Ch11
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Ch11 as PDF for free.
More details
- Words: 2,963
- Pages: 44
Distributed Systems Architectures Architectural design for software that executes on more than one processor
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 1
Objectives ●
●
●
●
To explain the advantages and disadvantages of distributed systems architectures To describe different approaches to the development of clientserver systems To explain the differences between clientserver and distributed object architectures To describe object request brokers and the principles underlying the CORBA standards
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 2
Topics covered ● ● ● ●
Multiprocessor architectures Clientserver architectures Distributed object architectures CORBA
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 3
Distributed systems ●
●
●
Virtually all large computerbased systems are now distributed systems Information processing is distributed over several computers rather than confined to a single machine Distributed software engineering is now very important
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 4
System types ●
●
●
Personal systems that are not distributed and that are designed to run on a personal computer or workstation. Embedded systems that run on a single processor or on an integrated group of processors. Distributed systems where the system software runs on a loosely integrated group of cooperating processors linked by a network.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 5
Distributed system characteristics ● ● ● ● ● ●
Resource sharing Openness Concurrency Scalability Fault tolerance Transparency
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 6
Distributed system disadvantages ● ● ● ●
Complexity Security Manageability Unpredictability
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 7
Design issue Resource identification
Communications
Quality of service
Software architectures
Description The resources in a distributed system are spread across different computers and a naming scheme has to be devised so that users can discover and refer to the resources that they need. An example of such a naming scheme is the URL (Uniform Resource Locator) that is used to identify WWW pages. If a meaningful and universally understood identification scheme is not used then many of these resources will be inaccessible to system users. The universal availability of the Internet and the efficient implementation of Internet TCP/IP communication protocols means that, for most distributed systems, these are the most effective way for the computers to communicate. However, where there are specific requirements for performance, reliability etc. alternative approaches to communications may be used. The quality of service offered by a system reflects its performance, availability and reliability. It is affected by a number of factors such as the allocation of processes to processes in the system, the distribution of resources across the system, the network and the system hardware and the adaptability of the system. The software architecture describes how the application functionality is distributed over a number of logical components and how these components are distributed across processors. Choosing the right architecture for an application is essential to achieve the desired quality of service.
Issues in distributed system design
Distributed systems archiectures ●
Clientserver architectures •
●
Distributed services which are called on by clients. Servers that provide services are treated differently from clients that use services
Distributed object architectures •
©Ian Sommerville 2000
No distinction between clients and servers. Any object on the system may provide and use services from other objects
Software Engineering, 6th edition. Chapter 11
Slide 9
Middleware ●
●
●
Software that manages and supports the different components of a distributed system. In essence, it sits in the middle of the system Middleware is usually offtheshelf rather than specially written software Examples • • •
©Ian Sommerville 2000
Transaction processing monitors Data convertors Communication controllers
Software Engineering, 6th edition. Chapter 11
Slide 10
Multiprocessor architectures ● ●
●
●
Simplest distributed system model System composed of multiple processes which may (but need not) execute on different processors Architectural model of many large realtime systems Distribution of process to processor may be pre ordered or may be under the control of a despatcher
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 11
T r a f i c f l o w T r a f i c l g h t c o n t r o l S e n s o r p o e s r p r o e s rcpS p o c L i g h t eorntsorl D iproscpelay c o n r o s pesl T r a f i c l g h t s T rafnicd flo w sreanors O perator consoles am
A multiprocessor traffic control system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 12
Clientserver architectures ●
●
● ●
The application is modelled as a set of services that are provided by servers and a set of clients that use these services Clients know of servers but servers need not know of clients Clients and servers are logical processes The mapping of processors to processes is not necessarily 1 : 1
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 13
c 3 c 2 c 4 c 1 2 c 1 S e r v p r o c e s c1c5s1s2s4s3c1c09C l i e n t p r o c e s c6c7 c8
A clientserver system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 14
c 1 c 2 c 3 , c 4 C 1 C 2 C 3 etw ork sS eC rm v 3,C s14coS sS 1,C s2 N tcom rlipeuntr p u e c5, c6, c7C c 8 , c 9 c 1 0 , c 1 , c 1 2 4C 5C 6
Computers in a C/S network
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 15
Layered application architecture ●
Presentation layer •
●
Application processing layer •
●
Concerned with presenting the results of a computation to system users and with collecting user inputs Concerned with providing application specific functionality e.g., in a banking system, banking functions such as open account, close account, etc.
Data management layer •
©Ian Sommerville 2000
Concerned with managing the system databases
Software Engineering, 6th edition. Chapter 11
Slide 16
rA P e s n t a i o n l a y e r pD laictat m io llayn n ryeg p crem o esnin g t
Application layers
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 17
Thin and fat clients ●
Thinclient model •
●
In a thinclient model, all of the application processing and data management is carried out on the server. The client is simply responsible for running the presentation software.
Fatclient model •
©Ian Sommerville 2000
In this model, the server is only responsible for data management. The software on the client implements the application logic and the interactions with the system user.
Software Engineering, 6th edition. Chapter 11
Slide 18
P r e s n t a i o n S e r v T h im n ocd lien tC D a t m a n g e m n t lientP A p l i c t i o r o e s r e s n t a i o n A p l i c p r o c e s i n g S e r v F am tocd lien tC lient m tangem D a nt
Thin and fat clients
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 19
Thin client model ●
Used when legacy systems are migrated to client server architectures. •
●
The legacy system acts as a server in its own right with a graphical interface implemented on a client
A major disadvantage is that it places a heavy processing load on both the server and the network
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 20
Fat client model ●
●
●
More processing is delegated to the client as the application processing is locally executed Most suitable for new C/S systems where the capabilities of the client system are known in advance More complex than a thin client model especially for management. New versions of the application have to be installed on all clients
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 21
A T M A T M A c o u n t s e r v T e l C u t o m e r p r o c s i n g a c u n t A T M m t o r d b a s A T M
A clientserver ATM system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 22
Threetier architectures ●
●
●
In a threetier architecture, each of the application architecture layers may execute on a separate processor Allows for better performance than a thinclient approach and is simpler to manage than a fat client approach A more scalable architecture as demands increase, extra servers can be added
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 23
P r e s n t a i o n S e r v S e r v C lient A tangem D a proliecsatiogn m nt
A 3tier C/S architecture
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 24
C lC ilieennttH T P interactionA D a t b a s e r v e r W e b s e r v S Q L q u e r y C u t o m c o u n t s e r v i c e S Q L a c u n t p r v i o n d b a s e C lC ilieenntt
An internet banking system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 25
Use of C/S architectures Architecture Twotier C/S architecture with thin clients
Twotier C/S architecture with fat clients
Threetier or multitier C/S architecture
©Ian Sommerville 2000
Applications Legacy system applications where separating application processing and data management is impractical Computationallyintensive applications such as compilers with little or no data management Dataintensive applications (browsing and querying) with little or no application processing. Applications where application processing is provided by COTS (e.g. Microsoft Excel) on the client Applications where computationallyintensive processing of data (e.g. data visualisation) is required. Applications with relatively stable enduser functionality used in an environment with wellestablished system management Large scale applications with hundreds or thousands of clients Applications where both the data and the application are volatile. Applications where data from multiple sources are integrated Software Engineering, 6th edition. Chapter 11
Slide 26
Distributed object architectures ●
●
●
●
There is no distinction in a distributed object architectures between clients and servers Each distributable entity is an object that provides services to other objects and receives services from other objects Object communication is through a middleware system called an object request broker (software bus) However, more complex to design than C/S systems
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 27
o 1 o 2 o 3 o 4 S (o1) S (o2)S S ( o 3 ) S ( o 4 ) o f t w a r e b u s o 5 o 6 () S (o5) S
Distributed object architecture
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 28
Advantages of distributed object architecture ●
●
● ●
It allows the system designer to delay decisions on where and how services should be provided It is a very open system architecture that allows new resources to be added to it as required The system is flexible and scaleable It is possible to reconfigure the system dynamically with objects migrating across the network as required
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 29
Uses of distributed object architecture ●
●
As a logical model that allows you to structure and organise the system. In this case, you think about how to provide application functionality solely in terms of services and combinations of services As a flexible approach to the implementation of clientserver systems. The logical model of the system is a clientserver model but both clients and servers are realised as distributed objects communicating through a software bus
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 30
D aD tatbbaassee 1 R e p o r t g e n . I n t e g r a t o r 1 2 V i s u a l i s e r I n t e g r a t o r 2 D atbase 3 D isplay
A data mining system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 31
Data mining system ●
●
●
The logical model of the system is not one of service provision where there are distinguished data management services It allows the number of databases that are accessed to be increased without disrupting the system It allows new types of relationship to be mined by adding new integrator objects
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 32
CORBA ●
● ●
●
CORBA is an international standard for an Object Request Broker middleware to manage communications between distributed objects Several implementation of CORBA are available DCOM is an alternative approach by Microsoft to object request brokers CORBA has been defined by the Object Management Group
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 33
Application structure ● ●
●
●
Application objects Standard objects, defined by the OMG, for a specific domain e.g. insurance Fundamental CORBA services such as directories and security management Horizontal (i.e. cutting across applications) facilities such as user interface facilities
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 34
A pobljiecatsionO H o r i z o n t a l D o m a i n C O R B A f c i e s f a c l t e s bject C reO qu eR sB tA b sro rervices k e
CORBA application structure
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 35
CORBA standards ●
An object model for application objects •
●
●
●
A CORBA object is an encapsulation of state with a well defined, languageneutral interface defined in an IDL (interface definition language)
An object request broker that manages requests for object services A set of general object services of use to many distributed applications A set of common components built on top of these services
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 36
CORBA objects ●
●
●
●
CORBA objects are comparable, in principle, to objects in C++ and Java They MUST have a separate interface definition that is expressed using a common language (IDL) similar to C++ There is a mapping from this IDL to programming languages (C++, Java, etc.) Therefore, objects written in different languages can communicate with each other
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 37
Object request broker (ORB) ●
●
●
The ORB handles object communications. It knows of all objects in the system and their interfaces Using an ORB, the calling object binds an IDL stub that defines the interface of the called object Calling this stub results in calls to the ORB which then calls the required object through a published IDL skeleton that links the interface to the service implementation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 38
o 1 o 2 S (Iso )D 1 S ( o 2 ) L I D L tO u b s k e l t o n bject R equest B ror
ORBbased object communications
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 39
InterORB communications ●
●
●
●
ORBs are not usually separate programs but are a set of objects in a library that are linked with an application when it is developed ORBs handle communications between objects executing on the sane machine Several ORBS may be available and each computer in a distributed system will have its own ORB InterORB communications are used for distributed object calls
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 40
o 4 o 3 o 1 o 2 I(D )LS I(D oL 4) S I(D o1 )LS ID (oL 2) S O b j e c t R e q u e s t B r o k e r O bject R equest B rokerN etw ork
InterORB communications
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 41
CORBA services ●
Naming and trading services •
●
Notification services •
●
These allow objects to discover and refer to other objects on the network These allow objects to notify other objects that an event has occurred
Transaction services •
©Ian Sommerville 2000
These support atomic transactions and rollback on failure
Software Engineering, 6th edition. Chapter 11
Slide 42
Key points ●
●
●
●
Almost all new large systems are distributed systems Distributed systems support resource sharing, openness, concurrency, scalability, fault tolerance and transparency Clientserver architectures involve services being delivered by servers to programs operating on clients User interface software always runs on the client and data management on the server
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 43
Key points ●
●
●
In a distributed object architecture, there is no distinction between clients and servers Distributed object systems require middleware to handle object communications The CORBA standards are a set of middleware standards that support distributed object architectures
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 44
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 1
Objectives ●
●
●
●
To explain the advantages and disadvantages of distributed systems architectures To describe different approaches to the development of clientserver systems To explain the differences between clientserver and distributed object architectures To describe object request brokers and the principles underlying the CORBA standards
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 2
Topics covered ● ● ● ●
Multiprocessor architectures Clientserver architectures Distributed object architectures CORBA
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 3
Distributed systems ●
●
●
Virtually all large computerbased systems are now distributed systems Information processing is distributed over several computers rather than confined to a single machine Distributed software engineering is now very important
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 4
System types ●
●
●
Personal systems that are not distributed and that are designed to run on a personal computer or workstation. Embedded systems that run on a single processor or on an integrated group of processors. Distributed systems where the system software runs on a loosely integrated group of cooperating processors linked by a network.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 5
Distributed system characteristics ● ● ● ● ● ●
Resource sharing Openness Concurrency Scalability Fault tolerance Transparency
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 6
Distributed system disadvantages ● ● ● ●
Complexity Security Manageability Unpredictability
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 7
Design issue Resource identification
Communications
Quality of service
Software architectures
Description The resources in a distributed system are spread across different computers and a naming scheme has to be devised so that users can discover and refer to the resources that they need. An example of such a naming scheme is the URL (Uniform Resource Locator) that is used to identify WWW pages. If a meaningful and universally understood identification scheme is not used then many of these resources will be inaccessible to system users. The universal availability of the Internet and the efficient implementation of Internet TCP/IP communication protocols means that, for most distributed systems, these are the most effective way for the computers to communicate. However, where there are specific requirements for performance, reliability etc. alternative approaches to communications may be used. The quality of service offered by a system reflects its performance, availability and reliability. It is affected by a number of factors such as the allocation of processes to processes in the system, the distribution of resources across the system, the network and the system hardware and the adaptability of the system. The software architecture describes how the application functionality is distributed over a number of logical components and how these components are distributed across processors. Choosing the right architecture for an application is essential to achieve the desired quality of service.
Issues in distributed system design
Distributed systems archiectures ●
Clientserver architectures •
●
Distributed services which are called on by clients. Servers that provide services are treated differently from clients that use services
Distributed object architectures •
©Ian Sommerville 2000
No distinction between clients and servers. Any object on the system may provide and use services from other objects
Software Engineering, 6th edition. Chapter 11
Slide 9
Middleware ●
●
●
Software that manages and supports the different components of a distributed system. In essence, it sits in the middle of the system Middleware is usually offtheshelf rather than specially written software Examples • • •
©Ian Sommerville 2000
Transaction processing monitors Data convertors Communication controllers
Software Engineering, 6th edition. Chapter 11
Slide 10
Multiprocessor architectures ● ●
●
●
Simplest distributed system model System composed of multiple processes which may (but need not) execute on different processors Architectural model of many large realtime systems Distribution of process to processor may be pre ordered or may be under the control of a despatcher
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 11
T r a f i c f l o w T r a f i c l g h t c o n t r o l S e n s o r p o e s r p r o e s rcpS p o c L i g h t eorntsorl D iproscpelay c o n r o s pesl T r a f i c l g h t s T rafnicd flo w sreanors O perator consoles am
A multiprocessor traffic control system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 12
Clientserver architectures ●
●
● ●
The application is modelled as a set of services that are provided by servers and a set of clients that use these services Clients know of servers but servers need not know of clients Clients and servers are logical processes The mapping of processors to processes is not necessarily 1 : 1
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 13
c 3 c 2 c 4 c 1 2 c 1 S e r v p r o c e s c1c5s1s2s4s3c1c09C l i e n t p r o c e s c6c7 c8
A clientserver system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 14
c 1 c 2 c 3 , c 4 C 1 C 2 C 3 etw ork sS eC rm v 3,C s14coS sS 1,C s2 N tcom rlipeuntr p u e c5, c6, c7C c 8 , c 9 c 1 0 , c 1 , c 1 2 4C 5C 6
Computers in a C/S network
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 15
Layered application architecture ●
Presentation layer •
●
Application processing layer •
●
Concerned with presenting the results of a computation to system users and with collecting user inputs Concerned with providing application specific functionality e.g., in a banking system, banking functions such as open account, close account, etc.
Data management layer •
©Ian Sommerville 2000
Concerned with managing the system databases
Software Engineering, 6th edition. Chapter 11
Slide 16
rA P e s n t a i o n l a y e r pD laictat m io llayn n ryeg p crem o esnin g t
Application layers
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 17
Thin and fat clients ●
Thinclient model •
●
In a thinclient model, all of the application processing and data management is carried out on the server. The client is simply responsible for running the presentation software.
Fatclient model •
©Ian Sommerville 2000
In this model, the server is only responsible for data management. The software on the client implements the application logic and the interactions with the system user.
Software Engineering, 6th edition. Chapter 11
Slide 18
P r e s n t a i o n S e r v T h im n ocd lien tC D a t m a n g e m n t lientP A p l i c t i o r o e s r e s n t a i o n A p l i c p r o c e s i n g S e r v F am tocd lien tC lient m tangem D a nt
Thin and fat clients
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 19
Thin client model ●
Used when legacy systems are migrated to client server architectures. •
●
The legacy system acts as a server in its own right with a graphical interface implemented on a client
A major disadvantage is that it places a heavy processing load on both the server and the network
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 20
Fat client model ●
●
●
More processing is delegated to the client as the application processing is locally executed Most suitable for new C/S systems where the capabilities of the client system are known in advance More complex than a thin client model especially for management. New versions of the application have to be installed on all clients
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 21
A T M A T M A c o u n t s e r v T e l C u t o m e r p r o c s i n g a c u n t A T M m t o r d b a s A T M
A clientserver ATM system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 22
Threetier architectures ●
●
●
In a threetier architecture, each of the application architecture layers may execute on a separate processor Allows for better performance than a thinclient approach and is simpler to manage than a fat client approach A more scalable architecture as demands increase, extra servers can be added
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 23
P r e s n t a i o n S e r v S e r v C lient A tangem D a proliecsatiogn m nt
A 3tier C/S architecture
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 24
C lC ilieennttH T P interactionA D a t b a s e r v e r W e b s e r v S Q L q u e r y C u t o m c o u n t s e r v i c e S Q L a c u n t p r v i o n d b a s e C lC ilieenntt
An internet banking system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 25
Use of C/S architectures Architecture Twotier C/S architecture with thin clients
Twotier C/S architecture with fat clients
Threetier or multitier C/S architecture
©Ian Sommerville 2000
Applications Legacy system applications where separating application processing and data management is impractical Computationallyintensive applications such as compilers with little or no data management Dataintensive applications (browsing and querying) with little or no application processing. Applications where application processing is provided by COTS (e.g. Microsoft Excel) on the client Applications where computationallyintensive processing of data (e.g. data visualisation) is required. Applications with relatively stable enduser functionality used in an environment with wellestablished system management Large scale applications with hundreds or thousands of clients Applications where both the data and the application are volatile. Applications where data from multiple sources are integrated Software Engineering, 6th edition. Chapter 11
Slide 26
Distributed object architectures ●
●
●
●
There is no distinction in a distributed object architectures between clients and servers Each distributable entity is an object that provides services to other objects and receives services from other objects Object communication is through a middleware system called an object request broker (software bus) However, more complex to design than C/S systems
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 27
o 1 o 2 o 3 o 4 S (o1) S (o2)S S ( o 3 ) S ( o 4 ) o f t w a r e b u s o 5 o 6 () S (o5) S
Distributed object architecture
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 28
Advantages of distributed object architecture ●
●
● ●
It allows the system designer to delay decisions on where and how services should be provided It is a very open system architecture that allows new resources to be added to it as required The system is flexible and scaleable It is possible to reconfigure the system dynamically with objects migrating across the network as required
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 29
Uses of distributed object architecture ●
●
As a logical model that allows you to structure and organise the system. In this case, you think about how to provide application functionality solely in terms of services and combinations of services As a flexible approach to the implementation of clientserver systems. The logical model of the system is a clientserver model but both clients and servers are realised as distributed objects communicating through a software bus
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 30
D aD tatbbaassee 1 R e p o r t g e n . I n t e g r a t o r 1 2 V i s u a l i s e r I n t e g r a t o r 2 D atbase 3 D isplay
A data mining system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 31
Data mining system ●
●
●
The logical model of the system is not one of service provision where there are distinguished data management services It allows the number of databases that are accessed to be increased without disrupting the system It allows new types of relationship to be mined by adding new integrator objects
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 32
CORBA ●
● ●
●
CORBA is an international standard for an Object Request Broker middleware to manage communications between distributed objects Several implementation of CORBA are available DCOM is an alternative approach by Microsoft to object request brokers CORBA has been defined by the Object Management Group
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 33
Application structure ● ●
●
●
Application objects Standard objects, defined by the OMG, for a specific domain e.g. insurance Fundamental CORBA services such as directories and security management Horizontal (i.e. cutting across applications) facilities such as user interface facilities
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 34
A pobljiecatsionO H o r i z o n t a l D o m a i n C O R B A f c i e s f a c l t e s bject C reO qu eR sB tA b sro rervices k e
CORBA application structure
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 35
CORBA standards ●
An object model for application objects •
●
●
●
A CORBA object is an encapsulation of state with a well defined, languageneutral interface defined in an IDL (interface definition language)
An object request broker that manages requests for object services A set of general object services of use to many distributed applications A set of common components built on top of these services
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 36
CORBA objects ●
●
●
●
CORBA objects are comparable, in principle, to objects in C++ and Java They MUST have a separate interface definition that is expressed using a common language (IDL) similar to C++ There is a mapping from this IDL to programming languages (C++, Java, etc.) Therefore, objects written in different languages can communicate with each other
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 37
Object request broker (ORB) ●
●
●
The ORB handles object communications. It knows of all objects in the system and their interfaces Using an ORB, the calling object binds an IDL stub that defines the interface of the called object Calling this stub results in calls to the ORB which then calls the required object through a published IDL skeleton that links the interface to the service implementation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 38
o 1 o 2 S (Iso )D 1 S ( o 2 ) L I D L tO u b s k e l t o n bject R equest B ror
ORBbased object communications
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 39
InterORB communications ●
●
●
●
ORBs are not usually separate programs but are a set of objects in a library that are linked with an application when it is developed ORBs handle communications between objects executing on the sane machine Several ORBS may be available and each computer in a distributed system will have its own ORB InterORB communications are used for distributed object calls
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 40
o 4 o 3 o 1 o 2 I(D )LS I(D oL 4) S I(D o1 )LS ID (oL 2) S O b j e c t R e q u e s t B r o k e r O bject R equest B rokerN etw ork
InterORB communications
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 41
CORBA services ●
Naming and trading services •
●
Notification services •
●
These allow objects to discover and refer to other objects on the network These allow objects to notify other objects that an event has occurred
Transaction services •
©Ian Sommerville 2000
These support atomic transactions and rollback on failure
Software Engineering, 6th edition. Chapter 11
Slide 42
Key points ●
●
●
●
Almost all new large systems are distributed systems Distributed systems support resource sharing, openness, concurrency, scalability, fault tolerance and transparency Clientserver architectures involve services being delivered by servers to programs operating on clients User interface software always runs on the client and data management on the server
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 43
Key points ●
●
●
In a distributed object architecture, there is no distinction between clients and servers Distributed object systems require middleware to handle object communications The CORBA standards are a set of middleware standards that support distributed object architectures
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 11
Slide 44
