Session03 XML Validation DTD

8/14/2019 Session03 XML Validation DTD

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2008 MindTree Consulting

XML Validation

DTD

Sep-2009


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Slide 2

Agenda

Introduction to XML Validation

DTD

XML Schema


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2008 MindTree Consulting

XML Validation


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Slide 4

An Introduction to XML Validation

One of the important innovations of XML is the ability to placepreconditions on the data the programs read, and to do this in a

simple declarative way.

XML allows you to say

that every Order element must contain exactly one Customer element,

that each Customer element must have an id attribute that contains an

XML name token,

that every ShipTo element must contain one or more Streets, one City,

one State, and one Zip, and so forth.

Checking an XML document against this list of conditions is called

validation.

Validation is an optional step but an important one.


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Slide 5

Validation

There are many reasons and opportunities to validate an XML document:When we receive one, before importing data into a legacy system

When we receive one, before importing data into a legacy system, when we have

produced or hand-edited one

To test the output of an application, etc.

Validation as firewall

to serve as actual firewalls when we receive documents from the external world

(as is commonly the case with Web Services and other XML communications),

to provide check points when we design processes as pipelines of transformations.

Validation can take place at several levels.

Structural validation

Data validation


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Slide 6

Schema Languages

There is more than one language in which you can express suchvalidation conditions. Generically, these are called schema

languages, and the documents that list the constraints are called

schemas.

Different schema languages have different strengths and

weaknesses.

The document type definition (DTD) is the only schema language

built into most XML parsers and endorsed as a standard part of XML.

The W3C XML Schema Language (schemas for short, though its

hardly the only schema language) addresses several limitations of

DTDs.

Many other schema languages have been invented that can easily

be integrated with your systems.


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Document Type Definition (DTD)


8/28Slide 8

Document Type Definition (DTD)

XML 1.0 included a set of tools for defining XML document structures,called Document Type Definitions (DTDs).

A DTD focuses on the element structure of a document. It says what

elements a document may contain, what each element may and must

contain in what order, and what attributes each element has. DTDs can be

used for:defining reusable content (entities),

some kinds of metadata information (notations).

mechanisms for providing default values for attributes.

Document type definitions (DTDs) serve two general purposes.They provide the syntax for describing/constraining the logical structure of

a document. (Element/attribute declarations are used for it)

They provide syntax for composing a logical document from physical

entities. (entity/notation declarations are used to accomplish it.)


9/28Slide 9

DTD Declarations

DTDs contain

several types

of

declarations

DOCTYPE ENTITY NOTATION ELEMENT ATTLIST


10/28Slide 10

The DOCTYPE declaration is the container for all other DTD

declarations.

The document type declaration is placed in the instance

documents prolog, after the XML declaration but before the root

element start-tag to associate the given document with a set of

declarations.

The name of the DOCTYPE must be the same as the name of the

documents root element.

Example:


11/28Slide 11

DOCTYPE Syntax

DOCTYPE may contain internal declarations (referred to as theinternal DTD subset ), may refer to declarations in external files

(referred to as the external DTD subset ), or may use a combination

of both techniques.


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Internal Declarations

The simplest way to define a DTD is through internal declarations. In this case, all

declarations are simply placed between the open/close square brackets. The obvious

downside to this approach is that you cant reuse the declarations across different

XML document instances.

]>

Billy Bob

33


13/28Slide 13

External Declarations

DOCTYPE can also contain a reference to an external resourcecontaining the declarations. This type of declaration is useful

because it allows you to reuse the declarations in multiple

document instances.

The DOCTYPE declaration references the external resource through

public and system identifiers.

A system identifier is a URI that identifies the location of the

resource; a public identifier is a location-independent identifier.

Processors can use the public identifier to determine how to retrieve the

physical resource if necessary. The PUBLIC token identifies a public

identifier followed by a backup system identifier.


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Using external declarations examples

Using external declarations (public

identifier)

Billy Bob

33

Using external declarations (systemidentifier)

Billy Bob

33


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Internal and external declarations

A DOCTYPE declaration can also use both the internal and external declarations.

This is useful when youve decided to use external declarations but you need to extend them

further or override certain external declarations.

Note: only ENTITY and ATTLIST declarations may be overridden.

Example

Billy Bob

33


16/28Slide 16

An ELEMENT declaration defines an element of the specified name with thespecified content model. The content model defines the elements allowed

children.

Content Model Basics

Syntax DescriptionANY Any child is allowed within the element.

EMPTY No children are allowed within the element.

(#PCDATA) PCDATA stands for parsed character data and means

the element can contain text.

(child1,child2,...) Only the specified children in the order given are

allowed within the element.

(child1|child2|...) Only one of the specified children is allowed within

the element.


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18/28Slide 18

Elements - Examples

Element and text content models

Billy

Smith

43

0.1

Jill

J

Smith

21

Mixed content model

< p SYSTEM "p.dtd">

This is an example of mixed

content!


19/28Slide 19

aName2 aType default ...>

Declaration Description

Value Default value for attribute. If the

attribute is not explicitly used on

the given element, it will still

exist in the logical documentwith the specified default value.

#REQUIRED Attribute is required on the given

element.

#IMPLIED Attribute is optional on the givenelement.

#FIXED

"value"

Attribute always has the

specified fixed value.

Type Description

CDATA Arbitrary character data

ID A name that is unique within the

documentIDREF A reference to an ID value in the

document

ENTITY The name of an unparsed entity

declared in the DTD

ENTITIES A space-delimited list of ENTITY

values

NMTOKEN A valid XML name (NMTOKEN is

essentially a word without spaces.)

NMTOKENS A space-delimited list of

NMTOKEN values

Default declarations - After the attribute type,you must specify either a default value for the

attribute or a keyword that specifies whether it is

required.

Attribute types-Attribute types make it possibleto constrain the attribute value in different ways.

See the following list of type identifiers for details.

Attribute enumerations


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Slide 20

Attribute enumerations

...)>

Example - Using attribute types

name CDATA #REQUIRED

species NMTOKEN #FIXED "human"

id ID #REQUIRED

mgr IDREF #IMPLIED

manage IDREFS #IMPLIED>

Example - Using attribute enumerations

title (president|vice-pres|secretary|sales)

#REQUIRED>

format NOTATION (cs|lf) "cs">

1927 N 52 E, Layton, UT, 84041

Its also possible to define an attribute as an enumeration of tokens. The tokens may be of type NMTOKEN or NOTATION . In

either case, the attribute value must be one of the specified enumerated values.


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Slide 21

Entities are the most atomic unit of information in XML. Entities are usedto construct logical XML documents (as well as DTDs) from physical

resources. There are several types of entities, each of which is declared

using an ENTITY declaration.

A given entity is either

General or parameter Internal or external Parsed or unparsed

General Entity may only be referenced in an XML document (not the DTD).

Parameter Entity may only be referenced in a DTD (not the XML document).

Internal Entity value defined inline.External Entity value contained in an external resource.

Parsed Entity value parsed by a processor as XML/DTD content.

Unparsed Entity value not parsed by XML processor.


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Slide 22

Entity Syntax

Distinct Entity Types Syntax Description

Internal

parameter

"systemId">

External

parameter

Internal general

"systemId">

External parsed

general

"systemId" NDATA nname>

Unparsed

Entity References Syntax Description

&name; General

%name; Parameter

Name is used as the value of

an attribute of type ENTITY

or ENTITIES

Unparsed

Note that unparsed entities

are always general and

external whereas

parameter/internal

entities are always

parsed.


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Slide 23

Internal parameter entities

Always parsed

Referenced

within

ELEMENT,ATTRIBUTE,

NOTATION,ENTITY

Used toparameterize

portions of theDTD

(%name;) is

replaced with

the parsed

content

Internalparameter

entities

Example: Parameter entities in the internal subset

%nameDecl;

]>

Billy Bob

Its common to override parameter entities defined in the

external subset with declarations in the internal subset

Parameter entities may not be referenced within other

declarations in internal subset but it can be in external subset

External parameter entities


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Slide 24

External parameter entities

Example

%decls;

]>

Billy Bob

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External parameter entities are

used to include declarations

from external resources.

External parameter entities are

always parsed. A reference to an

external parameter entity

(%name;) is replaced with the

parsed content.

This example uses an external

parsed entity (decls) to includethe set of declarations that are

contained in person-decls.dtd.


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Slide 25

Internal general entities

Internal general entities always contain

parsed XML content. The parsed content is

placed in the logical XML document

everywhere its referenced (&name;).

Example : Using internal general entities

"BillySmith">

]>

&n;

&a;

The resulting logical document couldbe serialized as follows:

Billy

Smith

33


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Slide 26

External general parsed entities and Unparsed entities

External general parsed entities

External general parsed entities are used the same

way as internal general entities except for the fact

that they arent defined inline. They always contain

parsed XML content that becomes part of the logical

XML document wherever its referenced (&name;).

Example:

]>

&n;

&a;

Unparsed entities

nname>

Unparsed entities make it possible to attach

arbitrary binary resources to an XML document.

Unparsed entities are always general and

external.

Because unparsed entities can reference any

binary resource, applications require additional

information to determine the resources type.

The notation name (nname) provides exactly this

type of information

Because unparsed entities dont contain XML

content, they arent referenced the same way as

other general entities (&name;), but rather

through an attribute of type ENTITY/ENTITIES.

]>

Aaron


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Slide 27

Questions


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Thank you

XML Technology, Semester 4

SICSR Executive MBA(IT) @ MindTree, Bangalore, India

By Neeraj Singh (toneeraj(AT)gmail(DOT)com

)
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]

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Session03 XML Validation DTD