1 Introduction to Design

2 Outline Basics of design Design approaches

3 What is Design? The process of creating the description of a solution to a problem. Design Process Specification document (i.e., SRS) Design document

4 Specification vs. Design Documents Specification document –A description of “what” the software is to do. Design document –A description of “how” the software is to achieve this.

5 Architectural vs Detailed Design Architectural design –Decompose system into modules (components or subsystems). –Identify interrelationships (e.g., interconnections or interactions) among modules. –Also known as system design, general design, logical design, and high-level design. Detailed design –Design each module separately in detail (e.g., interface, data structures, and algorithms). –Also known as modular design, physical design, and low-level design.

6 Definition of Design Revisited The process of identifying a set of modules and interfaces from a set of requirements relying on SE techniques, imagination, experience, and art!

7 Design Criteria and Principles Simple, understandable, modular, independent But the most important is “design for changes” –The design should allow maintainers to quickly modify the program to meet future needs. –Challenging because we may not know what the future needs are. –Why so important?

8 Approaches to Design Many techniques and approaches –Action-oriented (function-oriented) –Data-oriented –Object-oriented Common characteristics -Decomposes the system into elementary parts. -Applies the divide and conquer strategy to eventually build the system.

9 Action-Oriented Design Focus on the actions (functions or operations) that the system perform. E.g., DFD, Structure Design (functional decomposition).

10 address namefield Professor Advises Takes Teaches Course Student namecategory quarter name ssn Conceptual Modeling cid

11 Data – Oriented Design Data is considered first, i.e., the structure of data is determined first and then the procedures are designed to conform to the structure of the data. E.g., Entity-relationship diagram (ERD)

12 Data Modeling Data model is a plan for building a database

13 Data Modeling A data model is a conceptual representation of the data structures that are required by a database. The data structures include the data objects, the association between the data objects, and the rules, which govern operations on the objects

14 Data Modeling There are two methodologies in Data Modeling 1) Entity – Relationship 2) Object Model

15 Data Modeling In The Context Of Database Design There are Five steps involved in Database Design 1) Planning and Analysis 2) Conceptual Design 3) Logical Design 4) Physical Design 5) Implementation

16 Data Modeling Data modeling is one part of the conceptual design process The remaining are typically functional models The data model focuses on what data should be stored the database Functional model deals with how the data is processed

17 Data Modeling The data model component has two outputs 1) E – R Diagrams : which represents the data structures in a pictorial form 2) Data Document: This document describes in detail the data objects, Relationships, and rules required by the database