xml tutorial.04

5/20/2018 XML Tutorial.04

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New Perspectives on XML, 2nd EditionTutorial 4

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TUTORIAL 4

WORKING WITH SCHEMAS


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SCHEMAS

A schemais an XML document that defines the

content and structure of one or more XML

documents.

The XML document containing the content is

called the instance document.


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COMPARING SCHEMAS

AND DTDS

This figure compares schemas and DTDs


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SCHEMA VOCABULARIES

There is no single schema form. Several schema

vocabularies have been developed in the XML

language.

Support for a particular schema depends on the

XML parser being used for validation.


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SCHEMA VOCABULARIES

This figure shows a few schema vocabularies


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STARTING A SCHEMA FILE

A schema is always placed in a separate XML

document that is referenced by the instance

document.


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ELEMENTS AND ATTRIBUTES OF

THE PATIENTS DOCUMENT

This figure shows the elements and attributes of the patients.xml document


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SCHEMA TYPES

XML Schema recognize two categories of elementtypes: complex and simple.

A complextypeelement has one or moreattributes, or is the parent to one or more childelements.

A simpletype element contains only characterdata and has no attributes.


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SCHEMA TYPES

This figure shows types of elements


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SIMPLE TYPE ELEMENTS

Use the following syntax to declare a simple type elementin XML Schema:

Here, nameis the name of the element in the instancedocument and type is the data type of the element.

If a namespace prefix is used with the XML Schemanamespace, any XML Schema tags must be qualified withthe namespace prefix.


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UNDERSTANDING DATA TYPES

XML Schema supports two data types: built-in and user-

derived.

A built-in data typeis part of the XML Schema

specifications and is available to all XML Schema authors.

A user-derived data typeis created by the XML Schemaauthor for specific data values in the instance document.


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DECLARING AN ATTRIBUTE

An attribute is another example of a simple type. The

syntax to define an attribute is

Where name is the name of the attribute, type is the

data type, default is the attributes default value, andfixed is a fixed value for the attribute.


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ASSOCIATING ATTRIBUTES

AND ELEMENTS

The basic structure for defining a complex type elementwith XML Schema is

declarations

Where name is the name of the element and declarations isschema commands specific to the type of complex element

being defined.


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ASSOCIATING ATTRIBUTES

AND ELEMENTS

Four complex type elements that usually appear in an

instance document are the following:

The element is an empty element and contains only

attributes.

The element contains textual content and attributes but

no child elements.

The element contains child elements but not attributes.

The element contains both child elements and

attributes.


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EMPTY ELEMENTS

AND ATTRIBUTES

The code to declare the attributes of an empty elementis

attributes

Where attributes is the set of declarations that define

the attributes associated with the element. Forexample, the empty element


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SIMPLE CONTENT

AND ATTRIBUTES

If an element is not empty and contains textual content (but nochild elements), the structure of the complex type element isslightly different.

attributes


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SPECIFYING THE USE OF

AN ATTRIBUTE

An attribute may or may not be required with a particularelement. To indicate whether an attribute is required, youadd the use attribute to the element declaration or

reference. The use attribute has the following values: requiredThe attribute must always appear with the

element

optionalThe use of the attribute is optional with theelement

prohibitedThe attribute cannot be used with theelement


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REFERENCING AN ELEMENT

OR ATTRIBUTE

XML Schema allows for a great deal of flexibility in

designing complex types. Rather than nesting the attribute

declaration within the element, you can create a reference

to it. The code to create a reference to an element orattribute declaration is

Where elemName is the name used in an element

declaration and attName is the name used in an attribute

declaration


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WORKING WITH

CHILD ELEMENTS

Another kind of complex type element contains child elements,but no attributes. To define these child elements, use the codestructure

elements

Where elements is the list of simple type element declarationsfor each child element, and compositor defines how the childelements are organized.


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USING COMPOSITORS

XML Schema supports the following compositors:

sequence defines a specific order for the child

elementschoice allows any one of the child elements to

appear in the instance document

all allows any of the child elements to appear in

any order in the instance document; however, theymust appear either only once or not all.


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WORKING WITH CHILD

ELEMENTS AND ATTRIBUTES

The code for a complex type element that containsboth attributes and child elements is

elements

attributes


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SPECIFYING MIXED CONTENT

When the mixed attribute is set to the value true, XML Schema assumes that theelement contains both text and child elements. The structure of the child elements canthen be defined with the conventional method. For example, the XML content

Patient Cynthia Davis was enrolled in

the Tamoxifen Study on 8/15/2003.

can be declared in the schema file using the following complex type:


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APPLYING A SCHEMA

To attach a schema to the document, you must do the

following:

Declare a namespace for XML Schema in the instance

document.

Indicate the location of the schema file.

To declare the XML Schema namespace in the instance

document, you add the following attribute to the

documents root element:

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"


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APPLYING A SCHEMA

If there is no namespace for the contents of the

instance document, add the following attribute to

the root element:xsi:noNamespaceSchemaLocation="schema"


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A primitive data type, also called a base type, is

one of 19 fundamental data types not defined in

terms of other types.

A derived data typeis a collection of 25 data

types that the XML Schema developers created

based on the 19 primitive types.


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This figure shows the 44 built-in data types


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This figure shows a partial description of XML string data types


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This figure shows a partial description of XML numeric data types


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This figure shows a partial description of XML date and time data types


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DERIVING NEW DATA TYPES

Three components are involved in deriving new

data types:

Value space: the set of values that correspondto the data type.

Lexical space: the set of textual representations

of the value space.

Facets: the properties of the data type that

distinguish one data type from another.


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USER DERIVED DATA

New data types fall into three categories:

List: a list of values where each list is derived

from a base type.Union: the combination of two or more data

types.

Restriction: a limit placed on the facet of a

base type.


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DERIVING A RESTRICTED

DATA TYPE

The most common way to derive a new data type

is to restrict the properties of a base type. XML

Schema provides twelve constraining facets forthis purpose.


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CONSTRAINING FACETS

This figure shows the 12 constraining facets


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The Patterns Facet

A pattern can be created with a formatted text string called a

regular expression orregex.

To apply a regular expression in a data type, you use the code

Where regex is a regular expression pattern.


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PATTERN QUANTIFIERS

This figure shows pattern quantifiers


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WORKING WITH NAMED TYPES

Since content can be either simple or complex, it is not surprising that XMLSchema also allows schema authors to create customized complex types.

The advantage of creating a complex type is that the complex structure can bereused in the document.

For example, the following code declares an element named client containingthe complex content of two child elements named firstName and lastName:


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NAMED MODEL GROUPS

A named model group is a collection, or group,

of elements. The syntax for creating a model

group is

elements

Where name is the name of the model group, and

elements is a collection of element declarations


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WORKING WITH NAMED

ATTRIBUTE GROUPS

Attributes can be grouped into collections called namedattribute groups.

This is particularly useful for attributes that you want to

use with several different elements in a schema. Thesyntax for a named attribute group is

attributes

Where name is the name of the attribute group and

attributes is a collection of attributes assigned to the group.


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STRUCTURING A SCHEMA

One schema design is a Flat Catalog Design.

In this design, all element declarations are made

globally. The structure of the instance document is created

by referencing the global element declarations.

The syntax is:


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FLAT CATALOG DESIGN

This figure shows a Flat Catalog design


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STRUCTURING A SCHEMA

Schemas can be structured in a number of ways.

One structure is called a Russian Doll design.

This design involves sets of nested declarations.

While this design makes it easy to associate the

schema with the instance document, it can be

confusing and difficult to maintain.


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RUSSIAN DOLL DESIGN

This figure shows a Russian Doll design


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VENETIAN BLIND DESIGN

A Venetian blind design is similar to a flat catalog,

except that instead of declaring elements and

attributes globally, it creates named types and

references those types within a single global element

In this layout, the only globally declared element is

the patients element; all other elements and attributesare placed within element or attribute groups or, in the

case of the performance element, within a named

complex type


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Tutorial 4

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VENETIAN BLIND DESIGN


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COMPARING SCHEMA DESIGNS

This figure compares the three schema designs


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PLACING A SCHEMA IN A

NAMESPACE: TARGETING A

NAMESPACE To associate a schema with a namespace, you first

declare the namespace and then make that namespace

the target of the schema. To do this, you add the

following attributes to the schemas root element:

prefix:xmlns="uri"

targetNamespace="uri"

Whereprefix is the prefix of the XML Schemanamespace and uri is the URI of the target namespace


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VALIDATING A COMBINED

DOCUMENT

This figure shows how schemas are combined when the data is combined


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APPLYING A SCHEMA TO A

DOCUMENT WITH A NAMESPACE

To apply a schema to a document with a namespace, add

the following attributes to the instance documents root

element:

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="uri schema"

Where uri is the URI of the namespace andschema is the

location and name of the schema file.

All global elements and attributes from the schema must be

qualified in the instance document.


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INCLUDING AND IMPORTING

SCHEMAS

To include a schema from the same namespace, add the

following element as a child of the schema element:

Whereschema is the name and location of the schema file.

To import a schema from a different namespace, use the

syntax

Where uri is the URI of the imported schemas namespace

andschema is the name and location of the schema file.


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REFERENCING OBJECTS FROM

OTHER SCHEMAS

Once a schema is imported, any objects it contains

with global scope can be referenced

To reference an object from an imported schema, you

must declare the namespace of the imported schema in

the schema element

You can then reference the object using the ref

attribute or the type attribute for customized simpleand complex types

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