Writing Mobile Code Essential Software Engineering for Building Mobile Applications [Electronic resources] نسخه متنی

Introduction: Working with XML

XML is rapidly becoming the text format of choice for storing and passing around data. It is more useful than generic text files because of two important concepts: (1) hierarchydata can easily be stored with parent and child relationships, and (2) semistructurednessXML allows a great deal of flexibility in the amount of structure that is applied to the data being passed around. XML data can be tightly bound to a specific schema (the schema can also be specified as an XML document) or it can be passed around willy-nilly with no formal guidelines describing what the document contains.

XML bears a close resemblance to another popular information encoding, HTML. HTML stands for HyperText Markup Language, which is a fancy way of saying "text tags that describe how a document looks." Similarly XML stands for eXtensible Markup Language, which is a fancy way of saying "text tags that describe data." XML is a product of things learned through the evolution o140, and both derive from an older more abstract format called SGML. HTML's semistructured and hierarchical text format has proven in usage to be more flexible than many preexisting binary formats. Popular adoption o140 and then XML has shown that trading the compactness of binary formats for the flexibility, extensibility, and portability of text formats is often a good bargain. The tag and attribute syntax used by HTML to describe layout and content was seen by developers to be a powerful and extensible model for describing data. A downside o140 has also emerged as a result of it rapid evolution; because the format has evolved organically over the years, the syntax has many irregularities that would not have been allowed into the language if it had been designed in a planned way. Because of the evolved complexity of the format, browsers also tend to be tolerant of documents that are "less than well formed," meaning that they tolerate errors in document syntax and do their best to present the document to the user anyway. This makes the proper parsing o140 more difficult than it needs to be. XML borrows the text format approach and the tag and attribute syntax o140 but maintains a normalized syntax suitable for use by generic parsing engines. XML parsers usually also insist that the documents are well formed and complete; strict adherence to XML document syntax rules greatly increases interoperability. This makes commonly available XML parsers suitable for a wide variety of uses.