1. Jagdish Gangolly State University of New York at Albany
XML I
Jagdish Gangolly
State University of New York at Albany
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

2. Introduction to XML Structured Data vs. Documents
Document: Structure, Form, and Content
Markup languages
Basic HTML & its shortcomings
Why XML
Fundamentals of DTDs
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

3. XML I: Structured Data vs. Documents I
In structured data, the schema (metadata) is separate from the data
In documents, the metadata (pertaining to form, structure, as well as content) is contained in the document itself. Sometimes, therefore, such data is called self-describing.
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

4. XML I: Structured Data vs. Documents II
Two views of documents
Physical view: a byte-stream
Logical view: an abstract data structure (a tree of nodes)
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

5. XML I: Document: Structure, Form, and Content I
Structure: Data about the way the document is structured. For example, a letter might consist of
sender’s name and address
addressee’s name and address
date
salutation
paragraphs in the letter
Closing
signature
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

6. XML I: Document: Structure, Form, and Content II
Form: Data about how the document should appear to the reader (Formatting). For example, in a letter, you will need to specify things like
Left-justification of sender’s name
Right-justification of sender’s address
Bold-ing of sender’s name, Italicising of sender’s address
Italicising/bold-ing of certain text …
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

7. XML I: Document: Structure, Form, and Content III
Content: The semantics of the document content. For example, if it is a business letter, you may want to tag the letter content to specify the semantics of such content. Fdor example
If the letter refers to a purchase order, the meaning of such reference must be indicated by the tag
If it refers to an invoice, it must be similarly tagged
Such tagging makes it possible to integrate databases consisting of self-describing as well as structured data.
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

8. XML I: Markup languages
TeX/LaTeX
SGML
HTML
XML
EBXML, XBRL, …
MathML, XGMMl, …
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

9. XML I: Basic HTML & its shortcomings
Fixed tagset – no extensibility
Virtually no content tagging
Mostly formatting tags
Lack of discipline in document generation, very forgiving browsers
Almost exclusive preoccupation with how the document looks
Difficult/awkward/inefficient to interface with structured databases
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

10. XML I: Why XML? Extensible. One can develop custom tagset
Not necessary to have a DTD, but you can specify one
Possible to separate content from structure/form
Possible to develop custom tagsets based on an object model of the domain
Possible to interface efficiently with backend structured (usually relational) databases
Possible to use heterogenous namespaces and schema to build modular e-commerce systems
Evolving standards to support e-business
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

11. XML I: Fundamentals of DTDs I
Specified using an EBNF (Extended Backus-Naur Form) syntax. With the adoption of XML-Schema specifications, in future much will be replaced by schemas
Constraints:
Wellformedness
Tree structure (root element, each element must have just one parent)
Attribute values must be quoted ….
Valid (document has a DTD to which it conforms.)
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

12. XML I: Fundamentals of DTDs I
<?xml encoding="UTF-8"?>
<!ELEMENT personnel (person)+>
<!ELEMENT person (name, *,url*,link?)>
<!ATTLIST person id ID #REQUIRED>
<!ATTLIST person note CDATA #IMPLIED>
<!ATTLIST person contr (true|false) 'false'>
<!ATTLIST person salary CDATA #IMPLIED>
<!ELEMENT name ((family,given)|(given,family))>
<!ELEMENT family (#PCDATA)>
<!ELEMENT given (#PCDATA)>
<!ELEMENT (#PCDATA)>
<!ELEMENT url EMPTY>
<!ATTLIST url href CDATA '
<!ELEMENT link EMPTY>
<!ATTLIST link manager IDREF #IMPLIED>
<!ATTLIST link subordinates IDREFS #IMPLIED>
<!NOTATION gif PUBLIC '-//APP/Photoshop/4.0' 'photoshop.exe'>
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

13. XML I: Fundamentals of DTDs II
DTD Syntax:
XML Declaration & Character Encoding
<?xml version=‘1.0’ encoding=‘utf-8’ ?>
<? … ?> processing instructions
Utf-8 : 8-bit encoding, ideal for mostly ascii data
<!-- … --> comments
Character entities & Pre-declared entities
CDATA: quoted attribute values that are not parsed
PCDATA: Element content that is parsed
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

14. XML I: Fundamentals of DTDs III
DTD Syntax (Continued):
Element declarations
<!ELEMENT name content-model>
Repitition-factor characters
* ‘zero or more’ , + ‘one or more’, ? ‘zero or one’
Content-model
EMPTY (neither text nor child elements)
<!ELEMENT br EMPTY>
ANY (combination of text and child elements)
<!ELEMENT container ANY>
Children-only content models
<!ELEMENT exchange (greeting, response)>
Mixed content models (
<!ELEMENT p (#PCDATA | a | ul | b | i | em)*>
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

15. XML I: Fundamentals of DTDs IV
DTD Syntax (Continued):
Attribute declaration
<!ATTLIST element-name attribute-definitions>
where each attribute definition has
attribute-name attribute-type deefault-declarations
<!ELEMENT multiAttribute ‘EMPTY’>
<!ATTLIST multiAttribute
name CDATA #REQUIRED
nickname ID #REQUIRED
bfriend IDREF #IMPLIED
penname NMTOKEN #IMPLIED
authors NMTOKENS #REQUIRED
answer (YES | NO) “NO”
method CDATA #FIXED “TAXI”
goto (DISCO | MOVIES) #REQUIRED
>
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

16. XML I: Fundamentals of DTDs V
DTD Syntax (Continued):
CDATA: text in quotes
ID: text, but value must be unique in document
IDREF: text equal to value of an ID in the document
NMTOKEN: restricted text containing only ‘name characters’, can not contain whitespace
NMTOKENS: comma-separated list of NMTOKEN items
(YES | NO): Enumerated type
#REQUIRED: attribute is required
#IMPLIED: attribute is optional
#FIXED: the attribute must always have the specified default value
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

17. XML II General Entities & Parameter Entities XML Schema XML Namespaces
XSLT
XML Parsing with DOM and SAX
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

18. General Entities & Parameter Entities
General entities are used in the xml documents where as parameter entities are used in the DTDs
Entities can be referenced. Parameter entities can be referenced in the DTDs only
Parameter entities have the % character after keyword ENTITY in the DTD
General entities are referenced in the document or DTD by &, parameter entities are referenced in the DTD by %
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

19. XML Schema I The Purchase Order, po.xml <?xml version="1.0"?>
<purchaseOrder orderDate=" ">
<shipTo country="US"> <name>Alice Smith</name>
<street>123 Maple Street</street> <city>Mill Valley</city>
<state>CA</state> <zip>90952</zip> </shipTo>
<billTo country="US"> <name>Robert Smith</name>
<street>8 Oak Avenue</street> <city>Old Town</city> <state>PA</state> <zip>95819</zip> </billTo>
<comment>Hurry, my lawn is going wild!</comment>
<items> <item partNum="872-AA"> <productName>Lawnmower</productName> <quantity>1</quantity> <USPrice>148.95</USPrice> <comment>Confirm this is electric </comment> </item>
<item partNum="926-AA"> <productName>Baby Monitor</productName> <quantity>1</quantity> <USPrice>39.98</USPrice> <shipDate> </shipDate> </item> </items>
</purchaseOrder>
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

20. XML Schema II (From XML Schema Primer 0)
<xsd:schema xmlns:xsd=" <xsd:annotation> <xsd:documentation> Purchase order schema for Example.com. Copyright 2000 Example.com. All rights reserved. </xsd:documentation> </xsd:annotation>
<xsd:element name="purchaseOrder" type="PurchaseOrderType"/> <xsd:element name="comment" type="xsd:string"/>
<xsd:complexType name="PurchaseOrderType">
<xsd:sequence>
<xsd:element name="shipTo" type="USAddress"/>
<xsd:element name="billTo" type="USAddress"/>
<xsd:element ref="comment" minOccurs="0"/>
<xsd:element name="items" type="Items"/>
</xsd:sequence>
<xsd:attribute name="orderDate" type="xsd:date"/> </xsd:complexType>
REFER TO CLASS HANDOUT FOR REST OF THE SCHEMA
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

21. XML Namespaces I
Element (tag) names and attribute names can be specified by the XML application/DTD. Therefore, the same tag/attribute names may be used by different applications.
When a document contains portions of other documents, you can have name clashes, ie., use of the same tag with more than one sense. Specifying namespaces in xml solves the problem of name clashes
You can name a default namespace in a document
READ EXAMPLES IN WROX TEXT
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

22. XML Namespaces I
URIs used in specifying namespaces, but they are NOT used in validation. Therefore, such URIs are declared only to provide unique names.
You can use xmlns as an attribute of elements to disambiguate names.
Child elements can be blocked from default namespaces by setting xmlns attribute to an empty string “ “
XML namespace consists of three subspaces: element names, attribute names without prefixes, and attribute names with prefixes (see example in WROX text)
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

23. XML Parsing with SAX SAX
These notes use programs inb the course text Java and XML by Brett McLaughlin
Needs less memory since it lays out document as a sequence of events
Associates with each tag an event
Efficient, but awkward if processing an element depends on preceding/succeeding elements in the document
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

24. Parsing XML in SAX I (using Xerces Parser)
1. Instantiate the parser class (in xerces, an implementation of XMLReader interface)
XMLReader parser = new SAXParser();
Provide for command-line input of uri to be parsed
public static void main (String[] args){
if (args.length != 1) {
System.out.println(“give just the uri”);
System.exit(0); }
String uri = args[0];
SAXParserDemo parserDemo = new SAXParserDemo();
parserDemo.performDemo(uri);
(PerformDemo a method defined in the SAXParserDemo class)
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

25. Parsing XML in SAX II Parse the document
public void performDemo (String uri) {
try{
XMLReader parser = new SAXParser();
parser.parse(uri);
} catch (IOException e) {
System.out.println(“error reading uri”
+ e.getMessage());
} catch (SAXException e) {
System.out .println(“error parsing uri” }
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

26. Handlers - Interfaces ContentHandler ErrorHandler DTDHandler
EntityResolver
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

27. ContentHandler I ContentHandler ContentHandler
Public void setDocumentLocator(Locator locator)
Public void startDocument()
Public void endDocument()
Public void processingInstruction()
Public void startPrefixMapping(String prefix, String uri)
Public void endPrefixmapping(String prefix)
Public void startElement(String namespaceURI,
String localName, String rawName, Attributes atts)
Public void endElement(String namespaceURI, String localName,
String rawName)
Public void characters(char[] ch, int start, int end)
Public void ignorableWhitespace(char[] ch, int start, int end)
Public void skippedEntity(String name)
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018

28. ContentHandler II Imports org.xml.sax.Attributes
org.xml.sax.contentHandler
org.xml.sax.Locator
org.xml.sax.SAXException
org.xml.sax.XMLReader
Org.apache.xerces.parsers.SAXParser
Inf 703, Fall, (Jagdish S. Gangolly)
11/21/2018