lecture course service-oriented computing 3. basics: xml

Fuyuki Ishikawa （石川冬樹）[email protected]

Lecture CourseService-Oriented Computing

3. Basics: XML2012/04/25

1 Introduction

2 Basics: Distributed Objects

3 Basics: XML

4 Web Services: Foundations

5 Web Services: Composition

6 Web Services: Implementation

7 Related Topics (1): Reliability

SOC'12 @ Sokendai 2Fuyuki Ishikawa

Course Plan

8 Related Topics (2): Security

9 Related Topics (3): Engineering

10 Related Topics (4): Semantic Web

11 Cloud Computing (1): Overview

12 Cloud Computing (2): Experience

13 Discussion and Summary

14 Students’ Presentation


Course Plan

Web Services and XMLXML

Core ConceptsSchema LanguagesOther Essential SpecificationsProgramming Models

TOC

4SOC'12 @ Sokendai Fuyuki Ishikawa

A Web service is a software applicationidentified by a URI, whose interfaces and binding are capable of being defined, described and discovered by XML artifactsand supports direct interactions with other software applications using XML based messages via internet-based protocols

[W3C, 2002]


(Review) Web Services?

Infrastructures for distributed objectsAims at interoperability among objects based on different environments (platforms and languages)Implemented by common network formats and translation mechanisms in ORB for each environment

Some criticisms when compared with the Web (which became widespread at that time)

Different mechanisms existed and were not connected, such as CORBA, DCOM and Java RMIFirewall configuration was difficult due to dynamic port mapping mechanisms


Previous Issues in Distributed Objects

Popularity of XML as platform-independent data formats on the Web

XML 1.0 (W3C Recommendation in 1998)XHTML 1.0 (W3C Recommendation in 2000)MathML 1.01(W3C Recommendation in 1999)…

Use of XML for messaging formats between distributed objects

XML-RPC (Userland and Microsoft, 1998)SOAP (a widespread standard ver. 1.1 in 2000)

Movement


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XML-RPC<methodCall><methodName>examples.getStateName

</methodName><params><param><value><i4>41</i4></value></param>

</params></methodCall>

<methodResponse><params><param><value><string>South Dakota</string></value>

</param></params>

</methodResponse>

SOC'12 @ Sokendai Fuyuki Ishikawa



TOC


XML: eXtensible Markup LanguageMarkup language: a language for a set of annotations to describe structures of text dataExtensible: those annotations can be defined by users

For data exchange especially via the InternetHas the grammar and the parser requirements of defined by W3C (open standard)Does not depend on any programming languages or execution environments (platform independent)Attaches a text document with structural information about which part describes what (self-describing)


XML: Overview

SGML: Standard Generalized Markup Language(ISO standard in 1986)

Uses plain text formats with "tags" to involve meanings inside the text data Introduces ideas of

Validation based on syntax definition (DTD)Separation of data and their metadata (attributes)Separation of data and processing

11

XML History

<quote>This is a document about <keyword type=italic>Web Services</keyword>

</quote>


Problems in SGML: complexityComplexity of the specification, or difficulty in implementation of processing software

Syntax simplification into XML standardizationVer. 1.0 (W3C Recommendation in 1998)Ver. 1.1 (W3C Recommendation in 2004)

Allows for use of characters not included in Unicode 2.0Is often not necessary or supported by tools

Ver. 2.0 ???

12

XML History



XML Documents: Overview

<books><book category="computer">

<author> M. P. Singh and M. N. Huhns </author><title> Service-Oriented Computing:

Semantics, Processes, Agents </title><edition></edition>

</book><book category='fiction'>

<author> J.K.Rowling </author><title> Harry Potter and the Deathly Hallows </title><edition/>

</book></books>


XML Documents: Element (1)






</book></books>

Element: a container of data distinguished by a pair of start-tag and end-tag


XML Documents: Element (2)






</book></books> An empty-element tag can be used

instead of writing a start-tag immediately followed by an end-tag

Elements form a tree There is only one root element in an XML documentAn element can have only one parent at the most while it can have multiple children

Elements can only be nested (cannot overlap)


XML Documents: Elements (3)

booksbooks

bookbookauthorauthortitletitle

editionedition

bookbookauthorauthortitletitle

editionedition

<strong>this is a <italic>pen</strong></italic>

not allowed


XML Documents: Attribute






</book></books>

Attribute: metadata describing the element

Specification on "white spaces“(horizontal tab, LF, CR, and space in ASCII)

When they are inside element tags or attribute valuesExcluded (ignored) by a parserWhen they are included in element contents Kept by a parser for the application software

Standard attributese.g., “lang”: language ("ja", "en-US", …)

Referencese.g., “<” for “<“ (escape), “&#A9” for “©”, …


XML Documents: Other Pieces

XML declarationMay (should) appear first in an XML documents

Processing Instructions (PI)Gives information for the processor (application software)

Type Declaration (later detailed)


XML Documents: Meta Description (1)

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

<?xml-stylesheet type="text/css" href="mystyle.css"?>

<!DOCTYPE …>

CommentsAllows for insertion of comments

CDATA sectionAllows for insertion of (long) texts that are not interpreted as XML markups (such as XML sample texts)

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XML Documents: Meta Description (2)




<![CDATA[ <sample> Sample data </sample> ]]>


"Incorrect" XML Documents<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <books>

<book category=computer><author> M. P. Singh and M. N. Huhns </author><title> Service-Oriented Computing:

Semantics, Processes, Agents </title><edition>

</book></books><books>

<book category='fiction'><author> J.K.Rowling<title> Harry Potter and the Deathly Hallows

<edition> 2nd </title> </edition></book>

</books>

No quotation in attribute value

Lack of the end-tag

Lack of the end-tag

Overlaping tags

Multiple root elements

An XML document is said to be well-formedif, roughly speaking,

Non-empty elements are delimited by a start-tag and an end-tag, and empty elements may be marked with an empty-element tagAttribute values are quoted with either a pair of single quotes or a pair of double quotesTags may be nested but not overlapThere is exactly one root element

Correctness based on the criteria given in the XML standard specification (syntax-based)

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Well-formed




TOC



"Correct" XML Documents?

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <books>

<book category="computer"><author> M. P. Singh and M. N. Huhns </author><edition/><price> -350 </price>


<author><price> 200 </price>

</author><title> Harry Potter and the Deathly Hallows </title><edition/>

</book></books>

price value can be negative?

author value can be price?

book can lack title?

XML allows its users to define markups to annotate text dataNeeds a constraint definition on the user-defined markups: an XML schema

Vocabularies (e.g., element names)Structural constraints (e.g., allowed hierarchies of elements)Content of documents (e.g., type of attribute values)

Note: there is a specific language called “XML Schema” (later discussed) while the term schema is general

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Schema Definitions for XML


An XML document is said to be valid if it satisfies constraints given in the schema it is associated withCorrectness based on the criteria given in the associated schema (semantics or meaning-based)

26

Validity


DTD: Document Type DefinitionUses EBNF-based notations

27

DTD: Overview and Example

<!ELEMENT FruitBasket (Cherry?, (Orange | Apple)+)><!ELEMENT Cherry EMPTY><!ELEMENT Orange EMPTY><!ELEMENT Apple EMPTY>A "FruitBasket" element can contain only- No or one "Cherry" element- And subsequently, equal to or more than one of "Orange" or "Apple" elements

<FruitBasket><Apple/><Orange/><Apple/>

</FruitBasket>SOC'12 @ Sokendai Fuyuki Ishikawa

<FruitBasket><Cherry/><Apple/>

</FruitBasket>

Use of DTD with XML documentsDefined in the XML specification itself(though planned to be removed from XML 2.0)Uses the <!DOCTYPE> tag to include DTD descriptions or to refer to external DTD documents

28

DTD: Use with XML


<!DOCTYPE books [ … ] > Embedded definition

<!DOCTYPE booksPUBLIC "-//Book" "http://nii.ac.jp/dtd/Book.dtd" >

Reference by a URI (later described) and possibly an internal name (inside the SYSTEM or PUBLIC)

Problems found in DTDLacks support for reusability of definitions

Does not have a mechanism to resolve name collision or to extend existing definitions

Lacks a mechanism for data type definitionWhy not use the XML syntax!

More powerful languages are preferredXML Schema (W3C), RELAX NG (ISO), ...DTD is planned to be removed in XML 2.0

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DTD: Limitations


XML SchemaDefined as an XML languagePublished as W3C Recommendation in 2001Instantiated as an XSD (XML Schema Definition)Uses Namespaces (described later) to allow for reuse of existing definitions even if they share common names for different usagesSupports a large number of built-in data types and definition of derived data types

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XML Schema: Overview



XML Schema: Example<element name="FruitBasket">

<complexType><sequence>

<element name="Cherry" minOccurs="0" maxOccurs="1"><complexType/>

</element><group ref="OrangeOrApple" minOccurs="0"

maxOccurs="unbounded"/></sequence>

</complexType></element><group name="OrangeOrApple">

<choice><element name="Orange"><complexType/></element><element name="Apple"><complexType/></element>

</choice></group>

RELAX NG(REgular LAnguage for XML Next Generation)

Defined as an XML languageAlso includes a compact (non-XML) syntax and conversion into/from the XML-based syntax

Proposed against XML Schema, which became too large and complex pushed by large companies

Based on RELAX (M. Murata) and TREX (J. Clark)Standardized by OASIS in 2001Included in the ISO DSDL (Document Schema Description languages) standard, gathering different types of schemas for different tasks

32

RELAX NG: Overview



RELAX NG: Example<element name="FruitBasket">

<optional><element name="Cherry"><empty/></element>

</optional><zeroOrMore>

<choice><element name="Orange"><empty/></element><element name="Apple"><empty/></element>

</choice></zeroOrMore>

</element>

element FruitBascket {element Cherry { empty } ?...

}

Use of compact syntax

DTD: early standardSupported by many existing XML tools

XML Schema: popular in the industryUsed in many industrial specifications (e.g., WSDL)Supported by most tools

RELAX NG: popular to be against XML SchemaSupported by somewhat many tools

34

Notes: Comparing Schema Languages


Detailed differencesNumber of element occurrences

XML Schema: arbitrary with "min/maxOccurs"RELAX NG: "zeroOrMore", "oneOrMore", and "opitional" (*, +, ? in EBNF and DTD)

Built-in data formatsXML Schema: a variety of data types and their hierarchies (e.g., even including unsignedByte, nonPositiveInteger, duration, gYearMonth)RELAX NG: references to such external “data type libraries”

35

Notes: Comparing Schema Languages


Are they essential?



TOC


URI: Universal Resource IdentifierFor identification of a resource (e.g., location or name)

Supporting combination of interaction definition and identification as well as hierarchical structures Examples

http://www.ietf.org/rfc/rfc2396.txtmailto:[email protected]:comp.infosystems.www.servers.unixurn:oasis:names:specification:docbook:dtd:xml:4.1.2

(IRI: Internationalized …, XRI: eXtensible …)


URI

Namespaces in XMLFor identification of a vocabulary set when reusing (possibly conflicting) names from different schemas

38

Namespaces


nameaddress age

mailAddress

namemodelNumber

price size

IDnumber

IDnumber

g g pNames used in a markup language for user description

g g pNames used in a markup language for item description

Want to reuse these vocabulary definitions to define a markup language for invoice description(while resolving the name conflicts)

Needs an identifier for each set of names (name space)

Namespaces in XMLe.g., use in XML documents

39

Namespaces


<invoicexmlns=“http://hoge.co.jp/schema/invoice”xmlns:item=“http://example.com/def”>

<IDnumber xmlns=“http://sample.jp/schema/User”>2010u53243

</IDnumber><item:IDnumber>K1J2321P</item:IDnumber>

</invoice>

Default name space for this tag and the descendants

Labeled name space for …

A qualified name with the label prefix (QName)(instead of the full URI)

Namespaces in XMLe.g., use in XML schema definitions

40

Namespaces

- A user element must have justone IDnumber element as a child

- …


Schema definition for user descriptionSchema definition for user descriptionxmlns=“http://sample.jp/schema/User”

- A shop element must have justone IDnumber element as a child

- …

Schema definition for item descriptionSchema definition for item descriptionxmlns=“http://example.com/def”

- An invoice element must have just one user:IDnumber element as a child- An invoice element must have just one item:IDnumber element as a child- …

Schema definition for invoice descriptionSchema definition for invoice descriptionxmlns=“http://hoge.co.jp/schema/invoice”xmlns:user=“http://sample.jp/schema/User”xmlns:item=“http://example.com/def”

XSLT: eXtensible Stylesheet Language Transformations


XSLT

<xsl:template match="doc"><html><head><title><xsl:value-of select="title"/></title></head><body><xsl:apply-templates/></body></html></xsl:template><xsl:template match="doc/title"><h1><xsl:apply-templates/></h1></xsl:template>

<doc><title> About NII </title>…</doc> <html><head><title>About NII</title></head><body><h1> About NII </h1>…</body></html> (not exact: line feeds are adjusted for the layout)

XPathFor reference to nodes that satisfy a given condition

XIncludeFor import of other documents

Xquery, …

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Other Extensions


A//B/*[1]

<xi:include href="sample.txt" parse="text"/>

Choose the first element with any name (*[1]) among children of an element B (B/), which is a descendant of an element A (A//) (a relative path based on the current context)



TOC


DOM: Document Object ModelPlatform/language-independent standard object model/API for XML (or HTML)

Described as IDL definitionsOriginal motivation: Web browsers needed object models to facilitating manipulation of structures of HTML documents (e.g., in JavaScript code)

44

DOM

<html> <head>...</head><body>...<form name="myFORM">...<input type="text" name="myTEXT"> …

txt = document.myForm.myTEXT.value


DOM: Document Object Model (Cont'd)APIs for XML Manipulation

45

DOM

Interface Node {...DOMString nodeName;DOMString nodeValue;Node parentNode;NodeList childNode;Node previousSibling;Node nextSibling...Node insertBefore(Node newChild, Node refChild)Node replaceChild(Node newChild, Node oldChild)...

}SOC'12 @ Sokendai Fuyuki Ishikawa

DOM: Document Object Model (Cont'd)Essence: Allows for focusing on the structure, not the syntax to denote itHistory

Level1 (W3C Recommendation in 1998)Navigation and manipulation of HTML and XML

Level 2 (W3C Recommendation in 2000)XML Namespace support

Level 3 (W3C Recommendation in 2004)Support of many features (Load and Save, Validation, XML Base, etc.)

Support by many browsers and libraries46

DOM


SAX: Simple API for XMLEvent-driven API for serial access XML parser

47

SAX

<?xml version="1.0"?><books><book>XML</book>

</books>

Sequential ParsingSequential Parsing

Users implement these event handlers (callback methods)

call startDocument()call startElement(“books”)call startElement(“book”)call characters(“XML”)

call endElement(“book”)call endElement(“books”)


DOM vs. SAX: DOM parsers keep all the structure (or objects and their has-a relationships), while SAX parsers just see the "current" point

DOM takes much more memory (and thus is slower) than SAXDOM cannot handle XML documents larger than the memory amount, as it does not allow for streamed reading, while SAX canSAX is less suitable for tasks that need the whole tree structure, including validation, style-sheet transformation, XPath evaluation, and so on, while DOM is naturally suitable by its design

48

DOM vs. SAX


Difficulty in DOM or SAX: need to "retrieve" the structure of XML documentsUse of the native representation of the object that denotes an XML document

49

XML Data Binding

<?xml version="1.0"?><books><book>XML</book>

</books>

booksdoc.getBooks().getBookList().getFirst().getValue();

Class Books{List<Book> bookList;List<Book> getBookList() {...}...

}Class Book{...}


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XML Data Binding

Type

Instance

XML schema

XML OO Programming Lang.

XML document

Class

Object

unmarshall

marshall


51

Typical Tool Support (e.g., JAXB)

Type

Instance

XML schema

XML OO Programming Lang.

XML document

Class

Object

Class GeneratorClass Generator

Marshaller/UnmarshallerGenerator

Marshaller/Unmarshaller

Provided by a library/tool, used once during the coding phase


52

Typical Tool Support (e.g., JAXB)

Instance

OO Programming Lang.

XML document Object

Marshaller/Unmarshaller

Application Program

1.1. Obtain an XML document2. Call the unmarshallar and obtain the

corresponding object3. Manipulate the object4. Call the marshaller and obtain the modified

XML document


May 9Web Service Foundations

SOAPRESTWSDL(UDDI)

53Fuyuki Ishikawa

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