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| <title>Xerces 2 | Xerces</title> |
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| <h1>Evaluation of Xerces Code</h1> |
| <a name='Overview'></a> |
| <h2>Overview</h2> |
| <p> |
| Historically, the <a href='http://xml.apache.org/xerces-j/'>Xerces</a> |
| code was developed to be the fastest |
| <a href='http://www.w3.org/XML/'>XML</a> parser on the planet. |
| This impacted design decisions and caused the parser to be |
| written from the inside out. While this produced an extremely |
| fast XML parser with DTD validation, the overall design |
| suffered. Xerces developers have found it difficult to understand, |
| fix bugs, and add new features. Hence the Xerces 2 effort. |
| </p> |
| <a name='TheGood'></a> |
| <h2>The Good</h2> |
| <p> |
| <table border='0'> |
| <tr> |
| <th>Standards:</th> |
| <td> |
| The Xerces parser is an extremely complete XML parser. Besides |
| conforming to the XML and Namespace specifications, it offers |
| support for SAX 1 and 2; DOM Level 1 and 2; and most of |
| the latest working draft of XML Schema. |
| </td> |
| </tr> |
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| <th>Modularity:</th> |
| <td> |
| The current Xerces code made a decent attempt at modularity by |
| defining a set of interfaces between components of the parser |
| such as the scanner and validator. The parser is designed as |
| a pipeline of components. This is a good idea whose implementation |
| got complicated by performance considerations and feature creep. |
| </td> |
| </tr> |
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| <th>Validation:</th> |
| <td> |
| Xerces is able to validate documents with grammars specified |
| in DTD and XML Schema syntax. All validation is performed by |
| a universal validator that can validate the union of features |
| found in both syntaxes. This enables the parser to handle |
| current and future grammars in a consistent way. |
| </td> |
| </tr> |
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| <th>Performance:</th> |
| <td> |
| The Xerces parser has always performed well. Implementation of |
| XML Schema has caused the performance to slip but this is to |
| be expected -- you can't do a lot more work per element without |
| incurring a performance penalty. |
| </td> |
| </tr> |
| </table> |
| </p> |
| <a name='TheBad'></a> |
| <h2>The Bad</h2> |
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| <th>Size:</th> |
| <td> |
| The parser is too big but this is not all due to the code |
| required to parse XML files. A lot of contributed features |
| have been rolled into the Xerces jar file. For example: |
| HTML and WML DOM implementations; document serializers; etc. |
| It would be nice to find a way to package the features into |
| separate distributable jars. |
| </td> |
| </tr> |
| <tr> |
| <th>Simplicity:</th> |
| <td> |
| The code needs to be simplified. A lot of complexity of the |
| Xerces parser can be found in the entity readers and the use |
| of the string pool throughout the system. |
| </td> |
| </tr> |
| <tr> |
| <th>Documentation:</th> |
| <td> |
| This is little to no documentation of the Xerces code. And |
| frequently the javadoc comments are missing or incorrect. |
| More effort must be taken in Xerces 2 in order to make sure |
| that everything is well documented. |
| </td> |
| </tr> |
| </table> |
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