dtddoc step 2: Internal data structures (2/2) - exploring XML

dtddoc step 2: Internal data structures

Wutka's DTD parser

Wutka's DTD class looks similar to Bourret's, with the addition of a distinguished member identifying the root element. The individual DTDElements, however, have only three members:

member	value
attributes	The element's attributes.
content	The element's content.
name	The element's name.

This restricts navigation to a top-down approach, descending from the root element. For our documentation generation project we would have to derive the parents of a particular element ourselves.

perlSGML's DTDParser

As mentioned earlier, Perl programs make less use of classes, in favor of a more functional programming style around the built-in hash and array data types. The following functions can be invoked on a DTD object:

function	value
get_base_children($element)	An element's children (content elements).
get_elem_attr($element)	An element's attributes.
get_elements($nosort)	Returns all elements in a DTD, in sorted or order of appearance.
get_elements_of_attr($attr_name)	Retrieve all elements that have an attribute $attr_name defined in the DTD.
get_parents($element)	Get all elements that may be a parent of $element.
get_top_elements()	Get the top-most elements defined in the DTD. Top-most elements are those elements that cannot be contained within another element or can only be contained within itself.
is_child($element, $child)	returns 1 if $child can be a legal child of $element. Otherwise, 0 is returned.
is_element($element)	returns 1 if $element is defined in the DTD. Otherwise, 0 is returned.

There are more SGML-specific functions, which have been omitted for brevity. The functions listed above allow for both a top-down navigation of the DTD and a combination of parent and child traversal. All data structures are returned as Perl hashes or arrays, DTD is the only class in this package.

DTD Parser in phpxmlclasses

The PHP DTD parser is designed like Wutka's Java version, with the DTD object having a root element and an array of all elements. Those elements contain:

member	value
attributes	The element's attributes.
content	An element's content.
name	An elements name.

So here too, we would have to construct the parent relationships ourselves. Apart from that, everything needed for our project is present.

Conclusion

The DTD parsers fall into two categories: The ones that simply parse the DTD into a hierarchical structure of arrays or custom objects, and those that additionally provide full parent/child references. All parsers are suitable candidates for dtddoc, so we can choose the implementation language based on our development needs going forward.

Produced by Michael Claßen

URL: https://www.webreference.com/xml/column66/2.html
Created: Oct 14, 2002
Revised: Oct 14, 2002