object oriented design process.

• Apply design axioms to design classes, their attributes, methods, associations, structures and protocols.

• Design the access layer.

• Design the view layer classes

• Iterate and refine the whole design. Reapply the design axioms and if needed repeat the preceding steps.

OBJECT ORIENTED DESIGN AXIOMS

• AN axiom is a fundamental truth that always is observed to be valid and for which is no counterexample or exception.

• A theorem is a proposition that may be self –evident but can be proven from accepted axioms.

• The author has applied Suh’s design axioms to object-oriented design.

•

Corollary

• 1: Uncoupled design with less information content

• Corollary 2: Single purpose

• Corollary 3: Large number of simple classes

• Corollary 4: Strong mapping

• Corollary 5: Standardization

• Corollary 6: Design with inheritance

• Axiom 1 deals with relations between system components and axiom 2 deals with the complexity of design.

• AXIOM 1: THE INDEPENDENCE AXIOM: maintain the independence of the components.

• AXIOM 2: THE INFORMATION AXIOM: minimize the information content of the design.

Clienthost

Serverhost

Clienthost

Part of the rationale

• Specialization:– Clients specialize in user interface– Servers specialize in managing data and

application logic

• Sharing:– Many clients can be supported by few servers– Often data and logic are shared among

applications and users

Client/server

Peer-to-peerServer

“I want to access some information”

“I want to collaborate

with my colleague”

Client

Distinctions

• Client-server– Asymmetric relationship– Client predominately makes requests, server

makes replies

• Peer-to-peer– Symmetric relationship

ClientServer

Client

Email client sends message to server

Message is stored on POP server

Later, recipient’s email client retrieves message from server

Email application

Client

Server

Client

Chat clients send user’s typing to server

Chat server aggregates typing from all users and sends to all clients

Other user’s clients display aggregated typing from chat server

Chat application

Presentation

Applicationlogic

Shareddata

Local-area network

Note: many clients perapplication server, severalapplication servers per data server

Three-tier client/server

Client

Webbrowser

Webserver

Application logic

Databases and DBMS

Commongatewayinterchange

Host architecture

Application partition

Practice in defining tiers

• Online bookseller (e.g. amazon.com)

• Stock trading system (e.g. Schwab or E-trade)

amazon.com

Schwab

Question

• What types of social applications would be appropriate for a client/server architecture?

Departments

Enterprise

CommerceEnterprise-to-enterprise

Consumer

Customers

Consumer Enterprise

Customer-servicedepartment Technical-support

department

software4u.com

Web server

Customer logic

Customeraudit

Softwaredocumentation

Webbrowser

Problemknowledge

base

Databases

Agent logic

Consumerapplication

Enterpriseapplication

Technician logic

Web server

Webbrowser

Web server

Webbrowser

Cus

tom

er c

are

Accounts Products Orders

Customer logic

Databases

Agent logic

Customers Agents Technicians

Technician logic

Book distributioncenters

books4u.comCustomers

Financial institution

Consumer Enterprise Inter-enterprise

Web server

Customer logic

Customers Merchandise

Webbrowser

Orders

Acquirerbank

Bookdistributors

Databases

Outside links

Fullfillment logic

Consumere-commerce

Inter-enterprisee-commerce

Boo

k m

erch

ant

Clients

Customers Merchandise

Acquirerbank

BookdistributorsOrders

Customer logic

Databases

Fullfillment logic

Stock marketstocks4u.com

Customers

Information providers

Consumer Enterprise Inter-enterprise

Web server

Customer logic

Accounts Products

Webbrowser

Orders

Informationproviders

Financialmarkets

Databases

Outside links

Trading logic

Consumere-commerce

Inter-enterprisee-commerce

Sto

ck tr

ader

Clients

Accounts Products

Informationproviders

FinancialmarketsOrders

Customer logic

Databases

Trading logic

Local floristsflowers4u.com

Customers

Financial institution

Consumer Enterprise Inter-enterprise

Web server

Customer logic

Accounts Products

Webbrowser

Orders

Acquirerbank

Databases

Outside link

Fullfillment logic

Consumere-commerce

Inter-enterprisee-commerce

Push client

Push server

Flo

rist

del

iver

y

Accounts Products

Acquirerbank

Orders

Customer logic

Databases

Fullfillment logic

Customers Florists

Shortcomings of client/server

• Departmental solution

• Proliferates non-interoperable technologies and applications

• Hardwired applications lose flexibility

What are some goals and likely characteristics of future enterprise architectures?

Forms and entry windows

• It provide access to data that users can retrieve , display, and change in the application.

Dialog boxes

• It display status information or ask users to supply information or make a decision before continuing with a task.

• Ok or cancel

Application windows

• An application window is a container of application objects or icons. In other words , it contains an entire application with which users can interact.

Guidelines for designing forms and data entry windows

• In general, what kind of information will users work with and why? For eample, a user might want to change inventory information , entry orders or maintain prices for stock items.

• Do users need access to all the information in a table

• In what order do users want rows to appear?• Next identify

• Navigating rows in a table, such as moving forward and backward , and going to first and last record.

• Adding and deleting rows.

• Changing data in rows.

• Saving and abandoning changes.

• Menu push buttons

• Paper form such as a printed invoice, as the starting point for your design.

• Users scan a screen in the same way they read a page of a book, from left to right and top to bottom.

• When information is positioned vertically, align fields at their left edges.

• When entering data, users except to type information from left to right and top to bottom, as if they were using a typewriter.

Guidelines for designing dialog and error messages

• A dialog provides an exchange of information or a dialog between the user and the application.

• Your error message should be positive. For example instead of displaying “ you have typed an illegal date format” display the message “ enter date format mm/dd/yyyy”

Guidelines for the command buttons layout

• Layout out the major command buttons either stacked along the upper-right border of the dialog box or lined up across the bottom of the dialog box.

Guidelines for designing application windows

• A typical application window consists of a frame that defines its extent and a title bar that identifies what is being viewed in the window.

• File menu-new, open , print, save • Edit menu- cut, copy, paste• View menu• Window menu• Help menu

Guidelines for using colors

• For all objects on a window , you can use colors to add visual appeal to the form.

• You can use identical or similar colors to indicate related information. For example , savings account fields might appear in one color.

• For an object background , use a contrasting but complementary color.

Guidelines for using fonts

• Use commonly installed fonts, not specialized fonts that users might not have on their machines.

• Use bold for control labels, so they will remain legible when the object is dimmed.

• Using too many font styles , sizes and colors can be visually distracting and should be avoided.

Prototyping the user interface

• Rapid prototyping encourage the incremental development approach

Guidelines for designing dialog boxes and error messages: -

• 1. Your error message should be positive.

• 2. Your error message should be constructive.

• 3. Your message should be brief and meaningful.

• 4. Orient the controls in the dialog box in the direction people read.

Guidelines for the command buttons layout: -

• 1. Position the most important button• 2. If you see OK and Cancel buttons,

group them together.• 3. If you include a Help command button,

make it the last button in the set• 4. Avoid making this button the default

button • 5. Make buttons a consistent length.

Guidelines for designing application windows: -

• 1. File Menu: this provides an interface for the primary operations that apply to a file.

• 2. Edit Menu: Include general purpose editing commands on the Edit menu.

• 3. View menu and other command menus • 4. Window menu • 5. Help menu – contains commands that provide

access to Help information.• 6. Toolbars and status bars: special interfaces

constructs for managing sets of controls.

Guidelines for using colors: -

• 1. You can use identical or similar colors to indicate related information.

• 2. For an object background, use a contrasting but complementary color.

• 3. You can use dim colors to make other elements less noticeable.

• 4. using too many colors can be visually distracting and will make your application less interesting

• 5. Allow the user to modify the color configuration.

Guidelines for using fonts: -

• 1. Use commonly installed fonts, not specialized fonts that user might not have on their machines.

• 2. Use bold for control labels.• 3. Use fonts consistently within each form and

among all forms in your application• 4. Using too many font styles, sizes and colors

can be visually distracting and should be avoided.