Web services

Web Services
Michael Weiss
Carleton University
Web site for this tutorial:
www.scs.carleton.ca/~weiss/talks/mcetech06

Michael Weiss • Montreal Conference on eTechnologies • May 17-19, 2006
About Me
• PhD (1993), U of Mannheim
• Member of Strategic Technology
Group, Mitel (1994-1999)
• Assistant Professor, Carleton U
(since 2000)
• Areas of work: service-oriented
architecture, feature
interaction, patterns, business
models, open source
2

Topics Covered
• Service-Oriented Architecture
• Core standards (WSDL, SOAP, UDDI)
• Creating, deploying, and invoking web
services with Apache Axis
• Data mapping and business objects
• Service composition
• A look at some advanced issues
3

Web Services
• What are web services? In essence, a
technology for application integration based
on open standards (HTTP, XML)
• In what sense are they related to the Web
(capital “W” to refer to the WWW)?
• In fact, deploying web services over the web
is more of an artefact than a necessity ...
• What we care about is the web of services
(services assembled from other services)
4

Application Integration
5
Bus
Portal
Applications
User

Deﬁning Web Service
• Loosely coupled, document-based
• Application functionality packaged as a single
unit and exposed to the network
• Authentication service
• Flight departure monitoring service
• Mobile payment service
• The ﬁrst generation of web services were
“simple”, in the sense of non-composite, and
closed (over existing, trusted relationships)
6

Second Generation Services
• Complex, and aggregated from web services
provided by third parties (hence, open)
7
Rate Quotes
Transit Times Duty and
Taxation
Print Shipping
Labels
Shipping
<<uses>> Organizational
Boundaries
Service

Web of Services
• In second generation
services, applications
are assembled from
services dynamically
• Roles of service user
and provider blend
into what others call
servents (eg in P2P)
Service user
Service provider
Composite
services
8
Servent

Vision
• Build your applications
• Dynamically discover and orchestrate the
execution of services on the network
• Will be able to choose between alternative
implementations of the same service
Application
Services
Implementation
Interface
9
Semantics
on demand

Service-Oriented Architecture
• Objectives
• Implementation transparency (common
structure, neutral service description)
• Location transparency (no hard binding,
web-service agnostic interfaces)
• Roles
• Service Provider
• Service User
• Service Registry
10

Service-Oriented Architecture
11
Service
User
Service
User
Service
Registry
Service
Registry
Service
Provider
Service
Provider
Find
Bind + Invoke
Describe + Publish
UDDI
WSDLSOAP

Web Services Layers
12
Application Services
(transaction - eg ticket purchase, information - eg tourist guide)
Application ServicesApplication Services
((transactiontransaction -- egeg ticket purchase,ticket purchase, informationinformation -- egeg tourist guide)tourist guide)
SOAP, WSDL, UDDISOAP, WSDL, UDDISOAP, WSDL, UDDI
XML, HTTPXML, HTTPXML, HTTP
Collaboration Services
(orchestration, matchmaking, translation)
Collaboration ServicesCollaboration Services
(orchestration, matchmaking, translation)(orchestration, matchmaking, translation)
Utility Services
(security, billing, QoS, metering, routing, transactions, messaging)
Utility ServicesUtility Services
(security, billing,(security, billing, QoSQoS, metering, routing, transactions, messaging), metering, routing, transactions, messaging)

Topics Covered
• Core standards (SOAP,WSDL, UDDI)
13

SOAP
• Simple Object Access Protocol
• Cross-platform remote calls (de facto, while
technically also document exchange)
• Remote calls (typically) using HTTP as the
transport and XML as the encoding
• Designed to be as simple as possible, so to
make it easily understood and adopted
• But also complete enough to allow complex
data structures to be transmitted
14

SOAP Messages
• SOAP messages are XML documents usually
sent over HTTP with a certain format
15

SOAP Messages
• Components of a SOAP message
16
Envelope
Header Body
Payload Fault
1+
optional
required (one)
required (one or more)

SOAP Containers
• Container accepts incoming requests and
dispatches them to the service
• Translates between SOAP and the native
language of the service (Java, C#, ...)
• Clients only need to know the address of
the service, and messages it understands, but
not what language, platform, or location
17

SOAP Containers
18

Binding to a Service
• Clients get address and messages from a
WSDL description of the service
19

Client Proxy
• The binding process (dynamically) returns a
proxy to the remote web service
20

WSDL
• Web Service Description Language
• Neutral format for services to advertise
themselves on the network
• In future, we can choose between competing
providers of same service (price, ...)
• Components of a WSDL description
• Service > Ports > Operations > Messages
• Generating a WSDL description
21

WSDL Decription
• Components of a web service description
22
Description
Type
1+
Message
1+
Port Type
1+
Operation
1+
Binding
Style
1+
Service
Protocol Port
1+
Binding EndpointRequest Response
1+
optional
required (one)
required (one or more)

Interface
• Consider the interface for a Caching service
that allows users to cache content
23
public String findInCache(String key);
public void cache(String key, String content)
Caching
ﬁndInCache
cache

Messages
24
<wsdl:message name="findInCacheRequest">
<wsdl:part name="key" type="soapenc:string"/>
</wsdl:message>
<wsdl:message name="findInCacheResponse">
<wsdl:part name="result" type="soapenc:string"/>
</wsdl:message>

<wsdl:message name="cacheRequest">
<wsdl:part name="key" type="soapenc:string"/>
<wsdl:part name="content" type="soapenc:string"/>
</wsdl:message>
<wsdl:message name="cacheResponse"/>

Port Type
• Port Type
25
<wsdl:portType name="Caching">
<wsdl:operation name="cache" parameterOrder="key content">
<wsdl:input name="cacheRequest"

message="impl:cacheRequest"/>
<wsdl:output name="cacheResponse"

message="impl:cacheResponse"/>
</wsdl:operation>
<wsdl:operation name="findInCache" parameterOrder="key">
<wsdl:input name="findInCacheRequest"

message="impl:findInCacheRequest"/>
<wsdl:output name="findInCacheResponse"

message="impl:findInCacheResponse"/>
</wsdl:operation>
</wsdl:portType>

Service Binding
• Port Type
26
<wsdl:binding name="CachingSoapBinding" type="impl:Caching">
<wsdlsoap:binding style="rpc"

transport="http://schemas.xmlsoap.org/soap/http"/>
<wsdl:operation name="cache">
<wsdlsoap:operation soapAction=""/>
<wsdl:input name="cacheRequest">
<wsdlsoap:body use="encoded" encodingStyle="http://
schemas.xmlsoap.org/soap/encoding/" namespace="urn:Cache"/>
</wsdl:input>
<wsdl:output name="cacheResponse">
<wsdlsoap:body use="encoded" encodingStyle="http://
schemas.xmlsoap.org/soap/encoding/" namespace="urn:Cache"/>
</wsdl:output>
</wsdl:operation>

</wsdl:binding>

Service
• Service ties it all together: it deﬁnes one or
more ports, with binding and endpoint
27
<wsdl:service name="CachingService">
<wsdl:port name="Caching"

binding="impl:CachingSoapBinding">
<wsdlsoap:address location=

"http://localhost:9090/axis/services/Caching"/>
</wsdl:port>
</wsdl:service>

UDDI
• Universal Discovery and Directory Interface
• Service discovery protocol
• Kind of yellow pages which allows
applications to obtain information about
businesses and their web services
• Helps potential business partners to ﬁnd
each others’ business services
• A system will have some kind of directory,
but not always need all UDDI features
28

Service Directory
• A service directory allows publishers to
publish information about their services, and
users to locate them (and receive updates)
29
User
Provider
Directory
publish
delete
update
locate: ServiceInformation
subscribe
Service
Information
Service
Implementation

UDDI Structure
• UDDI stores service information in the
form of business entities, business services,
binding templates and technical models
30
Business
Entity
0,,*
Business
Service
Binding
Template
0,,*
0,,*
Technical
Model
0,,*0,,*

Topics Covered
31

Apache Axis
• Open source web service framework
• Client programming model of Axis provides
components for client to invoke a service
endpoint and receive the response message
• Server programming model based on a
listener for each transport protocol, a set of
message handlers, and service handlers
• A detailed discussion of its architecture can
be found at http://ws.apache.org/axis
32

Apache Axis Architecture
33
Tomcat Servlet Container
Apache
Axis
Servlet
Web
Service 1
Web
Service 2
Web
Service 3
Client

Architecture Adapter
• Frameworks such as Apache Axis allow you
to be fully web service-agnostic: to access
web services from Java use method calls via
architecture adapters (eg Java2WS)
34
Java B
eg .Net

Step by Step Guide to Axis
1. Provide a Java interface or class that
describes the service interface
2. Create WSDL using Java2WSDL tool
3. Create bindings through WSDL2Java tool
4. Implement the service interface
5. Deploy the service
6. Implement clients using generated stubs
35

Axis Artefacts and Flow
36
Service
Interface
WSDL
Java2WSDL
Service
Interface
Service
Locator
Service
Stub
WSDL2Java
Client-side files Server-side files
WSDD
Deploy
Service
Binding
Service
Skeleton
Service
WSDD
Undeploy
WSDL2Java
(optional)
Generated User-
defined

Provide a Java Interface
• Deﬁne the functionality you want to expose
as a web service using an interface
package cache;
public interface Caching {
public String findInCache(String key);
public void cache(String key, String content)
}
37
Caching
ﬁndInCache
cache
1

Interface Segregation
• Achieve greater coherence by limiting your
interfaces to related methods
• Implement multiple ports in one service
38
ContentProviderRetrieval
Billing
Billing
processBilling
Retrieval
retrieveArticle

Create WSDL from Java
• Create the WSDL (Caching.wsdl) from the
Java interface deﬁned earlier
• -o name of output ﬁle
• -l location of web service
• -n target namespace of the WSDL document
• -p mapping of namespace to packages
java org.apache.axis.wsdl.Java2WSDL
-o "cache/Caching.wsdl"
-l "http://localhost:8080/axis/services/Caching"
-n "urn:Cache" -p"cache" "urn:Cache"
cache.Caching
39
2
step2.sh

Create WSDL from Java
• Conversion to WSDL will also generate
XML types (using XML Schema) for all non-
primitive types references in the interface
• Supports bean classes, enumeration classes,
arrays, and holder classes (inout)
• No types in this simple example, but a more
complex one will be presented later
40

Create Bindings from WSDL
• While we can create our SOAP messages to
invoke a service at runtime (more later), ...
• ... it is generally better to use WSDL2Java to
convert a WSDL ﬁle into Java stubs
41
3

Create Bindings from WSDL
• Create a (static) client-side architecture
adapter using the WSDL2Java tool
• -o name of output ﬁle
• -N mapping of namespace to target package
• Adapter classes created
• public interface CachingService
• public class CachingServiceLocator
java org.apache.axis.wsdl.WSDL2Java -o .
-Nurn:Cache cache.stubs cache/Caching.wsdl
42
step3.sh

Implement Service Interface
• Implement the service by implementing the
Caching interface
43
4
public class Cache implements Caching {
protected LinkedHashMap cache = LinkedHashMap(100);
public String findInCache(String key) {
return (String) cache.get(key);
}
public void cache(String key, String content) {
cache.put(key, content);
}
}

• Separating interface from implementation is a
core element of loose coupling
Cache
ﬁndInCache
cache
Caching
ﬁndInCache
cache
Client
Interface-Implementation
Separation
44
Dependency Inversion
Principle

Deploy the Service
• In a Web Service Deployment Descriptor
(WSDD) tell Axis how to route requests to
the correct target (service) class
45
5
<deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:
java="http://xml.apache.org/axis/wsdd/providers/java">
<service name="Caching" provider="java:RPC">
<parameter name="className" value="cache.Cache"/>
<parameter name="scope" value="Application"/>
<parameter name="allowedMethods"
value="findInCache cache"/>
</service>
</deployment>

Start the Axis Server
• If the Axis engine is not running start it:
• as a servlet from within a servlet engine
(eg Tomcat): code in webapps/axis
• or as a standalone server (here ... and for
testing and simple applications)
• Invoking the standalone SimpleAxisServer
46
java org.apache.axis.transport.http.SimpleAxisServer
-p 9090
axis.sh

AdminClient
• Make the service available to clients by
deploying it using the AdminClient
• If deploying to the standalone Axis server,
also supply the port number
• Now we are ready to invoke the service
47
> java org.apache.axis.client.AdminClient
-p 9090 deploy.wsdd
Processing file cache/deploy.wsdd
<Admin>Done processing</Admin>
admin.sh

Create the Client
• There are two ways to invoke a service
• Dynamic client: create a Call object for
each method at runtime
• Static client: generate a static proxy from
the WSDL description
48
5

Dynamic Client
49
public class DirectCachingClient {

public static void main(String[] args) {

try {

String endpoint =

"http://localhost:9090/axis/services/Caching";

Service service = new Service();

Call call = (Call) service.createCall();

call.setTargetEndpointAddress(new java.net.URL(endpoint));

call.setOperation("findCache");

call.setReturnType(XMLType.XSD_STRING);

String ret = (String) call.invoke(

new String[] {"theAnswer"});

System.out.println("Received: " + ret);

} catch (Exception e) {

System.err.println("Exception: " + e);

}

}
}

Static Client
50
public class CachingClient {
try {
CachingService service = new CachingServiceLocator();
Caching port = service.getCaching();
// to access the service at a different endpoint:
// Caching port = service.getCaching(url);
String answer = port.findInCache("theAnswer");
if (answer == null) {
port.cache("theAnswer", "42");
}
answer = port.findInCache("theAnswer");
System.out.println(answer);
}
}
}

Setting up Axis
• Download Apache Axis from website
• http://ws.apache.org/axis
• Latest stable release is axis-bin-1_4.zip
• Install in a directory and put the .jar ﬁles in
the axis/lib directory into your class path
• In my Unix shell, I would say
51
set AXIS_HOME="$home/axis"
set CLASSPATH="${CLASSPATH}:$AXIS_HOME/lib/axis-ant.jar"
set CLASSPATH="${CLASSPATH}:$AXIS_HOME/lib/axis.jar"
...

Axis User Guide
http://ws.apache.org/axis/java/user-guide.html
52
for more information

Case Study: Bookstore
• As a larger example, consider an application
for ordering books from multiple stores
• This application needs to provide a portal
through which users can place orders
• It invokes the (different?) order processing
services provided by the bookstores
• First, the big picture ...
53

WSDL Repository/
UDDI Registry
Bookstore
1
Bookstore
2
Bookstore
3
Axis Engine
OrderProcessing
Stub 1
OrderProcessing
Stub 1
WSDL
Client
Stubs
Portal
OrderProcessing
Stub(s)
Deploy
Invoke
Actual
calls
1
1
2
3
4
5
Actors and Interactions
54

Interface
• The bookstore exposes an OrderProcessing
interface through which to place orders
• Orders can also be canceled given their OID
55
public interface OrderProcessing {
public String processOrder(String customer, String[] isbns,

int[] quantities);
public void cancel(String oid);
}
Bookstore
processOrder
cancel
OrderProcessing

WSDL and Stubs
• Generate the WSDL from the interface
• Generate client stubs from the WSDL
56
step2.sh bookstore_v1 OrderProcessing Bookstore
bookstore_v1
OrderProcessing.wsdl
step3.sh bookstore_v1 OrderProcessing Bookstore
bookstore_v1.stubs
OrderProcessingServiceLocator
OrderProcessingService
OrderProcessing
OrderProcessingStub

Service (1)
• Much of the following code is stubbed out,
as it is not related to web services
57
public class Bookstore implements OrderProcessing {
// ...
public String processOrder(String customer, String[] isbns,

int quantities[]) {
String oid = generateOid();
Order order = new Order(customer, isbns, quantities);
orders.put(oid, order);
// do whatever else to initiate payment processing
// and shipping (not shown ...)
return oid;
}

Service (2)
• And to ﬁnish off ...
58

// ...
public void cancel(String oid) {
Order o = (Order) orders.get(oid);
if (o != null) {
orders.remove(oid);
// do whatever is needed to cancel the order
}
}
private String generateOid() {
return "o" + nextOid++;
}
}

Deploy the Service
• Deployment descriptor for the bookstore is
similar to that for the Caching service
59
<deployment xmlns="http://xml.apache.org/axis/wsdd/"
xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">
<service name="OrderProcessing" provider="java:RPC">
<parameter name="className" value="bookstore_v1.Bookstore"/>
<parameter name="scope" value="Application"/>
<parameter name="allowedMethods" value="processOrder cancel"/>
</service>
</deployment>

Client
60
public class BookstoreClient {

try {

OrderProcessingService service =

new OrderProcessingServiceLocator();

OrderProcessing port = service.getOrderProcessing();

String oid = port.processOrder("joe@doe.com",

new String[] {"123456", "732541"},

new int[] {2, 1});

System.out.println("order " + oid + " placed");

port.cancel(oid);

System.out.println("order " + oid + " canceled");

}
}
}

Topics Covered
61

Business Objects
• Represent highly cohesive business concepts
such as order, line item, or address
• Also known as data objects or beans, ie they
only contain data access operations
• Business objects often collected in groups
• But rich object structures are in conﬂict
with the ﬂat nature of web services
• Focus of web services on loose coupling, so
unlike CORBA or RMI no OO focus
62

Taking Orders now!
• Business objects can contain primitive and
complex data as in the Order example
63
Order
customer: String
lineItems: LineItem[]
setCustomer
getCustomer: String
setLineItems
getLineItems: LineItem[]
LineItem
isbn: String
quantity: int
setIsbn
getIsbn: String
setQuantity
getQuantity: int
*

Data Mapping to XML
• Basic mapping deﬁned by JAX-RPC spec
• Mapping of primitive types
• Complex types that follow the JavaBeans
convention (BeanSerializer)
• Arrays and some Collection types
• Exceptions
• Key consideration is the interoperability
between SOAP implementations !
64

Mapping of Primitive Types
• Primitive types
deﬁned in
standard SOAP
encoding
65

Complex Types
• Axis can serialize and deserialize any classes
that follow the JavaBeans convention ...
• ... without requiring you to write any code !
• Simple properties
• setAddress and getAddress
• Indexed properties (arrays of values)
• Customer[]
• setCustomers and getCustomers
66

Bean Mapping
• Need to deﬁne a bean mapping in WSDD by
adding a <beanMapping> tag
• Maps a Java bean to an XML qualiﬁed name
(qname) associated with a namespace
<beanMapping qname="ns:Order" xmlns:ns="urn:Bookstore"
languageSpecificType="java:bookstore_v2.Order"/>
67

Orders in XML
• XML schema for the Order type
68
<complexType name="Order">
<sequence>
<element name="customer" type="soapenc:string" .../>
<element name="lineItems" type="impl:ArrayOfLineItem" .../>
</sequence>
</complexType>
<complexType name="LineItem">
<sequence>
<element name="isbn" type="soapenc:string" .../>
<element name="quantity" type="xsd:int" .../>
</sequence>
</complexType>

Order (simple)
• The Java Beans convention distinguishes
simple and indexed properties
public class Order {

protected String customer;

public String getCustomer() {

return customer;

}

public void setCustomer(String customer) {

this.customer = customer;

}
// ...
69

Order (indexed)
• In the Order class, line items are indexed
// ...

private LineItem[] lineItems;

public LineItem[] getLineItems() {
return lineItems;
}
public void setLineItems(LineItem[] lineItems) {
this.lineItems = lineItems;
}
}
70

Arrays and Collections
• Some Java collections (Vector, Hashtable, ...)
have serializers, but interoperability between
SOAP implementations in not guaranteed
• Most reliable way, thus, is to use arrays
<complexType name="ArrayOfLineItem">
<complexContent>
<restriction base="soapenc:Array">
<attribute ref="soapenc:arrayType"
wsdl:arrayType="impl:LineItem[]"/>
</restriction>
</complexContent>
</complexType>
71

Bookstore
• New interface to our bookstore that uses
business objects (ie Order)
72
public class Bookstore implements OrderProcessing {

// ...
public String processOrder(Order order) {
String oid = generateOid();
orders.put(oid, order);
// do whatever else to initiate payment processing
// and shipping (not shown ...)
return oid;
}

// ...
}

Bookstore Client
public class BookstoreClient {
try {

OrderProcessingService service =

new OrderProcessingServiceLocator();

OrderProcessing port = service.getOrderProcessing();

Order order = new Order("joe@doe.com", new LineItem[] {

new LineItem("123456", 2),

new LineItem("732541", 1)

});
String oid = port.processOrder(order);
System.out.println("order " + oid + " placed");
port.cancel(oid);
System.out.println("order " + oid + " canceled");
}
}
}
73

WSDD for Bookstore
• Deﬁne complex types on which the service
implementation relies in the WSDD
• namespace (urn:Bookstore)
• serializers (beanMapping to ns:Order)
<deployment xmlns="http://xml.apache.org/axis/wsdd/"
xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">
<service name="OrderProcessing" provider="java:RPC">

<parameter name="className" value="bookstore_v2.Bookstore"/>

<parameter name="allowedMethods" value="processOrder cancel"/>

<beanMapping qname="ns:Order" xmlns:ns="urn:Bookstore"

languageSpecificType="java:bookstore_v2.Order"/>

<beanMapping qname="ns:LineItem" xmlns:ns="urn:Bookstore"

languageSpecificType="java:bookstore_v2.LineItem"/>
</service>
</deployment>
74

Topics Covered
75

Business Processes
• Means by which one or more activities are
accomplished in an operating business
• Business process models include
• Roles of users
• Deﬁnition of activities
• Can be represented diagrammatically as as
activity diagrams, use case maps, ...
• Concerned with structure and interfaces
76

Business Process Components
• Business processes model business
operation, vs business objects which model
(data) entities within a business
• Purely look at a business from the aspect of
the activities the business conducts
• Activities can be composed into larger
business processes, and may be business
processes themselves, or web services
• We are concerned with composition
77

Ordering Process
78
Select Products
to Order
Enter Customer
Information
Submit Product
Order
Create Order
Remove from
Warehouse
Ship ProductsReceive
Products
Customer Store

Business Processes in Practice
• Business process concepts overlap with
existing architectures and styles
• The tended to be part of the custom logic
outside the business object model
• Business process implementations differ
largely between organizations
• Large business processes often span multiple
companies (need to integrate processes)
• Motivates need to support ﬂuidity
79

Business Process Modeling
• Several standards for modeling and
representing business processes
• Business Process Execution Language (BPEL)
• IBM, Microsoft, BEA
• Business Process Modeling Language (BPML)
• XML-based explicit representation of
business process ﬂow model
80

Marginalized Objects
• We have discussed this before ...
• Applied to business processes this means
that business processes require a flat
component model with interface definition
and implementation
• Each interface is implemented as the
composition of web services
• Also applied to flow logic by moving it out
from the programming language (BPEL !)
81

Process Logic in BPEL
Client Web Service
businessProcess()
BPEL Container
invoke()
receive()
reply()
wait()
terminate()
sequence()
pick()
flow()
BPEL Flows
82

Business Process Pattern
<<interface>>
BusinessActivity
run()
BusinessActivityImpl
run()
<<interface>>
BusinessProcess
run()
ActivitySequence
next()
get()
Data
get()
set()
BusinessProcessImpl
run()
83

Participants
• BusinessProcess
• Interface to the business process
• BusinessProcessImpl
• Logic of the business process, which can
be a simple ActivitySequence
• ActivitySequence
• Sequence of business activities that must
occur before process is complete
84

More Participants
• Data
• Captures side effects of business activities
(in this pattern: a shared data pool)
• BusinessActivity
• Unit of work in the business process,
which may itself be a process, a service, or
just a single method on an object
85

Ordering Process
• Customer submits an order
• Business process puts order into data pool
• ... determines if products exist (success) in
warehouse, and reserves them
• ... checks state of data pool and launches
create order business activity
• ... notiﬁes warehouse staff to ship
• ... returns an order identiﬁer to the user
86

Product Order Process
<<interface>>
BusinessActivity
setData()
run()
isComplete()
getReturnValue()
isSuccessful()
CreateOrder
run()
RemoveProduct
Quantity
run()
ActivitySequence
next()
get()
ProductOrderImpl
createProductOrder()
run()
ShipProducts
run()
BusinessProcess
run()
ProductOrderWeb
Service
createProductOrder()
Hashtable
87

Topics Covered
88

Advanced Issues
89
Workﬂows
Mobile
Services
QoS/Policy
Security
Coordination
Semantics
Web
Services

Client-Server
Desktops
N-Tier
Spaces
Embedded Networks
Agents
Web services
Grids
P2P
Distributed Objects
}
Social Computing
Utility
Semantic Web
Coordination Media
} Semantic Grid
} MirrorWorld
1990's
2000's
20??'sUbiquitous Computing
Convergence
90

Summary
• Concepts
• Service-oriented architecture, core standards,
data mapping, and business processes
• Principles
• Interface/implementation separation, top-down/
bottom-up design, interface segregation, ...
• Patterns
• SOA,Architecture Adapter, Service Directory,
Business Object, Service Composition
• Tools
• Apache Axis
91

Further Reading
• Taylor, From P2P toWeb Services and Grids:
Peers in a Client/Server World, Springer
• Monday,Web Service Patterns,APress
• Pashtan, Mobile Web Services, Cambridge
• Sotomayor, Globus Toolkit 4: Programming
Java Services, Morgan Kaufmann
• Papazoglou,Web Services and Cross
Enterprise Computing,Addison-Wesley
92

Web services

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