April 2002
Intermediate to advanced
218 pages
6h 12m
English
Content preview from Perl and XMLBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 4. Event Streams
Now that you’re all warmed up with parsers and have enough knowledge to make you slightly dangerous, we’ll analyze one of the two important styles of XML processing: event streams. We’ll look at some examples that show the basic theory of stream processing and graduate with a full treatment of the standard Simple API for XML (SAX).
Working with Streams
In the world of computer science, a stream is a sequence of data chunks to be processed. A file, for example, is a sequence of characters (one or more bytes each, depending on the encoding). A program using this data can open a filehandle to the file, creating a character stream, and it can choose to read in data in chunks of whatever size it chooses. Streams can be dynamically generated too, whether from another program, received over a network, or typed in by a user. A stream is an abstraction, making the source of the data irrelevant for the purpose of processing.
To summarize, here are a stream’s important qualities:
It consists of a sequence of data fragments.
The order of fragments transmitted is significant.
The source of data (e.g., file or program output) is not important.
XML streams are just clumpy character streams. Each data clump, called a token in parser parlance, is a conglomeration of one or more characters. Each token corresponds to a type of markup, such as an element start or end tag, a string of character data, or a processing instruction. It’s very easy for parsers to dice up XML in ...
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