An ad-hoc wireless network architecture for face-to-face mobile collaborative applications
ARCS'06 Proceedings of the 19th international conference on Architecture of Computing Systems
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From the Book:PrefaceMore and more, developers are looking at incorporating mobile devices, such as Pocket PC and Handheld PC 2000 (HPC 2000) devices, into mainstream computing projects, as either stand-alone applications or applications that integrate into existing systems. Using the eMbedded Visual Basic development tool is the easiest way of creating such applications, particularly because it allows developers to draw on their desktop and server application development skills.For this book, I have tried to select topics that will inform developers needing to provide access to data on the move. First I introduce eMbedded Visual Basic development (Chapter 1); then I explain how to develop user interfaces with eMbedded Visual Basic (Chapter 2). Next I show how to store data locally using SQL Server for Windows CE (Chapter 3). Using these techniques, you can quickly develop stand-alone applications that store data locally on a Pocket PC or HPC 2000 device.The most significant challenge in developing mobile applications is to provide access to databases located on servers while users are out and about. SQL Server for Windows CE provides various techniques for exchanging data with database servers (Chapter 4). Remote Data Access (RDA) provides a simple "push" and "pull" facility that will work with all versions of Microsoft SQL Server and other database servers such as Oracle. The most sophisticated technique in SQL Server for Windows CE is merge replication, which works only with Microsoft SQL Server 2000. Using this technique, mobile users can access local data in an SQL Server for Windows CE database while not connected to the network, and then use merge replicationto provide an automatic two-way update of data when a connection is made.Many application architectures do not provide for direct database access from client applications; there is generally a "middle tier" consisting of business objects providing secure access to the database. In this case, web-development techniques such as ASP (Active Server Page) and HTTP (Hypertext Transfer Protocol) can be used to access business components and thus transfer data (Chapter 5). Your application can decide on the format used for transferring data or you can use XML (Extensible Markup Language) as a standard but more verbose data exchange format. XML documents can be parsed and represented as a Document Object Model (DOM) on Pocket PC and HPC 2000 applications (Chapter 6). ASP is designed predominantly for developing web pages that will be accessed through a web browser but can be adapted to allow applications to make requests. SOAP (Simple Object Access Protocol) uses HTTP to allow function-based calls to be made through web servers. Chapter 7 shows how to make SOAP calls from eMbedded Visual Basic.ASP.NET, which can be programmed using Visual Studio.NET, takes SOAP and HTTP programming techniques and allows Web Services to be created (Chapter 7). Web Services are function-oriented interfaces that can be easily called from eMbedded Visual Basic applications. Rich data sets can be transferred using techniques described in this book, including accessing databases using ADO.NET and returning data as XML documents.An important aspect of creating mobile applications is making and managing connections to a network. Chapter 8 shows how to make a connection using RAS (Remote Access Services) through, for example, a modem and a mobile phone. RAS functions are difficult to call directly from eMbedded Visual Basic, so an ActiveX component is provided with this book to make the RAS function calls. The source code for this ActiveX component is also included.In addition to databases, there are other facilities for storing data. These include POOM (Pocket Outlook Object Model) for storing contact, calendar, and task information (Chapter 9) and the Object Store for files and registry data (Chapter 10). Finally, Chapter 11 describes how to create setup files and Chapter 12 discusses important architecture and design issues you should consider when creating an application.While eMbedded Visual Basic provides a flexible and productive development environment, it does not provide complete access to all Pocket PC and HPC 2000 features. There may be times when you need to use C or C++ to access API functions. My previous book, Windows CE 3.0 Application Programming (by Nick Grattan and Marshall Brain, Prentice Hall PTR, 2001; ISBN 0-13-025592-0), describes how to call many of these API functions.Please feel free to contact me by email at nick@softwarepaths.com if you have questions or suggestions, or visit my website, www.nickgrattan.net, where updates will be posted. I will try to answer your questions but cannot always promise to do so. I hope you enjoy developing mobile solutions with eMbedded Visual Basic.