System Design Ashima Wadhwa

What is system design? High level design identifying the system processes, functional components and their interfaces Derived from system requirements Provides an overview of the project Define the components that are needed Establish how components “communicate” with other components Determine how to modularize the project into discrete work packages Identify critical interfaces that must be well defined Used to provide initial cost, schedule & resource estimates Usually little or few implementation details As system design is refined, and lower level subsystems are included, implementation issues may need to be addressed

System design steps Define project goal and objectives Develop the project system requirements Identify the major system components that satisfy the system requirements Identify the major system interfaces Refine the system design Define subsystems making up each component Specify interfaces between subsystems Establish management controls for the system interfaces

Coupling between modules in a software system must be minimized. Modularity Modularity means breaking a large project into smaller parts that can be understood and handled easily. In other words, modularity means dividing a large task into small tasks that can communicate with each other. The structure chart discussed in the previous section shows the modularity in the elevator system. There are two main concerns when a system is divided into modules: coupling and cohesion. Coupling is a measure of how tightly two modules are bound to each other. i Coupling between modules in a software system must be minimized.

Cohesion between modules in a software system must be maximized. Another issue in modularity is cohesion. Cohesion is a measure of how closely the modules in a system are related. We need to have maximum possible cohesion between modules in a software system. i Cohesion between modules in a software system must be maximized.

Software quality The quality of software created at the implementation phase is a very important issue. A software system of high quality is one that satisfies the user’s requirements, meets the operating standards of the organization, and runs efficiently on the hardware for which it was developed. However, if we want to achieve a software system of high quality, we must be able to define some attributes of quality.

Software quality factors Software quality can be divided into three broad measures: operability, maintainability and transferability. Each of these measures can be further broken down as shown in Figure 10.10.

Data Validation Data validation is the process of checking database to ensure that the information gathered from different data sources is clean, accurate and in a standard format. Data validation can be simple or complex, depending upon the way it is performed. For example, validating email address, or phone numbers is easy. On the other hand, checking different data fields for consistency and accuracy in a master database will be complex.

Types of data validation techniques : Form Level Validation: It ensures that all the fields marked as mandatory in the web form are filled correctly before the user clicks the submit button on the page Field Level Validation: It makes certain that users enter correct value across a specific data field. For example, “Name” field can’t have a numeric value, and “email” field should contain a value having “.” and “@” Data Saving Validation: Data saving validation is used for multiple data entry forms and option screens. User is allowed to save data on any or all tabs/pages before leaving the page. Search Criteria Validation: This type of validation is used when there are multiple search criteria in a form, and user wants to save the search results before navigating to a different page Range Validation: This validation type is used to make sure that the numeric value, characters or date entered is within the specific range

The Human machine Interface The interface is the system which helps users communicate with the computer system and/or the application system

User Interface Design Objectives To design a better user interface, use the following objectives: Effectiveness as achieved through design of interfaces that allow the user to access the system in a way that is congruent with their individual needs Efficiency as demonstrated through interfaces that increase speed of data entry, and reduce errors

User Interface Design Objectives Further interface design objectives User consideration as demonstrated in designing suitable interfaces, and providing appropriate feedback to users from the system Generating usable queries Productivity as shown through following sound principles of design for user interfaces and work spaces

Components of the HM Interface The user interface has two main components Presentation language, which is the computer-to-human part of the transaction Action language that characterizes the human-to-computer portion

Types of Human Machine Interfaces There are several types of interfaces: Natural-language interfaces Question-and-answer interfaces A menu interface Form-fill interfaces Command-language interfaces Graphical User Interfaces (GUIs)

Natural-Language Interfaces Natural-language interfaces permit users to interact with the computer in their everyday or "natural" language

Question-and-Answer Interfaces The computer displays a question for the user on the screen The user enters an answer via the keyboard The computer acts on that input information in a preprogrammed manner New users may find the question-and-answer interface most comfortable

A Menu Interface A menu interface, which provides the user with an onscreen list of available selections A nested menu is a menu which can be reached through another menu

Advantages of Nested Menus The advantages of nested menus are Nested menus give a less cluttered screen Nested menus eliminate menu options which do not interest a user Nested menus allow users to move quickly through the program

Graphical User Interface (GUI) Menus GUI menus guidelines The main menu is always on the screen The main menu uses single words The main menu should have secondary menus grouped into similar features

Graphical User Interface (GUI) Menus Further GUI menus guidelines The secondary drop-down menus often consist of more than one word Secondary options perform actions or display additional menu options Menu items in gray are unavailable for the current activity

Form-Fill Interfaces Form-fill interfaces are onscreen forms displaying fields containing data items or parameters that need to be communicated to the user Form-fill interfaces may be implemented using the Web

Advantages and Disadvantages of Web Forms Advantages of using a Web-based form User enters the data Data may be entered 24 hours a day, globally Disadvantages of a Web-based form The user may not know what to enter if the form is not clear User might be nervous about using a credit card over the Internet

Command-Language Interfaces Command-language interfaces are more popular than the previous ones Allow the user to control the application with a series of keystrokes, commands, phrases, or some sequence of these

Graphical User Interfaces (GUIs) GUIs provide a strong metaphor of the application Allow direct manipulation of the graphical representation on the screen Can be accomplished with keyboard input, joystick, or mouse Requires more system sophistication than other interfaces

Dialog Dialog is the communication between a person and the computer Three key points to be considered Meaningful communication Minimal user action Standard operation and consistency

Thank You!!