Annex C: Extensible Markup Language (XML)
287
view, and integrate XML information. XML's tag structure and textual syntax make
it as easy to read as HTML, and it is clearly better for conveying structured information. A growing set oftools is available for XML development.
General
The Extensible Markup Language (XML) is a subset ofISO 8879:1986 Standard
Generalized Markup Language (SGML). XML has been designed for ease of implementation and for interoperability with both SGML and HTML. It is a format designed to bring structured information to the Web and in effect a language for electronic data interchange. XML is an open technology that is maintained by the W orld
Wide Web Consortium (Bray et al. 1998).
XML defines a class of data objects called XML documents. A software module
called an XML processor is used to read XML documents and provide access to
their content and structure. An XML document is composed of pairs of tags, each
pair consisting of a beginning and an end tag, like the
Tag pairs may contain character strings and/or other tag pairs. A tag pair is called an
element. In combination with its advanced linking capabilities, XML can encode a
wide variety of information structures. The rules that specify how the tags are structured are called a Document Type Declaration or DTD. Alternately XML Schema
can be used to give the rules. XML is in that respect similar to UML and has a declarative model (DTD) and an instance model (XML document). In HTML, the DTD
Is pre-specified, with the writer allowed the use only of the tags specified in the
HTML DTD, while in XML, writers may create their own DTDs with their own tag
structure.
XML documents come in two flavours, i.e. well-formed XML documents and
valid XML documents.
An XML document is well-formed if it conforms to the XML standard, and if it
contains exactly one root element and any number of content elements where the
elements, delimited by start- and end-tags, nest properly within each other.
A XML document is valid if it is well-formed and if it conforms to its DTD. An
XML processor can be non-validating or validating. That means that a nonvalidating XML processor only checks if the XML document is well-formed. A
validating XML processor checks whether the XML document conforms with its
DTD as weil.
XML element
The logical structure of an XML document consists of properly nested XML elements and entity references. An XML element may have attributes and a content.
An element always has a start tag that may include the element's attributes, a content
and an end tag. The content can be empty, a sequence of elements, one of an alternative list of elements, repetitions of elements, plain text or mixed elements and text
data. An example of a simple XML element called Road with no attributes and plain
text as content is:
287
view, and integrate XML information. XML's tag structure and textual syntax make
it as easy to read as HTML, and it is clearly better for conveying structured information. A growing set oftools is available for XML development.
General
The Extensible Markup Language (XML) is a subset ofISO 8879:1986 Standard
Generalized Markup Language (SGML). XML has been designed for ease of implementation and for interoperability with both SGML and HTML. It is a format designed to bring structured information to the Web and in effect a language for electronic data interchange. XML is an open technology that is maintained by the W orld
Wide Web Consortium (Bray et al. 1998).
XML defines a class of data objects called XML documents. A software module
called an XML processor is used to read XML documents and provide access to
their content and structure. An XML document is composed of pairs of tags, each
pair consisting of a beginning and an end tag, like the
Tag pairs may contain character strings and/or other tag pairs. A tag pair is called an
element. In combination with its advanced linking capabilities, XML can encode a
wide variety of information structures. The rules that specify how the tags are structured are called a Document Type Declaration or DTD. Alternately XML Schema
can be used to give the rules. XML is in that respect similar to UML and has a declarative model (DTD) and an instance model (XML document). In HTML, the DTD
Is pre-specified, with the writer allowed the use only of the tags specified in the
HTML DTD, while in XML, writers may create their own DTDs with their own tag
structure.
XML documents come in two flavours, i.e. well-formed XML documents and
valid XML documents.
An XML document is well-formed if it conforms to the XML standard, and if it
contains exactly one root element and any number of content elements where the
elements, delimited by start- and end-tags, nest properly within each other.
A XML document is valid if it is well-formed and if it conforms to its DTD. An
XML processor can be non-validating or validating. That means that a nonvalidating XML processor only checks if the XML document is well-formed. A
validating XML processor checks whether the XML document conforms with its
DTD as weil.
XML element
The logical structure of an XML document consists of properly nested XML elements and entity references. An XML element may have attributes and a content.
An element always has a start tag that may include the element's attributes, a content
and an end tag. The content can be empty, a sequence of elements, one of an alternative list of elements, repetitions of elements, plain text or mixed elements and text
data. An example of a simple XML element called Road with no attributes and plain
text as content is: