2 Approaches to Requierements Engineering Reference: Systems Analysis and Design in a Changing World, 3 rd Edition, chapter 2 and chapter 6

2 Systems Analysis and Design in a Changing World, 3rd Edition 2 Overview u Systems development life cycle (SDLC) l Provides overall framework for managing system development process u Two main approaches to SDLC l Traditional approach: structured systems development and information engineering l Object-oriented approach: object technologies requires different approach to analysis, design, and programming u All projects use some variation of SDLC

2 Systems Analysis and Design in a Changing World, 3rd Edition 3 Traditional and Object-Oriented Views of Activities

2 Systems Analysis and Design in a Changing World, 3rd Edition 4 Requirements Models for the Traditional and OO Approaches

2 Systems Analysis and Design in a Changing World, 3rd Edition 5 Structured Analysis u Define what system needs to do (processing requirements) u Define data system needs to store and use (data requirements) u Define inputs and outputs u Define how functions work together to accomplish tasks u Data flow diagrams and entity relationship diagrams show results of structured analysis

2 Systems Analysis and Design in a Changing World, 3rd Edition 6 Context Diagrams u DFD that summarizes all processing activity u Highest level (most abstract) view of system u Shows system boundaries u System scope is represented by a single process, external agents, and all data flows into and out of the system

2 Systems Analysis and Design in a Changing World, 3rd Edition 7 Context Diagram for RMO Order-Entry Subsystem

2 Systems Analysis and Design in a Changing World, 3rd Edition 8 Data Flow Diagrams u Graphical system model that shows all main requirements for an IS in one diagram l Inputs / outputs l Processes l Data storage u Easy to read and understand with minimal training

2 Systems Analysis and Design in a Changing World, 3rd Edition 9 DFD Fragment from the RMO Case

2 Systems Analysis and Design in a Changing World, 3rd Edition 10 Data Flow Diagram (DFD) created using Structured Analysis Technique

2 Systems Analysis and Design in a Changing World, 3rd Edition 11 Data Flow Diagram Symbols

2 Systems Analysis and Design in a Changing World, 3rd Edition 12 Entity-Relationship Diagram (ERD) created using the Structured Analysis technique

2 Systems Analysis and Design in a Changing World, 3rd Edition 13 Structured Analysis Leads to Structured Design and Structured Programming

2 Systems Analysis and Design in a Changing World, 3rd Edition 14 Object-Oriented Approach u Views information system as collection of interacting objects that work together to accomplish tasks l Objects - things in computer system that can respond to messages l No processes, programs, data entities, or files are defined – just objects u Object-oriented analysis (OOA) l Defines types of objects that do work of system l Shows how objects interact with users to complete tasks

2 Systems Analysis and Design in a Changing World, 3rd Edition 15 Object-Oriented Approach to Systems

2 Systems Analysis and Design in a Changing World, 3rd Edition 16 Object-Oriented Approach ( continued ) u Object-oriented design (OOD) l Defines object types needed to communicate with people and devices in system l Shows how objects interact to complete tasks l Refines each type of object for implementation with specific language of environment u Object-oriented programming (OOP) l Writing statements in programming language to define what each type of object does u Benefits of OOA include naturalness and reuse

2 Systems Analysis and Design in a Changing World, 3rd Edition 17 Class Diagram Created During OO Analysis

2 Systems Analysis and Design in a Changing World, 3rd Edition 18 Summary ( continued ) u System development methodologies are based on traditional approach or object-oriented approach u System development methodology provides guidelines to complete every activity in the SDLC

2 Systems Analysis and Design in a Changing World, 3rd Edition 19 Summary u Data flow diagrams (DFDs) used in combination with event table and entity-relationship diagram (ERD) to model system requirements IN TRADITIONAL APPROACH TO REQUIREMENS u DFDs model system as set of processes, data flows, external agents, and data stores u DFDs easy to read - graphically represent key features of system using small set of symbols u Many types of DFDs: context diagrams, DFD fragments, subsystem DFDs, event-partitioned DFDs, and process decomposition DFDs