Practical XML

1
Practical XML

• Uses for XML in the Real World

2
Document Type Definitions

• Creating Your Own XML Language

3
Document Type Definitions

• Files that specify the structure of an XML file
• You might use DTDs to define your own file
  format, to use for
• Exchanging data between 2 different programs
• Generic output to be converted into HTML,
  wireless output (e.g.WML), or other format
• Configuration options (like .inf, .ini, .conf)

4
Example 1

• A file format that describes computers
• Lets say we are developing a program that
  accesses a database, summarizing prices for
  computers at a particular store
• Perhaps this program (a content provider) would
  be accessed by another program (a content
  assembler) which would collect and display
  information from a number of other content
  providers
• Customers could view prices from several stores
  on the same page

5
Example 1

• If our content assembler is to display prices
  from several locations, a common file format is
  needed to describe the inventory
• lt!DOCTYPE inventory SYSTEM "computer_inventory.dtd
  "gt
• ltinventory storenameABC Computers Inc.
  urlhttp//www.abccomputersinc.comgt
• ltcomputer nameVAIO 250gt
• ltcpu brandAMD typeAthlongt800lt/cpugt
• ltmemory speed133gt256lt/memorygt
• lthd brandMaxtor typescsigt40GBlt/hdgt
• ltpricegt1899.99lt/pricegt
• lt/computergt
• lt/inventorygt

6
Example 1

• We might assume that some of these elements are
  optional, some are required
• We might assume the same about some of the
  attributes of the elements
• Lets assume that we are only interested in
  computers in our inventory
• So how to we formally define this document type?

7
Inventory Document Type

• One inventory node, with attributes storename
  and url (required)
• One or more computer nodes with attributes
  name (optional), each with
• One cpu node with attributes brand, type
  (required), containing some text
• One memory node with attributes speed
  (optional), containing some text
• Etc.
• This is the thought pattern when developing a
  document type

8
DTD Terminology

• Tags are called elements in DTDs
• ltmytaggthellolt/mytaggt
• Parameters are called attributes in DTDs
• ltmytag nameBob/gt

9
Element Definitions Basic

• lt!ELEMENT mytag ANYgt
• Describes a tag named mytag that has no
  attributes and can contain any text inside it
• E.g. ltmytaggthellolt/mytaggt
• lt!ELEMENT yourtag EMPTYgt
• Describes a tag named yourtag that has no
  attributes, but must be empty
• E.g. ltyourtag /gt

10
Element Definitions Subtags

• lt!ELEMENT mytag (mysubtag)gt
• lt!ELEMENT mysubtag ANYgt
• Describes a tag named mytag that has no
  attributes and can contain mysubtag as a subtag
• E.g.
• ltmytaggt
• ltmysubtaggttestlt/mysubtaggt
• lt/mytaggt

11
Element Definitions Subtag OR

• lt!ELEMENT mytag (fooddrinknothing)gt
• lt!ELEMENT food ANYgt
• lt!ELEMENT drink ANYgt
• lt!ELEMENT nothing EMPTYgt
• Describes a tag named mytag that has no
  attributes and can contain one of food,
  drink, or nothing inside it
• E.g.
• ltmytaggt ltmytaggt ltmytaggt
• ltnothing /gt ltfoodgtlt/foodgt ltdrinkgtlt/drinkgt
• lt/mytaggt lt/mytaggt lt/mytaggt

12
Element Defns Subtag AND

• lt!ELEMENT mytag (food,drink,nothing)gt
• lt!ELEMENT food ANYgt
• lt!ELEMENT drink ANYgt
• lt!ELEMENT nothing EMPTYgt
• Describes a tag named mytag that has no
  attributes contains all of food, drink, and
  nothing as subtags
• Normally, order should be preserved
• e.g. ltmytaggt
• ltfoodgtlt/foodgt
• ltdrinkgtlt/drinkgt
• ltnothing /gt
• lt/mytaggt

13
Element Defns Subtag Multiples

• lt!ELEMENT mytag (food)gt
• lt!ELEMENT food EMPTYgt
• Describes a tag named mytag that has no
  attributes contains zero or more food subtags
• e.g.
• ltmytaggt ltmytaggt ltmytaggt
• ltfood /gt ltfood /gt lt/mytaggt
• ltfood /gt lt/mytaggt
• ltfood /gt
• lt/mytaggt

14
Element Defns Subtag Multiples

• lt!ELEMENT mytag (food)gt
• lt!ELEMENT food EMPTYgt
• Describes a tag named mytag that has no
  attributes contains one or more food subtags
• e.g
• ltmytaggt ltmytaggt
• ltfood /gt ltfood /gt
• ltfood /gt lt/mytaggt
• ltfood /gt
• lt/mytaggt

15
Element Defns Possible Subtags

• lt!ELEMENT mytag (food?)gt
• lt!ELEMENT food EMPTYgt
• Describes a tag named mytag that has no
  attributes that may or may not contain one food
  subtag
• E.g.
• ltmytaggt ltmytaggt
• ltfood /gt lt/mytaggt
• lt/mytaggt

16
Element Defns Subtag Combos

• lt!ELEMENT mytag ((fooddrink),nothing?)gt
• lt!ELEMENT food ANYgt
• lt!ELEMENT drink ANYgt
• lt!ELEMENT nothing EMPTYgt
• Describes a tag named mytag that has no
  attributes and contains one or more food or a
  drink subtag and possibly a nothing subtag
• E.g. ltmytaggt ltmytaggt
• ltmytaggt ltfoodgtlt/foodgt ltfoodgtlt/foodgt
• ltdrinkgtlt/drinkgt ltfoodgtlt/foodgt ltfoodgtlt/foodgt
• ltnothing /gt ltfoodgtlt/foodgt ltnothing /gt
• lt/mytaggt lt/mytaggt lt/mytaggt

17
Subtag Definitions

• You can use as complex an expression for your
  subtag definitions as you like
• Examples
• A (B,C) (A or (both B and C))
• (A,B)(D,(EF),G?)
• Etc.

18
The ANY Content

• ANY content can be anything
• Short text
• Long text
• Other types Numbers, dates, etc.
• Subtags
• Unfortunately, if there are subtags, there is no
  way to validate those tags (since they are
  interpreted as text)
• Care should be taken to use subtags, not ANY when
  subtags are to exist inside a tag
• ANY is generally not used in practice, but
  PCDATA, which represents long text (same as ANY)

19
Attribute Definitions

• lt!ELEMENT mytag EMPTYgt
• lt!ATTLIST mytag
• age CDATA IMPLIED
• phone CDATA REQUIRED gt
• Describes an attribute list for mytag with one
  optional attribute (age) and one required
  attribute (phone)
• E.g.
• ltmytag age23 phone[phone] /gt
• ltmytag phone[phone] /gt

20
computer_inventory.dtd

• lt!ELEMENT inventory (computer)gt
• lt!ATTLIST inventory storename CDATA REQUIRED
• url CDATA REQUIRED gt
• lt!ELEMENT computer (cpu,memory,hd,dvd?,price)gt
• lt!ELEMENT cpu (PCDATA)gt
• lt!ATTLIST cpu brand CDATA REQUIRED
• type CDATA
  REQUIRED gt
• lt!ELEMENT memory (PCDATA)gt
• lt!ATTLIST memory speed CDATA IMPLIED gt
• lt!ELEMENT hd (PCDATA)gt
• lt!ATTLIST hd brand CDATA IMPLIED
• type CDATA
  IMPLIED gt
• lt!ELEMENT dvd (PCDATA)gt
• lt!ATTLIST dvd brand CDATA IMPLIED
• speed CDATA
  REQUIRED gt
• lt!ELEMENT price (PCDATA)gt

21
CDATA and PCDATA?

• If you notice, the data type used for most
  attributes is CDATA
• This stands for character data, i.e. a string
• Inside tags that contain a text body, PCDATA is
  used instead
• This stands for a pointer to character data
• Thus, PCDATA is used for much longer (potentially
  greater than 255 characters) strings

22
Demonstration

• XML DTDs in Action
• (Using a web browser to view)

23
Advanced XML

• More detail about the uses of XML

24
Usefulness of XML

• Other than a configuration file format, for
• servlets (web.xml)
• EJBs (deployment descriptors)
• JSPs (TLDs)
• We have yet to see what makes XML so great
• Later in this XML series, we will see some
  examples where XML is vital

25
Usefulness of XML

• One thing that I have stated is that XML is
  easily understandable by humans and computers
• Humans can read it, since it is merely text that
  is augmented with hierarchically structured tags
• Computers can parse it, since it uses a
  standardized syntax
• In fact, the syntax of XML is what defines it as
  a class of languages
• The node structure is different, depending on the
  documents purpose

26
Parsing XML

• So how do computers parse XML?
• XML follows a standard structure
• A number of elements (as called tags), with zero
  or more attributes
• Between the delimiters of these elements is
  either some text and/or one or more sub-elements
• Some elements are stand-alone, so they do not
  have end delimiters
• These elements cannot contain any sub-elements or
  text

27
Parsing XML

• Since XML elements follow a hierarchical
  structure, it makes sense for computers to store
  XML documents using a tree structure
• This tree stores a number of nodes
• Elements (tags)
• Attributes (parameters)
• Values (embedded text or attribute values)
• Links to child elements (sub-tags)

28
Parsing XML

• Consider this XML file
• ltphoto-albumgt
• ltphoto typeKidsgt
• ltdescriptiongtLuke 1 Year Oldlt/descriptiongt
• ltpicturegtluke1b.giflt/picturegt
• lt/photogt
• ltphoto typeHolidaysgt
• ltdescriptiongtThanksgiving 2000lt/descriptiongt
• ltpicturegtturkey2k.jpglt/picturegt
• lt/photogt
• lt/photo-albumgt

29
Parsing XML

• This may be the internal representation

photo-album
photo
description
Luke 1 Year Old
picture
luke1b.gif
type
Kids
photo
description
Thanksgiving 2000
picture
turkey2k.jpg
Element
type
Holidays
Attribute
Value
30
Parsing XML

• Since there are only really four entities in XML
• Elements (forms ltagtblt/agt or lta/gt)
• Element values (b from above)
• Attributes (inside elements, form c d)
• Attribute values (d from above)
• It is possible to parse by creating 4 sets of
  simple rules for recognizing each of these
  entities and placing them into a tree structure

31
XSL

• Extensible Stylesheet Language

32
XSL

• It is relevant to talk about XSL following a
  discussion about XML parsing
• XSL are stylesheets for XML
• These stylesheets involve modifying XML documents

33
XSL

• XSL is really a collection of 3 languages, each
  for its own purpose
• Transforming one document into another type
• XSLTs
• Formatting documents for rendition
• XSLFs (similar to CSS)
• Accessing the document structure
• XPath

34
XSLT

• An XML language used (along with XSLT processors)
  to convert a document from one XML document type
  to another
• XSLT processors read the document, and the XSLT
  file (into tree structures) and use those
  structures to build the new documents tree
  structure
• This new tree structure is exported to an XML
  file to complete the transformation

35
Web Presentation with XSLT

• An XSLT processor is embedded into Internet
  Explorer
• It can be accessed via client-side VBScript and
  (soon) JavaScript
• Thus, IE clients can receive XML files as output,
  along with XSLT files, and IE will transform
  those documents into a presentation language
  automatically
• We can also use an XSLT processor to translate
  files before they are transmitted to the client
  (for other browsers, such as wireless devices)
• This is one of the uses of XSLT that is gaining
  popularity

36
Web Presentation with XSLT
XSLT HTMLIE
Server
Client
Internet Explorer
XML Document
Netscape
XSLT HTMLNS
Wireless Device (PDA, PCS Phone)
XSLT WML
37
Web Presentation with XSLT

• In the example, the XML could be translated on
  the client side for IE
• Client-side VBScript or JavaScript would activate
  the MSXML XSLT processor
• Alternatively, the XML could be translated on the
  server side
• Server-side ASPs (or something else) would
  activate the MSXML XSLT processor (or another)
• The MSXML component would be given an XSLT that
  translates our XML language into XHTML to be
  recognized by IE

38
Web Presentation with XSLT

• The XML would be translated on the server side
  for Netscape, and wireless devices
• Server-side programs (JSPs, Servlets, ASPs, etc.)
  will activate some XSLT processor
• Such as Saxon (JSPs/Servlets), MSXML (ASPs)
• This XSLT processor would be given an XSLT that
  specifies how to translate from our XML language
  to some other language for the client
• Wireless WML/WAP, iMode, WHTML
• Netscape XHTML

39
XSLT Translation Reality

• Despite the potential benefits of client XSLT
  processing, most applications use complete server
  side processing
• This is due to the fact that a single translation
  mechanism is much simpler and more convenient
• Client XSLT processing will likely never occur
• e.g. Wireless devices use WML and iMode
  specifically because they have bandwidth (and
  other) limitations
• It defeats the purpose to translate XSLT on the
  client device

40
Xalan

• Is an XSLT processing library
• Can be used with Java (and C)
• Can be used with multiple XML parsers
• Allows 3 methods to transform XML
• A command line tool
• An interface to be used inside Java programs
• A reusable set of classes (called Translets) that
  can can be called to translate XML documents

41
XSLTs

• XSLTs are specified in an XML language
• This language defines
• Default output XML
• XML that will be inserted into all output files
• Rules for translating input XML into output XML
• XML that will be generated by processing the
  input file and inserted into the output file

42
XPath

• XPath is a language for describing entities in an
  XML document
• Rather than cover XPath in depth. Ill just give
  a few examples here
• Absolute
• / - the root of the document
• //inventory the root node inventory
• Relative
• memory the memory element that is a child of
  the current element
• cpuattributebrand the brand attribute of
  the cpu child element of the current element

43
Example XSLT

• This example converts files using our computer
  inventory XML language to some XHTML document
  displaying them
• We will look at the rules one at a time

44
Example XSLT

• lt?xml version"1.0"?gt
• ltxslstylesheet version"1.0" xmlnsxsl"http//ww
  w.w3.org/1999/XSL/Transform"gt
• ltxsloutput method"html"/gt
• define rules here
• lt/xslstylesheetgt

45
Example XSLT

• This is the basic structure of an XSLT
• The first line describes it as an XML file
• The second line describes it as an XSLT
• The third line describes our output format (html
  in this case)

46
Example XSLT

• ltxsltemplate match"/"gt
• lthtmlgt
• ltheadgt
• lttitlegtComputer Inventorylt/titlegt
• lt/headgt
• ltbodygt
• ltxslapply-templates select"//inventory"
  /gt
• lt/bodygt
• lt/htmlgt
• lt/xsltemplategt

47
Example XSLT

• This rule is known as the default rule or root
  rule
• All rules are defined inside tags called
  ltxsltemplategt
• Inside the tags is some output XML
• In this case, its mostly static XML
• Between the ltbodygt output tags, notice the
  ltxslapply-templatesgt tag
• This tag tells the XSLT processor that it should
  invoke another rule (in this case, the one for
  inventory)

48
Example XSLT

• ltxsltemplate match"inventory"gt
• lth1gtPrices for
• ltxslelement name"a"gt
• ltxslattribute name"href"gt
• ltxslvalue-of select"attributeurl
  " /gt
• lt/xslattributegt
• ltxslvalue-of select"attributesto
  rename" /gt
• lt/xslelementgtlt/h1gt
• lttable border"1" cellpadding"5"gt
  lttrgt
• ltthgtNamelt/thgt ltthgtCPUlt/thgt
  ltthgtMemorylt/thgt
• ltthgtHard Disklt/thgt ltthgtPricelt/thgt
  lt/trgt
• ltxslapply-templates select"computer"
  /gt
• lt/tablegt
• lt/xsltemplategt

49
Example XSLT

• This rule is much more complicated
• The first part (between the lth1gt tags) defines a
  header for the page
• The header contains Prices for followed by an
  anchor tag
• When doing complex things with output tags (such
  as using non-static values for attribute values),
  we must do them a different way
• Here I use ltxslelementgt to create an anchor HTML
  element
• I use the storename attribute of the
  inventory element in the input file as the body
  of the ltagt tags
• I use the url attribute of the inventory
  element as the href attribute of the new (ltagt)
  element

50
Example XSLT

• After that, the rule is not too complicated
• The next part defines a table in HTML
• Including a header row with some labels
• The body of the table is going to be generated by
  another rule, so we invoke it
• That rule is for ltcomputergt, which represents a
  single computer
• The XSLT processor will invoke this rule for each
  computer node it finds

51
Example XSLT

• ltxsltemplate match"computer"gt
• lttrgt
• lttdgt
• ltxslvalue-of select"attributename" /gt
• lt/tdgt
• ltxslapply-templates select"cpu" /gt
• ltxslapply-templates select"memory" /gt
• ltxslapply-templates select"hd" /gt
• ltxslapply-templates select"price" /gt
• lt/trgt
• lt/xsltemplategt

52
Example XSLT

• The rule for computer simply inserts lttrgt before
  and lt/trgt after the processing of computers
  subnodes
• cpu, memory, hd, price
• This rule is fairly simple

53
Example XSLT

• ltxsltemplate match"cpu"gt
• lttdgt
• ltxslvalue-of select"." /gt
• (ltxslvalue-of select"attributebrand"/gt
  
• ltxslvalue-of select"attributetype"/gt)
• lt/tdgt
• lt/xsltemplategt

54
Example XSLT

• The rule for cpu places the value of the node
  (.) inside lttdgt tags with some additional
  information in brackets
• The information in brackets is of the form
  (Brand Type)
• Where Brand is the value of the cpu nodes
  brand attribute, and
• Type is the value of the cpu nodes type
  attribute

55
Example XSLT

• The rules for ltmemorygt and lthdgt are similar to
  ltcpugt
• The rule for ltpricegt demonstrates how to do
  conditional inserts (inserting XML when specific
  conditions are met)
• The many ways you can specify the condition that
  needs to be met is fairly complicated, and will
  not be discussed here

56
Example XSLT

• ltxsltemplate match"price"gt
• lttdgt
• ltxslchoosegt
• ltxslwhen test "_at_currency'USD'"gtlt/xslw
  hengt
• ltxslwhen test "_at_currency'CAD'"gtlt/xslw
  hengt
• ltxslwhen test "_at_currency'GBP'"gtxa3lt/
  xslwhengt
• ltxslwhen test "_at_currency'JPY'"gtxa5lt/
  xslwhengt
• lt/xslchoosegt
• ltxslvalue-of select"." /gt (ltxslvalue-of
  select"attributecurrency"/gt)
• lt/tdgt
• lt/xsltemplategt

57
Example XSLT

• The ltxslchoosegt tag is similar to the switch
  statement in C and Java
• The ltxslwhengt is similar to the case clauses
  in the switch statement
• They represent each possible condition
• There is also an ltxslifgt statement to use for
  simple tests of true or false

58
Example XSLT

• The rule for ltpricegt checks the value of the
  currency attribute
• If it is CAD or USD (Canadian or US dollars), it
  inserts a dollar sign before the price
• If it is GBP (Great Britain Pounds), it inserts a
  pound sign
• If it is JPY (Japanese Yen), it inserts a yen
  symbol
• For all rules, the value of the currency
  attribute is placed in brackets after the price

59
XSLTs

• Just as there was conditional processing
  (ltxslifgt and ltxslchoosegt), there is iterative
  processing also
• This allows things similar to Java and C FOR
  loops
• ltxslfor-each selectsome conditiongt
• This statement will be executed for everything
  that satisfies the condition
• Normally this is used to process a subset of the
  matching elements

60
XSLTs

• You can also specify that elements should be
  sorted on some condition
• This is used in combination with an
  ltxslfor-eachgt tag
• ltxslfor-each selectcomputergt
• ltxslsort selectpricegt
• ltxslsort selectnamegt
• ltxslfor-eachgt

61
Using Xalan

• For the first program, we will use Xalan to
  convert an output XML file into XHTML
• It will operate through the command line
• XSLTransform ltinputfilegt ltxslgt ltoutputfilegt

62
Creating an XML Transformer

• TransformerFactory tFactory TransformerFactory.n
  ewInstance()
• StreamSource transformSource new
  StreamSource(transformXSLFile)
• transformer tFactory.newTransformer(transformSou
  rce)

63
Transforming an XML File

• StreamSource inputSource new StreamSource(inputX
  MLFile)
• StreamResult outputResult outputResult new
  StreamResult(new FileOutputStream(outputXMLFile))
  
• transformer.transform(inputSource, outputResult)

64
Demonstration

• XML Transformation Using XSL

65
Automatic Translation

• Obviously, it would be much more convenient if we
  could generate XML and have it translated
  automatically
• There are a few ways we can do this
• Generate the XML, store it in a file, translate
  it into an output file, then
• Load the output file and send it to the client
• Redirect the clients browser to the output file

66
Automatic Translation

• Our XML output will be generated by a JSP which
  reads data from the database
• This output will be stored in a temporary file
• The XML output will be translated by our
  XSLTransform class
• The transformed output will be stored in another
  temporary file
• The transformed output will be read and sent to
  the client

67
Demonstration

• XSLT Transformations on Dynamically Generated
  Output

68
Cocoon

• Cocoon is another project, based on the same
  technologies as Xalan, which goes one step
  further
• Cocoon uses the XML parser specifically for web
  content translation
• Cocoon conveniently translates all XML content
  (using XSLT) into some other format
• Features are in place to allow different formats
  to be generated depending which client is used
• The nice thing about Cocoon, is that we do not
  write any of this code, we simply write XML files
  (or generate them dynamically) and Cocoon
  translates them automatically

69
Demonstration

• Cocoon in Action

70
Comments

• Even though weve only seen how to translate into
  XHTML, clearly other output formats could also be
  generated, notably
• WML Used in browsers on wireless devices
• WML is a subset of XHTML, but it is rendered
  differently (more compactly)
• Similar protocols are in use in Japan for
  wireless phones there, called iMode and mMode
  (which includes non-text media)
• VoiceXML Used in voice-based browsers (for the
  visually impaired)
• ebXML, BizTalk, SOAP for B2B communication
• Styled XHTML suiting user preferences
• These data formats are all XML languages

71
WAP

• Wireless Application Protocol

72
WAP

• WAP is a set of wireless-related technologies
• They combined to enable web access for wireless
  devices
• Devices include PDAs, PCS phones, text messagers,
  enhanced pagers, wireless-enabled digital
  cameras, and hybrids
• New devices coming out will be even more
  powerful
• eBook readers, communicative credit/debit cards,
  identity/certificate cards

73
WAP

• The WAP specification includes the following
  technologies
• WML The Wireless Mark-up Language
• WMLScript Wireless client-side scripting
• WSP Wireless Session Protocol (TCP-like network
  protocol)
• WDP Wireless Datagram Protocol (UDP-like
  network protocol)
• Caching, error handling, transaction, and
  security management protocols

74
WAP

• Wireless devices are very different from
  fully-functional web browsers, such as IE
• They have smaller displays
• Inferior graphical capabilities (or none)
• They have smaller memory spaces
• They have lower bandwidth
• Network latency is proportionally higher
• They have different interaction mechanisms
• No mice, may not have keyboards
• Typically require cursor-based selectors, instead
  of mouse-based

75
WML

• It is relevant to speak of WML in the context of
  XHTML, since they are similar technologies for
  different devices
• We will cover WML in this course, but none of the
  other technologies
• WML is a subset of HTML with some minor
  extensions, suited for wireless devices

76
WML

• WML is an XML-compliant language
• Thus, it uses a tag-based syntax like XHTML
• Think of WML pages as a deck of 'cards'
• Cards are screens that can be shown at different
  times
• The user can switch between cards with his or her
  actions
• These actions can include choosing links
  (anchors), timer events, etc.

77
WML Example 1

• lt!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML
  1.1//EN" "http//www.wapforum.org/DTD/wml_1.1.xml"
  gt
• ltwmlgt
• ltcard id"abc"gt
• ltpgt
• Click
• lta href"http//www.yahoo.com"gt
• here
• lt/agt
• to visit Yahoo.
• lt/pgt
• lt/cardgt
• lt/wmlgt

78
Demonstration

• Viewing 'simple.wml' in a WAP Emulating Browser

79
WML Example 2

• Let's try a more complicated example
• The main card will show a menu, containing two
  items
• Computers
• Computer parts
• Each will be a link to a card containing a list
  of prices
• Computer prices
• Computer part prices

80
WML Example 2

• This example demonstrates
• Multiple cards
• Card transitions using anchors (ltagt)
• Card transitions using GO buttons (ltgogt)
• HTML-like tables (lttablegt)
• Templates (lttemplategt)

81
WML GO Buttons

• GO buttons are two buttons that most WAP-capable
  devices support
• However, some have only 1 such button
• Most devices provide an alternative way of
  choosing these items (e.g. a touch menu in a PDA)
• If more than one operation is assigned to a GO
  button, the GO button shows a (menu-like) list of
  operations available when it is clicked

82
WML Tables

• WML tables use the same tags as HTML tables
  (lttablegt,lttrgt,lttdgt,ltthgt)
• The lttablegt tag has one required attribute
• Columns, which defines the number of columns in
  the table
• An optional attribute (align) specifies the
  alignment of each column (format "LLCR")
• Left, left, centre, right justification,
  respectively
• Many of the attributes used in HTML are
  unavailable in the WML version, but it works

83
WML Templates

• Templates describe common elements for each card
• For this example, I used the template tag to
  define a 'Back' button for all the cards
• This 'Back' button uses the GO buttons to
  activate their behaviour
• It simply uses the ltprev/gt tag that sends the
  browser to the previous card or deck
• Usually, templates are used to create something
  analogous to a navigation toolbar

84
Demonstration

• Viewing 'computers.wml' in a WAP Emulating Browser

85
WAP URIs

• A URI of the following form in HTML would direct
  the browser to scroll down to the paragraph
  called 'parag1'
• /index.htmparag1
• URIs in WAP are used in the same way, except they
  direct the browser to skip to a specific card
• /index.wmlcard1

86
WML Events

• The most common event handlers in WML are timer
  events
• Let's expand our file to show the prices for 5
  seconds, then go back to the previous card
  automatically

87
Demonstration

• Viewing 'computers2.wml' in a WAP Emulating
  Browser

88
WML Forms

• Forms can be added using ltinputgt tags similar to
  those used in HTML
• Input into text fields and similar gadgets is
  done differently, obviously
• Let's make a form that inputs a few text fields,
  and then sends the data to a JSP file
• Unfortunately, my WAP browser does not work well
  with JSP-generated WML files