Understanding XML An Introduction to XML Sandeep Bhattaram

Summary of Introduction * n n HTML was designed to ‘Display’ and format data based on ‘Syntax’ XML is designed to ‘Describe’ and structure data based on ‘Semantics’

Types of ‘Data’ * n Structured Data n Semi-Structured Data n Unstructured Data

Semi-Structured Data - An Example n n Schema information is mixed with data objects and values No predefined schema for the data to conform to.

Unstructured Data n n No structure for the data to conform to. Example : HTML <table> <TR> <TD> XML Class </TD> <TD> very interesting</TD> </TR> </table>

Basics of XML * n n XML stands for e. Xtensible Markup Language XML is a mark up language User defines his own tags in XML is Self-Descriptive

Basic example of XML <note> <to>Everyone</to> <from>Sandeep</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note> n n XML doesn’t “DO” anything With XML your data is stored outside your HTML

Basics Contd. . n n Exchange of data between incompatible systems via XML can be used to Store Data Definition: XML is a cross-platform, software and hardware independent tool for describing and transmitting information.

XML Syntax * n The syntax rules of XML are very simple, self-describing & very strict. <? xml version="1. 0" encoding="ISO-8859 -1"? > <note> <to>Everyone</to> <from>Sandeep</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>

XML Syntax Rules n XML Data Model has TWO structuring concepts 1. Elements 2. Attributes

XML Syntax Rules Contd. . . All XML elements must have a closing tag n XML tags are case sensitive n All XML elements must be properly nested… NOT -> <B> <I> abc </B> </I> n

XML Syntax Rules Contd. . . n All XML documents must have a root element – Tree Model <root> <child> <subchild>. . . </subchild> </root>

XML Syntax Rules Contd. . . n Attribute values must always be quoted <? xml version="1. 0" encoding="ISO-8859 -1"? > <note date=12/11/2002> <to>Everyone</to> <from>Sandeep</from> </note> n Comments in XML

XML Elements * n 1. 2. 3. 4. Elements classified w. r. t Contents element content mixed content simple content empty content

XML Elements Contd. . . Element – content example <book> <title>My First XML</title> <prod id="33 -657” media="paper"></prod> <chapter>Introduction to XML <para>What is HTML</para> <para>What is XML</para> </chapter> </book> n

XML Elements Contd. . . n XML Elements are Extensible <note> <to>Everyone</to> <from>Sandeep</from> <body>Don't forget me this weekend!</body> </note> <date>2004 -04 -08</date>. Will the application crash ? ?

XML Element Naming Rules XML elements must follow these basic naming rules: n Names can contain letters, numbers, and other characters n Names must not start with a number or punctuation character n Names must not start with the letters xml (or XML or Xml. . ) n Names cannot contain spaces

XML Attributes * n n n <img src='data:image/svg+xml,%3Csvg%20xmlns=%22http://www.w3.org/2000/svg%22%20viewBox=%220%200%20760%20570%22%3E%3C/svg%3E' data-src="computer. gif"> - HTML <person sex="female"> -

XML Attributes * n n n <img src="computer. gif"> - HTML <person sex="female"> - XML So is this right? ? <note day="12" month="11" year="2002" to=“Everyone" from=“Sandeep” heading="Reminder" body="Don't forget me this weekend!"> </note>

XML Attributes Contd. . . n n 1. 2. NO ! Use Child Elements: <date>12/11/2002</date> <day>12</day> <month>11</month> <year>2002</year> </date> Not <date day = “ 11” month = “ 12”. . . ></date>

XML Attributes Contd. . . Problems using attributes n n n attributes cannot contain multiple values attributes are not easily expandable attributes cannot describe structures attributes are more difficult to manipulate by program code attribute values are not easy to test against a Document Type Definition (DTD) - which is used to define the legal elements of an XML document When do we use attributes ?

XML Documents * n n 1. 2. 3. n Basic object in XML Types: Data-Centric Document-Centric Hybrid XML Documents Document Declaration <? xml version="1. 0" encoding="ISO-8859 -1” standalone = “yes”? >

XML Document Type Definition n n Well Formed XML Document = syntax Valid XML Document = Well Formed XML Document + Conforms to DTD/XSD rules. Definition A DTD defines the legal elements of an XML document.

XML DTD Contd. . . n n Inline DTD Document <!DOCTYPE root-element [element-declarations]> <? xml version="1. 0"? > <!DOCTYPE note [ <!ELEMENT note (to, from, heading, body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]> <note> <to>Everyone</to> <from>Sandeep</from> <heading>Reminder</heading> <body>Don't forget me this weekend</body> </note>

XML DTD Contd. . . n External DTD <!DOCTYPE root-element SYSTEM "filename"> n n <!DOCTYPE note SYSTEM "note. dtd"> <note>. . . </note> <!DOCTYPE note SYSTEM "http: //www. uark. edu/dtd/note. dtd"> <note> … </note>

XML DTD Contd. . . n 1. 2. 3. 4. 5. 6. Building blocks of XML DTD Elements Tags Attributes Entities - < , > , & , " , ' PCDATA – Parsed Character DATA CDATA – Character Data

XML DTD Contd. . . n 1. 2. 3. 4. DTD Element Declarations (w. r. t content) Empty - <!ELEMENT element-name EMPTY> Character - <!ELEMENT element-name (#PCDATA)> Any - <!ELEMENT element-name ANY> Children – <!ELEMENT element-name (child-element-name, . . . )> n + (required multivalued), * optional multivalued, | (or), ? (optional singlevalued), required single valued

XML DTD Contd. . . n XML DTD Attribute Declaration <!ATTLIST element-name attribute-type default-value> n n Attribute Types Default Types: value, EMPTY, #REQUIRED, #IMPLIED, #FIXED “value”

XML DTD Contd. . .

XML DTD Contd. . . Limitations of DTD: 1. 2. 3. Data types in DTD are not very general DTD needs specialized processors Unordered elements are not permitted

XML SCHEMA * n n 1. 2. 3. XML Schema is used to structure the XML Document into ‘legal’ blocks. Advantages: Supports data types Written in XML Facilitates secure data communication.

XML Schema – Key Points XML Schema defines n Elements n Attributes n What are the data types of elements and attributes n Number of Children, Copies for an element n Which elements are children, or have text or are empty n Order of Children

XML Schema-Key Points contd XML Schema supports n Name Spaces df/f: note, df/f: note xmlns: df/f = “www…. . ” n Data Types n Extensible to future additions XML Schema is a W 3 C Recommendation now!

XML SCHEMA- Example XML file and DTD

XML SCHEMA - Example Schema

XML Schema – Reference to DTD, XML schema

XML Schema - Simple Elements * n n n A simple element is an XML element that can contain only text <xs: element name="xxx" type="yyy"/> Example - <lastname>Refsnes</lastname> <xs: element name="lastname" type="xs: string"/> n XML Schema Datatypes: xs: string, xs: decimal, xs: integer, xs: boolean, xs: date, xs: time n n <xs: element …… default = “aaa” /> <xs: element …… fixed = “bbb” />

XML Schema – Attributes * n n n All attributes are declared as simple types. Only complex elements can have attributes! <xs: attribute name="xxx" type="yyy"/> Example -<lastname lang="EN">Smith</lastname> <xs: attribute name="lang" type="xs: string"/> fixed = “ ”, default = “ ” use = “optional/required”

XML Schema – Facets * n Facets are restrictions applied on Elements and Attributes 4. Facets , Constraint used– Single value, min. Inclusive max. Inclusive etc Series of values, enumeration White spaces, white. Space Length, length min. Length max. Length etc n Restrictions on Datatypes n 1. 2. 3.

XML Schema – Single value Facet, Facet on set of values

XML Schema – Facets on Series of values n n Pattern constraint – [], [][]. . , ([][]. . )*, ([][]. . )+, ([]|[]|. . ), [] {} Example: <xs: element name="letter"> <xs: simple. Type> <xs: restriction base="xs: string"> <xs: pattern value="[a-z]"/> ///or [a-z. A-Z] </xs: restriction> </xs: simple. Type> </xs: element>

XML Schema – Facets on White space characters n n n <xs: element name="address"> <xs: simple. Type> <xs: restriction base="xs: string"> <xs: white. Space value="preserve"/> </xs: restriction> </xs: simple. Type> </xs: element> <xs: white. Space value="replace"/> <xs: white. Space value="collapse"/>

XML Schema – Facets on Length n n Constraints = length, min. Length, max. Length Example: <xs: element name="password"> <xs: simple. Type> <xs: restriction base="xs: string"> <xs: length value="8"/> </xs: restriction> </xs: simple. Type> </xs: element>

XML Schema – Facets for Datatypes

XML Schema –Complex Elements* n n 1. 2. 3. 4. A complex element is an XML element that contains other elements and/or attributes. There are four kinds of complex elements: empty elements that contain only other elements that contain only text elements that contain both other elements and text

XML Schema – Complex Elements example – Elements only n EXAMPLE: <employee> <firstname>. . </firstname> <lastname>. . </lastname> </employee> <xs: element name="employee" type="personinfo"/> <xs: complex. Type name="personinfo"> <xs: sequence> <xs: element name="firstname" type="xs: string"/> <xs: element name="lastname" type="xs: string"/> </xs: sequence> </xs: complex. Type>

XML Schema – Complex Elements example – Empty elements only n EXAMPLE: <product prodid="1345" /> <xs: element name="product” type="prodtype"/> <xs: complex. Type name="prodtype"> <xs: attribute name="prodid" type="xs: positive. Integer"/> </xs: complex. Type> </xs: element> n Similarly for Text Only elements and Mixed ele

XML Schema – Indicators * n n n Indicators are used to control How these elements are used in the documents. Order Indicators: All, Choice, Sequence Occurrence Indicators: max. Occurs, min. Occurs Group Indicators: Group name, attribute. Group name See Text Book Example.