XML Schemas: Definition, Features, and Data Types, Slides of Semantics of Programming Languages

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Lecture 4

 DTD Review

Review DTD

****

A head element

contains (in that order):

a from element

at least one to element

zero or more cc

elements

a subject element

Review DTD

****

A body element contains

a text element, possibly

followed by a number

of attachment elements.

Review DTD

The encoding attribute

of an attachment

element must have

either the

value “mime” or

“binhex”,

the former being the

default value.

7

XML Schemas

 XML Schemas are the Successors of DTDs

 XML Schemas will be used in most Web applications

as a replacement for DTDs. Here are some reasons:

 XML Schemas are extensible to future additions

 XML Schemas are richer and more powerful than DTDs

 XML Schemas are written in XML

 XML Schemas support data types

 XML Schemas support namespaces

8

XML Schema?

 The purpose of an XML Schema is to define the legal

building blocks of an XML document, just like a DTD.

 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

10

XML Schemas

 XML Schemas use XML Syntax

 Schemas are XML documents

 Benefits of Schemas as XML docs

 You don't have to learn a new language

 You can use your XML editor to edit your Schema files

 You can use your XML parser to parse your Schema files

 You can manipulate your Schema with the XML DOM

 You can transform your Schema with XSLT

11

XML Schemas

 XML Schemas are Extensible

 XML Schemas are extensible, because XML is

extensible

 With an extensible Schema definition you can:

 Reuse your Schema in other Schemas

 Create your own data types derived from the standard

types

 Reference multiple schemas in the same document

13

XML Schemas

 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

gross of laser printers, instead of 5 laser printers. With XML Schemas, most of these

errors can be caught by your validating

software.

14

XML Schemas

 Simple XML Document "note.xml":

Tove

Jani

Reminder

Don't forget me this

weekend!

16

XML Schemas

---

---

<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>

<element name="firstname" type="string“ minOccurs="0“ maxOccurs="unbounded"/>

Another Example

19

XML Schemas

 This XML document has a reference to a

Schema:

<note xmlns= “http://www.w3schools.com” xmlns:xsi="http://www.w3.org/2001/XMLSchema instance“ xsi:schemaLocation="http://www.w3schools.com note.xsd">

Tove Jani Reminder

Don'tforget me this weekend!

20

XML Schemas

 The Element

 The element is the root element of

every XML Schema:

<xs:schema>

</xs:schema>