Semantic Web Technologies
41
• The document can use the element types Employee, name, and email.
• The order of a name element and an email element contained in Employee element
is followed strictly.
• Contents of name element and an email element can be varied. In DTDs, elements
are expressed using #PCDATA atomic type only.
However, there are certain practical limitations of writing such DTDs.
3.1.2 XML Schema
Structure of XML documents can be represented in a broader and richer way using
XML schema. Syntax of XML schema is based on XML itself. The key features of
XML schema are as followsDefinition of new types either by extending or restricting existing ones.
Well defined set of data types.
Other schemas can be built upon existing schemas.
Reusing and refining existing schemas.
Now, let’s see simple example of schema element which contains the definition
of element and attribute type which are defined using data type.
New elements or attributes can be extended from existing data types. The original
type is related to extended type by a hierarchical (Super to sub, parent to child)
relationship. Objects instantiated from the extended type are quiet obvious to contain
all the properties of the original type. In addition to that, they many hold extra
information, but they do not contain less or wrong type information.
The meaning is that employeeType element in an XML document include exactly
one fname elements of type string and must include exactly one emailaddress element
of type string.
Tree representation of XML documents is appreciated; A formal data model for
XML is represented by trees. This representation is often instructive.
3.2 Ontologies
Ontologies are basic components of the semantic web. These are files which define
the terms relationships. Ontologies help in the classification of data and knowledge as classes or taxonomies. As per definition of ontology suggested by T. R.
41
• The document can use the element types Employee, name, and email.
• The order of a name element and an email element contained in Employee element
is followed strictly.
• Contents of name element and an email element can be varied. In DTDs, elements
are expressed using #PCDATA atomic type only.
However, there are certain practical limitations of writing such DTDs.
3.1.2 XML Schema
Structure of XML documents can be represented in a broader and richer way using
XML schema. Syntax of XML schema is based on XML itself. The key features of
XML schema are as followsDefinition of new types either by extending or restricting existing ones.
Well defined set of data types.
Other schemas can be built upon existing schemas.
Reusing and refining existing schemas.
Now, let’s see simple example of schema element which contains the definition
of element and attribute type which are defined using data type.
New elements or attributes can be extended from existing data types. The original
type is related to extended type by a hierarchical (Super to sub, parent to child)
relationship. Objects instantiated from the extended type are quiet obvious to contain
all the properties of the original type. In addition to that, they many hold extra
information, but they do not contain less or wrong type information.
The meaning is that employeeType element in an XML document include exactly
one fname elements of type string and must include exactly one emailaddress element
of type string.
Tree representation of XML documents is appreciated; A formal data model for
XML is represented by trees. This representation is often instructive.
3.2 Ontologies
Ontologies are basic components of the semantic web. These are files which define
the terms relationships. Ontologies help in the classification of data and knowledge as classes or taxonomies. As per definition of ontology suggested by T. R.