2. UNIT I INTRODUCTION TO XML
XML document structure – Well formed and valid
documents – Namespaces – DTD – XML Schema
– X-Files.
3. XML Schema
Referred as XML Schema Definition (XSD)
An XML Schema describes the structure of an XML
document.
4. DTD VS XSD
• In short, DTD provides less control on XML structure whereas XSD (XML
schema) provides more control
No. DTD XSD
1 DTD stands for Document Type Definition. XSD stands for XML Schema Definition.
2 DTDs are derived from SGMLsyntax. XSDs are written in XML.
3 DTD doesn't support datatypes.
XSD supports datatypes for elements and
attributes.
4 DTD doesn't support namespace. XSD supports namespace.
5 DTD doesn't define order for child
elements.
XSD defines order for child elements.
6 DTD is not extensible. XSD is extensible.
7 DTD is not simple to learn.
XSD is simple to learn because you don't
need to learn new language..
8 DTD provides less control on XML
structure.
XSD provides more control on XML
structure.
5. What You Should Already Know
• Before you continue, have a basic understanding of the
following:
– HTML
– XML
– A basic understanding of DTD
6. What is an XML Schema?
• An XML Schema
– Describes the structure of an XML document, just like a DTD.
• An XML document with correct syntax is called "Well Formed".
• An XML document validated against an XML Schema is both
"Well Formed" and "Valid".
7. What XML Schema Defines?
• An XML Schema:
– Defines elements that can appear in a document
– Defines attributes that can appear in a document
– Defines which elements are child elements
– Defines the order of child elements
– Defines the number of child elements
– Defines whether an element is empty or can include text
– Defines data types for elements and attributes
– Defines default and fixed values for elements and attributes
8. Why Use XML Schemas?
• XML Schemas Support Data Types
• XML Schemas use XML Syntax
• XML Schemas Secure Data Communication
• XML Schemas are Extensible
9. Why Use XML Schemas?
• Well-Formed XML document is not Enough
– Even if documents are well-formed they can still contain errors, and
those errors can have serious consequences.
• Think of the following situation:
– You order 5 dozens of laser printers, instead of 5 laser printers.
– With XML Schemas,
• Most of these errors can be caught by your validating software.
10. XSD - The <schema> Element
General Form :
<?xml version="1.0"?>
<xs:schema>
...
...
</xs:schema>
The <schema> element may contain some attributes.
11. Example
A Simple XML Document called "note.xml":
<?xml version="1.0"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
DTD file called "note.dtd"
That defines the elements of the above XML document
<!ELEMENT note (to, from, heading, body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
12. An XML Schema
• An XML Schema file "note.xsd"
– That defines the elements of the XML document above ("note.xml")
<?xml version="1.0"?>
<xs:schema xmlns:xs = "http://www.w3.org/2001/XMLSchema"
targetNamespace = "http://www.w3schools.com"
xmlns = "http://www.w3schools.com"
elementFormDefault = "qualified">
<xs:element name="note">
<xs:complexType>
<xs:sequence>
<xs:element name="to" type="xs:string"/>
<xs:element name="from" type="xs:string"/>
<xs:element name="heading" type="xs:string"/>
<xs:element name="body" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
Other elements (to, from, heading, body)
are simple types because they do not contain
other elements.
Note element is a complex
type because it contains other
elements.
13. Description of XML Schema
• <xs:element name="note">
– Defines the element name employee
• <xs:complexType>
– Defines that the element ‘note' is complex type
• <xs:sequence>
– Defines that the complex type is a sequence of elements
• <xs:element name="to" type="xs:string"/>
– Defines that the element ‘to' is of type string (text)
14. Description of XML Schema
• xmlns:xs = http://www.w3.org/2001/XMLSchema
– Indicates that the elements and data types used in the schema
come from the "http://www.w3.org/2001/XMLSchema" namespace.
– And specifies, that namespace should be prefixed with xs:
• targetNamespace = http://www.w3schools.com
– Indicates that the location of namespace.
15. Description of XML Schema
• xmlns=http://www.w3schools.com
– Indicates that the default namespace is "http://www.w3schools.com".
• elementFormDefault="qualified“
– indicates that any elements used by XML instance document which
were declared in this schema must be namespace qualified.
16. What is a Simple Element?
• A simple element is an XML element that can contain only text
– It cannot contain any other elements or attributes.
• Text can be of many different types.
– It can be one of the types included in XML Schema definition
(boolean, string, date, etc.), or
– It can be a custom type that you can define yourself.
• Syntax for defining a simple element is:
<xs:element name="xxx" type="yyy"/>
17. Most Common Types
• XML Schema has a lot of built-in data types.
• Most common types are:
xs:string
xs:decimal
xs:integer
xs:boolean
xs:date (YYYY-MM-DD)
xs:time (HH:MM:SS)
18. Fixed Values for Simple Elements
• A fixed value is automatically assigned to the element,
– You cannot specify another value.
• In the following example the fixed value is "red":
<xs:element name="color"
type="xs:string" fixed="red"/>
19. Default Values for Simple Elements
• A default value is automatically assigned to the element
– When no other value is specified.
• In the following example the default value is "red":
<xs:element name="color"
type="xs:string" default="red"/>
20. XSD Attributes
• Simple elements cannot have attributes.
• If an element has attributes,
– It is considered to be of a complex type.
• But the attribute itself is always declared as a simple type.
<xs:attribute name="xxx" type="yyy"/>
xxx is the name of the attribute
yyy specifies the data type of the attribute.
21. Example of XSD Attributes
• Here is an XML element with an attribute:
<lastname lang="EN">Smith</lastname>
• And here is the corresponding attribute definition:
<xs:attribute name="lang" type="xs:string"/>
22. Optional and Required Attributes
• Attributes are optional by default.
• To specify that the attribute is required, use the "use" attribute:
<xs:attribute name="lang"
type="xs:string"
use="required"/>
23. Restrictions on Values
• Example : Define an element called "age" with a restriction.
– The value of age cannot be lower than 0 or greater than 120:
<xs:element name="age">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:minInclusive value="0"/>
<xs:maxInclusive value="120"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
24. Restrictions on a Set of Values
• Limit the content of XML element to a set of acceptable values
– Use the enumeration constraint.
• Ex : Define an element called "car" with a restriction.
– The only acceptable values are: Audi, Golf, BMW:
<xs:element name="age">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:minInclusive value="0"/>
<xs:maxInclusive value="120"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
25. Restrictions on a Series of Values
• Ex : Defines an element called “letter" with a restriction.
– Acceptable value is one of the LOWERCASE letters from a to z:
<xs:restriction base="xs:string">
<xs:pattern value="[a-z]"/>
26. Value must be min. 5 characters and max. 8 characters:
Restrictions on Length
Value must be exactly 8 characters:
<xs:element name="password">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:length value="8"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="password">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:minLength value="5"/>
<xs:maxLength value="8"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
28. XML Document Structure
• An XML document consists of a number of discrete components
• Not all the sections of an XML document may be necessary,
– But their inclusion helps to make for a well-structured XML document
• A well-structured XML document can
– Easily be transported between systems and devices
29. Major portions of an XML document
• The major portions of an XML document include the following:
– The XML declaration
– The Document Type Declaration (DTD)
– The element data
– The attribute data
– The character data or XML content
30. XML Declaration
• XML Declaration is a definite way of stating exactly
– What the document contains.
• XML document can optionally have an XML declaration
– It must be the first statement of the XML document
• XML declaration is a processing instruction of the form
<?xml ...?>
31. Components of XML Declaration
Component Meaning
<?xml Starts the beginning of the processing instruction
Version= “xxx” Describes the specific version of XML being used
standalone= “xxx” Defines whether documents are allowed to contain
external markup declarations
encoding= “xxx” Indicates the character encoding that the document uses.
The default is “US-ASCII” but can be set to any value
Example :
32. Document Type Declaration (DTD)
• A DTD defines the structure and the legal elements and
attributes of an XML document.
• An application can use a DTD to verify that XML data is valid.
• If the DTD is declared inside the XML file, it must be wrapped
inside the <!DOCTYPE> definition:
• Document Type Declaration (DOCTYPE) gives a name to the
XML content
• A Document Type Declaration (DOCTYPE)
– Names the document type and
– Identifies the internal content
33.
34. OOA
• OOA emphasis on
– Finding and describing the objects (or concepts in the problem
domain)
• OOD emphasis on
– Defining software What the system does (its static structure and
behavior),
• OOD focuses on
– How the system does it (it’s run-time implementation).
35. OOA
• During OOA, the most important purpose is
– To identify objects and describing them in a proper way.
• Objects should be identified with responsibilities.
• Responsibilities are the functions performed by the object.
– Each and every object has some type of responsibilities to be performed.
• When these responsibilities are collaborated the purpose of the system is
fulfilled.
36. OOD
• Second phase is OOD. During this phase
– Emphasis is given upon the requirements and their fulfillment.
• In this stage,
– The objects are collaborated according to their intended association.
• After the association is complete the design is also complete.
• Third phase is object oriented implementation.
– In this phase the design is implemented using object oriented languages like
Java, C++ etc.
37. UML
• OO design is transformed into UML diagrams according to the
requirement.
• Input from the OO analysis and design is the input to the UML diagrams.
• UML is a modeling language used to model s/w and non s/w systems.
• Although UML is used for non software systems
– Emphasis is on modeling object oriented software applications.
38. Conceptual model of UML
• A conceptual model can be defined as
– A model which is made of concepts and their relationships
• A conceptual model is the first step before drawing a UML diagram.
• It helps to
– Understand the entities in the real world and how they interact with each other.
• Conceptual model of UML can be mastered by learning the 3 major
elements:
1. UML building blocks
2. Rules to connect the building blocks
3. Common mechanisms of UML
39. UML building blocks
• Three building blocks of UML are:
– Things
– Relationships
– Diagrams
40.
41. Object
• Object is a term used to represent a real world entity within
the system being modeled
• Objects has its own attributes and operations (methods).
– Consider the real world object “Car”
make = ford
model = escape
year = 2002
color = green
maximum speed = 130 mph
current speed = 50 mph
accelerate ()
decelerate ()
refuel ()
42. Network
• During the OOA phase object-modeling techniques are used
• To reflect the structure and behaviour of the system
– A range of models can be created using such objects
