Problems To Chapter

Learning objectives

After completing this chapter, you are able to

• demonstrate an understanding of XML,

Practice problems

Practice problem solutions

7.1: XML describes a class of data objects called XML documents and partially describes the behavior of the computer programs that process them. XML is an application profile or restricted form of the SGML.

XML documents are made up of storage units called entities, which contain either parsed or unparsed data. Parsed data is made up of characters, some of which form character data and some of which form markup. Markup encodes a description of the document's storage layout and logical structure. XML provides a mechanism to impose constraints on the storage layout and logical structure.

A software module called an XML processor is used to read XML documents and provide access to their content and structure. It is assumed that an XML processor is doing its work on behalf of another module called the application. XML processor reads XML data and provides the information to the application.

7.2: The RDF is a foundation for processing metadata; it provides interoperability between applications that exchange machine-understandable information on the Web. RDF uses XML to exchange descriptions of Web resources but the resources being described can be of any type, including XML and non-XML resources. RDF emphasizes facilities to enable automated processing of Web resources. RDF can be used in a variety of application areas, for example, in resource discovery to provide better search engine capabilities; in cataloging for describing the content and content relationships available at a particular Web site, page, or digital library, by intelligent software agents to facilitate knowledge sharing and exchange; in content rating; in describing collections of pages that represent a single logical document; in describing intellectual property rights of Web pages; and in expressing the privacy preferences of a user as well as the privacy policies of a Web site. RDF with digital signatures is the key to building the Web of Trust for electronic commerce, collaboration, and other applications.

RDF can be used to create a general, yet extensible framework for describing user preferences and device capabilities. This information can be provided by the user to servers and content providers. The servers can use this information describing the user's preferences to customize the service or content provided. The ability of RDF to reference profile information via URLs assists in minimizing the number of network transactions required to adapt content to a device, while the framework fits well into the current and future protocols.

7.3: A CC/PP is a collection of the capabilities and preferences associated with user and the agents used by the user to access the World Wide Web. These user agents include the hardware platform, system software, and applications used by the user. User agent capabilities and references can be thought of as metadata or properties and descriptions of the user agent hardware and software.

The basic data model for a CC/PP is a collection of tables. Though RDF makes modeling a wide range of data structures possible, it is unlikely that this flexibility will be used in the creation of complex data models for profiles. In the simplest form, each table in the CC/PP is a collection of RDF statements with simple, atomic properties. These tables may be constructed from default settings, persistent local changes, or temporary changes made by a user. One extension to the simple table of properties data model is the notion of a separate, subordinate collection of default properties. Default settings might be properties defined by the vendor. In the case of hardware, the vendor often has a very good idea of the physical properties of any given model of product. However, the current owner of the product may be able to add options, such as memory or persistent store or additional I/O devices that add new properties or change the values of some original properties. These would be persistent local changes. An example of a temporary change would be turning sound on or off.

When used in the context of a Web-browsing application, a CC/PP should be associated with a notion of a current session rather than a user or a node. HTTP and WSP both define different session semantics. The client, server, gateways, and proxies may already have their own, well-defined notions of what constitutes a connection or a session. The protocol strategy is to send as little information as possible and if anyone is missing something, they have to ask for it. If there is good reason to believe that someone is going to ask for a profile, the client can elect to send the most efficient form of the profile that makes sense.

The goal of the CC/PP framework is to specify how client devices express their capabilities and preferences (the user agent profile) to the server that originates content (the origin server). The origin server uses the user agent profile to produce and deliver content appropriate to the client device. In addition to computer-based client devices, particular attention is paid to other kinds of devices such as mobile phones.

The requirements on the framework emphasize three aspects: flexibility, extensibility, and distribution. The framework must be flexible, since we cannot today predict all the different types of devices that will be used in the future, or the ways that those devices will be used. It must be extensible for the same reasons: it should not be hard to add and test new descriptions and it must be distributed, since relying on a central registry might make it inflexible.

Mobile Telecommunications Protocols For Data Networks. Anna Hac Copyright © 2003 John Wiley & Sons, Ltd.

ISBN: 0-470-85056-6

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