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Review of XML IST 421 Spring 2004 Lecture 5
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XML eXtensible Markup Language
Used for digital representation of documents Store, process, search, transmit, display and print documents - current information about XML
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XML Basic building block is the element, defined by tags
Root element contains all of the other elements Attributes describe properties of elements XML uses delimiters to differentiate character data Less than < and greater than > called a tag
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XML Elements Name the contents of the element.
Typically in pairs with a start and end tag. Some elements take attributes. The structure describes the relationship between the elements. Example: <order_no>101</order_no>
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XML Elements Letters Digits Underscore character Dot Hyphen
May start with a letter or an underscore May consist of: Letters Digits Underscore character Dot Hyphen Cannot start with the string “xml”
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XML Elements XML names are case sensitive unlike HTML tags which are not Must have one root element Similar to the <HTML>; </HTML> in html type of document Programmer defines a root name First line must be xml declaration <?xml version=“1.0”?> (Note: ? Means information is passed)
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XML Comments <!-- ………--> Any text desired can be placed within
the <! > Example: <!-- Updated Apr 3 -->
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XML Processing Instructions
Enables the passing of information to another application Format: <?… ?> Specifies version. Example: <?xml version “1.0”?>
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Let’s Practice Open Microsoft Notes (not XML notes!)
Declare the XML version as “1.0” Create a Root Element, called class_listing Note that every element must have both a beginning and ending tag Save as: class_listing.xml Add some other elements! Create data within each element! Test this in the browser.
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Review the Practice XML data is hierarchical
Elements contained within other elements are called children Elements that contain children are called parent elements – nesting Each XML document contains a root element Element names describe the data
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Components of XML Documents
XML Declaration First line of document Declaration tag begins with: <?xml version=“1.0” encoding=“UTF-8” standalone=“no”?> May contain 3 attributes: version=“1.0” encoding=“UTF-8” (default if not given) standalone=“yes” or standalone=“no” (default) UTF-8 = 8-bit Unicode character-encoding scheme. Others are UTF-16, UTF-32, and ISO UCS-2.
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Attributes Attributes may be attached to elements Attributes have:
Names Values Name is separated from value by “=“ sign Value must have “ “ around it
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Attributes Creates additional information
It is often information about the ELEMENT content Nesting an ELEMENT within others may accomplish the same purpose
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Let’s Practice Add attribute to define categorize of student status
<student status=“sr”> Add this attribute to all students Remember to save with .xml extension.
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XML Entities Entities are used as placeholders for content
Two types of entities: General Parameter
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XML General Entities Placeholders for any information contained in the root element Three types: Character – used in place of special characters Content – used to mark the place of a common block of content that you type often Unparsed – used for binary or nontext data like images or video clips
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Character Entities Some tag delimiter characters have special meaning in XML <?xml version=“1.0”?> <equation> 50 < 100 </equation> Cause a syntax error
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Character Entities Solve problem by using character entities:
> > < < “ " ‘ '
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Content Entities Used to mark the place of a common block of content that you type often or that may change Internal entities – defined as part of the DTD within the XML document Example: <!DOCTYPE class_listing [ <!ENTITY campus "Harrisburg"> ]> <class_campus>Penn State &campus;</class_campus> External entities – information saved in an external file with a .xml extension
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Unparsed Entities Used for binary or nontext data like images or video clips <!ENTITY picture SYSTEM “sunset.gif” NDATA GIF> NDATA = notation data The unparsed entity declaration tells the processing system not to parse the data but rather to pass it through as is.
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Well-Formed XML Document that adheres to XML syntax rules – well formed Rules: Must contain only one root element All elements must have a start and end tag Elements must be nested properly and cannot overlap <book><chapter> ….</book></chapter>
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Well-Formed XML Rules (cont.)
All attributes must have a value and must be enclosed in quotes <student status=“sr”> Attributes must be placed in the start tag of an element and may appear only once Element names are case-sensitive <STUDENT> vs. </student>
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Well-Formed XML Rules (cont.)
Certain markup characters are reserved such as < and >. Must use a character entity instead Element names may start with letters or an underscore; names may contain only letters, numbers, hyphens, periods, and underscore Element names may not start with xml
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XML Parser XML Parser is a program that checks an XML document to ensure it follows the rules and is well formed. Nonvalidating parser – looks for syntax errors according to the language rules Validating parser – checks your document against a DTD or schema Like compilers, one error may cause many messages
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Homework Create an XML document for the following:
Camping Trip Gear List The following is a list of items that are essential on any camping trip: Flashlight Hiking boots Sleeping bag Pocket knife Bug spray Compass Hatchet Lantern Shovel Tent Bucket Ground cloth
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