DOMNode - getChildNodes - wrote efficient list implementation
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Key: XERCESC-1299
URL: http://nagoya.apache.org/jira/browse/XERCESC-1299
Project: Xerces-C++
Type: Improvement
Components: DOM
Versions: 2.5.0
Environment: VC7, Windows XP
Reporter: Michael Williams
Problem:
The DOMNode in xerces has a method called getChildNodes, which returns a
DOMNodeList of child elements. This DOMNodeList basically provides a thin
wrapper for the internal linked list, and is not efficient when doing element
traversals, and direct array-type lookups with the DOMNodeList.item call.
Solution:
The solution to this lies in creating a proper implementation of the xerces
DomNodeList class. We will extend this class to implement the following method
virtual DOMNode *itemByTagNameNS(XMLSize_t index, const XMLCh *namespaceURI,
const XMLCh *localName) const {return 0;};
Retrieve an item in a specific collection by index, tag name, and namespace
virtual XMLSize_t getLengthByTagNameNS(const XMLCh *namespaceURI, const XMLCh
*localName) const {return 0;};
Get the length of a specific collection by index, tag name, and namespace
virtual bool insertElementAtByTagNameNS(DOMNode *, XMLSize_t index);
Insert an item into the list by index of the collection of elements with
matching namespace URI and localname. Returns false if the index < 0 or
greater than the number of elements of the appropriate type (namespace and
element name match).
virtual DOMNode *removeElementAtByTagNameNS(XMLSize_t index, const XMLCh
*namespaceURI, const XMLCh *localName)
Remove an element by index of the collection of elements with matching
Namespace URI and localname. Returns the removed node upon success, or false
if the index < 0 or greater than the number of elements of the appropriate type.
virtual bool insertElementAt(DOMNode *, XMLSize_t index) = 0;
Inserts an element into the list of child elements by index. Returns false if
the index < 0 or greater than the number of child elements.
virtual DOMNode *removeElementAt(XMLSize_t index) = 0;
Remove an element by index of the collection of elements with matching
Namespace URI and localname. Returns the removed node upon success, or false
if the index < 0 or greater than the number of child elements.
Comments regarding element navigation:
All methods of navigating elements will probably yield about the same level of
performance, and linked list navigation or array navigation can be mixed
without any adverse performance effects.
Comments regarding element deletion and insertion:
Choose one of the following three methods for deleting and inserting children
elements into an element, and for the same element, do not mix the methods.
Otherwise performance will most likely suffer.
1. Inserting and deleting by linked list methods (original xerces methods)
2. Inserting and deleting into the vector of ALL children (not using namespace
and nodename identifiers)
3. Inserting and deleting by NS and nodename.
The reason is that because algorithms to insert or delete from a linked list
can be very efficient, but then to try to find the element to be deleted in an
array will yield slow performance, because there is no good way to know the
array index of the element beforehand.
Also, the algorithms to partition an elements children into a general child
array, and arrays by namespace and element name, will not yield good
performance if these two sets of arrays (partitioned and general) are both used
in the same element for inserting and deleting elements.
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