Hide Notes 

Slide 1: XML in a Nutshell
Slide 2: Outline • XML Basics • Displaying XML with CSS • Transforming XML with XSLT • Serving XML to Web Users • Resources • Tips & Advice
Slide 3: Documents • XML is expressed as “documents”, whether an entire book or a database record • Must haves: – At least one element – Only one “root” element • Should haves: – A document type declaration; e.g., <?xml version="1.0"?> – Namespace declarations • Can haves: – One or more properly nested elements
Slide 4: Elements • Must have a name; e.g., <title> • Names must follow rules: no spaces or special characters, must start with a letter, are case sensitive • Must have a beginning and end; <title></title> or <title/> • May wrap text data; e.g., <title>Hamlet</title> • May have an attribute that must be quoted; e.g., <title level=“main”>Hamlet</title> • May contain other “child” elements; e.g., <title level=“main”>Hamlet <subtitle> Prince of Denmark</subtitle></title>
Slide 5: Element Relationships • Every XML document must have only one “root” element • All other elements must be contained within the root • An element contained within another tag is called a “child” of the container element • An element that contains another tag is called the “parent” of the contained element • Two elements that share the same
Slide 6: The Tree <?xml version="1.0"?> Root element <book> Parent of <lastname> <author> <lastname>Tennant</lastname> <firstname>Roy</firstname> Child of <author> </author> <title>The Great American Novel</title> <chapter number=“1”> <chaptitle>It Was Dark and Stormy</chaptitle> Siblings <p>It was a dark and stormy night.</p> <p>An owl hooted.</p> </chapter> </book>
Slide 7: Comments & Processing Instructions • You can embed comments in your XML just like in HTML: <!-- Whatever is here (whether text or markup) will be ignored on processing --> • A processing instruction tells the XML parser information it needs to know to properly process an XML document: <?xml-stylesheet type="text/css" href="style2.css"?>
Slide 8: Well-Formed XML • Follows general tagging rules: – All tags begin and end • But can be minimized if empty: <br/> instead of <br></br> – All tags are case sensitive – All tags must be properly nested: • <author> <firstname>Mark</firstname> <lastname>Twain</lastname> </author> – All attribute values are quoted: • <subject scheme=“LCSH”>Music</subject> • Has identification & declaration tags
Slide 9: Valid XML • Uses only specific tags and rules as codified by one of: – A document type definition (DTD) – A schema definition • Only the tags listed by the schema or DTD can be used • Software can take a DTD or schema and verify that a document adheres to the rules • Editing software can prevent an author from using anything except allowed tags
Slide 10: Namespaces • A method to keep metadata elements from different schemas from colliding • Example: the tag <name> may have a very different meaning in different standards • A namespace declaration specifies from which specification a set of tags is drawn <mets xmlns="http://www.loc.gov/METS/" xsi:schemaLocation= "http://www.loc.gov/standards/mets/mets.xsd">
Slide 11: Character Encoding • XML is Unicode, either UTF-8 or UTF-16 • However, you can output XML into other character encodings (e.g., ISOLatin1) • Use <![CDATA[ ]]> to wrap any special characters you don’t want to be treated as markup (e.g., &nbsp;)
Slide 12: Displaying XML: CSS • A modern web browser (e.g., MSIE, Mozilla) and a cascading style sheet (CSS) may be used to view XML as if it were HTML • A style must be defined for every XML tag, or the browser displays it in a default mode • All display characteristics of each element must be explicitly defined • Elements are displayed in the order they are encountered in the XML • No reordering of elements or other processing is possible
Slide 13: Displaying XML with CSS • Must put a processing instruction at the top of your XML file (but below the XML declaration): <?xml-stylesheet type="text/css" href="style.css"?> • Must specify all display characteristics of all tags, or it will be displayed in default mode (whatever the browser wants)
Slide 14: CSS Demonstration XML Doc Cascading Stylesheet (CSS) Web Server
Slide 15: Transforming XML: XSLT • XML Stylesheet Language — Transformations (XSLT) • A markup language and programming syntax for processing XML • Is most often used to: – Transform XML to HTML for delivery to standard web clients – Transform XML from one set of XML tags to another – Transform XML into another syntax/system
Slide 16: XLST Primer • XSLT is based on the process of matching templates to nodes of the XML tree • Working down from the top, XSLT tries to match segments of code to: – The root element – Any child node – And on down through the document • You can specify different processing for each element if you wish
Slide 17: XSLT Processing Model XML Doc XML Parser Source Tree Transformatio n Formatted Output Formatting XSLT Stylesheet Result Tree From Professional XSL, Wrox Publishers
Slide 18: Nodes and XPath • An XML document is a collection of nodes that can be identified, selected, and acted upon using an Xpath statement • Examples of nodes: root, element, attribute, text • Sample statement: //article[@name=‘test’] = Select all <article> elements of the root node that have a name attribute with the value ‘test’
Slide 19: Templates • An XSLT stylesheet is a collection of templates that act against specified nodes in the XML source tree • For example, this template will be executed when a <para> element is encountered: <xsl:template match="para"> <p><xsl:value-of select="."/></p> </xsl:template>
Slide 20: Calling Templates • A template can call other templates • By default (tree processing): <xsl:apply-templates/> [processes all children of the current node] • Explicitly: <xsl:apply-templates select=“title”/> [processes all <title> elements of the current node] <xsl:call-template name=“title”/> [processes the named template, regardless of the source tree]
Slide 21: XSLT Structures • Decision: – Choose: when you want an “otherwise” (default) condition – If: when you don’t need a default condition • Looping: – For-each: processes each selected node in turn
Slide 22: XSLT Primer: Doing HTML • Typical way to begin: <xsl:template match="/"> <html> <head> <title><xsl:value-of select="title"/></title> <link type="text/css" rel="stylesheet" href="xslt.css" /> </head> <body> <xsl:apply-templates/> </body> </html> </xsl:template> • Then, templates for each element appear below
Slide 23: XSLT Demonstration XSLT Stylesheet XML Processor (xsltproc) XHTML representation Cascading Stylesheet (CSS) XML Doc CGI script Web Server
Slide 24: XML vs. Databases (a simplistic formula) • If your information is… – Tightly structured – Fixed field length – Massive numbers of individual items • You need a database • If your information is… – Loosely structured – Variable field length – Massive record size • You need XML
Slide 25: Serving XML to Web Users • Basic requirements: an XML doc and a web server • Additional requirements for simple method: – A CSS Stylesheet • Additional requirements for complex, powerful method: – An XSLT stylesheet – An XML parser – XML web publishing software or an in-house CGI or Java program to join the pieces – A CSS stylesheet (optional) to control how it looks in a browser
Slide 26: XML Web Publishing Software • Software used to add XML serving capability to a web server • Makes it easy to join XML documents with XSLT to output HTML for standard web browsers • A couple examples, both free…
Slide 27: Requires a Java servlet container such as Tomcat (free) or Resin (commercial)
Slide 28: Requires mod_perl
Slide 29: http://texts.cdlib.org/escholarship/
Slide 30: XML & XSLT Resources • Eric Morgan’s “Getting Started with XML” a good place to begin • Many good web sites, and Google searches can often answer specific questions you may have • Be sure to join the XML4Lib discussion
Slide 31: Tips and Advice • Begin transitioning to XML now: – XHTML and CSS for web files, XML for static documents with long-term worth – Get your hands dirty on a simple XML project • Do not rely on browser support of XML • DTDs? We don’t need no stinkin’ DTDs! • Buy my book! (just kidding…)
Slide 32: Contact Information Roy Tennant California Digital Library roy.tennant@ucop.edu http://roytennant.com/ 510-987-0476