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Development of a Demand Driven Dom Parser

Kråkenes, Ole-Jakob; Gausnes, Ole Martin; Alvestad, Gaute Odin
Master thesis
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URI
http://hdl.handle.net/11250/2571065
Date
2006
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  • Institutt for datateknologi og informatikk [5023]
Abstract
XML is a tremendous popular markup language in internet applications as well as a

storage format. XML document access is often done through an API, and perhaps the

most important of these is the W3C DOM. The recommendation from W3C defines a

number of interfaces for a developer to access and manipulate XML documents. The

recommendation does not define implementation specific approaches used behind the

interfaces.

A problem with the W3C DOM approach however, is that documents often are loaded

in to memory as a node tree of objects, representing the structure of the XML document.

This tree is memory consuming and can take up to 4-10 times the document size. Lazy

processing have been proposed, building the node tree as it accesses new parts of the

document. But when the whole document has been accessed, the overhead compared

to traditional parsers, both in terms of memory usage and performance, is high.

In this thesis a new approach is introduced. With the use of well known indexing

schemes for XML, basic techniques for reducing memory consumption, and principles

for memoryhandling in operation systems, a new and alternative approach is introduced.

By using a memory cache repository for DOM nodes and simultaneous utilize

principles for lazy processing, the proposed implementation has full control over memory

consumption. The proposed prototype is called Demand Driven Dom Parser, D3P.

The proposed approach removes least recently used nodes from the memory when the

cache has exceeded its memory limit. This makes the D3P able to process the document

with low memory requirements. An advantage with this approach is that the parser is

able to process documents that exceed the size of the main memory, which is impossible

with traditional approaches.

The implementation is evaluated and compared with other implementations, both lazy

and traditional parsers that builds everything in memory on load. The proposed implementation

performs well when the bottleneck is memory usage, because the user can

set the desired amount of memory to be used by the XML node tree. On the other hand,

as the coverage of the document increases, time spend processing the node tree grows

beyond what is used by traditional approaches.
Publisher
NTNU

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