JavaScript Description

Transcript JavaScript Description

XML
A web enabled data description language
4/22/2001
By Mark Lawson &
Edward Ryan L’Herault
XML HISTORY
• Developed by work group, under authority
of the W3C
• First seen in 1996, and standardized by the
W3C in 1998
• Simplified dialect of the SGML
SGML "Standard Generalized
Markup Language"
• A method for creating interchangeable,
structured documents
• Standardized in 1986 (ISO8879:1986)
• Can assemble a single document from
many sources
• Defines a document structure using a
special grammar called a Document Type
Definition
• Adds markup to show the structural units in
a document
HTML vs XML vs SGML
• HTML is an SGML application (a DTD and
set of processing conventions)
– As such it’s much more limited than SGML and
XML
– It’s easy to learn
• SGML is the mother of XML and HTML
– It’s complicated – hundreds of pages in it’s
definition
– It has many extraneous features that aren’t
needed on the web
HTML vs XML vs SGML II
• XML is a subset of SGML
–
–
–
–
–
–
Valid SGML
Only uses the parts that are useful on the web
Requires more syntax checking than HTML
Is extendable like SGML
Has a small definition (25 pages)
Easy to learn
How do I execute or run
an XML file?
• You can't and you don't.
• XML is not a programming language,
so XML files don't ‘run’ or ‘execute’.
• XML is a markup specification
language and XML files are data.
Constructing your own XML
You must supply a Document Type Definition
What is a Document Type Definition (DTD)?
• A context-free grammar like Extended BNF
• Provides the rules that define the elements
and structure of your new language
• Thousands of SGML DTDs already in
existence
• SGML DTDs need to be converted to XML
for use with XML systems
How is a DTD implemented?
• A DTD is a file (or several files to be used
together), written in XML's Declaration
Syntax
• It contains a formal description of a
particular type of document
• It sets out what names can be used for
element types, where they may occur, and
how they all fit together
• Any browser (or application) with an XML
parser could interpret an XML document
instance by "learning" the rules defined by
the DTD.
Defining the structure &
Semantics of XML
XML structure is defined in a schema
• Defines shared markup vocabularies
• Provide a means for defining the structure,
content and semantics of XML
• Introduces new levels of flexibility that may
accelerate the adoption of XML for
significant industrial use
Schemas
• Schemas support inheritance and
overriding old values
• Schemas are not yet a formal
Recommendation, but a number of
sites are starting to serve useful
applications as both DTDs and
Schemas
An XML example
• Example: Elements and Attributes
This group of elements, attributes describe the
contents of an address book. It includes a DTD
which describes how all of the pieces work as XML.
<?xml version=‘1.0’ ?>
<!DOCTYPE address-book SYSTEM ‘address-book.dtd’>

<address-book>
<entry>
<name>
<fname>Jack</fname>
<lname>Smith</lname>
</name>
<tel>513-555-3465</tel>
<email
href=‘mailto:[email protected]’/>
</entry>
</address-book>
Required
1.
The XML Declaration
• <?xml version="1.0"
standalone="no"?>
•
2.
This is what tells an XML parser that
the document is XML
XML Declaration w/ character set
• <?xml version="1.0"
encoding="ISO-8859-1"?>
Basic Syntax
• All tags must be closed
• The exception is an empty tag
(i.e. <line-break/> )
• All nested tags must close before the tag
they are nested in
• All attributes must have quotes
• Case sensitive
Tags and DTD
The DTD describes every object that can
appear in the document
An example section of a DTD is:
<!ELEMENT address-book (entry+)>
This is an entry that says the element
<address-book> is composed of one or
more <entry> elements.
Optional modifiers
for the entries:
1. No modifier: Object appears once
and only once in the element
2. +: Object appears at least once
and can be repeated
3. *: Object appears zero or more
times
4. ?: Object appears zero or one
times
Elements composed of
multiple entries
An element can be composed of multiple entries, for
example an entry in the address book has: a
name, phone number, and email
<!ELEMENT entry (name,tel*,fax*,email*)>
Inside the parentheses are the elements that make
up entry these can take the forms:
• (e1 , e2): These elements will appear once each in
order e1 e2
• (e1 | e2): One of these elements will appear (either or)
• These can be combined as in:
– (e1, (e2 | e3) )
Attributes of Elements
Some elements have attributes, which are
part of their data description. An attribute
has:
– The attribute tag opening: <!ATTLIST
– The name of the element it belongs to:
email
– The attribute name: href
– The attribute type: CDATA
– Optionally a default value: #REQUIRED
– The close bracket: >
Attributes of Elements II
There can be more than one attribute listed
in one attribute tag:
<!ATTLIST email href CDATA #REQUIRED
preferred (true |false) 'false'>
Referencing the DTD
A DTD is referenced in the document using it
with the tag:
<!DOCTYPE address-book SYSTEM "address-book.dtd">
Referencing the DTD II
The section of the tag:SYSTEM "addressbook.dtd">
Can be replaced with or followed by a [ and
the actual DTD as in:
<!DOCTYPE name [
<!ELEMENT name (#PCDATA |fname |lname)*>
<!ELEMENT fname (#PCDATA)>
<!ELEMENT lname (#PCDATA)>
]>
Viewing the XML: XSL
Because XML is just for describing data it isn’t
inherently displayed in a particular way by
a browser. XSL allows how things are
displayed to be specified
• XSLT transforms the data into new forms
• XSLFO allows the style of the objects to be set
• A similar thing to XLSO which is more
supported is CSS
Uses of XML
1.
2.
3.
4.
5.
intelligent agents - content
personalization via smart pull/push
(possibly with a date-stamped XML
repository)
structured records (purchase order)
object with methods and data (Java, and
potentially JavaScript)
meta-content about your web site
(improves searches) query results
graphical user interface of an application
persistent storage format (e.g. ODBMSpowered XML repository)
Uses of XML II
6. electronic service manuals
7. online process/procedures
documentation
8. EDI (electronic data interchange) mapping data between purchasing
and inventory departments of same
or different companies
References
http://www.w3.org/XML/
http://www.ucc.ie/xml
http://www.xml.com/
http://www.gca.org/whats_xml/whats_xml_xmlfiles.htm
http://www.schema.net/
most informative site:
http://wdvl.com/Authoring/Languages/XML/Intro/
Also:
XML for Dummies
XML by Example by Que