WML (Wireless Markup Language)

WML (Wireless Markup Language)

Wen-Chen Hu (University of North Dakota, USA)
DOI: 10.4018/978-1-59140-769-0.ch006
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Abstract

Wireless application protocol (WAP) (Open Mobile Alliance, 2003) is a suite of network protocols that specifies ways of sending data across the airwaves. A wireless device is said to be WAP-compatible if, and only if, it has software that is fully capable of handling all WML 1.1 DTD entities. WML (Wireless Markup Language) (Open Mobile Alliance, 2001) is the XML-based language that is used in conjunction with WAP to format documents. As with all such protocol suites, WAP is organized hierarchically. At the bottom there are low-level protocols that are used for basic operations such as establishing connections, coding alphanumeric characters, and so on. At the top are the high-level protocols such as WML, which passes on page information. For more information on other WAP protocols, please visit http://www.wapforum.org/. WML script writing and applications will be discussed in Chapters VI through IX: • Chapter VI: The current chapter introduces fundamental WML components such as tables and images. • Chapter VII: Advanced WML, especially dynamic WML pages using CGI (Common Gateway Interface), will be introduced. • Chapter VIII: WMLScript, a lightweight JavaScript language used in conjunction with WML, is explained. • Chapter IX: The construction of a database-driven mobile web site using WML is explained step-by-step.
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Introduction

Wireless application protocol (WAP) (Open Mobile Alliance, 2003) is a suite of network protocols that specifies ways of sending data across the airwaves. A wireless device is said to be WAP-compatible if, and only if, it has software that is fully capable of handling all WML 1.1 DTD entities. WML (Wireless Markup Language) (Open Mobile Alliance, 2001) is the XML-based language that is used in conjunction with WAP to format documents. As with all such protocol suites, WAP is organized hierarchically. At the bottom there are low-level protocols that are used for basic operations such as establishing connections, coding alphanumeric characters, and so on. At the top are the high-level protocols such as WML, which passes on page information. For more information on other WAP protocols, please visit http://www.wapforum.org/. WML script writing and applications will be discussed in Chapters 6 through 9:

  • Chapter 6: The current chapter introduces fundamental WML components such as tables and images.

  • Chapter 7: Advanced WML, especially dynamic WML pages using CGI (Common Gateway Interface), will be introduced.

  • Chapter 8: WMLScript, a lightweight JavaScript language used in conjunction with WML, is explained.

  • Chapter 9: The construction of a database-driven mobile web site using WML is explained step-by-step.

Background

From inception, WAP has been designed to take into account the limitations inherent in handsets and networks. Because networks are slow, and handsets are unable to carry significant amounts of either memory or power, it is important that all of its elements are as efficient as possible. It is not yet clear whether this has been achieved at the cost of functionality; this will only become apparent when fast mobile networks are commonplace and handset technology has improved. However, it seems reasonable to expect that WAP’s efficiency will continue to contribute towards its success. WAP protocols are not the same as web (HTTP) protocols, although WML content can be stored on Web servers. WML content is served up to mobile phones (and other portables) through ‘gateways’ that stand at the borders of WAP and Web networks. These gateways act as intermediaries between the two types of network, translating from one system to the other and as they are provided by the mobile phone network providers WML developers do not need to install gateway software into their products.

WML is the language now used to write content for WAP phones; the alternative, HDML (Handheld Device Markup Language), has effectively become obsolete. WML is a markup language, which means that WML pages are written and saved as text files using tags like those found in HTML [W3C (World Wide Web Consortium), 1999]. Programmers familiar with HTML should find learning WML fairly easy. There are, however, some important general differences between HTML and WML. These stem from the fact that WML is specified in XML (eXtensible Markup Language) [W3C (World Wide Web Consortium), 2004] and XML specifies a general way to define different types of markup languages, with the following quirks:

  • XML-specified languages are case sensitive. For example, the tag <Wml> is different from the tag <wml>. In HTML, case is generally ignored.

  • XML-specified languages are strict. Most HTML editors are very forgiving about badly coded HTML pages, and do their best to show some content, but WML editors will simply report an error if given a badly coded WML page.

  • All the attributes of elements must be contained within either double (“) or single (') quotes. This is slightly different from HTML, where attributes need not be contained within quotation marks for most browsers.

  • One way in which WML is strict is that all tags require closure: an opening <wml> tag must have a closing </wml> tag. Some tags do not come in pairs and are allowed to close themselves; these must have a forward slash at the end of their text, for example <br />

WML is all about text. Tags that would slow down communications with handheld devices are not a part of the WML standard, and the use of tables and images is strongly restricted. Since WML is an XML application, all tags are case sensitive (<wml> is not the same as <WML>), and all tags must be properly closed.

Complete Chapter List

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Table of Contents
Preface
Wen-Chen Hu
Chapter 1
Wen-Chen Hu
With the introduction of the World Wide Web, electronic commerce revolutionized traditional commerce, boosting sales and facilitating exchanges of... Sample PDF
Fundamentals of Mobile Commerce Systems
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Chapter 2
Wen-Chen Hu
Commerce, the exchange or buying and selling of commodities on a large scale involving transportation of goods from place to place, benefits from... Sample PDF
Mobile Commerce Applications
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Chapter 3
Wen-Chen Hu
Mobile users interact with mobile commerce applications by using small wireless Internet-enabled devices, which come with several aliases such as... Sample PDF
Mobile Handheld Devices
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Chapter 4
Wen-Chen Hu
Without ways to conduct secure commercial information exchange and safe electronic financial transactions over mobile networks, neither service... Sample PDF
Essential Mobile-Commerce Technology
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Chapter 5
Wen-Chen Hu
As handheld computing is a fairly new computing area, there is as yet no generally accepted formal definition. For the purposes of this book... Sample PDF
Mobile World Wide Web Content
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Chapter 6
Wen-Chen Hu
Wireless application protocol (WAP) (Open Mobile Alliance, 2003) is a suite of network protocols that specifies ways of sending data across the... Sample PDF
WML (Wireless Markup Language)
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Chapter 7
Advanced WML  (pages 180-206)
Wen-Chen Hu
Chapter VI discusses the creation of static web pages, which have a fixed content at all times. In order to change static web pages to dynamic ones... Sample PDF
Advanced WML
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Chapter 8
WMLScript  (pages 207-228)
Wen-Chen Hu
WML is a markup language used for text formatting and displaying (Open Mobile Alliance, 2001). However, the functions of a markup language are... Sample PDF
WMLScript
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Chapter 9
Wen-Chen Hu
Numerous server-side handheld applications are available for devices. Some popular applications include: • Instant messages, which require service... Sample PDF
Database-Driven Mobile Web Content Construction
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Chapter 10
Wen-Chen Hu
There are two kinds of handheld computing and programming, namely client- and server- side handheld computing and programming. The most popular... Sample PDF
Client-Side Handheld Computing and Programming
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Chapter 11
Wen-Chen Hu
Most client-side handheld programming uses either Java or C/C++. This chapter introduces Java ME (previously known as J2ME), which is a version of... Sample PDF
Java ME (Java Platform, Micro Edition) Programming
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Chapter 12
Wen-Chen Hu
Chapter XI introduced the basics of Java ME programming. This chapter will build on this, focusing on advanced Java ME programming. The following... Sample PDF
Advanced Java ME Programming
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Chapter 13
Palm OS Programming  (pages 333-350)
Wen-Chen Hu
Programming for Palm devices is not a trivial task and it is especially hard for beginners starting their first assignment. This chapter is not... Sample PDF
Palm OS Programming
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Chapter 14
Wen-Chen Hu
The introduction to Palm OS programming given in the previous chapter provided an overview of its structure and basic concepts. This chapter... Sample PDF
Advanced Palm OS Programming
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