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Understanding XML in Enterprise Computing

Learn about XML, its role in enterprise computing, document structure, relationships with HTML and SGML, popular applications, presentation methodologies, XML rules, DTD, and well-formed XML documents.

colin-dickson
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Understanding XML in Enterprise Computing

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  1. XML and Enterprise Computing

  2. What is XML? • Stands for “Extensible Markup Language” • similar to SGML and HTML • document “tags” are used to define content not just formatting • can be defined for individual industries • Allows e-commerce applications to publish databases to Web more easily • merging of relational, O-O, and XML models

  3. What is meant by a “document”? • A form of presentation • paper, browser screen, voice, etc. • Structure and organization of elements • memo, contract, recipe, etc. • Informational content • text and numbers organized in relation to each other

  4. Relationship Among Markup Languages HTML SGML XML

  5. What are some current XML applications? • On-line banking • Push technology • Web automation • Database Publishing • Software Distribution

  6. Some sample HTML <!-- snippet of HTML --> <h1>Personal Computers For Sale</h1> <h2>Maker: Acme PC Inc.</h2> <h3>Model: Blaster 555</h3> <table border = 1> <tr> <td>Storage:</td> </tr> <tr> <td>RAM<td>72 MB</td> <tr> <td>Hard Disk</td><td>2 GB</td> </tr> </table>

  7. XML Sample <!--Snippet of an XML Document --> <PcForSale> <Make>Acme PC Inc</Maker> <Model>Blaster 555</Model> <Storage> <Ram Units = “MB”>72</Ram> <HardDisk Unites = “GB”>2</HardDisk> </Storage> </PcForSale>

  8. How is XML Presented? • XML includes a DTD (Document Type Definitions) • lists the element types and the order you are allowing them to occur • XML parser tests to see them are valid DTDs • XSL (XML Style Language) • similar to cascading style sheets • contain presentation information

  9. Another Example • Convert a business card into an XML document • start with representative XML content • define DTD elements

  10. XML Rules • Open and close tags define “elements” and each element must have a closing tag (except for “empty” elements) • Elements appear in a strict hierarchy; upper elements are parents of lower “child” elements. • DTD is not mandatory but it ensures two parties define a docement’s contents the same. • DTDs constrain the data, the hierarchy of content, and the number of times it may appear

  11. XML Rules (cont.) • Elements • XML is case sensitive • must have 1 and only 1 “root” element • elements consist of an “element name” and “element content” • element content may consist of character or other data or even other elements embedded • an XML schema or “tree” describes hierarchy of elements • empty elements are indicated by a trailing backslash

  12. Well-Formed XML Documents • Have one root element • All non-empty elements have start and stop tags that match exactly • All empty elements have correct trailing slash • Elements are strictly nested with no overlapping elements

  13. Attributes • Allow designer to add richer metadata to elements • Consist of attribute name and attribute value • attribute values are bounded by quotes • can specify as many attributes for each element as you want • some authors use UC text for attribute names to easily distinguish <addresses> <address ADDTYPE=“shipto” <firstname>Robert</firstname> ……… </address> </addresses>

  14. Defining a DTD • Element declaration begins with “<!ELEMENT” and ends with > • this contains an element name and content model surrounded by parentheses • elements can contain data or other elements or be empty • to indicate it contains data we use (#PCDATA) • if it contains other elements we list them in brackets (name, title, address, etc) • empty elements use the key word “EMPTY”

  15. Further DTD Specifications • Designer can specify the number of times an element may appear • “?” means it may occur 0 or 1 times in document • “*” means it may occur 0 or more times • “+” means it may appear 1 or more times • can enumerate possible alternative with “|” • can specify an attribute is required with #REQUIRED • #IMPLIED means attribute may not have a value

  16. Try another example • Think of your resume, posted say on Monster.com • What does html for this look like? • Write your resume in XML???? • What is the “root” element? • Why would this be valuable?

  17. Another Example • Creating an “order” in XML • include a “prolog”of XML document • header information before root element • may include processing instructions and DTD declaration ex. <?xml version=“1.0”?> <!DOCTYPE order SYSTEM “order.dtd”> • may include comments in prolog or after • start with <!- and end with ->

  18. XML Document XML App XML Processor XML DTD

  19. Some XML Processors • Processors are either “validating” or “non-validating” • Msxml • developed by MS Corp. Java and ActiveX versions • Aelfred • Java-based XML. Microstar Corp. • XP • Java-based XML processor by James Clark

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