Transcript XML, DTD, XSL, JSON - GVSU School of Computing and

CS 371 Web Application
Programming
XML and JSON
Encoding Data
CS 371 Web Application
Programming
School of Computing and
Information Systems
Data Encoding
transporting data from script to another
data needs to be organized
fixed length, comma delimited or proprietary
formats can be efficient but structure must be
“known” by sender and receiver
DBMS is not an option because they cannot
be accessed by clients
need a portable format where the structure
is independent of the scripts
CS 371 Web Application
Programming
School of Computing and
Information Systems
Exensible Markup Language
subset of SGML
enforces well-formed tags (or elements)
tags are not predefined
users can define structure of data
allows groups to agree to a standard and
easily enforce it.
tags are nested, self-described and case
sensitive
CS 371 Web Application
Programming
School of Computing and
Information Systems
Data Flow
DTD
or
schema
Sending
script
XML
document
(data)
XML
document
(data)
Validator
Parser
Receiving
script
CS 371 Web Application
Programming
School of Computing and
Information Systems
Structure of an XML Document
elements (tags) and attributes like XHTML
to be well-formed
all elements must be terminated
elements must be case sensitive
elements must be properly nested
must have a root element
attribute values must be quoted
white space is preserved
declarative tag <?xml version “1.0”?>
CS 371 Web Application
Programming
School of Computing and
Information Systems
XML Example
root tag
attributes
name and homeTown
are children of student
<?xml version="1.0" encoding="UTF-8"?>
<students>
<student id='123' campusLoc="on">
<name>Thomas Cruise</name>
<homeTown>Saginaw</homeTown>
</student>
<student id='456' campusLoc="off">
<name>Jack Nicholson</name>
<homeTown>Grand Rapids</homeTown>
</student>
</students>
element
text node
CS 371 Web Application
Programming
School of Computing and
Information Systems
Rules for Elements
names
composed of letters, numbers and other chars
cannot start with a number or punctuation
cannot start with xml (XML, etc)
no spaces - also avoid "."
can have content
attributes
attributes can have values
values must be quoted
CS 371 Web Application
Programming
School of Computing and
Information Systems
Content
normally everything is parsed (#PCDATA)
built-in entities:
&amp;, &lt;, &quot;
&xx; (&39; is a single quote)
use <![CDATA[text here]]> to pass data
through parser as simple text
CS 371 Web Application
Programming
School of Computing and
Information Systems
Examples
well-formed
<team type="divII">Grand Valley</team>
<a><b attr="val"><c>text</c></b></a>
<lesson title="html"/>
not quite well-formed
<ul><li>first bullet<li>second</ul>
<team type=divII>Grand Valley</team>
<student><name>Jason</student></name>
<student name>Mikey</student name>
CS 371 Web Application
Programming
School of Computing and
Information Systems
Validation
To be well-formed a document must also
conform to a dtd (document type definition)
dtd defines the structure of an xml doc:
name of root element
what is valid/invalid content for an element
what attributes can be used
type of data (parsed or unparsed)
dtd can be internal or external
xml schema is alternative to dtd
many xml validators – just google it
CS 371 Web Application
Programming
School of Computing and
Information Systems
DTD Construction
reference in xml file
external:
<!DOCTYPE teams SYSTEM “teams.dtd">
internal
<!DOCTYPE teams [ …element defs. … ]>
prologue in dtd file
(<?xml version="1.0" encoding="UTF-8"
standalone=”no” ?>
CS 371 Web Application
Programming
School of Computing and
Information Systems
DTD Construction (cont)
defining elements:
<!ELEMENT ename def>
content models
elements can be empty
can have text
can have other elements
avoid use of ANY
ex: <!ELEMENT student (id,name,grade)>
student must have id, name and grade
CS 371 Web Application
Programming
School of Computing and
Information Systems
DTD Construction Recurrence
comma means strict order
| (pipe) is like or
+ is one or more, * is zero or more
? means that the element is optional
use parens () for grouping
CS 371 Web Application
Programming
School of Computing and
Information Systems
DTD Construction Examples
<!ELEMENT student EMPTY>
<student/> in the xml file
<!ELEMENT homeTownDesc (#PCDATA)>
contents can include any parsed data
<!ELEMENT student (name, id, major, minor*)>
must have name, id, major and any # of minors
<!ELEMENT student (name,(hobbies|sports)*,
age)>
name, any number of hobbies or sports and age
<!ELEMENT cust (#PCDATA|(name, addr) )>
contains parsed data or name and address
CS 371 Web Application
Programming
School of Computing and
Information Systems
DTD Attribute Types
<!ATTLIST element attr type defVal>
ex: <!ATTLIST student id CDATA>
type can be
CDATA
(en1|en2|…)
ID
IDREF
NMTOKEN
ENTITY
a few others…
character data
one from the list
a unique identifier
references an ID
valid XML name
value is an entity (&st;)
CS 371 Web Application
Programming
School of Computing and
Information Systems
DTD Attribute Types (cont)
<!ATTLIST element attr type defVal>
defVal (default value) can be:
value
#REQUIRED
#IMPLIED
#FIXED
an actual value
attribute is required
not required
attribute value is fixed
CS 371 Web Application
Programming
School of Computing and
Information Systems
Caveats
hosting an xml file – make sure it has
executable permissions
CS 371 Web Application
Programming
School of Computing and
Information Systems
XML Parsers
parsers are used to traverse xml tree
tree-based (DOM)
loads entire document into memory
random access, readable and writable
contains objects: doc, node, nodeList, error
stream-based (SAX)
fires events when encountering new entity
ex: <author> fires startElement(“author”,attr)
DOM and SAX parsers in .net, java, etc.
CS 371 Web Application
Programming
School of Computing and
Information Systems
xml parsers
javaScript
already familiar with dom parser
(getElementsByTagName)
see www.w3schools.com/xml/xml_parser.asp
no sax parser (why not?). (3rd party)
PHP
dom parser – see
php.net/manual/en/book.simplexml.php
sax parser – see
php.net/manual/en/book.xml.php
CS 371 Web Application
Programming
School of Computing and
Information Systems
XSL: Stylesheets for XML
XSL is like a template used with an xml file
like xhtml with special tags for trans. xml
use XPATH for navigation
select (student) // selects all child nodes
select (/student[0]) // first student from root
elements:
template element defines scope of xml
<xsl:template match=“/”>
<xsl:for-each select=“students/student”>
<xsl:value-of select=“name”/>
CS 371 Web Application
Programming
School of Computing and
Information Systems
JSON
basic syntax
{“var1”:val,”var2”:val…}
just like array initialization in javascript (hmm)
in php use json_encode($object) to create
a JSON string
in javascript:
var myObject = JSON.parse(text, reviver);
where reviver is opt function called for
every key and value
CS 371 Web Application
Programming
School of Computing and
Information Systems