Chapter 13 Review Questions

13.1

• Give a definition of architecture in an information systems context.

13.1 Answer

• System architecture shows the big picture. • High-level view of the system.• Architecture is the fundamental organization

of a system which is modelled in terms of major components and the way they are connected to each other and to the environment.

13.5

• How do existing systems influence the architecture of new systems in the same organization?

13.5 Answer

• Firstly, the choice of existing technical aspects such as operating system, middleware, development language, database and the component or service structure of existing systems will influence those choices for the new system.

13.5 Answer

• Secondly, where there are reusable assets, such as components or services, the new system will be able to reuse these.

• Thirdly, there may be existing systems whose architecture does not provide a pattern for future systems, and the architecture of the new system may have to interface to these through some kind of middleware or adapters.

13.6

• Explain the difference between a PIM(A platform-independent model) and PSM(platform-specific model ).

13.6 Answer

• A platform-independent model (PIM) is a model that does not contain any features that restrict it to implementation on a particular platform.

13.6 Answer

• A platform-specific model (PSM) is a transformation from a PIM to produce a model that can be implemented on a specific platform.

13.8

• What are the advantages of dividing a system into a collection of subsystems?

13.8 Answer

• It has the following advantages:– It produces smaller units of development.– It helps to maximize reuse at the component level.– It helps the developers to cope with complexity.– It improves maintainability.– It aids portability.

13.9

• What is the difference between client-server and peer to peer communication?

13.9 Answer

• Styles of communication between subsystems– Client-server– Peer to peer

13.9 Answer

• Client–server communication requires the client to know the interface of the server subsystem, but the communication is only in one direction.

• The client subsystem requests services from the server subsystem and not vice versa.

13.9 Answer

• Peer-to-peer communication requires each subsystem to know the interface of the other, thus coupling them more tightly. The communication is two way since either peer subsystem may request services from the other.

13.10

• Why is an open layered architecture more difficult to maintain?

13.10 Answer

• Open layered architectures are more difficult to maintain because each layer may communicate with all lower layers hence increasing the degree of coupling in the architecture. A change to one layer may ripple too many layers.

13.11

• What are the disadvantages of the closed layered architecture?

13.11 Answer

• A closed layer architecture many require more processing, as messages have to be passed through intervening layers.

13.15

• How do architectural divisions of systems help with project management?

13.15 Answer

• By breaking a system into subsystems, work can be allocated to teams more easily, with each team responsible for a particular subsystem.

Deciding Application Architecture

• Data Processing System• Transaction Processing System• Event Processing System• Language Processing System

Deciding Application Architecture

• Data Processing System– Data-driven– is explicit user interventions during the processing.– Large amount of data– input and outputs are processed from a file or database

rather than input from and output to user terminal. – Low functionality(similar operations are carried out on

a large amount of data.)– Example applications : market applications,telephone

billing system

Deciding Application Architecture

• Transaction Processing System– Applications that requires the inputs from a user

and give outputs back to the user.– Most common type of interactive business

systems. – User actions can’t interfere with each other.– The integrity of the database is maintained.– Example applications :interactive banking

systems,e-commerce systems,booking systems.

Deciding Application Architecture

• Event Processing System– Real-time systems– Events can occur unpredictably – Example applications : Games, car parking systems

Deciding Application Architecture

• Language Processing System– compiler

System Architecture

• Client\Server• Layered• Data Centered(Repository architecture)

Client\Server

• Consider this style if;– The application is Server based and supports

multiple clients.– You are creating Web based applications exposed

through browser.– You want to centralize data storage, backup and

management functions.

Layered

• Used when – building new facilities on top of existing systems;– There is a requirment for multi-level security.– Development is spread across several teams.

Layered

• 3 main layers– the Data Access layer– the Business Logic layer– the Graphical User Interface layer

Layered

• Consider the layered architecture style if;– Your application is complex– You want to improve the maintainability and

extensibility of the application– clear separation of responsabilities

Layered

• User Interface• Authentication and Authorization• Core Business(system utilities)• Database

Data Centered(Repository architecture)

• All data is accessible to all system components. Components do not interact directly, only through the repository.

Data Centered(Repository architecture)

• Components are independent. They dont need to know each other.

• All data can be managed consistently.