namespaces
    person name:first-name="Akiko" name:last-name="Johnson"

    # a tag with values, attributes, namespaces, and children
    my_namespace:person "Akiko" "Johnson" dimensions:height=68 {
        son "Nouhiro" "Johnson"
        daughter "Sabrina" "Johnson" location="Italy" {
            hobbies "swimming" "surfing"
            languages "English" "Italian"
            smoker false

    // (notice the separator style comment above...)

    # a log entry
    #     note - this tag has two values (date_time and string) and an
    #            attribute (error)
    entry 2005/11/23 10:14:23.253-GMT "Something bad happened" error=true

    # a long line
    mylist "something" "another" true "shoe" 2002/12/13 "rock" \
        "morestuff" "sink" "penny" 12:15:23.425

    # a long string
    text "this is a long rambling line of text with a continuation \
       and it keeps going and going..."

    # anonymous tag examples

    files {

    # To retrieve the files as a list of strings
    #     List files = tag.child("files").children_values("content");
    # We us the name "content" because the files tag has two children, each of
    # which are anonymous tags (values with no name.)  These tags are assigned
    # the name "content"

    matrix {
        1 2 3
        4 5 6

    # To retrieve the values from the matrix (as a list of lists)
    #     List rows = tag.child("matrix").children_values("content");

Example of getting the “location” attribute from the “daughter” tag above (ignoring exceptions)

     root ="myfile.sdl"))
     daughter = root.child("daughter", true) // recursive search
     location = daughter.attribute("location")

SDL is normally stored in a file with the .sdl extension. These files should always be encoded using UTF8. SDL fully supports unicode in identifiers and literals.

Ruby and SDL types

The following list gives what types are used in Ruby in order to represent SDL types.

unicode string:String
unicode character:single-character String
integer (32 bits signed):Integer (Fixnum or Bignum)
long integer (64 bits signed):Integer (Fixnum or Bignum)
float (32 bits signed):Float
double float (64 bits signed):Float
decimal (128+ bits signed):BigDecimal
boolean:true (TrueClass) and false (FalseClass)
date (day):Date
date time:DateTime (see SDL4R#new_date_time if you want to get Time instances from the parsers)
time span:SdlTimeSpan
binary:SdlBinary (to avoid confusion with simple strings)
null:nil (NilClass)

TO FIX: the handling of floating numbers in Ruby being different from the Java world, the behavior of SDL4R at limits might not be perfect for the time being.

UTF-8 Support

In Ruby 1.8, in order to enable UTF-8 support, you may have to declare the following lines:

    $KCODE = 'u'
    require 'jcode'

This will give you correct input and output and correct UTF-8 “general” sorting. Alternatively you can use the following options when launching the Ruby interpreter:

    /path/to/ruby -Ku -rjcode

Ruby Support

SDL4R has been tested on:

 * Ruby 1.8.7
 * Ruby 1.9.1
 * Ruby 1.9.2
 * JRuby 1.5.1


Simple Declarative Language (SDL) for Ruby

Copyright 2005 Ikayzo, inc.

This program is free software. You can distribute or modify it under the terms of the GNU Lesser General Public License version 2.1 as published by the Free Software Foundation.

This program is distributed AS IS and WITHOUT WARRANTY. OF ANY KIND, INCLUDING MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this program; if not, contact the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.