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71 Pages

Extensible Markup Language1

Course: FACULTY OF WXGE6320, Winter 2009
School: University of Malaya
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Markup Extensible Language XML Introduction New eXtensible Markup Language: XML Can use XML to define new languages Distributes easily on the Web Can mix different types of data together Basic XML Rules Technical details Always need end tags Special emptyelement tags Always quote attribute values Like this example ..... <?xml version="1.0" encoding="iso88591"?> <html xmlns="http://www.w3.org/TR/xhtml1" > <head> <title> Title of text XHTML Document </title> </head><body> <div class="myDiv"> <h1> Heading of Page </h1> ..... <p>And here is another paragraph, this one containing an <img src="image.gif" alt="waste of time" /> inline image, and a <br /> line break. </p> </div> </body></html> Evolution of XML Many XML languages, optimised for different roles MathML for mathematics SMIL for synchronised multimedia RDF for describing "things" XUL for describing the Navigator 5 user interface MathML Designed to express semantics of maths Also can express layout Cut & paste into Maple, Mathematica x2 + 4x + 4 =0 <mrow> <mrow> <msup> <mi>x</mi> <mn>2</mn> </msup> <mo>+</mo> <mrow> <mn>4</mn> <mo>&invisibletimes;</mo> <mi>x</mi> </mrow> <mo>+</mo> <mn>4</mn> </mrow> <mo>=</mo> <mn>0</mn> </mrow> SMIL Synchronised Multimedia Integration Language Integration of multimedia with text, audio, video Support in RealPlayer G2 SMIL Example <smil> <head> <meta name="title" content="Online Teaching Services promo" /> <meta name="author" content="Jay Moonah, CAT" /> <layout type="text/smil-basic-layout"> <root-layout width="280" height="316" background-color="white"/> <region id="AnimChannel1" title="AnimChannel1" left="0" top="0" height="265" width="280" fit="hidden"/> </layout> </head> <body> <par title="Online Teaching Services promo" author="Jay Moonah, CAT" > <audio src="final.rm" id="Soundtrack" title="Soundtrack"/> <animation src="otscompfin.swf" id="Animation" region="AnimChannel1" title="Animation" fill="freeze"/> <text src="cc.rt" id="caption" region="cc" title="cc" fill="freeze"/> </par> </body></smil> XHTML: NextGen HTML <?xml version="1.0" encoding="iso88591"?> <html xmlns="http://www.w3.org/TR/xhtml1" > <head> <title> Title of text XHTML Document </title> </head> <body> <div class="myDiv"> <h1> Heading of Page </h1> <p> here is a paragraph of text. I will include inside this paragraph a bunch of wonky text so that it looks fancy. </p> <p>Here is another paragraph with <em>inline emphasized</em> text, and <b> absolutely no</b> sense of humor. </p> <p>And another paragraph, this one with an <img src="image.gif" alt="waste of time" /> image, and a <br /> line break. </p> </div> </body></html> XHTML Just like HTML, but based on XML rules Will support integration of different data into a single document XHTML and other Data <?xml version="1.0" encoding="iso88591"?> <html xmlns="http://www.w3.org/TR/xhtml1" > <head> <title> Title of XHTML Document </title> </head><body> <div class="myDiv"> <h1> Heading of Page </h1> <mathml xmlns="http://www.w3.org/TR/mathml"> ... MathML markup ... </mathml> <p> more html stuff goes here </p> <smil xmlns="http://www.w3.org/TR/smil1"> ... SMIL markup ... </smil> </div> </body></html> Other Use: Data Abstraction XML as a universal format for data interchange Machines exchange data as XMLformat messages Eliminates proprietary data formats Lots of XML processing software available XML Messaging Factory Place order Supplier Supplier Supplier Response XML Messaging Database Request/send data Other DB Other DB Other DB Request/send data Example Message <partorders xmlns="http://myco.org/Spec/partorders.desc"> <order ref="x2321122342" date="25aug199912:34:23h"> <desc> Gold sprockel grommets, with matching hamster</desc> <part number="2323221a12" /> <quantity units="gross"> 12 </quantity> <deliverydate date="27aug199912:00h"> </order> <order ref="x2321122342" date="25aug199912:34:23h"> .... Order something else ..... </order> </partorders> The XML Family Tree SMIL XHTML HTML TEI SpeechML XUL MathML RDF ... ... XML SGML The XML Suite XML Namespaces XML Schema XSL/XSLT/XSLFO/XPath Xlink XML Query DOM XPointer XML Base XML Key Management XML Encryption XML Signature XForms SOAP/XMLP Among Some Emerging Complementary Standards XSL: The style language XLink: The hypertext language Actually, two more or less separate components: XSL Transformations (XSLT): for transforming XML documents associating style properties with elements (XSLFO) associated with XPointer, for pointing to a piece of data in an XML document (based on XPath) Structuring XML Structuring a) DTDs b) XML Schema Structuring XML Documents Define all the element and attribute names that may be used Define the structure If such structuring information exists, the document can be validated what values an attribute may take which elements may or must occur within other elements, etc. Structuring XML Dcuments (2) An XML document is valid if There are two ways of defining the structure of XML documents: it is wellformed respects the structuring information it uses DTDs (the older and more restricted way) XML Schema (offers extended possibilities) DTD: Element Type Definition <lecturer> <name> David Billington </name> <phone> +61 - 7 - 3875 507 </phone> </lecturer> DTD for above element (and all lecturer elements): <!ELEMENT lecturer (name,phone)> <!ELEMENT name (#PCDATA)> <!ELEMENT phone (#PCDATA)> The Meaning of the DTD The element types lecturer, name, and phone may be used in the document A lecturer element contains a name element and a phone element, in that order (sequence) A name element and a phone element may have any content In DTDs, #PCDATA is the only atomic type for elements DTD: Disjunction in Element Type Definitions We express that a lecturer element contains either a name element or a phone element as follows: <!ELEMENT lecturer (name|phone)> A lecturer element contains a name element and a phone element in any order. <!ELEMENT lecturer((name,phone)|(phone,name))> Example of an XML Element <order orderNo="23456" customer= "John Smith" date= "October 15, 2002"> <item itemNo= "a528" quantity="1"/> <item itemNo= "c817" quantity="3"/> </order> The Corresponding DTD <!ELEMENT order (item+)> <!ATTLIST order orderNo ID customer CDATA date CDATA #REQUIRED #REQUIRED #REQUIRED> <!ELEMENT item EMPTY> <!ATTLIST item itemNo ID quantity CDATA comments CDATA #REQUIRED #REQUIRED #IMPLIED> Comments on the DTD The item element type is defined to be empty + (after item) is a cardinality operator: ?: appears zero times or once *: appears zero or more times +: appears one or more times No cardinality operator means exactly once Comments on the DTD (2) In addition to defining elements, we define attributes This is done in an attribute list containing: Name of the element type to which the list applies A list of triplets of attribute name, attribute type, and value type Attribute name: A name that may be used in an XML document using a DTD DTD: Attribute Types Similar to predefined data types, but limited selection The most important types are CDATA, a string (sequence of characters) ID, a name that is unique across the entire XML document IDREF, a reference to another element with an ID attribute carrying the same value as the IDREF attribute IDREFS, a series of IDREFs (v1| . . . |vn), an enumeration of all possible values Limitations: no dates, number ranges etc. DTD: Attribute Value Types #REQUIRED Attribute must appear in every occurrence of the element type in the XML document #IMPLIED The appearance of the attribute is optional #FIXED "value" Every element must have this attribute "value" This specifies the default value for the attribute XML Schema Significantly richer language for defining the structure of XML documents Its syntax is based on XML itself not necessary to write separate tools Expand or delete already existent schemas Reuse and refinements of schemas Sophisticated set of data types, compared to DTDs (which only supports strings) XML Schema (2) An XML schema is an element with an opening tag like version="1.0"> <schema http://www.w3.org/2000/10/XMLSchema Structure of schema elements Element and attribute types using data types Element Types <element name="email"/> <element name="head" minOccurs="1" maxOccurs="1"/> <element name="to" minOccurs="1"/> Cardinality constraints: minOccurs="x" value (default 1) maxOccurs="x" (default value 1) Generalizations of *,?,+ offered by DTDs Attribute Types <attribute name="id" type="ID" use="required"/> < attribute name="speaks" type="Language" use="default" value="en"/> Existence: use="x", where x may be optional or required Default value: use="x" value="...", where x may be default or fixed Data Types There is a variety of builtin data types Numerical data types: integer, Short etc. String types: string, ID, IDREF, CDATA etc. Date and time data types: time, Month etc. There are also userdefined data types simple data types, which cannot use elements or attributes complex data types, which can use these Data Types (2) Complex data types are defined from already existing data types by defining some attributes (if any) and using: sequence, a sequence of existing data type elements (order is important) all, a collection of elements that must appear (order is not important) choice, a collection of elements, of which one will be chosen A Data Type Example <complexType name="lecturerType"> <sequence> <element name="firstname" type="string" minOccurs="0" maxOccurs="unbounded"/> <element name="lastname" type="string"/> </sequence> <attribute name="title" type="string" use="optional"/> </complexType> XML Schema: The Email Example <element name="email" type="emailType"/> <complexType name="emailType"> <sequence> <element name="head" type="headType"/> <element name="body" type="bodyType"/> </sequence> </complexType> XML Schema: The Email Example (2) <complexType name="headType"> <sequence> <element name="from" type="nameAddress"/> <element name="to" type="nameAddress" minOccurs="1" maxOccurs="unbounded"/> <element name="cc" type="nameAddress" minOccurs="0" maxOccurs="unbounded"/> <element name="subject" type="string"/> </sequence> </complexType> XML Schema: The Email Example (3) <complexType name="nameAddress"> <attribute name="name" type="string" use="optional"/> <attribute name="address" type="string" use="required"/> </complexType> Similar for bodyType Addressing and Querying XML Documents In relational databases, parts of a database can be selected and retrieved using SQL The central concept of XML query languages is a path expression Same necessary for XML documents Query languages: XQuery, XQL, XMLQL Specifies how a node or a set of nodes, in the tree representation of the XML document can be reached XPath XPath is the core for XML query languages Language for addressing parts of an XML document. It operates on the tree data model of XML It has a nonXML syntax XML Tree ? Conceptually, an XML document is a tree structure node, edge root, leaf child, parent sibling (ordered), ancestor, descendant Nodes in XML Trees Text nodes: carry the actual contents, leaf nodes Element nodes: define hierarchical logical groupings of contents, each have a name Attribute nodes: unordered, each associated with an element node, has a name and a value Comment nodes: ignorable metainformation Processing instructions: instructions to specific processors, each have a target and a value Root nodes: every XML tree has one root node that represents the entire tree Namespaces An XML document may use more than one DTD or schema Since each structuring document was developed independently, name clashes may appear The solution is to use a different prefix for each DTD or schema prefix:name <vu:instructors xmlns:vu="http://www.vu.com/empDTD" xmlns:gu="http://www.gu.au/empDTD" xmlns:uky="http://www.uky.edu/empDTD"> Namespace Declarations Namespaces are declared within an element and can be used in that element and any of its children (elements and attributes) A namespace declaration has the form: If a prefix is not specified: xmlns="location" then the location is used by default xmlns:prefix="location" location is the address of the DTD or schema Namespaces Namespace declarations bind URIs to prefixes <... xmlns:foo="http://www.w3.org/TR/xhtml1"> ... <foo:head>...</foo:head> ... </...> Default namespace (no prefix) declared with xmlns="..." Attribute names can also be prefixed Namespaces A namespace (= "language") Defines a collection of names (a vocabulary) For UK : {address, county, postCode, .... } Usually has an associated syntax (e.g. Schema definition) address = ... county, postCode, ... Syntax may be available to S/W processing it Implies a semantics the (programmer writing) S/W processing a UK:address knows what it means Provides a unique prefix for disambiguating names from different originators UK vs. US vs. INT Namespaces Names To get uniqueness of namespace name, use a URI The URI might be a real URL, for accessing the syntax definition, documentation, .... But it may be just an identifier within the internet domain owned by the namespace owner Namespace Prefixes In an XML document declare a namespace prefix, as an attribute of an element xmlns:UK= HTTP://www.UKstandards.org/Web/XML/Forms then use that for names in that namespace UK:postCode UK:post code is called a QName (qualified name) What This Means It is as if every XML document were prefaced with an SGML declaration that sets a number of optional features, and changes some defaults. Mostly, these just say you can't take advantage of some generally available but difficultyprovoking SGML features. There are also some difference from the SGML "reference concrete syntax" (i.e., the set of delimiters you get if you don't declare anything). Example of a Well Formed Document (adapted from Bray) <email> <head> <from> <name>Tim Bray</name> <address>tbray@textuality.com</address> </from> <to> <name>Paul Dreyfus</name> <address>pdreyfus@netscape.com</address> </to> <subject> First draft of XML intro </subject> </head> <body> <p>Here's a draft of that XML article. I'll be on the road but ... </p> <attach encoding="mime" name="xmldraft.html"/> </body> </email> Corresponding Content Model, for Inclusion in DTD <!ELEMENT email (head, body)> <!ELEMENT head (from, to+, cc*, subject)> <!ELEMENT from (name?, address)> <!ELEMENT to (name?, address)> <!ELEMENT name (#PCDATA)> <!ELEMENT address (#PCDATA)> <!ELEMENT subject (#PCDATA)> <!ELEMENT body (p | attach)*> <!ELEMENT p (#PCDATA)> <!ELEMENT attach EMPTY> <!ATTLIST attach encoding (mime|binhex) "mime" name CDATA #REQUIRED> Use this to preface the document <!DOCTYPE email SYSTEM "http://www.hostname.dom/DTDs/email.dtd"> <email> <head> <from> <name>Tim Bray</name> <email>tbray@textuality.com</email> </from> <to> <name>Paul Dreyfus</name> <email>pdreyfus@netscape.com</email> </to> ... XML Implementations MSXML Mozilla IBM Alphaworks (Javabased) Apache Xerces (Java + C++) Some XML Applications MS's Channel Definition Format (CDF): Open Financial Exchange (OFX): "push" architecture description Open Software Distribution (OSD): data representation for software distribution on the Internet. Descriptions of transactions between customers and banks. Joint effort of MSFT, Intuit, Checkfree Actually began in SGML. Joint effort of MSFT, Marimba, others. Some XML Applications Cold Fusion (Allaire Corp.): Automatically constructs HTML forms from SQL queries Uses an "XMLlike" language, CFML, but is extensible using XML. Numerous intermediate data representations E.g., Notes Flat File is an XMLbased data representation for importing data into Lotus Notes. Various scientific notations: Chemical Markup Language (CML): describes molecules out of atoms and bonds. MathML: Capture semantics of mathematics. XHMTL: HTML as an XML, rather than SGML, application Online Resources http://www.w3.org/TR/xml11/ http://www.w3.org/TR/xmlnames11 http://www.unicode.org/ References All slides from the web page of the book A Semantic Web Primer: Grigoris Antoniou and Frank van Harmelen http://www.ics.forth.gr/isl/swprimer/ Richard Hopkins, XML documents ISSGC'05, National eScience Centre, Edinburgh, June 2005 (web) XML Basics A data object is a XML document if it is wellformed, i.e., (essentially) can be parsed into a treestructure. I.e.: Being wellformed is the only essential condition for using an XML document. All the tags are there. The begin and endtags match. All the entities are declared. All the attribute values are quoted. XML Basics (con't) An XML document is valid if it has an associated document type declaration the document complies with the constraints it expresses. Consequently, every valid XML document is also a conforming SGML document. Wellformed and Valid Wellformed means it conforms to the XML syntax, e.g. Start and end tags nest properly with matching names Valid means it conforms to the syntax defined by the namespaces used Can't check this without a definition of that syntax Normally a Schema DTD (document Type Definitions) deprecated Others type definition system some more sophisticated than Schemas Wellformedness Every XML document must be wellformed in other words, it defines a proper tree structure XML parser: given the textual XML document, constructs its tree representation start and end tags must match and nest properly exactly one root element ...

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