This project is an attempt to define an implementation of SAX using Objective C and Apple's Foundation framework. It may be portable with the GNUstep frameworks, though this has not been tested.

Last month we began our exploration of more advanced SAX topics with a look at how SAX events can be generated from non-XML data. This month, we conclude the series by introducing SAX filters and their use in XML data transformation.

In last month's column we began our introduction to XML::SAX::Machines, a group of modules which greatly simplifies the creation of complex SAX application with multiple filters. This month we pick up where we left off by further illustrating how XML::SAX::Machines can be used to remove most of the drudgery of building SAX-based XML processing applications. If you have not read last month's offering, please do so now.

Most SAX parsers are built on top of a pull parsing layer. It is an interesting challenge to expose to the user both pull and push layers. This allows an application to use pull parsing when needed without having to stop using SAX API.

Last month we began our exploration of more advanced SAX topics with a look at how SAX events can be generated from non-XML data. This month, we conclude the series by introducing SAX filters and their use in XML data transformation.

A Unmarshaller is the opposite of the Marshaller: It takes as input XML in either of several representations (byte or character stream, DOM node, or a series of SAX events) and returns a JAXB object with the same contents

In recent columns we have seen that SAX provides a modular way to generate and filter XML content. For those just learning how SAX works, though, the task of hooking up to the correct parser-generator-driver and building chains of filters can be tricky. More experienced SAX users may have a clearer picture of how to proceed, but they often find that initializing complex filter chains is tedious and lends itself to lots of duplicated code.

In an earlier Python and XML column I discussed ways to achieve proper XML output from Python programs. That discussion included basic considerations and techniques in generating XML output in Python code. I also introduced a couple of useful functions for helping with correct output: xml.sax.saxutils.escape from core Python 2.x and Ft.Xml.Lib.String.TranslateCdata from 4Suite.

In a previous column, we covered the basics of the Simple API for XML (SAX) and the modules that implement that interface in Perl. Over the course of the next two months we will move beyond these basic topics to look at two slightly more advanced ones: creating drivers that generate SAX events from non-XML sources and writing custom SAX filters. If you are not familiar with the way SAX works, please read High-Performance XML Parsing With SAX before proceeding.

SAX is referred to as an event-driven model or system. SAX parses an XML document and as it encounters the different parts of an element it performs different functions. The different functions performed depend on how the programmer sets up the code.

Instead of using the Document Object Model (DOM), you can use the Simple API for XML (SAX) to provide a lower-level API to parse XML data that can result in a much greater performance gain under certain scenarios. For example, a messaging scenario where you preprocess and reroute XML documents to other servers.

The error handling section checks to see if the XML parser is not at the end of the XML file when an error occurs. If there is an error and we're not at the end of the file, then we capture and send the error code and the line where the error occurred to the browser:

In the startElement function we define what HTML is associated with which element. The function startElement is called by the xml_set_element_handler function in the code. The startElement function must have three parameters:

In this section we will read an XML file and display it as an HTML table, using SAX.

This article describes an alternative way of converting XML to HTML using the SAX parser. For each tag you want to convert, you write a conversion function. This function is called with two arguments: contents and attributes. The return value of the function will replace the tag and its contents in the finished document.

If a SAX application needs to implement customized error handling, it must implement this interface and then register an instance with the SAX parser using the parser's setErrorHandler method. The parser will then report all errors and warnings through this interface.

At the heart of Cocoon there are the different sitemap components. When you start writing your own components the component you will probably end up writing the most is a transformer. Transformers receive SAX events from a previous component in the pipeline and send SAX events to the following component. Transformers therefore allow you to directly influence and change an XML stream. Based on an example I want to show you how you can write a customized transformer.

Parsing XML streams can be done with two different methods. They each have their pros and cons. Although the simplest, and probably most usual way to manipulate XML files is to represent them in a tree and manipulate it through the DOM interface (see next chapter).

The SAX2 interface is an event-driven mechanism to provide the user with document information. "Event" in this context has nothing to do with the term "event" you probably know from windowing systems; it means that the parser reports certain document information while parsing the document. These reported information is referred to as "event".

If a SAX application needs to implement customized error handling, it must implement this interface and then register an instance with the XML reader using the setErrorHandler method. The parser will then report all errors and warnings through this interface.