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
Download Presentation The PPT/PDF document "Document description languages" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
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).Slide28Slide29
<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
<
;
<
less
than
>
;
>
greater
than
&
;
&
ampersand
&apos
;
'
apostrophe
"
;
"
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.