"Everybody" knows that precompiling your XPath expressions ahead of time, usually in static .ctors, improves execution performance. But what's actually happening at that "compilation" time? Unlike what many believe, compiled IL is NOT being generated, neither on-the-fly assemblies or anything like it. It's NOT like RegEx compilation, sadly. But what's going on is important for performance because it involves parsing, AST (abstract syntax tree) building, etc.

This tutorial introduces XPath and covers most aspects of it. It is aimed at people who do not know XPath or want a refresher. If you plan to use XSLT, you should take this tutorial first. You will learn: What XPath is, the syntax and semantics of the XPath language, how to use XPath location paths, how to use XPath expressions, how to use XPath functions, and how XPath relates to XSLT. XPath is a W3C standard. This tutorial covers version 1.0.

Dare Obasanjo discusses the XPathReader, which provides the ability to filter and process large XML documents in an efficient manner using an XPath-aware XmlReader. With the XPathReader, one can sequentially process a large document and extract an identified sub-tree matched by an XPath expression.

The XML team has recently started getting questions about our position on XQuery 1.0, XPath 2.0 and XSLT 2.0. Yesterday my boss, Mark Fussell, posted about why we have decided to implement XQuery 1.0 but not XSLT 2.0 in the next version of the .NET Framework. Some people misinterpreted his post to mean that the we chose to implement XQuery 1.0 over XSLT 2.0 because we prefer the syntax of the former over that of the latter. However decisions of such scale aren't made that lightly.

Two of XML's biggest strengths are its abilities to represent arbitrary types of data (e.g., purchase orders, financial transactions, calendar items) and to provide a platform-neutral format for exchanging data between business partners. Once you've decided to exchange XML data with your business partner, you need to agree on the XML grammar you'll use to exchange the data. You'll either invent your own custom XML grammar or adopt a predefined, industry-standard grammar such as the XML Common Business Library, xCBL (see http://www.xcbl.org for details about xCBL), if one is relevant to your application. In most cases, you'll build or obtain the XML Schema Definition (XSD) schema that defines the grammar you've created or selected. Although it's not a strict requirement, a schema provides a formal agreement between you and your business partner on the format of the exchanged data.

Question / Answers with Aaron Skonnard about Object Graphs, XPath, String Comparisons, and More.

If you've been watching the Microsoft® XML Web site (http://msdn.microsoft.com/xml), you've probably noticed the increased pace of MSXML releases. MSXML 2.0 shipped with Microsoft Internet Explorer 5.0 while MSXML 2.5 shipped with Windows® 2000. There was also an interim MSXML 2.6 release which included most of the features in the current 3.0 release with a few exceptions. There have also been several additional MSXML 3.0 releases this year. In this month's column, I'll describe the major enhancements made to MSXML since the original, version 2.0. These enhancements include new support for the official W3C XPath 1.0 and XSLT 1.0 specifications, improved support for the Microsoft XML Schema dialect known as XML-Data Reduced (XDR), and new support for the popular stream-based Simple API for XML (SAX). If you're not familiar with some of these terms, refer to The XML Files in the May 2000 issue, where I covered how all the core XML technologies fit together.

When I wrote the first installment of The XML Files for the premiere issue of MSDN™ Magazine, I dove right into a discussion of XML-based persistence behaviors. This month I'd like to give you a proper introduction to this column. The XML Files will focus primarily on XML and the technologies that support it. Upcoming columns will provide a study of the technology specifications and standards (as defined by W3C, IETF, and so on), and the support for these technologies in Microsoft® products. The main goal of this column is to distill XML's undeniable merits from the noisy industry hype.

In my May 2000 column, I reviewed the set of W3C recommendations that most developers consider the current core of XML. The XML Information Set (Infoset) specification was probably new to most readers, including those already actively using XML. This lack of awareness mostly stems from the fact that XML was originally defined in terms of a concrete syntax, as opposed to an abstract data model. This makes it hard to approach XML without first thinking about angle brackets. The Infoset specification (http://www.w3.org/TR/xml-infoset) takes a few steps back and standardizes the abstract data model implied by the XML 1.0 and Namespaces recommendations.

Inspiration for this article arose from a weekend where nothing that I expected to work on actually panned out. My significant other decided to take a celebratory trip to Las Vegas with a coworker, which coincided quite nicely with my plans to go to Ikea and pickup a bookcase so I could finally unpack my books since moving to Redmond a few months ago. After trundling around Ikea for two hours, I found a bookcase on display that fit the color scheme of my living room only to find out that some the necessary pieces were out of stock. I ended up ordering the bookcase and went home empty-handed. Unfortunately I had already unpacked my books at home and they were strewn all over my living room. This became the perfect opportunity to catalog my burgeoning library, and of course I chose to use XML to achieve this task.

Guest author Prajakta Joshi discusses how to create custom functions for XPath using System.Xml APIs from the .NET Framework SDK. Topics include adding extension functions to XPath 1.0, a look forward to XPath 2.0, and using extension functions in XSLT.

Dare Obasanjo builds a C# application that retrieves and displays news feeds from various Web sites. The application utilizes XPath, XSLT, XML Schema, the DOM, and XML Serialization in the .NET Framework.

Steve Saxon discusses the ObjectXPathNavigator, which provides the power and flexibility of the XML programming model without the overhead of having to serialize an entire object graph into an XmlDocument object.

Dare Obasanjo combines his efforts from a previous article on EXSLT with those of Oleg Tkachenko's article on creating multiple outputs from a single XSLT transformation to create a customer EXSLT library for the .NET Framework that includes support for EXSLT functions to regular XPath queries.

Two of XML's biggest strengths are its abilities to represent arbitrary types of data (e.g., purchase orders, financial transactions, calendar items) and to provide a platform-neutral format for exchanging data between business partners. Once you've decided to exchange XML data with your business partner, you need to agree on the XML grammar you'll use to exchange the data.

Get a head start on XPath 2.0 by reviewing the new features.

This section display some XPath utilities.

Xpath is a standard from W3C (a "recommendation" in W3C parlance as opposed to "working drafts") that can be used to navigate/address parts of an XML document and is meant to be used with XSLT & XPointer standards from W3C which are the languages for document-transformation and Multi-directional links respectively. This project attempts to evaluate the structure-shyness of Xpath.

XPath is described in XPath 1.0 standard. In this tutorial selected XPath features are demonstrated on many examples.

XPath is everywhere. It's established itself as the workhorse of XML processing. The XPath engine is one of the parts of 4Suite that has had the most development and exercise. Much of it is implemented in C for performance sake, and this is one of the key differences between the XPath library in current 4Suite and that in PyXML, which is based on an older release of 4XPath, and is almost entirely in Python.