F E A T U R EWRITTEN BY BERNDT HAMBOECK28 PBDJ volume9 issue4www.SYS-CON.COM/pbdj/
WAP stands for WirelessApplication Protocol and isbased on Wireless MarkupLanguage (WML), which isclosely related to Hypertext MarkupLanguage (HTML). WAP enablesyou to quickly and easily deliverinformation and services to mobileusers. It’s independent from anyother mobile or network standardand is compatible with all popularmobile communication networks.WAP is a communications protocol andapplication environment that can be built onany operating system, including PalmOS,EPOC, Windows CE, FLEXOS, OS/9, andJavaOS. It even provides service interoperabilitybetween different device families. The WAPForum defines this protocol and believeseveryone should have access to these specificationsto develop WAP applications.The WAP ForumAn industry association with over 500 members,the WAP Forum has developed this defacto world standard for wireless informationand telephony services on digital mobilephones and other wireless terminals. Their primarygoal is to bring together companies fromall segments of the wireless industry valuechain to ensure product interoperability andgrowth of the wireless market.WAP Forum members represent over 90% ofthe global handset market: carriers, subscribers,leading infrastructure providers, softwaredevelopers, and other organizations thatprovide solutions to the wireless industry (youcan find a list on the WAP Forum Web site).What Can You Do with It?You can build a lot of applications with WAP,but keep in mind that you’re transferring datato mobile phones and that WML is designed forthe constraints of small narrowband devices.These constraints include:• A small display and limited user input facilities.A small mobile device such as a phonehas only a few lines of textual display, witheach line containing 8–12 characters.• Narrowband network connection GSM canonly transfer data at 9,600 bits per second,while GPRS will have a speed of up to115,000 bit per second.• Limited memory and computationalresources (limited power constraints).• The user has to pay for the regular connectiontime between the device and the networkterminal. General Packet Radio Service(GPRS) makes it possible to bill for the transferreddata, so the user can be online withoutany added costs on the phone bill. GPRSis also much faster than the GSM transfer.Possible WAP applications are:• Paying your bills• Checking your bank account and wiringmoney• Reading and sending e-mail• Staying informed about the stock market• Checking weather, traffic, and events calendars• Navigating the Net• Automating your house• Developing customer service• Creating a mobile organizerHow Does It Work?Usually a Web page is a file (document)stored on a Web server that’s sent to a Webbrowser when requested. In WAP, the documentsare called decks and are stored on Webservers. Each deck contains one or more cards,the contents of which are displayed in the WAPbrowser window, although the display windowis scrollable. On the Web the markup languagefor documents is usually HTML; in WAP, it’sWML. WML inherits most of its syntactic constructsfrom XML. The two might look verysimilar, and for this article we’ll pretend theyare, but there are some important differences.Your Web browser will usually talk to a Webserver directly to ask for a certain page. In WAPthere’s another device involved, a WAP gateway.This device sits somewhere on the networkbetween your WAP device and the Webserver and helps the Web server send data tothe WAP device and vice versa.Although the WAP gateway has very little intelligence,it converts the WML code to a smallerformat, to save time, before the code is sent to theWAP browser. This also means that WML documentsmust have correct syntax (see Listing 1).XML is case-sensitive and WML inherits thischaracteristic. No case folding is performedwhen parsing a WML deck. This implies that allWML tags and attributes are case sensitive aswell as any enumerated attribute values.In a WML file the header is important. Thefirst character received by the WAP gatewaymust be the < character that starts the line. Any other character willbreak the card.The tag you see is the “deck.” InWML, a deck is the container for one or morecards. The deck provides necessary informationabout the document type, markup language,and navigational templates for the cardsincorporated in it.In WML, a card is the page that’s displayed tothe user and it must be contained in a WMLdeck.Notice the and tags. The tagsare typically used to begin a new paragraphand most WML tags must be closed, in this casewith a . Between the paragraph we wanttwo input fields displayed to the user, one forthe user’s name and one for the password.The do element provides a general mechanismfor the user to act upon the current card.In our case we want to verify the entered datathrough the Struts framework.FIGURE 1FIGURE 2WML browserLogging inwww.SYS-CON.COM/pbdj/PBDJ volume9 issue429
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