Components and Architecture. Page 2 Building Reliable Component-based Systems Chapter 3 -...

Components and Architecture

Building Reliable Component-based Systems

Chapter 3 - Architecting Component-Based Systems

The Software Architecture“The software architecture of a program or computing system is the structure or structures of the system, which comprise software components [and connectors], the externally visible properties of those components [and connectors] and the relationships among them.”

Architecture Design Process Can be seen as a function that:

Takes a requirement specification as input. Generates an architectural design as output. Is not an automated process, necessitating great effort

and creativity from the involved software architects.

Is comprised of three steps: Functionality-based design. Assessment of the quality attributes. Architecture Transformation.

General software architecture design process

Applicationarchitecture

Requirementspecification

Requirementselection

Functionality-basedarchitectural design

(Partial)requirementspecification

Estimate qualityattributes

Architecturetransformation

QA-optimizingsolutions

MoreRequirements?

not OK

Functionality-based Design The design process starts with functionality-

based design and consists of four steps: Defining the boundaries and context of the

system. Identification of archetypes. Decomposition of the system into its main

components. The first validation of the architecture by

describing a number of system instances.

Assessment of the quality attributes

The second phase is the assessment of the quality attributes in which: Each quality attribute is given an estimate. If all estimated quality attributes are as good or

better than required, the architectural design process is finished.

If not the third phase of software architecture design is entered: architecture transformation

Architecture Transformation Is concerned with selecting design solutions to

improve the quality attributes while preserving the domain functionality. The design is again evaluated and the same process is

repeated if necessary. The transformations (i.e. quality attribute optimizing

solutions) generally improve one or some quality attributes while they affect others negatively.

Architecture-driven Component Development

The goal for the embodiment phase of design is to either build or select components and connectors that possess the quality attributes identified during the architecting phase of development.

Three types of components: Custom built components Reusable components Commercial components

Custom Components Demands both time and money. Are most likely to pay off in cases of software that are:

Very unusual Safety critical Highly secure

The component assembly will possess the quality attributes it was designed around.

Pre-existing Components There are two main classes of pre-

existing components: Reusable components Commercial components

Is a fundamentally different problem than custom design. The requirements to use specific

components and component frameworks drive the architecture.

Reusable Components Can exist on a wide scale of reusableness

within any organization. They must be adapted;

In most cases it will be necessary to create adaptors, often referred to as glue code.

Are developed with reuse in mind. Product line development exemplifies the

use of pre-planned reusable components.

Commercial Components Introduce a large degree of uncertainty. Tend to be

Complex Idiosyncratic Unstable

Component-driven Architecture Development

Constraints due to the use of pre-existing components: Design freedom is limited to component

selection. Sufficient information about how a component

will behave is not generally provided. Component properties must be verified. The framework into which components are to be

plugged influences the architecture and the process by which the system is designed.

Such components can not be optimized.

Component-driven Architecture Development

It is expected that more reliable systems will be produced, with greater speed and at lower expense due to the restrictions on design freedom.

Chapter 4 - Component Models and Technology

Chapter 4Chapter 4

Component Models and TechnologyComponent Models and Technology

Windows purpose : moving integration between applicative functions to O.S. level

it needs effective communication mechanisms between applications

Excel-generated pie chart embedded in a Word document displayed in a PowerPoint presentation

Different applications need to share data or procedures

A little history: starting with evolution of Microsoft approach

clipboard

ActiveX

DDE (Dynamic Data Exchange)

What if spreadsheet and word processor need to share data?

Microsoft comes out with Dynamic Data Exchange (DDE), circa 1989 Lets different Windows programs share data through links Suppose some spreadsheet data were linked into word

processor When you changed data in spreadsheet, the new data

would appear in word processor Limitation: you couldn’t update the data in the word

processor; you had to invoke the spreadsheet to update the date there

Worse, links were fragile and would break if you moved data files around in file system

Object Linking and Embedding OLE (circa 1991) A way for Windows to create documents containing objects from other

programs. Embedding lets users copy a snapshot of data into word

processor and save it there• The objects are components (word processor document, spreadsheet,

picture) can be linked together and pass messages to each other according to a standard protocol, Object Linking and Embedding (OLE).

Components containers can be re-used by many applications to for E.g. place a chart from Excel and a slide from PowerPoint into a Word document

But OLE is a platform-specific solution.

OLE Technology (circa 1993)

A set of APIs to create and display a (compound) document Now possible to share code as well as data

Component Object Model (COM) COM now includes OLE as part of a larger concept

OLE becomes a set of standard COM interfaces COM protocols let components connect to origination

program: E.g. word processor can tell spreadsheet, “the user just

clicked on the spreadsheet, so start yourself up, look for data here, and let me know when you’re done.”

If the user decides to edit the embedded data, Windows activates the originating application and loads the embedded document

For example, a desktop system might include a picture in a bitmap editor using OLE

Component Object Model

The component object model (COM) provides a specification for using components produced by various vendors within a single application running under the Windows operating system.

COM objects can be created with a variety of programming languages. Object-oriented languages, such as C++, provide programming mechanisms that simplify the implementation of COM objects.

not an object-oriented language but a binary standard

Microsoft COM

COM encompasses: COM interfaces (implemented as COM objects) COM Object locations are stored in registry

a set of mechanisms for registering and passing messages between COM interfaces.

COM interfaces are defined in Microsoft Interface Description Language (MIDL).

COM components in Registry

Windows has many COM components.Registered under “\HKEY_CLASSES_ROOT\CLSID” on the registry.

OLE Extensions (OCX)

With Windows 95 came a new standard: OCX (OLE Custom eXtension component) A piece of code, smaller than application program,

but with its own user interface Let users bundle OCX controls to form customized

applications (component composition)

OCX Charting and Graphing example code for Visual Basic

• When installing the ProEssentials product, the setup program installs the ProEssentials DLL and OCX Charting interfaces into the system directory.•The setup program also registers the OCX Charts with the operating system, which prepares Visual Basic for inclusion of ProEssentials components

OCX Charting and Graphing example code for Visual Basic

the [Components] dialog and places those items selected into Visual Basic's ToolBox as shown.

ActiveX (circa 1996)

Active X, like Java Applets, supports Internet xistributed computing. ActiveX components communicate with each other via events.

Writing a program to run in the ActiveX environment creates a self-sufficient program that can run anywhere in ActiveX network

This component is known as an ActiveX control, and is often used to attach a program to a web page

Distribution option spectrum

Increasing costand effort

Server: Interaction controlData validationServicesDatabase

Client: Presentation

Server:DatabaseServer: Services

Database

Client: PresentationInteraction controlData validation

Client: PresentationInteraction controlData validationServices

The Thick client option is where the server simply provides data management and application services are implemented on the client by using ActiveX component

Thick client

ActiveX Comp

Three-tier architecture for an Internet banking system

31Chapter 18 Distributed software engineering

ActiveX - implementation

An ActiveX control can be created using one of several languages or development tools, including C++ and Visual Basic, or with scripting tools such as VBScript.

ActiveX controls originally were Windows only Other vendors later provided Mac and Unix/Linux support

for ActiveX Security issues: ActiveX controls have full file access (no

sandbox) Can be signed for authentication

Creating ActiveX Component

Creator

Creator Developer

End User

Design Time Run Time

No Customization

Customization

For each component The Component Creator can enable Customization (where developer can insert code in the design time for customization) by defining

• Events (handling user interface ) ActiveX component Could be mapped to internal User Contol events by using RaiseEvent . Eg. Button Click, Mouse Down

• Properties Using Get and Let

•mapped to internal UserContol properties. E.g button Caption

•New Property

• Methods New methods

Example Creating ActiveX Component

Example Mapping Events (written by creator)

Get: just returns the current string found in the Caption property of the command button Let: takes a new string and just assigns it to the Caption property of the command button

Example Mapping Propriety

Using ActiveX Component

At design time developer could write the following code to customize the Bitton Component

nn= Bitton1.Caption .. This will call the Get sub in to nn

Bitton1.Caption = “ok” …. This will call the Set subPrivate Sub Bitton1_Click ()

Msgbox (“hello world”)End Sub

Private Sub Bitton1_MouseDown (Button As Integer, Shift As Integer, X As Single, Y)

Msgbox (“I am moving”)

End Sub

Tax Components

For this SC what are the events, properties, methods For no customization (using it as it is created) For customization

Enter Amount

Enter Tax %

Result

Show Result Clear

Tax Components

(not customizable) Events such as Show Result , Clear event are internal

Private Sub Command1_click ()

TextField3.value = TaxTotal()

End Sub

TextField3.text = “ “

End Sub

Enter Amount

Enter Tax %

Result

Show Result Clear

Tax Components

(simple customizable) Mapping property Properties ResultColor done by creator

Property Get ResultColor ()ResultColor = TextField.color

End Properity

Property Let ResultColor (cc)TextField.color = cc

End Properity Using this Property by simply done by designer

TaxComponent1. ResultColor = “red”

Enter Amount

Enter Tax %

Result

Show Result Clear

Tax Components

(advanced customizable) Events such as button click

RaiseEvent Click

End Sub

Enter Amount

Result

Show Result Clear

Special Function

Tax Components

(advanced customizable) Properties Such as caption

Property Get caption ()

caption = button3.caption

End Property

Property Let caption ()

button3.caption = tt

End Property

Enter Amount

Result

Show Result Clear

Special Function

Tax Components

(advanced customizable) At design time a designer wants to add new

function AmountAfterTax to button 3

TaxComponent1.Caption = “ Amount After Tax”

Private Sub TaxComponent1_Click()AmountAfterTax=Textfield1.value*TaxPer/100)

Result = AmountAfterTax

End Sub

Enter Amount

Result

Show Result Clear

Special Function

Tax Components

At Run time

Enter Amount

Result

Show Result Clear

Amount After Tax

Microsoft Visual Studio (clothes ordering)

Using at Design Time

Business Component

For Customization:

LOGO, Address, Title, colors, font, etc

GUI Component

Grid entry table

For customization:

Number of rows, columns, header’s captions, borders, etc

Order Form

The JavaBeans API

JavaBeans API makes it possible to write component software in Java Components are self-contained, reusable software units that can be

visually composed into composite components, applets, applications, and servlets using visual application builder tools.

A Java Bean component may have a visual representation, for example, a user-interface component, or may be non-visual, for example, a database connectivity component .

Java Bean components communicate with each other by sending events.. Components have properties which can be set by the programmer to achieve some customisation.

Enterprise JavaBeans (EJB) is an extension of the Java Bean model that provides a mechanism for encapsulating a Java Bean component

Features of JavaBeans Support for introspection

Allows development tools to query a component to determine member variables, methods, and interfaces

Support for customization so that when using an application builder a user can customize

the appearance and behavior of a bean Support for events (when beans want to intercommunicate)

Notification of a change in state User activities (typing, mouse actions, …)

Support for properties both for customization and for programmatic use Properties can be customized at design-time using property editor

Support for Methods Invoked to execute component code

Support for persistence so that a bean can be customized in an application builder and

then have its customized state saved away and reloaded later implement Serializable or Externalizable

e.g. public class Button implements java.io.Serializable { ... }

Background: What Are Beans?

• Java classes that follow certain conventions

– Must have a zero-argument (empty) constructor

– Should have no public instance variables (fields): use accessor methods instead of allowing direct access to fields

– Persistent values should be accessed through methods called getXxx and setXxx

Why You Should Use Accessors, Not Public Fields

You can put constraints on values

public void setSpeed(double newSpeed) {

if (newSpeed < 0) {

sendErrorMessage(...);

newSpeed = Math.abs(newSpeed);

speed = newSpeed;

– If users of your class accessed the fields directly, then

they would each be responsible for checking constraints

Visually Manipulated, Builder Tools (BDK...)

Property Sheet

Method Tracer

BeanBoxToolBox

Support Multi-tiered Application Model

Client tier Web clients,

Applets, Applications

Web tier Business tier EIS-tier

J2EE Architecture

JSP Using Beans: Basic Tasks• jsp:useBean<jsp:useBean id="beanName“ class="package.Class" />

e.g<jsp:useBean id="book1" class="coreservlets.Book" />

• jsp:getProperty– This element reads and outputs the value of a bean property. <jsp:getProperty name="beanName“ property="propertyName" />

e.g. <jsp:getProperty name="book1" property="title" />is equivalent to the following JSP expression<%= book1.getTitle() %>

jsp:setProperty– This element modifies a bean property. It is normally used as follows:<jsp:setProperty name="beanName“ property="propertyName"e.g.

<jsp:setProperty name="book1“ property="title“ value="Core Servlets and JavaServer Pages" />

is equivalent to the following scriptlet<% book1.setTitle("Core Servlets and JavaServer Pages"); %>

UserInfo

Component DiagramWeb

Userinfo javabean example

Client

HomeInterface

HomeStub

RemoteInterface

EJBStub

EJB Server

EJB Container

Home Interface

EJBHome

Remote Interface

EJB Object

Bean Class

Any enterprise bean must define two interfaces 1- Home interface – The Home Stubs extends EJBHome which defines a

bean’s “life cycle” methods, eg. create bean, remove bean, find bean, etc.

• Initially A client initiate interacts with its server object via a container interface: the container calls the bean’s life cycle methods to create bean instance .

Client

HomeInterface

HomeStub

RemoteInterface

EJBStub

EJB Server

EJB Container

Home Interface

EJBHome

Remote Interface

EJB Object

Bean Class

2- Remote interface- defines a bean’s external interface- EJB Stub extend EJBObject (which in turn extends

java.rmi.Remote)•Clients never interact directly with a bean class, they use EJB stubs (which connect to “containers” which call the bean class interface using RMI)

Client

HomeInterface

HomeStub

RemoteInterface

EJBStub

EJB Server

EJB Container

Home Interface

EJBHome

Remote Interface

EJB Object

Bean Class

- Bean ClassThe java class that actually implements the bean’s external interface, e.g. the bean class provides implementations for the bean’s “business methods”

CORBA• The Common Object Requesting Broker Architecture

(CORBA) is a standard defined by the (Object Management Group OMG); that enables software components written in multiple computer languages and running on multiple computers to work together.

• It forms part of a larger model, Object Management Architecture (OMA) that defines at a high level of abstraction

A CORBA component provides functionality via an interface defined in the CORBA Interface Definition Language, and interacts with other components only via that interface.

It is a system software that provides interoperability services for applications, such as distributed object computing, and hides some aspects of hardware and operating system differences in heterogeneous, distributed environment

CORBA architecture

Interface Definition Language (IDL) Similar to interfaces in Java or C++ abstract

classes Defines protocol to be used between devices Allows “wrappers” for legacy systems

Object Request Broker (ORB) Middleware establishing client/server

relationship Allows transparent invocation of methods Intercepts calls, and deals with them

1- Servant object publish its interfaces using DSI to ORB2- ORB install locally at client machine all its interfaces {run-time library}, at IDL STUB3- The {client} calls (using DII) the - 'IDL-stub to perform some task 4- The stub transmits parameters over the network5- Once the request is reconstructed by 'ORB', it has to interpret it 6. 'ORB‘ will Find an object that can implement the request, pass it the parameters, invoke its

method to the object’s {server- skeleton} 6- the skeleton (server-side interpreter, it need to know the method signature: a. the method name, and

b. the type of input.. 7- The proxies and skeletons provide the object-specific information needed8- the skeleton returns the results to the caller in a reverse manner so that the IDL stub can read the

result and pass it to the client object

1. Facets: Facets are interfaces that a component provides. For instance, the Stock_Quote interface provides a stock price

2- Receptacles:. Receptacles provide a standard way to specify interfaces required for the component to function correctly. The Stock_Exchange component uses the SEC (Securities and Exchange Commission) interface to function correctly.

Example: CORPA component

3- Event sources/sinks: Components can also interact by monitoring asynchronous events. These loosely coupled interactions, are commonly used in distributed applications. A component declares its interest to publish or subscribe to events by specifying event sources and event sinks in its definition (subscribe ). For example, the Stock_Exchange component can be an event sink that processes Buy_Offers and Sell_Offers events and it can be an event source that publishes Price_Change events.

The COM Programming ModelA scalable programming model

ClientClient ComponentComponentCOMCOM

Client ProcessClient Process ServerServer ProcessProcess On the same machine On the same machine (component – (component – component)component) Fast, secure LPCFast, secure LPC

DCOM extends COM to support communication among objects on different computers

What is DCOM?

Com Object Creation

Proxy & Stub

COM server

Three ways in which a client can access COM objects provided by a server:

• In-Process Server (if COM object has been previously activated at the client machine)

• Local Object Proxy (if COM object resides at the client machine)

• Remote Object Proxy (if COM object resides at a server machine)

How DCOM Works: Example

Client on Windows machine Server (CustServer) on Solaris

UNIX machine Client needs to call ChangeAddress

method of the server’s ICustInfo interface/class

Both client and server are C++ modules

How DCOM Works: ExampleStep 1: Client Initiation

COMCOMLibraryLibraryCOMCOM

LibraryLibrary

CLSID_CustServerIID_ICustInfo

ClientClientClientClient

CoInitializeCoCreateInstanceEx

Call Stack

Description of Slide:COM Library - Collection of routines (API) implemented by COM. Routines typically begin with Co…

Process:The first thing any COM client or server calls is CoInitialize. To connect to the server (client side), the client then calls CoCreateInstanceEx, passing the CLSID of the server it wishes to call plus all of the desired Interface IDs.

Description of Slide:COM Library - Collection of routines (API) implemented by COM. Routines typically begin with Co…

Process:The first thing any COM client or server calls is CoInitialize. To connect to the server (client side), the client then calls CoCreateInstanceEx, passing the CLSID of the server it wishes to call plus all of the desired Interface IDs.

How DCOM Works: ExampleStep 2a: Server Activation (Client Side)

Call Stack

LibraryLibrary SCMSCMSCMSCM

CLSID_CustServerCLSID_CustServer

ProxyProxyProxyProxy

IUnknownIUnknown

ClassClassTableTable

RegistryRegistry

Process:•The CoCreateInstanceEx call is relayed to the local SCM (Service Control Manager ) , • which first checks the Class Table to see if the requested object is already running. •If not, it looks in the registry, using the CLSID_CustServer, to find out whether the server is local or remote. •If it is remote, it gets the name of the server machine to contact.•A “default” proxy is loaded which exports the IUnknown interface.

How DCOM Works: ExampleStep 2b: Server Activation (Server Side)

Call Stack

LibraryLibrary SCMSCMSCMSCM SCMSCMSCMSCM

CoInitializeCoRegisterClassObject

Call Stack

CLSID_CustServerCLSID_CustServer

ServerServerServerServer

ClassFactory

IUnknownIUnknown

IClassFactoryIClassFactory

IUnknownIUnknown

StubStubStubStub

LibraryLibrary

RegistryRegistry

RegistryRegistryProcess:On the remote machine, the SCM repeats the process of checking in the Class Table and Registry. If the object is already running, it skips to the next step. If not, it finds out the name of the executable from the registry, and starts that module.The class and the pointer to the ClassFactory are entered in the Class Table.A “default” stub is loaded into the server’s process which will facilitate communication to the client.

Process:On the remote machine, the SCM repeats the process of checking in the Class Table and Registry. If the object is already running, it skips to the next step. If not, it finds out the name of the executable from the registry, and starts that module.The class and the pointer to the ClassFactory are entered in the Class Table.A “default” stub is loaded into the server’s process which will facilitate communication to the client.

How DCOM Works: ExampleStep 3: The Class Factory

Call Stack

ServerServerServerServer

Call Stack

IUnknownIUnknown

ICustInfoICustInfo

IID_IUnknown

ClassFactory

IUnknownIUnknown

StubStubStubStub CCustInfo

LibraryLibrary

RegistryRegistry

Process:Once the server has started, the system calls a method on the IClassFactory interface called CreateInstance. This method creates a new instance of the CCustInfo class, so that it is ready to accept later calls.

How DCOM Works: ExampleStep 4: Multiple QueryInterface

Call Stack

IID_ICustInfo

ClientClientClientClientProxyProxyProxyProxy

IUnknownIUnknown

StubStubStubStubServerServerServerServer

IUnknownIUnknown

ICustInfoICustInfo

ClassFactory

CCustInfo

LibraryLibrary

RegistryRegistry

Process:Once the server has started and the Class Factory has created a new instance for us, the system will call the QueryInterface function of the server object for all of the Interface IDs (IIDs) supplied in the CoCreateInstanceEx call. QueryInterface will either return interface pointers or errors if the interface requested is not supported.

Step 5: Proxy/Stub loading

Call Stack

pCustInfoClientClientClientClient

IUnknownIUnknown

ICustInfoICustInfo

ClassFactory

CCustInfo

LibraryLibrary

ICustInfo_ProxyICustInfo_ProxyICustInfoICustInfo

ICustInfo_StubICustInfo_Stub

RegistryRegistry

IID_ICustInfoIID_ICustInfoIID_ICustInfoIID_ICustInfo

Process:Once an interface pointer has been located, it must be “marshalled” over to the client side. At this time, using the IID as a key to the registry, the system loads a special pair of modules to act as proxy and stub for future calls. And register it

How DCOM Works: ExampleStep 6: Method Call

CoInitializeCoCreateInstanceExpCustInfo->ChangeAddress

Call Stack

ClientClientClientClientProxyProxyProxyProxy

IUnknownIUnknown

ICustInfoICustInfo

ClassFactory

CCustInfo

LibraryLibrary

ICustInfo_ProxyICustInfo_ProxyICustInfoICustInfo

ICustInfo_StubICustInfo_Stub

RegistryRegistry

Process:Once a pointer to the ICustInfo interface has been obtained, the program can call methods as though the server module is local. The client simply calls the ChangeAddress method of the ICustInfo interface (referenced by pCustInfo), passing all of the necessary parameters.

Location Transparency

COM Object locations are stored in registry Applications make calls using the globally

unique CLSID. Path to COM server, or remote computer to

run DCOM server is not needed by the application. Location transparent –server and client can be

anywhere since they share the same network protocol

Language Neutrality

Various languages can be used to create components. VB, Delphi for rapid development VC++, Java for advanced development E.g. A component build in VB can be imported to

VC++ Even more languages can be used to use

COM components Additionally scripting languages like VB Script,

JScript

Connection Management Low Bandwidth

Header is 28 bytes over DCE-RPC Keep-Alive Messages bundled for all connections between

Machines

COM employs an efficient pinging protocol to detect if clients are active

COM uses reference counting mechanism to do garbage collection Internal component’s reference counter –increments

when client establishes connection with component Decrements counter –if client releases its connection If counter reaches zero –component can free itself

preferred transport protocol : UDP

Platform Neutrality

DCOM run-time is available for various platforms Win32 platforms, Solaris, DEC UNIX, HPUX,

Linux, MVS, VMS, Mac Cross-Platform Interoperability Standard

Per-Platform binary standard Unlike java, DCOM can utilize powerful platform-

specific services and optimizations Less abstraction layers prevents additional

overheads

Security by Configuration

1) DCOM obtains user name

2) Authenticate user

3) Is user in the list?

4) Fail or allow call

Weaknesses of COM/DCOM

COM/DCOM is hard to use COM is not robust enough for enterprise

deployments

• COM/DCOM are best supported on Windows 95 and NT platforms

• low cost development tools provide the ability to build and access COM components for Windows platforms, for other platforms the prices are considerably more expensive

Creating a simple COM server

ATL COM AppWizard

New ATL Object

Add New Method

Interface Definition Language

object,

uuid(79522A15-BA3D-46A5-92D6-DA4BE60646F4),

helpstring("ISimple Interface"),

pointer_default(unique)

interface ISimple : IDispatch

[id(1, helpstring("method StringLen")] HRESULT StringLen([in] BSTR str, [out,retval] long* length);

Source & Header File

Source:STDMETHODIMP CSimple::StringLen(BSTR str, long* length)

*length = SysStringLen(str);

return S_OK;

Header:...

public:

STDMETHOD(StringLen)(/*[in]*/ BSTR str, /*[out,retval]*/ long* length);

Creating a Simple COM Client

#include <stdio.h>#import "SimpleCom.exe"

int main(int argc, char* argv[]){

SIMPLECOMLib::ISimplePtr pSimple;long len;CoInitialize(NULL);pSimple.CreateInstance(__uuidof(SIMPLECOMLib::Simple));len = pSimple->StringLen("sample");printf("Length = %d\n", len);CoUninitialize();return 0;

Exception Handling

len = pSimple->StringLen("sample");

catch (_com_error &e)

printf(“%s\n”, e.Description());

Registering COM Objects

COM dll To register: regsvr32 mycom.dll To un-register: regsvr32 –u mycom.dll

COM exe To register: mycom.exe /regserver To un-register: mycom.exe /unregserver

Configure as DCOM

Protocols for DCOM

Comparison

A Service Oriented Architecturewhy to buy if it is cheaper to rent

Web service can be used to: tools: calendar, chat, etc Information providers: weather, news, flight information

The ultimate aim of the web services programme is to build a service-oriented architecture (SOA) with the properties (Web service can be seen as distributed component taken to extreme): Access to services is standardised (interfaces defined) Network nodes make (reusable) services available to other

nodes, independent of physical location (location transparency) The publishing of information about available services is

standardised (a service directory) SOA should be independent of implementation technology – e.g.

services can interoperate regardless of implementation environment or language (Java, C#, . . . )

E.g. Photos can be shared from sites like Flickr to social network sites like Facebook and MySpace.

Video content can be embedded on sites which are served by another host.

Advantages Easier to reuse (no setup is required) Scalability: adding more services, and users Fault tolerant Lower cost

Disadvantage: Availability (connection is lost, server down, overloading

many request) Reliability (relatively slow)

What is SOAP?

Simple Object Access Protocol (SOAP) is based on XML protocol, used for information exchange in distributed systems. SOAP establishes client-server interaction and regulates operation factors transmission and return value. To submit any information transmitted from client to server and vice versa XML is used

SOAP uses Internet Protocols

Simple Object Access Protocol (SOAP)

Developed by IBM, Lotus Development Corporation, Microsoft, DevelopMentor, and Userland Software

SOAP message Envelope

A structure describes a method call Body

Request Contains a Remote Procedure Call (RPC); request

for another machine to perform a task. It specifies the method to be invoked and any parameters

Response HTTP response document contains results from

other method call

[from What the heck is SOAP anyway by David Platt ]

HolidayReservation ServiceFront End Flight

Reservation System

HotelReservation

System

Application Servers

Service Composition

Tools using SOAP for Web Services

• Microsoft SOAP Toolkit 2.0 • Provides necessary components for both client-side and server-side, and other operations for Web Services• Available on web site: http://msdn.microsoft.com/downloads/default.asp?URL=/code/sample.asp?url=/msdn-files/027/001/580/msdncompositedoc.xml

• IBM Apache SOAP• Based on the IBM SOAP4J implementation.• Available on web site: http://xml.apache.org/soap/

A Component now Becomes a Service Running Outside the Consumer Boundaries

CCI CCI CCI

ERP CRM

Service Service Service

Registry

11register

ConsumerConsumer

SOAP SOAP SOAP

XML XML XML

33 Communicate22

Discover/learnability

Policies

Web services with SOAP

Emerging standards support web services, all in XML:

1- discovery phase - discover What web Services that sever is hosting UDDI (Universal Description, Discovery and Integration) describes a way to publish & (directory)

2- Learning about what interfaces that service supports:WSDL (Web Service Definition Language file) describes services as a set of endpoints operating on message

3- Communication phase – placing a request for information and receive the responses•SOAP (Simple Object Access Protocol) defines the overall message structure of web service request

Example

1- a RoomService web Services project that contain multiple services, such as ReservationService, RateQuoateService, etc2- the actual UDDI file RoomService.vsdisco3- For Discovery the client application request information

http://servername/roomservice/roomservice.vsdisco

4- the Server send back this XML part (document reference that contain all the services names)

< docRef = “/roomService1.asmx” 5- the Learnability client request the WSDL from a web Service

http://servername/roomservice/roomService1/ ReservationService.asmx?WSDL

Input - Output

Name = “RoomNum”, Type = “int”

Name = “AvailabilityResult”, Type = “Boolean”

Implementation Web Service Example in C#

ReservationService.asmxReservationService.asmx

<%@ WebService Language="C#" %><%@ WebService Language="C#" %>using System;using System;using System.Web.Services;using System.Web.Services;

public class public class ReservationInterfaceReservationInterface{{ [WebMethod][WebMethod] public string public string opCheckAvaliabilityopCheckAvaliability(int (int RoomRoomNum)Num) {{ //// Implementation hereImplementation here, check database, etc, check database, etc }}}}

<%@ WebService Language="C#" %><%@ WebService Language="C#" %>using System;using System;using System.Web.Services;using System.Web.Services;

public class public class ReservationInterfaceReservationInterface{{ [WebMethod][WebMethod] public string public string opCheckAvaliabilityopCheckAvaliability(int (int RoomRoomNum)Num) {{ //// Implementation hereImplementation here, check database, etc, check database, etc }}}}

Microsoft SOAP toolkit

Another ASP.NET Web Services example

Links to Web

service methods

Link to service description

1 <%@ WebService Language="JScript" Class="NumberService" %>

3 // Fig. 23.38: number.asmx

4 // A simple Web Service

6 import System;

7 import System.Web.Services;

9 public class NumberService extends WebService

11 // Determines whether all the characters in a String are digits

12 WebMethod public function isNum( number : String ) : Boolean

14 var digitArray : char[];

15 digitArray = number.ToCharArray();

17 for ( var i : int = 0; i < digitArray.Length ; i++ )

19 if ( !Char.IsDigit( digitArray[ i ] ) )

21 return false;

25 return true;

26 } // end isNum

28 WebMethod public function Add( a : float, b : float) : float {

29 return a + b;

31 } // end class NumberService

ASP.NET Web Services

Invoking a method of a Web service from a Web browser.

Results of invoking a Web-service method from a Web browser.

Assignment 3

Build your project using one of the components frameworks

Compositional Forms we identify two kinds of entities that are

com-posed: components and frameworks. Given this, there are three major classes of interactions that arise in component-based systems:

Component–Component (C–C):

composition that enables interaction among compo-nents. These interactions deliver application functionality, and so the contracts that spec-ify these interactions might be classified as application-level contracts.

Framework–Component (F–C):

• A composition that enables interactions between a com-ponent framework and its components. These interactions enable frameworks to manage component resources, and so the contracts that specify these interactions might be classi-fied as system-level contracts.

Framework–Framework (F–F):

A composition that enables interactions between frame-works. These interactions enable composition of components that are deployed in het-erogeneous frameworks, and so these contracts might be classified as interoperation con-tracts.

..\CBSE-2012-2013[1]\Technical Concepts of Component-Based Software Engineering,.pdf

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