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Document description languages Document description languages

Document description languages - PowerPoint Presentation

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Document description languages - PPT Presentation

SGMLHTMLXML SGML Standard General Markup Language A great variety of documents ex web articles catalogoues lists data tables etc Each document has its logical structure article title author data The standard format used for all documents is ASCII but different con ID: 338405

element xml document html xml element html document elements title data text tags tag body language web heading markup

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Slide1

Document description languages

SGML,HTML,XMLSlide2

SGML

(Standard General Markup Language)

A great variety of documents (ex. web): articles, catalogoues, lists, data tables etc..

Each document

has its logical structure

(article: title , author, data,..) . The standard format used for all documents is ASCII, but different conventions are used in representing information ( ex.,name and surname or viceversa, different number of bytes reserved , name delimited by “$”..).

The management of the archive is difficult. (searching for a text, for the author name or for all its the books,..)

It is necessary to adopt a standard

markup language

. A markup language defines how documents

shoud be formatted. Slide3

In the early days of computer type setting, there were many different typsetting systems, and each used its own proprietary markup language.

This language consisted of special control characters to indicate the beginning and the end of some formatting.

SGML

(

S

tandard

G

eneral

M

arkup

L

anguage).

developped

in

1986 by International Organization for Standardization (ISO

) .

SGML is a metalanguage

: a language that describes a formatting and markup language.

HTML

(

H

yper

T

ext

M

arkup

L

anguage) is the first simplified language

deriving by SGML

It is characterize by a set of tags and rules for their use.

Slide4

HTML( Hypertext Markup Language)

HTML is a

markup

language because is

not include detailed formatting information.

For example, although HTML contains extensions that allow an author to specify the

size of the text

,

the font to be

used or

the width of a line

, most authors choose instead to specify only a level of importance as a number from 1 to 6.

The browser choses a font and display size appropriate for each level.

Simarly HTML does not specify exactly

how a browser marks an item as selectable.

Some browsers

underline

selectable items, others display selectable items in a

different co

lor and some do both.

Consequently two browsers

may display an HTML document differentlySlide5

Syntactically, each HTML document is represented as a text file that contains

tags.

HTML tags provide structure for the document as well as formatting hints.

Some tags specify an action that takes effect immediately (e.g., move to a new line on the display); the tag is placed exactly where the action should occur.

Other tags are used to specify a formatting operation that applies to all text following the tag. Such tags occur in pairs, with a leading tag and a trialing thread tha start and terminate the action, respectively .Slide6

A tag appears as a

tag name

bracketed by

less-than

and

greater than

symbols:

<TAGNAME>

The corresponding tag used to end an operation begins with two- character sequence

less-tha

n and

slash

and ends with a

greater than- symbol:

</TAGNAME>

Slide7

General form of a HTML document

<HTML>

<HEAD>

<TITLE>

text that forms the document title

</TITLE>

</HEAD>

<BODY>

body of the document appears here

</ BODY >

</HTML>

Note that an indentation is used to show the structure. However , the browser

ignores all such spacing.Slide8

Examples HTML formatting tags

Hello there. <BR>This is an example<BR>of HTML

Hello there.

This is an example

of HTML

Hello there. <BR><BR>This shows <BR> HTML spacing

Hello there.

This shows

HTML spacingSlide9

Headings

Html contains

six pairs

of tags that can be used to display heading in the output.

A tag of the form

<Hi>

marks the start of a level i heading, and a tag of the form

</Hi>

marks the end.

Text with te most important level of heading is bracketed between <H1> and </H1>.

Example:

Hello.<BR><H1> This is A Heading </H1><BR> Back to normal

Hello

This Is A Heading

Back to normalSlide10

LISTS

HTML allows a document to contain lists. The simplest form is an

unordered list

, which requests the browser to display a list of items.

Here is a list of 5 names:

<UL>

<L1> Scott

<L1> Sharon

<L1> Jan

<L1> Stacey

<L1> Rebecca

</UL>

This text occurs after the list

Here is a list of 5 names

Scott

Sharon

Jan

Stacey

Rebecca

This text occurs after the list

Slide11

<HTML>

<HEAD>

<TITLE> First example </TITLE>

</ HEAD>

<BODY>

First example of a web page written in XML

.

Even if the text begins a new paragrafh, to begin a new paragraph in the displyed page it is necessary to use the tag<BR>oppure il tag <P> that also to begin a new paragraph inserts an empty row

</BODY>

</HTML>

First example of a web page written in XML . Even if the text begins a new paragrafh, to begin a new paragraph in the displyed page it is necessary to use the tag

or the tag

that also to begin a new paragraph inserts an empty row.Slide12

tags

<CENTER>…</CENTER> the content is inserted in the center of the window

<OL>…</OL>.ordered lists

<HR WIDTH=“100%”> an horizontal line large as the window is createdSlide13

<HTML>

<HEAD><TITLE> examples </TITLE></HEAD>

<BODY BGCOLOR=Yellow>

<H1><CENTER> centered title </CENTER> </H1>

<H2><CENTER> centered sub-title </CENTER> </H2>

<H3><CENTER> centered sub-sub-title </CENTER> </H3>

<HR WIDTH= “100”%>

<H2> unordered list </H2>

<UL>

<LI> First element </LI>

<LI> Second element </LI>

<LI> Third element </LI>

</UL>

<HR WIDTH= “100”%>

<H2> ordered list </H2>

<OL>

<LI> First element </LI>

<LI> Second element </LI>

<LI> Third element </LI>

</OL>

</BODY>

</HTML>Slide14

Centered title

Centered sub-title

Centered sub-sub-title

----------------- ----------------------------------------------------------------------------------------------------

not ordered list

First element

Second element

third element

----------------- --------------------------------------------------------------------------------------------

ordered list

1. Firts element

2. Second element

3. third elementSlide15

Embedding Graphics Images in A Web Page

Non textual information such as

graphical information or a digitized photo

is not inserted directly in a HTML document. Instead the data resides in a separate location, and the document contains a reference to the data.

When a browser encounters such a reference, the brower goes to the specified location, obtains a copy of the image and inserts the image in the displayed document.

<IMG SRC= “fred_photo.gif”>

specifies that the file

fred_photo.gif

contains an image that the browser should insert in the document.

Image files are not stored as text files. Each image file contain binary data and the file is stored in

graphics interchange format

(gif)Slide16

IMG tag includes additional parameters that can be used to suggest positioning.

The keyword ALIGN can be used to specify whether the top, middle, or bottom of the image should be aligned with others items on the line.

Here is a picture. <IMG SRC=“ fred_photo.gif” ALIGN=middle>.

Here is a picture.

Position of the imageSlide17

Hypertext Links from one document to Another

The HTML mechanism for specifyng a hypertext reference is known as an

anchor.

To permit arbitrary text and graphics to be included in as inglereference, HTML uses tags <A> and </A> as a bracket for the reference.

For example:

This Book is published by

<A HREF=://www.prenhall.com”>

Prentice Hall,</A> one of

the larger publishers of Computer Science textbooks.

When displayed the input produces:

This book is published by

Prentice Hall

,one of the larger

publishers of Computer Science textbooks.Slide18

HTML limitations

The tags of the language are

fixed and no modifiable

. Also,it is oriented to the

description

of hypertext documents.

Partially structured. It depends from the characteristics of the used browser.

A web page must be designed for a particular display characterized by specific features. Slide19

As the web grew in popularity, HTML was extended for new purposes; however , soon it becames apparent that proprietary extensions to HTML were counter-productive and ill-suited to general use.

For each new version of browser a propritary extension of HTML was proposed.

As a result of such situation, it was impossible to display the same pages of a web site on different browsers.

So, to solve the problems of interoperability and scalabilty on the web without extending HTML, the W3C began work on a

simplified version of SGML

which is called the

Extensible Mark-up Language (XML).

\Slide20

However, even if the initial objectives of XML were relative to the solution to a standard problem for the web, XML is not limited only to web context.

It is used primarily for

the exchange of data between two network applications.

It allows , moreover , the representation of complex data types.

XML is a software and hardware independent tool for carrying information.

XML is now as important for the web as HTML was to the foundation of the web.

XML is the most common tool

for data transmission among all sorts of applicationsSlide21

What is XML?

XML stands for Extensible Markup Language

XML is a markup language much like HTML

XML is designed to carry data, not to display data

XML tags are not predefined. You must define your own tags

XML is desigend to be self-descriptive

XML is a W3C recomandationSlide22

The Difference Between XML and HTML

XML is not a replacement for HTML

XML and HTML are designed with different goals:

XML was designed to transport and store data, with focus on what data is.

HTML was designed to display data, with focus on how data looks.

HTML is about displayng information, while XML

is about carrying informationSlide23

The following example is a note to Tove, from Jany, stored as XML

<note>

<to> Tove </to>

<from >Jani </from>

<heading > Reminder </heading>

<body > D’ont forget me this weekend! </body>

</note>

The tags in the example above (like <to> and <from>) are

not defined in any XML standard.

These tags are

invented

by the author of the XML document.

This XML document does not do anything. It is just information wrapped in tags. Someone must write a piece of software to send, receive or display it.Slide24

A XML document is a text file which contains tags, attributes and text following well defined syntactic rules .

XML logical structure

A XML document has a hierarchical structure. Its components are called elements. Each element represents a logical component of the document and may contain others elements of the text.

Informations can be associated to the elements, describing their properties. These informations, in the form of a name/value, are called attributes.

.

The elements are hierarchically organized with a principal element called root element.

The root contains the set of others elements of the document l'insieme degli altri elementi del documento. From a graphical point of view thestrucure can be represented as a treee (document tree).Slide25

XML is used in many aspects of web development, often to simplify data storage and sharing

.

XML Simplifies Data Sharing

In the real world, computer systems and databases contain data in

incompatible formats.

XML data is stored in plain text format. This provides a software- and

hardware-independent way of storing data.

This makes it much easier to create data that can be shared by different

applications.

XML Simplifies Data Transport

One of the most time-consuming challenges for developers is to

exchange data between incompatible systems over the Internet

.

Exchanging data as XML greatly reduces this complexity, since the data

can be read by different incompatible applications

.Slide26

<?xml version="1.0" encoding="ISO-8859-1"?>

<note>

  <to>

Tove

</to>

  <from>

Jani

</from>

  <heading>Reminder</heading>

  <body>Don't forget me this weekend!</body>

</note>

TREE STRUCTURE

The first line is the XML declaration. It defines the XML version (1.0) and the

encoding used (ISO-8859-1 = Latin-1/West European character set).

The next line describes the 

root element 

of the document :

<note>

The next 4 lines describe 4 

child elements

 of the root (to, from, heading, and body)

The last line defines the end of the root element: </note>Slide27

XML documents must contain a 

root element

. This element is "the parent" of all

other elements.

The elements in an XML document form a document tree. The tree starts at the root and branches to the lowest level of the tree.

All elements can have sub-elements (child elements):

<root>

  <child>

    <

subchild

>.....</

subchild

>

  </child>

</root>

The terms parent, child, and sibling are used to describe the relationships between

elements. Parent elements have children. Children on the same level are called siblings (brothers or sisters).

All elements can have

text content and attributes

(just like in HTML).Slide28
Slide29

<bookstore>

 

<

book category="COOKING">

   

<title

lang

="en">Everyday Italian</title>

   

<

author>

Giada

De

Laurentiis

</author>

  

 

<year>2005</year>

 

 

  <price>30.00</price>

 

</

book>

 

<

book category="CHILDREN">

   

<

title

lang

="en">Harry Potter</title>

  

 

<

author>J K. Rowling</author>

   

<

year>2005</year>

  

 

<price>29.99</price>

 

</

book>

 

<

book category="WEB">

   

<

title

lang

="en">Learning XML</title>

   

<

author>Erik T. Ray</author>

   

<year>2003</year>

   

<price>39.95</price>

 

</

book>

</bookstore>Slide30

XML 

Syntax Rules

All XML Elements Must have a closing tag

.

In XML, it is illegal to omit the closing tag. All elements 

must

 have a

closing tag:

<p>This is a paragraph.</p>

<

br

/>

XML Tags are Case Sensitive

XML tags are case sensitive. The tag <Letter> is different from the tag <letter>.

Opening and closing tags must be written with the same case:

<Message>This is incorrect</message>

<message>This is correct</message>Slide31

XML Elements Must be Properly Nested

In HTML, you might see improperly nested elements:

<b><

i

>This text is bold and italic</b></

i

>

In XML, all elements 

must

 be properly nested

within each other:

<b><

i

>This text is bold and italic</

i

></b>

In the example above, "Properly nested" simply means that since the <

i

> element is opened inside the <b> element, it must be closed inside the <b> element.Slide32

XML Documents Must Have a Root Element

XML documents

must contain one element that is the parent

 of all other elements.

This element is called the 

root

 element.

<root>

  <child>

     <

subchild

>.....</

subchild

>

  </child>

</root>

XML Attribute Values Must be Quoted

XML elements can have attributes in

name/value pairs

just like in HTML.

<note date="12/11/2007">

 

<to>

Tove

</to>

  <from>

Jani

</from

>

<

heading>Reminder</heading>

 

<body>Don't forget me this weekend!</body>

</note>Slide33

&lt

;

<

less

than

&gt

;

>

greater

than

&amp

;

&

ampersand

 

&apos

;

'

apostrophe

&quot

;

"

quotation

mark

Some characters have a

special meaning

in XML. (

entity references)

If you place a character like "<" inside an XML element, it will generate an error

because the parser interprets it as the start of a new element.

This will generate an XML error:

<message>if salary < 1000 then</message>

To avoid this error, replace the "<" character with an 

entity reference

:

<message>if salary 

&

lt

;

 1000 then</message>

There are

5 predefined

entity references in XML:

.Slide34

Comments in XML

The syntax for writing comments in XML is similar to that of HTML.

<!

--

This

is

a

comment

--

>

White-space is preserved in XML

HTML truncates multiple white-space characters to one single white-space:

With XML,

the white-space in a document is not truncated

.Slide35

What is an XML Element?

An XML element is everything from (including) the element's

start tag

to (including) the element's

end tag

.

An

element

can

contain

:

other

elements

text

attributes

or a mix of all of the above...Slide36

<bookstore>

 

<

book category="CHILDREN">

   

<

title>Harry Potter</title>

  

  <author>J K. Rowling</author>

   

<

year>2005</year>

   

<price>29.99</price>

 

</book>

 

<book category="WEB">

   

<title>Learning XML</title>

   

<author>Erik T. Ray</author>

  

  <year>2003</year>

   

<price>39.95</price>

 

</book>

</bookstore>

In the example above, <bookstore> and <book> have 

element contents

,

because they contain other elements. <book> also has an 

attribute

 

(category="CHILDREN"). <title>, <author>, <year>, and <price> have 

text content

 because they contain text.Slide37

XML Naming Rules

XML elements must follow these naming rules:

Names can contain letters, numbers, and other characters

Names cannot start with a number or punctuation character

Names cannot start with the letters xml (or XML, or Xml, etc)

Names

cannot

contain

spaces

Any name can be used, no words are reserved.

Best Naming Practices

Make names descriptive. Names with an underscore separator are nice:

<

first_name

>, <

last_name

>.

Names should be short and simple, like this:

<

book_title

>

not like this:

<

the_title_of_the_book

>Slide38

XML Attributes

In XML, attributes provide additional information about elements

Attribute values must always be

quoted.

Either single or double quotes can be used.

For a person's sex, the person element can be written like this:

<person sex="female">

or like this:

<person sex='female'>Slide39

XML 

Validator

Errors in XML documents will stop your XML applications.

The W3C XML specification states that a program should stop processing an XML document if it finds an error. The reason is that XML software should be small, fast, and compatible.

HTML browsers will display documents with errors (like missing end tags). HTML browsers are big and incompatible because they have a lot of unnecessary code to deal with (and display) HTML errors.

With XML, errors are not allowed.

Well

formed

document

.

A

XML

document

is

well

formed

if

it

follows

all

the

syntax

rules

contained

in the XML specificationSlide40

Some syntactic differences between XML and HTML

XML elements (composed of a start and end tag) must be stricly nested.

<B><I> improper nesting </B></I> is legali i n HTML, but illegal in XML.

In XML every start tag must have an end tag.

XML documents allow only one root element, the top level element that contains all other elements.

All attributes values in XML must be sorrounded by single or double quotes.

XML tags are case sensitives.

Whitespace between tags is ignored in HTML, but is preserved in XML and considered relevant.

Well formed document.

A XML document is well formed if it follows all the syntax rules scontained in the XML specificationSlide41

<?xml version=“1.0” encoding = ISO-8859-1”>

<music>

<producer>

<name> Karim</name>

<city> Roma</ city>

<catalog>

<disc year= “1961”>

<title>Nuvole Barocche </title>

<singer>Fabrizio De Andrè </singer>

</disc>

<disc year= “1965”>

<title> La città vecchia </title>

< singer >Fabrizio De Andrè </ singer >

</disc>

……

</catalog>

</producer>

……..

</music>Slide42

The elements and the attributes represent the key indicators of the structure or purpose of our content.

We must now to determine which tags we can use in a document.

In other words we must define a

grammar

for the particular markup language

A grammar is a set of rules that defines the.words (elements) and the structure by which it is possible to construct sentences (documents).

A grammar defines a specific markup language . If a XML document respects the rules defined by a grammar it is

valid

for the corresponding language.

To be automatically elaborated a XML document must be

well formed and valid.Slide43

Components of XML

XML is a formalization of rules for “marking up” documents.

There are six types of

markup:elements, attributes, comments, processing instructions, entity references and CDATA sections

.

Elements

. Are the more common aspect of markup languages. An element is a logical construct of a document. A normal element is composed of a start and end tags that surround content, others elements or both..

<street> 4296 Razor Hill Road</street>Slide44

Attributes

. An element may have attributes that are specified in name/value pairs and are placed after the start-tag name. In this example the width and height are the attributes:

<Applet width=“100” height=“200”>

Comments

A comment allows fre text description tha it is ignored by an XML processor. For example:

<!– Keep this part is really important.-->

Processing instructions

Are used to pass information to a processing application.

Example:

<?application data?>Slide45

Entity references.

Entity references are used to put reserved characters or abbreviations in markup. For example, the left angle bracket(<) is a reserved character.

CDATA Sections.

A Cdata section is a section of text that shoud not be processed but instead passed directly to theapplication. This is useful for passing source code to an applicationSlide46

DTD (Document Type Definition)

Tag names are not fixed in XML. Syntactic rules are defined relatives to their definition and use.

A DTD declares all the

legal elements

in a document; the

legal attributes

those elements can have; and the

hierarchy

,

nesting

and

occurence indicators

for all elements. In order for a document to be valid it must specify what DTD it adheres to.

A XML document that satisfies the specifications of a DTD is

validated with reference to that DTD

.

Automatic tools exist to validate a XML document.Slide47

<?xml version="1.0"?>

<!DOCTYPE note [

<!ELEMENT note (to,from,heading,body)>

<!ELEMENT to (#PCDATA)>

<!ELEMENT from (#PCDATA)>

<!ELEMENT heading (#PCDATA)>

<!ELEMENT body (#PCDATA)>

]>

<note>

<to>Tove</to>

<from>Jani</from>

<heading>Reminder</heading>

<body>Don't forget me this weekend</body>

</note>Slide48

!DOCTYPE note

 defines that the root element of this document is

note

!ELEMENT note

 defines that the note element contains four elements: "to,from,heading,body"

!ELEMENT to

 defines the

to

element  to be of type "#PCDATA"

!ELEMENT from

 defines the

from

element to be of type "#PCDATA"

!ELEMENT heading

 defines the

heading

element to be of type "#PCDATA"

!ELEMENT body

 defines the

body

element to be of type "#PCDATA"Slide49

Why Use a DTD?

With a DTD, each of your XML files can carry a description of its own format.

With a DTD, independent groups of people can agree to use a

standard DTD for interchanging data

.

Your application can use a standard DTD to verify that the data you receive from the outside world is valid.

You can also use a DTD to verify your own data.Slide50

The class of documents that are consistent with the document structure may be defined by the following DTD :

<!ELEMENT music (producer +)>-

<!ELEMENT producer (name, city, catalog)>

<!ELEMENT name (#PCDATA)

<!ELEMENT city (#PCDATA)

<!ELEMENT catalog (disc+)>

<!ELEMENT disc (title,singer)>

<!ATTLIST disc year CDATA#REQUIRED>

<!ELEMENT title (#PCDATA)>

<!ELEMENT singer (#PCDATA)>

Music

is

the root element. It contains a list of producers (one or more).

Each producer is constituted by three elements: :

name, city and catalog

.

The first two (as in the following,

title and singer

) contain only text .(PCDATA), instead

catalog

contains a list of one or more disc elements, each of them with the attribute year (REQUIRED, cannot be omitted) , a title and the singer name.Slide51

EXAMPLE

<Phone _book

>

<item>

<Name> Mario Bianchi </Name>

<Number> 0665745689 </Number>

<Address> street della viola 37 00132 Roma </Address>

</item>

.………..

<item>

<Name> Sandro Verdi </Name>

<Number>0235769856</Number>

<Address>via delle rose 63 20127 Milano </Address>

</item>

</Phone_book>Slide52

DTD

<!DOCTYPE phonebook

<!ELEMENT phonebook (VOICE+)>

<!ELEMENT item (NAME, NUMBER, ADDRESS)>

<!ELEMENT NAME (#PCDATA)>

<!ELEMENT NUMBER (#PCDATA)>

<!ELEMENT ADDRESS(#PCDATA)>

]>Slide53

In order to assigne a

semantic value to the elements and attributes

of a XML document , standards have been created for different application domains.

SBML (System Biology Markup Language)(http://sbml.org)

GML ( Geography Markup Language)(http://www.opengeospatial.org)

HealthCareLevel Seven (

http://www.hl7.org

)

XBRL (XML based Business Reporting standard (

http://www.xbrl.org

)

GJXDM (Global Justice XML Data Model) (

http://it.oip.gov/jxdm

).

Rosetta net consortium has defined a number of document types and their semantic to use in B2B transactions in the ICT sector.

Standard for the definition of XML application domains Slide54

Al momento è necessario (web services) concordino sull’uso dei termini della transazione che si vuole realizzare.

XML offre solo interoperabilità di tipo sintattico e strutturale, ma non una reale condivisione di conoscenza, quando non vi sia già una semantica condivisa.

Ontologie.

Web semanticoSlide55

Tranformation

The

browser

cannot interprete the tags (differently from HTML).

XML does not allow the

description

of the

graphic presentation

of the logical elements of the text. Special purpose languages (

stylesheets

) are used.

It is possible to obtain from the same XML document different kinds of pubblication (paper www, audio,..) by using different style

sheets

A common stylesheets is

XSL (eXtensible Stylesheet

Language

).

It is possible not only to decide the graphic format, but also to decide which parts of the document must be displayed.

Transformation languagesSlide56

Query

Xpath.

Sintax like to file

pathname

in order to find element depending on their position in the XML tree.

Ex:

doc (music.xml)//catalog/disc

Estracts all the disc elements contained in the catalog element of the xml music document

doc (music xml)//catalog/disc [singer “Bob Dylan”]

doc (music.xml)//catalog/disc[singer“Bob Dylan”]/titleSlide57

Parsing

Parsing is the process of

dissecting a body of text

into its individual

component pieces.

For example, if that body of text is a paragraph, parsing will break the paragraph into sentences. It would then break a sentence into subject and predicate. In turn, the subject and the predicate would then be broken down into their components like nouns, verbs and adjectives.

Lexical analysis breaks the body of text into tokens. Tokens are the smallest atomic components of the stream of data. In the paragraph example, tokens would be words (scanner)

Grammatical analysis. Involves

recognizing the syntactical structure

of a language. In other words , how words are combined to form larger structures and how those structures form even larger ones (parser).

SAX, DOMSlide58

DOM (Document Object Model)

The XML DOM defines a standard way for accessing and manipulating XML documents.

The DOM presents an XML document as a

tree-structure

.Slide59

Base Software

XML Browser. Allows the simple reading of XML documents

Open source, Internet Explorer..,

Validationion parser and XSLT are available as open source products

XML Editor (file di testo) : provide features for syntactic validation and DTD validation

MS XML Notepad, XML Pro,ect. XML SPYSlide60

XMLand data-base

It is possible to obtain a XML form of a query

Example: Microsoft SQL Server allows to obtain the XML form of a query by using “FOR XML”

It is possible to modify a relational database using XML data.Slide61

XHTML

(e

X

tensible

H

ypertext

M

arkup

L

anguage)

Sfruttando le somiglianze sintattiche è stato definito un linguaggio di markup per le

pagine web

che mette a disposizione le possibilità di

HTML

con una sintassi

XML

Semplifica la programmazione di browser per computer e cellulari

Software di baseSlide62

La DTD può essere inserita all’inizio del documento XML o memorizzata in un file diverso cui fa riferimento.

La DTD può essere privata (scritta dall’utente stesso) oppure pubblica (reperita in rete).

La DTD di un documento XML

non fornisce alcuna informazione semantica

: definire che un certo elemento deve essere contenuto in un documento XML

non è sufficiente per chiarire la sua semantica e come l’informazione verrà utilizzata da chi riceve il documento

.

Quando l’informazione viene estratta, deve esserci un programma che comprende la semantica.Slide63

Ontologie

Specifiche formali di concettualizzazioni che descrivono una comprensione comune di un dominio, la quale è concordata da una pluralità di soggetti e può essere deliberatamente condivisa tra persone diverse ed applicazioni diverse.

Semantic web

Affidare al meccanismo di scambio di dati alla base dei web services anche una descrizione dei domini realizzata tramite ontologie.