Config::Model - Model to create configuration validation tool

Configuration instance
Configuration class
Load pre-declared model

load( <model_name> )

Model query

get_model( config_class_name )
get_element_name( class => Foo, for => advanced )

Error handling
Log and Traces
AUTHOR
SEE ALSO

Model elements
Model utilities

NAME

Config::Model - Model to create configuration validation tool

SYNOPSIS

 # create new Model object
 my $model = Config::Model->new() ;

 # create config model
 $model ->create_config_class 
  (
   name => "SomeRootClass",
   element => [ ...  ]
  ) ;

 # create instance 
 my $instance = $model->instance (root_class_name => 'SomeRootClass', 
                                  instance_name => 'test1');

 # get configuration tree root
 my $cfg_root = $instance -> config_root ;

 # You can also use load on demand
 my $model = Config::Model->new() ;

 # this call will look for a AnotherClass.pl that will contain
 # the model
 my $inst2 = $model->instance (root_class_name => 'AnotherClass', 
                              instance_name => 'test2');

 # then get configuration tree root
 my $cfg_root = $inst2 -> config_root ;

DESCRIPTION

Using Config::Model, a typical configuration validation tool will be made of 3 parts :

The user interface
The validation engine which is in charge of validating all the configuration information provided by the user.
The storage facility that store the configuration information

Config::Model provides a validation engine according to a set of rules.

User interface

The user interface will use some parts of the API to set and get configuration values. More importantly, a generic user interface will need to explore the configuration model to be able to generate at run-time relevant configuration screens.

A generic Curses interface is under development. More on this later.

One can also consider to use Webmin (http://www.webmin.com) on top of config model.

Storage

The storage will often be a way to store configuration in usual configuration files, like /etc/X11/xorg.conf

One can also consider storing configuration data in a database, ldap directory or using elektra project http://www.libelektra.org/

Validation engine

Config::Model provides a way to get a validation engine from a set of rules. This set of rules is now called the configuration model.

Configuration Model

Before talking about a configuration tree, we must create a configuration model that will set all the properties of the validation engine you want to create.

Constructor

Simply call new without parameters:

 my $model = Config::Model -> new ;

This will create an empty shell for your model.

declaring the model

The configuration model is expressed in a declarative form (i.e. a Perl data structure which is always easier to maintain than a lot of code.)

Each node of the configuration tree is attached to a configuration class whose properties you must declare by calling create_config_class.

Each configuration class contains mostly 2 types of elements:

A node type element that will refer to another configuration class
A value element that will contains actual configuration data

By declaring a set of configuration classes and refering them in node element, you will shape the structure of your configuration tree.

The structure of the configuration data must be based on a tree structure. This structure has several advantages:

Unique path to get to a node or a leaf.
Simpler exploration and query
Simple hierarchy. Deletion of configuration items is simpler to grasp: when you cut a branch, all the leaves attaches to that branch go down.

But using a tree has also some drawbacks:

A complex configuration cannot be mapped on a simple tree. Some more relation between nodes and leaves must be added.
Some configuration part are actually graph instead of a tree (for instance, any configuration that will map a service to a resource). The graph relation must be decomposed in a tree with special reference relation. See Value Reference in the Config::Model::Value manpage

Note: a configuration tree is a tree of objects. The model is declared with classes. The classes themselves have relations that closely match the relation of the object of the configuration tree. But the class need not to be declared in a tree structure (always better to reuse classes). But they must be declared as a DAG (directed acyclic graph).

Configuration instance

A configuration instance if the staring point of a configuration tree. When creating a model instance, you must specify the root class name, I.e. the configuration class that is used by the root node of the tree.

 my $model = Config::Model->new() ;
 $model ->create_config_class 
  (
   name => "SomeRootClass",
   element => [ ...  ]
  ) ;

 my $inst = $model->instance (root_class_name => 'SomeRootClass', 
                              instance_name => 'test1');

You can create several separated instances from a model.

When using autoread or autowrite feature

Configuration class

A configuration class is made of series of elements which are detailed in the Config::Model::Node manpage.

Whatever its type (node, leaf,... ), each element of a node has several other properties:

permission

By using the permission parameter, you can change the permission level of each element. Authorized privilege values are master, advanced and intermediate (default).

level

Level is important, normal or hidden.

The level is used to set how configuration data is presented to the user in browsing mode. Important elements will be shown to the user no matter what. hidden elements will be explained with the warp notion.

status

Status is obsolete, deprecated or standard (default).

Using a deprecated element will issue a warning. Using an obsolete element will raise an exception.

description

Description of the element. This description will be used when generating user interfaces.

class_description

Description of the configuration class. This description will be used when generating user interfaces.

generated_by

Mention with a descriptive string if this class was generated by a program. This parameter is currently reserved for a model editor (yet to be written).

include

Include element description from another class.

  include => 'AnotherClass' ,

In a configuration class, the order of the element is important. For instance if foo is warped by bar, you must declare bar element before foo.

When including another class, you may wish to insert the included elements after a specific element of your including class:

  # say AnotherClass contains element xyz
  include => 'AnotherClass' ,
  include_after => "foo" ,
  element => [ bar => ... , foo => ... , baz => ... ]

Now the element of your class will be:

  ( bar , foo , xyz , baz )

Example:

  my $model = Config::Model -> new ;

  $model->create_config_class 
  (
   config_class_name => 'SomeRootClass',
   permission        => [ [ qw/tree_macro warp/ ] => 'advanced'] ,
   description       => [ X => 'X-ray' ],
   level             => [ 'tree_macro' => 'important' ] ,
   class_description => "SomeRootClass description",
   element           => [ ... ] 
  ) ;

Again, see the Config::Model::Node manpage for more details on configuration class declaration.

For convenience, permission, level and description parameters can also be declared within the element declaration:

  $model->create_config_class 
  (
   config_class_name => 'SomeRootClass',
   class_description => "SomeRootClass description",
   'element'
   => [ 
        tree_macro => { level => 'important',
                        permission => 'advanced',
                      },
        warp       => { permission => 'advanced', } ,
        X          => { description => 'X-ray', } ,
      ] 
  ) ;

Load pre-declared model

You can also load pre-declared model.

load( <model_name> )

This method will open the model directory and execute a .pl file containing the model declaration,

This perl file must return an array ref to declare models. E.g.:

 [
  [
   name => 'Class_1',
   element => [ ... ]
  ],
  [
   name => 'Class_2',
   element => [ ... ]
  ]
 ];

do not put 1; at the end or load will not work

If a model name contain a :: (e.g Foo::Bar), load will look for a file named Foo/Bar.pl.

Returns a list containining the names of the loaded classes. For instance, if Foo/Bar.pl contains a model for Foo::Bar and Foo::Bar2, load will return ( 'Foo::Bar' , 'Foo::Bar2' ).

Model query

get_model( config_class_name )

Return a hash containing the model declaration.

get_element_name( class => Foo, for => advanced )

Get all names of the elements of class Foo that are accessible for level advanced.

Level can be master (default), advanced or intermediate.

Error handling

Errors are handled with an exception mechanism (See the Exception::Class manpage).

When a strongly typed Value object gets an authorized value, it raises an exception. If this exception is not catched, the programs exits.

See Config::Model::Exception for details on the various exception classes provided with Config::Model.

Log and Traces

Currently a rather lame trace mechanism is provided:

Set $::debug to 1 to get debug messages on STDOUT.
Set $::verbose to 1 to get verbose messages on STDOUT.

Depending on available time, a better log/error system may be implemented.

AUTHOR

Dominique Dumont, (ddumont at cpan dot org)