NAME

XML::RelaxNG::Compact::DataModel - RelaxNG Compact http://relaxng.org/compact-tutorial-20030326.html schema expressed in perl

VERSION

Version 0.03

DESCRIPTION

This is a user's guide module for documentation only. It describes the perlish expression of the RelaxNG Compact schema. Some limitations are:

• there is no datatyping,

• there is no support for minLength,maxLength xsd:string constraints, although conditional logic is supported

• there is no support for annotations

• support for includes and inherit are provided by the data model developer, means you can split your model in different packages and inherit it. Just remember that PXB deals with references to hashes and arrays. See below.

Everything else can be expressed by perl constructs and will be supported by the created API. Every element from the schema can be expressed as perl hash reference:

   <element-variable>  =  '{ attrs => {' <attributes-definition> ', '  
                                       'xmlns  => ' <namespace-prefix> '},'   
				        'elements  =>  [' <elements-definition> '],'   
				        'text   =>' <text-content> ','   
				        'sql => {' <sql-mapping-definition or any other mapping to external data model> '}'   
			      '}'    

Where each <xxxx-definition> can be expressed in EBNF as:

   <attributes-definition>  = (attribute-name  '=>'  attribute-value) ( ','  <attributes-definition>)*	

   attribute-name = string   

   namespace-id = string   

   attribute-value  = 'scalar' | ('enum:'(attribute-name ( ','  attribute-name)*))    

   <elements-definition> =   ( '[' element-name  '=>'  (   
						              <element-variable>  |
                                                   ’'['   ‘   <element-variable> '’]’' | 
                                                   ’'[‘' (    <element-variable> '’,'’)+’ ']’' |
                                                   '’[‘' ('['‘ <element-variable> '’]’,'’?)+ ’']'’ ) 
                                                  ',' conditional-statement? ']’')*

    conditional-statement =  ('unless'|'if')':'(registered-name (',' registered-name)*)   

    registered-name = attribute-name|element-name   

    element-name  = string   

    <text-content> = 'scalar'|conditional-statement   

    <sql-mapping-definition> = (sql-table-name '=> {' sql-table-entry '}' ) ( ',' <sql-mapping-definition>)*   

    sql-table-entry =  (sql-entry-name '=> {' entry-mapping '}' ) ( ','   sql-table-entry )*   

    sql-table-name = string

    sql-entry-name = string   

    entry-mapping = 'value' '=>'( element-name|( '[' element-name (',' element-name)+ ']')) ( ',' if-condition)?     

    if-condition = 'if =>' attribute-name ':' attribute-value	

In the attributes definition the xmlns attribute is reserved for the namespace prefix. This name must be registered within Namespace class in order to provide some level of validation. This constraint will be fixed in future releases. Its recommended to have unique id attribute in each element, it will allow to utilize mapping by id for the complex element types.

There is some conditional logic allowed for attributes. An attribute value can be scalar which stays for scalar string or enumerated list of the allowed names. The list of elements is represented as array reference. The choice between several possible elements is introduced as array reference to the list and having multiple elements of one kind is represented as reference to array consisted with single element variable of that kind.

For example:

• elements => [parameter => $parameter] - defines single "parameter" sub-element

• elements => [parameter => [$parameter]] - defines list of "parameter" sub-elements

• elements => [parameters => [$parameters, $select_parameters]] - defines choice between 
              two single "parameters" sub-elements of different type

• elements => [datum => [[$pinger_datum],[$result_datum]] ] - defines choice between two
              lists of "datum" sub-elements of different type 

In elements-definition the third member is an optional conditional statement which represents validation rule. For example unless:value conditional statement will be translated into the perl's conditional statement && !($self->value) where value must be registered attribute or sub-element name and this condition will be placed in every piece of code where perl object is serialized into the XML DOM object or from it.

Note: You have to define element bottom-to-top in order for them to "know" about each other.

SYNOPSIS

      ## for example lets define some RelaxNG schema  in Compact notation and then express it as perl data structure
      #   this is a base schema from the L<http://ogf.org/schema/network/topology/base> namespace
      #
      # start =
      #  (
      #          element nmwg:message {
      #                  MessageContent
      #          } 
      #  )
      #
      #  MessageContent =
      #       Identifier? & 
      #       MessageIdentifierRef? &
      #       Type &
      #       Parameters? &                        
      #       (
      #               Metadata  
      #       )+
      #
      #  Identifier = attribute id { xsd:string }
      #
      #  IdReference =    attribute idRef { xsd:string }
      #      
      #  Type = attribute type { xsd:string }   
      #  MetadataIdentifierRef = attribute metadataIdRef { xsd:string }
      #
      #  MessageIdentifierRef =  attribute messageIdRef { xsd:string }
      # 
      # Metadata = 
      #    element nmwg:metadata {
      #  	  (
      #  		  Identifier &
      #  		  MetadataIdentifierRef? &
      #  		  MetadataContent
      #  	  )
      #    }
      #
      # MetadataBlock =
      #    Parameters?
      #
      # MetadataContent = 
      #  (
      #	   MetadataBlock 	     
      #  ) &	     
      #  EventType? &
      #
      # EventType =  element nmwg:eventType { xsd:string }      
      # 
      #  Parameters = 
      #    element nmwg:parameters {
      # 	    ParametersContent
      #    }
      #  
      # ParametersContent =	 
      #	  Identifier &
      #	  Parameter+
      #  
      # Parameter =   element nmwg:parameter { 
      #  	attribute name { 
      #  			 "count" | "packetInterval" | "endTime"| 
      #  			 "packetSize" | "ttl" |  "startTime" | 
      #  			 "valueUnits"  
      #  		       } &
      #  	(
      #  		attribute value { text } |
      #  		text
      #  	)
      #   }
 

 
     $parameter	=  {attrs  => {name => 'enum:count,packetInterval,packetSize,ttl,valueUnits,startTime,endTime',  
                               value => 'scalar', 
			       xmlns => 'nmwg'},
                    elements => [],
		    text => 'unless:value',
	         }; 		 
     $parameters =  {attrs  => {id => 'scalar',   
                                xmlns => 'nmwg'},
                     elements => [
		                    [parameter => [$parameter]], 
			      
			        ], 
	           };
   
  
     $metadata = {attrs  => {id => 'scalar', metadataIdRef => 'scalar',
                             xmlns => 'nmwg'},
 	          elements => [
 			         [parameters =>   $parameters],
 			         [eventType  =>  'text'] 
			    ], 
 	        }; 

     $message  = {attrs  => {id => 'scalar', type => 'scalar', xmlns => 'nmwg'}, 
                  elements => [ 
		                 [parameters =>  [$parameters]],
		                 [metadata => [$metadata]], 
			         [data	   => [$data]]
			      ], 
	         };
     
     ## this is it, as you can see it takes much less code to express the same RelaxNG compact schema 
     ## and of course that means even less code in case of  XML schema
    

SQL MAPPING

After ( or at the time of ) defining your elements you can set your sql mapping. Actually, it could be mapping to any external data model. Lets see how we can map parameters from parameter element into some fields from some SQL DB table

# take C<$parameter> element from the previous example 

       $parameter->{sql} =     
     
       #   for example this statement   will map 'count' field of the metadata table to be populated
       #  from attribute  'value' or text when attribute 'name' == 'count'
       #
       #  actually it will return this structure:
       #    metaData => { count => <value> }
       #  
       #
       
      {metaData => {count => { value =>  ['value' , 'text'], if => 'name:count'},
	
			  		 packetInterval=> { value =>  ['value' , 'text'], if => 'name:packetInterval'},
			  		 packetSize=> { value => ['value' , 'text']  , if => 'name:packetSize'},
			  		 ttl=> { value =>   ['value' , 'text'] , if => 'name:ttl'},
			  		 protocol => { value =>   ['value' , 'text'] , if => 'name:protocol'},
			  		 transport => { value =>   ['value' , 'text'] , if => 'name:transport'},
                          		 },
	 # next statement will define where to get time range 	and will return it as 'time' range data structure
	 #  for example: time => { 'ge' => '111111111', 'le' => '222222222' }
	 #  
	 # that means you absolutely free on how to use this mapping			 
			    time     => { 'ge' =>  { value =>	['value' , 'text'],  if => 'name:startTime'},
                          		  'le'  =>   { value =>  ['value' , 'text'],  if => 'name:endTime'},
                          		}, 
		            }; 

DEVELOPING DATA MODELS

The best design pattern would be writing your data model by following your schema design. Create DataModel.pm package for the base schema and export all necessary data structures and then somewhere in the building script add any extra sql mapping or even redefine some elements by replacing particular element definitions with new data structure. Of course you can mix elements with the same names from the different namespaces, just name them differently but it would be easier to define them in separate data model packages.

AUTHOR

Maxim Grigoriev, maxim at fnal_gov

LICENSE

Fermitools license (open source, modified BSD type), see http://fermitools.fnal.gov/about/terms.html

COPYRIGHT

Copyright (C) 2007-2008 by Fermitools, Fermilab

cpanm XML::RelaxNG::Compact::PXB

perl -MCPAN -e shell
install XML::RelaxNG::Compact::PXB