Using XML Effectively in VS .NET

Generation UPC-A Supplement 5 in VS .NET Using XML Effectively

This chapter doesn t include an exhaustive list of XML features, but it does discuss the most common When you have questions about current XML usage, always refer to the XML standard You can find it at

The document that defines the standard can be a little confusing to read, however, so use the annotated version to answer questions about the interpretation of the standard You can find this version at

XML is a standard for combining data with context, such as a Word processor does by combining the text you type (data) with formatting (context) The context can include everything from the arrangement of the data to techniques for formatting it The idea is to preserve the data and the information you use when you re working with the data Nothing in the XML standard limits the interpretation of XML the standard leaves the interpretation up to whoever is applying the standard (that is, the implementer) Many other standards define how to interpret XML, but XML itself doesn t define anything but the basic requirements for the document in particular, the format of the data within the document One of the reasons that XML is so popular is that its documents appear in plain text Every computer can read and understand text In fact, text is the common format for all computers, even computers too old to perform useful work today Given enough time, anyone can read and understand an XML document by using a simple text editor such as Notepad You have other means of reading XML at your disposal, but you don t have to use any special application Many applications now produce XML output By discovering the interpretation of the XML document, you can create your own presentations on a Web site The presentation doesn t have to precisely match the presentation of the document in the application that creates it Because XML is freeform, you transform it to meet whatever needs you might have You can also create documents of your own Effective use of XML requires that you define the structure of the content you want to create A document could include formatting or structure information, or even both You decide how someone should interpret the content of the XML document As long as your document follows the XML rules, you won t experience any difficulty in storing the information you need in the way you want These rules are discussed in the next section

XML doesn t have very many rules to consider but the few it does have are absolute When a document you create follows all the rules, applications designed to work with XML see it as well formed A well-formed XML document includes specific features that clue the reader (the application parsing, working with, the content) in on the content of the document and tell it how to display the information

Every XML document begins with a processing instruction The processing instruction tells an application designed to work with XML what to do with the document You must begin the XML document with this processing instruction or the reader won t interpret it correctly Here s a typical example of this processing instruction:

A processing instruction always appears within a combination of angle brackets and question marks like this: < > This processing instruction defines the document as an XML document It has two attributes: The version attribute identifies the version of XML used for this document (All XML documents currently use version 10, but that could change in the future) The encoding attribute defines the character set used for the document In this case, the document uses 8-bit Unicode Transformation Format (UTF-8), which is essentially plain text An XML document can have other processing instructions unique to the document these appear only when needed to change the interpretation of the document Normally, you won t see these other processing instructions unless a special transformation instruction creates a particular presentation for your document Then you may see additional special processing instructions in word processed or other complex documents The only standard processing instruction is the XML header that appears at the beginning of every XML document Other processing instructions are application and document specific, so you need to consult the documentation provided by the vendor or other party who created the document schema for descriptions of other processing instructions Most processing instructions are titled after the application that uses them For example, the required XML processing instruction refers to all XML