Information Technology Reference
In-Depth Information
An XML is a supplement to HTML such that it is not a replacement for HTML.
It will be used to structure and describe the Web data while HTML will be used to
format and display the same data. XML can keep data separated from an HTML
document. XML can also store data inside HTML documents (Data Islands). XML
can be used to exchange and store data.
With the development of Internet, the third generation of post-relational database
may be an XML database, which uses an XML document as its fundamental unit,
defines a model such as elements, attributes, PCDATA, etc., for an XML instance,
and is stored as either binary code or text file. XML has been widely used on the
Internet for business transaction in both B2B and B2C. We can expect a strong need
to migrate relational databases into XML documents for the reengineering and the
interoperability of the relational and XML databases.
An XML schema can be described in the form of Data Type Declaration (DTD)
which is a mechanism (set of rules) to describe the structure, syntax, and vocabulary
of XML documents. DTD defines the legal building blocks of an XML document.
It has a set of rules to define document structure with a list of legal elements, and
declared inline in the XML document or as an external reference. All names are user
defined. One DTD can be used for multiple documents.
An XML element is made up of a
start tag
, an
end tag
, and data in between. The
name of the element is enclosed by the less than and greater than characters, and
these are called tags. The start and end tags describe the data within the tags, which
is considered the
value
of the element. For example, the following XML element is
a <Hospital> element with the value “Queen's.”
<Hospital>Queen's</Hospital>
XML has three kinds of tags as follows:
•
Start-Tag
In the example <Patient> is the start tag. It defines type of the element and pos-
sible
attribute specifications
.
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All XML documents must have a root (start) tag.
Documents must contain a single tag pair to define the root element.
All other elements must be nested within the root element.
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