NAME

Config::Model - Model to create configuration validation tool

DESCRIPTION

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

1. The user interface

2. The validation engine which is in charge of validating all the configuration information provided by the user.

3. 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 you 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 Config::Model::Value

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).

More on DAGs

Each configuration class declaration specifies:

• Most importantly, the type of the element (mostly leaf, or node)

• The properties of each element (boundaries, check, integer or string, enum like type ...)

• The default values of parameters (if any)

• Mandatory parameters

• Targeted audience (intermediate, advance, master)

• On-line help (for ach parameter or value of parameter)

• The level of expertise of each parameter (to hide expert parameters from newbie eyes)

See Config::Model::Node for details on how to declare a configuration class.

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.

Configuration class

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

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.

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.

Example:

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

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

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

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 Exception::Class).

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, domi@komarr.grenoble.hp.com

SEE ALSO

Config::Model::Instance, Config::Model::Node, Config::Model::HashId, Config::Model::ListId, Config::Model::Value

cpanm Config::Model

perl -MCPAN -e shell
install Config::Model