Chapter 2: Basic Standards for Web Services

Transcript Chapter 2: Basic Standards for Web Services

Basic Standards for Web Services
CS 696 – Services Computing
Fall 2008
Chapter 2: Service-Oriented Computing:
Semantics,
Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005
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Highlights of this Chapter
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eXtensible Markup Language (XML)
Simple Object Access Protocol (SOAP)
Web Services Description Language
(WSDL)
Directory Services
Universal Description, Discovery, and
Integration (UDDI)
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Standards for Web Services
ebXML
Registries
UDDI
ebXML
CPA
OWL-S Service
Model
OWL-S
Service
WSCL
Profile
OWL-S Service
Grounding
OWL
RDF
PSL
BPEL4WS
BPML
WS-AtomicTransaction and WSXLANG
BusinessActivity
WS-Reliable
WS-Coordination
Messaging
WS-Security
WSCL
WS-Policy
WSDL
SOAP
BTP
WSCI
ebXML
BPSS
Discovery
Contracts and
agreements
Process and workflow
orchestrations
QoS: Transactions
QoS: Choreography
QoS: Conversations
ebXML
QoS: Service
CPP
descriptions and bindings
ebXML
messaging Messaging
XML, DTD, and XML Schema
Encoding
HTTP, FTP, SMTP, SIP, etc.
Transport
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XML Web Service Foundation
Open and with broad industry support
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Publish, Find, Use Services
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Service Interactions
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WSDL
Ubiquitous Communications
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XML
Description Language
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SOAP
Universal Data Format
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UDDI
TCP/IP, HTTP, SMTP, SIP, Reliable messaging
Security (authentication and authorization)
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WS-Security, SAML
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Markup History
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None, as in comma separated values
Ad hoc tags
SGML (Standard Generalized Markup L):
complex, few reliable tools
HTML (HyperText ML): simple, unprincipled,
mixes structure and display
XML (eXtensible ML): simple, yet extensible
subset of SGML to capture new vocabularies
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Machine processible
Comprehensible to people: easier debugging
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Brief Introduction to XML
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Basics
Parsing
Storage
Transformations
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XML Basics and Namespaces
<?xml version="1.0"?> <!– not part of the document per se 
<arbitrary:toptag
xmlns=“http://one.default.namespace/if-needed”
xmlns:arbitrary=“http://wherever.it.might.be/arbit-ns”
xmlns:random=“http://another.one/random-ns”>
<arbitrary:atag attr1=“v1” attr2=“v2”>
Optional text also known as PCDATA
<arbitrary:btag attr1=“v1” attr2=“v2” />
</arbitrary:atag>
<random:simple_tag/>
<random:atag attr3=“v3”/> <!–compare with arbitrary:atag 
</arbitrary:toptag>
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XML Example
<?xml version="1.0"? Encoding=‘UTF-8’?>
<temperature scale=“Celsius”>
<value>25</value>
<accuracy>2</accuracy>
<ambience condition=“shade”/>
</temperature>
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XML Example
<?xml version="1.0"?>
<temperature accuracy=“2” scale=“Celsius”>
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<ambience condition=“shade”/>
</temperature>
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HTML Example of same data
<TABLE BORDER=1>
<TR>
<TH>Value</TH>
<TH>Accuracy</TH>
<TH>Scale</TH>
<TH>Ambience Condition</TH>
</TR>
<TR>
<TD>25</TD>
<TD>2</TD>
<TD>Celsius</TD>
<TD>Shade</TD>
</TR>
</TABLE>
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XML Query Languages
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XPath
XPointer
XSLT
XQuery
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XPath
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Model XML documents as trees with
nodes
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Elements
Attributes
Text (PCDATA)
Comments
Root node: above root of document
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XPath
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Parent in XPath is like parent as
traditionally in computer science
Child in XPath is confusing:
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An attribute is not the child of its parent
Makes a difference for certain kinds of
recursion (e.g., apply-templates discussed
in XSLT)
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XPath Paths
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Leading /: root
/: indicates walking down a tree
.:current node
..:parent node
@attr: to access values for the given
attribute
text()
comment()
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XPath Navigation
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Select children according to position,
e.g., [j], where j could be 1 … last()
Descendant-or-self operator, //
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.//elem finds all elems under the current
//elem finds all elems in the document
Wildcard, *:
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@*: finds all attribute values
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XPath Queries
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Incorporate selection conditions in XPath
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Attributes: //Song[@genre=“jazz”]
Elements: //Song[starts-with(.//group, “Led”)]
Existence of attribute: //Song[@genre]
Existence of subelement: //Song[group]
Boolean operators: and, not, or
Set operator: union (|); none others
Arithmetic operators: >, <, …
String functions: contains(), concat(), length(),
Aggregates: sum(), count()
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XPointer
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Combines XPath with URLs
URL to get to a document; XPath to
walk down the document
Can be used to formulate queries, e.g.,
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SongURL#xpointer(//Song[@genre=“jazz”])
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XSLT
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A functional programming language
A stylesheet specifies transformations
on a document
<?xml version=“1.0”?>
<?xml-stylesheet type=“text/xsl”
href=“URL-to-dot-xsl”?> <!– the sheet to use 
<main-tag>
…
</main-tag>
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XSLT Stylesheets
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Use the XSLT namespace,
conventionally abbreviated as xsl
Includes primitives:
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Copy-of
<for-each select=“…”>
<if test=“…”>
<choose >
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XML file referencing XSL stylesheet
<?xml version=“1.0”?>
<?xml:stylesheet type=“text/xsl” href=“TempTable.xsl”?>
<TempCollection>
<temperature scale=“Celsius”>
<value>25</value>
<accuracy>2</accuracy>
</temperature>
<temperature scale=“Kelvin”>
<value>123</value>
<accuracy>5</accuracy>
</temperature>
<temperature scale=“Fahrenheit”>
<value>32</value>
<accuracy>1</accuracy>
</temperature>
</TempCollection>
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Stylesheet (TempTable.xsl)
<xsl:Stylesheet version=“1.0” xmlns:xsl=“http://www.w3.org/1999/XSL/Transform”>
<xsl:template match=“/”>
<HTML>
<BODY>
<xsl:apply-templates />
</BODY>
</HTML>
</xsl:template>
<xsl:template match=“TempCollection”>
<TABLE BORDER=“2”>
<TR>
<TH>Value</TH>
<TH>Accuracy</TH>
<TH>Scale</TH>
</TR>
<xsl:apply-templates/>
</TABLE>
</xsl:template>
<xsl:template match=“temperature”>
<TR>
<TD><xsl:value-of select=“value”/></TD>
<TD><xsl:value-of select=“accuracy”/></TD>
<TD><xsl:value-of select=“@scale”/></TD>
</TR>
</xsl:template>
</xsl:stylesheet>
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XSLT Templates: 1
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A pattern to specify where a given
transform should apply
This match only works on the root:
<xsl:template match=“/”>
…
</xsl:template>
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XSLT Templates: 2
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Can be applied recursively on the children via
<xsl:apply-templates/>
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By default, if no other template matches,
recursively apply to children of current node
(ignores attributes) and to root:
<xsl:template match=“*|/”>
<xsl:apply-templates/>
</xsl:template>
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Parsing and Validating
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An XML document maps to a parse tree.
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Each tag ends once: nesting structure (one root)
Each attribute occurs at most once; quoted string
Well-formed XML documents can be parsed
Applications have an explicit or implicit syntax
for their particular XML-based tags
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If explicit, may be expressed in DTDs and XML
Schemas
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Best referred to definitions elsewhere
XML Schemas, expressed in XML, are superior to DTDs
When docs are produced by external components,
they should be validated
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DTD (Document Type Definition) Example
<?xml version="1.0"? Encoding=‘UTF-8’?>
<TempCollection> <temperature scale=“Celsius”>
<value>25</value>
<accuracy>2</accuracy>
<ambience condition=“shade”/>
</temperature></TempCollection>
<?xml encoding="UTF-8"?>
<!ELEMENT TempCollection (temperature)+>
<!ELEMENT temperature (value, accuracy,ambience)>
<!ELEMENT value (#PCDATA)>
<!ELEMENT accuracy (#PCDATA)>
<!ELEMENT ambience (#EMPTY)>
<!ATTLIST temperature scale (Celsius|Fahrenheit|Kelvin) #REQUIRED>
<!ATTLIST ambience condition CDATA “shade”>
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#PCDATA – Parsed Character data, can contain markup
CDATA – Character data, is not parsed for markup
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XML Schema
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A data definition language for XML: defines a
notion of schema validity; helps us define
desired grammars for documents
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Same syntax as regular XML documents
Local scoping of subelement names
Incorporates namespaces
Types
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Primitive (built-in): string, ID, IDREF, integer, float, date,
simpleType constructors: list, union
Restrictions: intervals, lengths, enumerations, regex
patterns,
Flexible ordering of elements
Key and referential integrity constraints
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XML Schema example
<?xml version=“1.0”?>
<xsd:schema xmlns:xsd=“http://www.w3.org/2001/XMLSchema”
…>
<xsd:element name="TempCollection">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="temperature" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="temperature">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="value" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="accuracy" minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
<xsd:attributeGroup ref="TempAttributes"/>
</xsd:complexType>
</xsd:element>
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XML Schema example
<xsd:attributeGroup name="TempAttributes">
<xsd:attribute name="scale" use="required">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="Celsius"/>
<xsd:pattern value="Fahrenheit"/>
<xsd:pattern value="Kelvin"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:attributeGroup>
<xsd:element name="value" type="xsd:integer"/>
<xsd:element name="accuracy" type="xsd:nonNegativeInteger"/>
</xsd:schema>
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XML Schema: complexType
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Specifies types of elements with
structure:
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Must use a compositor if > 1 subelements
Subelements with types
Min and max occurrences (default 1) of
subelements
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XML Schema: Compositors
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Sequence: ordered
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All: unordered
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Can occur within other compositors
Allows varying min and max occurrence
Must occur directly below root element
Max occurrence of each element is 1
Choice: exclusive or
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Can occur within other compositors
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XML Schema: Key Namespaces
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http://www.w3.org/2001/XMLSchema
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http://www.w3.org/2001/XMLSchemainstance
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Conventional prefix: xsd
Terms for defining schemas: schema, element,
attribute, …
The tag schema has an attribute targetNamespace
Conventional prefix: xsi
Terms for use in instances: schemaLocation, null
targetNamespace: user-defined
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XML Schema Instance Doc
<Music
xmlns=http://a.b.c/Muse
xmlns:xsi=“the standard-xsi”
xsi:schemaLocation=“a-schema-as-a-URI
a-schema-location-as-a-URL”>
…
</Music>
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Creating Schema Docs: 1
<schema xmlns=“the-standard-xsd”
targetNamespace=“the-target”>
<include schemaLocation=“part-one.xsd”/>
<include schemaLocation=“part-two.xsd”/>
</schema>
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Creating Schema Docs: 2
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Use imports instead of include
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Specify namespaces from which schemas
are to be imported
Location of schemas not required and may
be ignored if provided
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Document Object Model (DOM)
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Basis for parsing XML, which provides a nodelabeled tree in its API
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Conceptually simple: traverse by requesting tag,
its attribute values, and its children
Processing program reflects document structure
Can edit documents
Inefficient for large documents: parses them first
entirely to build the tree even if a tiny part is
needed
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DOM Example [Simeoni 2003]
Element s = d.getDocumentElement();
NodeList l =
s.getElementsByTagName(“member”);
Element m = (Element) l.item(0);
int code = m.getAttribute(“code”);
NodeList kids = m.getChildNodes();
Node kid = kids.item(0);
String tagName =
((Element)kid).getTagName();
…
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Simple API for XML (SAX)
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Parser generates a sequence of events:
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Programmer implements these as
callbacks
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startElement, endElement, …
More control for the programmer
Processing program does not reflect
document structure
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SAX Example [Simeoni 2003]
class MemberProcess extends DefaultHandler {
public void startElement (String uri, String n, String
qName, Attributes attrs) {
if (n.equals(“member”)) code =
attrs.getValue(“code”);
if (n.equals(“project”)) inProject = true;
buffer.reset(); }
public void endElement (String uri, String n, String
qName) {
if (n.equals(“project”)) inProject = false;
if (n.equals(“member”) && !inProject)
name = buffer.toString().trim(); } }
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Programming with XML
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Current approaches concentrate on
structure but ignore meaning
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Difficult to construct and maintain
Treat everything as a string
Inadequate type checking can hide errors
Emerging approaches (e.g., JAXB)
provide superior binding from XML to
programming languages
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Primitives such as unmarshal to materialize
an object from XML
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Uses of XML
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Exchanging information across software
components
Storing information in nonproprietary format
XML documents represent structured
descriptions:
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Products, services, catalogs
Contracts
Queries, requests, invocations (as in SOAP)
Data-centric versus document-centric
(irregular, heterogeneous data, depend on
entire doc for app-specific meaning) views
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Data-Centric View
<relation>
<tuple><attr1>V11</attr1>…
<attrn>V1n</attrn></tuple>
…
<tuple><attr1>Vm1</attr1>…
<attrn>Vmn</attrn></tuple>
</relation>
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Extract and store into DB via mapping
to DB model
Regular, homogeneous tags
May be expensive if repeatedly parsed
and instantiated
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Document-Centric View
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Storing docs in DBs
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Use character large objects (clobs) within
DB
Store paths to external files containing
docs
Combine with some structured elements
with search conditions for both structured
elements and unstructured clobs or files
Heterogeneity also complicates mappings
to traditional typed OO programming
languages
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Directions
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Limitations of XML
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Doesn’t represent meaning
Enables multiple representations for the
same information; transform if models
known
Trends: sophisticated approaches for
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Querying and manipulating XML, e.g., XSLT
Binding to PLs and DBs
Semantics, e.g., RDF, DAML, OWL, …
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XML Summary
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XML enables information sharing
XML is well established
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Several aspects are worked out
Lots of tools
Works with databases and programming
languages
XML provides a useful substrate for
service-oriented computing
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Web Services: Basic Architecture
Service
Broker
Publish or
announce
(WSDL)
Service
Provider
Not well-known
Registry; well-known
Find or
discover
(UDDI)
Bind or
invoke
(SOAP)
Service
Requestor
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Basic Profile (BP 1.0)
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The Web Services Interoperability
Organization (WS-I) has specified the
following Basic Profile version 1.0:
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SOAP 1.1
HTTP 1.1
XML 1.0
XML Schema Parts 1 and 2
UDDI Version 2
WSDL 1.1
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Describing a Service
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Name
e.g., GetTemperature
Types of Input Parameters
e.g., (String, String)
Types of Output Parameters
e.g., Integer
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Interactions
Via Methods
Via Messages
Dell Purchasing
Intel Sales
SubmitPO
invoke
CatalogService()
AckPO
catalog
Purchasing()
confirmation #
invoke
Order()
SubmitASN
SubmitInvoice
SubmitPayment
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SOAP (Simple Object Access Protocol)
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Used to exchange messages via HTTP, SMTP, and SIP
(Session Initiation Protocol for Internet telephony)
Originally designed for remote-procedure calls (RPC)
Works through firewalls on port 80
Character-based, so easy to encrypt/decrypt and thus
easy to secure
Inefficient due to character, not binary, data and
large headers
Does not describe bidirectional or n-party interaction
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Ex. SOAP Request
POST /temp HTTP/1.1
Host: www.socweather.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
SOAPAction: "http://www.socweather.com/temp"

<?xml version=“1.0”?>
<env:Envelope
xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"
env:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
<env:Body>
<m:GetTemp xmlns:m="http://www.socweather.com/temp.xsd">
<m:City>Honolulu</m:City>
<m:When>now</m:When>
</m:GetTemp>
</env:Body>
</env:Envelope>
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Ex. SOAP Response
HTTP/1.1 200 OK
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
SOAPAction: "http://www.socweather.com/temp"
<?xml version=“1.0”?>
<env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/"
env:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
<env:Body>
<m:GetTempResponse
xmlns:m="http://www.socweather.com/temp.xsd">
<DegreesCelsius>30</DegreesCelsius>
</m:GetTempResponse>
</env:Body>
</env:Envelope>
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WSDL: Web Services Description Language
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Describes a programmatic interface to a
Web service, including
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Definitions of data types
Input and output message formats
The operations provided by the service
Network addresses
Protocol bindings
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WSDL Data Model
definitions
targetNamespace=thisNamespace
xmins:tns=thisNamespace
types
message name=in
message name=out
portType name=foo
operation
input message=tns:in
output message=tns:out
binding name=foobar
type=tns:foo
[binding information]
Types contains data type definitions
Messages consist of one or more parts
A portType describes an abstract set
of operations
A binding describes a concrete set of
formats and protocols for the foo
portTypes
service name=foobar Service
Port name=foobarPort
binding=tns:foobar
[endpoint information]
A port describes an implementation
of the foobar binding
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WSDL Example
<?xml version="1.0"?>


<wsdl:definitions name="Temperature"
targetNamespace="http://www.socweather.com/schema"
xmlns:ts="http://www.socweather.com/TempSvc.wsdl"
xmlns:tsxsd="http://schemas.socweather.com/TempSvc.xsd"
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">
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WSDL Example

<wsdl:types>

<xsd:schema targetNamespace="http://namespaces.socweather.com"
xmlns:xsd="http://www.w3.org/1999/XMLSchema">

<xsd:element name="GetTemp">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="City" type="string"/>
<xsd:element name="When" type="string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
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WSDL Example

<xsd:element name="GetTempResponse">
<xsd:complexType>
<xsd:all>
<xsd:element name="DegreesCelsius" type="integer"/>
</xsd:all>
</xsd:complexType>
</xsd:element>

<xsd:element name="GetTempFault">
<xsd:complexType>
<xsd:all>
<xsd:element name="errorMessage" type="string"/>
</xsd:all>
</xsd:complexType>
</xsd:element>
</xsd:schema>
</wsdl:types>
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WSDL Example


<wsdl:message name="GetTempRequest">
<wsdl:part name="body" element="tsxsd:GetTemp"/>
</wsdl:message>

<wsdl:message name="GetTempResponse">
<wsdl:part name="body" element="tsxsd:GetTempResponse"/>
</wsdl:message>

<wsdl:portType name="GetTempPortType">
<wsdl:operation name="GetTemp">

<wsdl:input message="ts:GetTempRequest"/>
<wsdl:output message="ts:GetTempResponse"/>
<wsdl:fault message="ts:GetTempFault"/>
</wsdl:operation>
</wsdl:portType>
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WSDL Example

<wsdl:binding name="TempSvcSoapBinding" type="ts:GetTempPortType">

<soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/>

<wsdl:operation name="GetTemp">

<soap:operation soapAction="http://www.socweather.com/TempSvc"/>
<wsdl:input>
<soap:body use="literal" namespace="http://schemas.socweather.com/TempSvc.xsd"/>
</wsdl:input>
<wsdl:output>
<soap:body use="literal" namespace="http://schemas.socweather.com/TempSvc.xsd"/>
</wsdl:output>
<wsdl:fault>
<soap:body use="literal" namespace="http://schemas.socweather.com/TempSvc.xsd"/>
</wsdl:fault>
</wsdl:operation>
</wsdl:binding>
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WSDL Example
<wsdl:service name="TemperatureService">
<wsdl:documentation>socweather.com temperature service
</wsdl:documentation>

<wsdl:port name="GetTempPort" binding="ts:TempSvcSoapBinding">

<soap:address location="http://www.socweather.com/TempSvc"/>
</wsdl:port>
</wsdl:service>
</wsdl:definitions>
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Directory Services
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Support discovery: enable applications,
agents, Web service providers, Web service
requestors, people, objects, and procedures
to locate each other
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White pages – entries found by name
Yellow pages – entries found by characteristics
and capabilities
A basic directory might be a simple database
(passive) or a broker/facilitator (active, that
provides alerts and recruits participants)
UDDI – both white pages and yellow pages,
but passive
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