XML template engine
From Wikipedia, the free encyclopedia
A XML template engine (or XML template processor) is a specialized Template processor for XML input and/or XML output, working in a XML template system context. There are two main types:
- "XML-suite standards" compliant engines:
- Others, like Web template engine.
[edit] XSLT processors
XSLT processors may be delivered as standalone applications, or as software components or libraries intended for use by applications. Many web browsers and web server software have XSLT processor components built into them.
Most current operating systems have an XSLT processor installed. For example, Windows XP comes with the MSXML3 library, which includes an XSLT processor. Earlier versions may be upgraded and there are many alternatives, see the External Links section.
Early XSLT processors had very few optimizations; stylesheet documents were read into Document Object Models and the processor would act on them directly. XPath engines were also not optimized.
By 2000, however, implementors saw optimization opportunities in both XPath evaluation and template rule processing. For example, the Java programming language's Transformation API for XML (TrAX), later subsumed into the Java API for XML Processing (JAXP), acknowledged one such optimization: before processing, the XSLT processor could condense the template rules and other stylesheet tree information into a single, compact Templates object, free from the constraints and bloat of standard DOMs, in an implementation-specific manner. This intermediate representation of the stylesheet tree allows for more efficient processing by potentially reducing preparation time and memory overhead. Additionally, the formal API allows for the object to be cached and reused for multiple transformations, potentially providing higher performance if several input documents are to be processed with the same XSLT stylesheet. Parallels are often drawn between this optimization and the compilation of programming language source code to bytecode: the stylesheets are said to be "compiled", even though they don't usually produce native programming language bytecode; rather, they produce intermediate structures and routines that are stored and processed internally.[1]
XPath evaluation also has room for significant optimizations, and most processor vendors have implemented at least some of them, for speed. For example, in <xsl:if test="/some/nodes"> the test will evaluate to true if /some/nodes identifies any nodes, so evaluaton can stop as soon as the first matching node is found; continuing to look for the entire set of matching nodes would not change the result. Similar optimizations can be undertaken when processing xsl:when and xsl:value-of, as well as expressions relying on, either implicitly or explicitly, string(), boolean(), or number(), and those that use numeric and position()/last()-based predicates.
