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XML Overview

tion and restriction, in addition to supporting various built in simple types, 

such as integer, float, date, and time.

The following convention applies to the rest of the chapter: The noun

 schema  or  XML schema  designates the grammar or schema to which an XML

document must conform and is used regardless of the actual schema language

(DTD, XSD, and so forth). 

Note:

 While XSD plays a major role in Web services,

Web services may still have to deal with DTD based schemas because of legacy

reasons.

As an additional convention, we use the word  serialization  to refer to XML

serialization and deserialization. We explicitly refer to Java serialization when

referring to serialization supported by the Java programming language. Also note

that we may use the terms  marshalling  and  unmarshalling  as synonyms for

XML serialization and deserialization. This is the same terminology used by

XML data binding technologies such as JAXB.

4.1.2 XML Horizontal and Vertical Schemas

XML schemas, which are applications of the XML language, may apply XML to

horizontal or vertical domains. Horizontal domains are cross industry domains,

while vertical domains are specific to types of industries. Specific XML schemas

have been developed for these different types of domains, and these horizontal and

vertical applications of XML usually define publicly available schemas.

Many schemas have been established for horizontal domains; that is, they

address issues that are common across many industries. For example, W3C speci 

fications define such horizontal domain XML schemas or applications as Exten 

sible HyperText Markup Language (XHTML), Scalable Vector Graphics (SVG),

Mathematical Markup Language (MathML), Synchronized Multimedia Integra 

tion Language (SMIL), Resource Description Framework (RDF), and so forth.

Likewise, there are numerous vertical domain XML schemas. These schemas

or applications of XML define standards that extend or apply XML to a vertical

domain, such as e commerce. Typically, groups of companies in an industry

develop these standards. Some examples of e commerce XML standards are Elec 

tronic Business with XML (ebXML), Commerce XML (CXML), Common Busi 

ness Language (CBL), and Universal Business Language (UBL).

When designing an enterprise application, developers often may define their

own custom schemas. These custom schemas may be kept private within the

enterprise. Or, they may be shared just with those partners that intend to exchange