slike bài giảng ứng dụng xây dựng hệ thống thông tin chương 6 the traditional approach to requirements

6 Chapter 6: The Traditional Approach to Requirements Systems Analysis and Design in a Changing World, 3 rd Edition 6 Systems Analysis and Design in a Changing World, 3rd Edition 2 Learning Objectives ◆ Explain how the traditional approach and the object-oriented approach differ when an event occurs ◆ List the components of a traditional system and the symbols representing them on a data flow diagram ◆ Describe how data flow diagrams can show the system at various levels of abstraction 6 Systems Analysis and Design in a Changing World, 3rd Edition 3 Learning Objectives (continued) ◆ Develop data flow diagrams, data element definitions, data store definitions, and process descriptions ◆ Develop tables to show the distribution of processing and data access across system locations ◆ Read and interpret Information Engineering models that can be incorporated within traditional structured analysis 6 Systems Analysis and Design in a Changing World, 3rd Edition 4 Overview ◆ What the system does what an event occurs: activities and interactions ◆ Traditional structured approach to representing activities and interactions ◆ Diagrams and other models of the traditional approach ◆ RMO customer support system example shows how each model is related ◆ How traditional and IE approaches and models can be used together to describe system 6 Systems Analysis and Design in a Changing World, 3rd Edition 5 Traditional and Object-Oriented Views of Activities 6 Systems Analysis and Design in a Changing World, 3rd Edition 6 Requirements Models for the Traditional and OO Approaches 6 Systems Analysis and Design in a Changing World, 3rd Edition 7 Data Flow Diagrams ◆ Graphical system model that shows all main requirements for an IS in one diagram ● Inputs / outputs ● Processes ● Data storage ◆ Easy to read and understand with minimal training 6 Systems Analysis and Design in a Changing World, 3rd Edition 8 Data Flow Diagram Symbols 6 Systems Analysis and Design in a Changing World, 3rd Edition 9 DFD Fragment from the RMO Case 6 Systems Analysis and Design in a Changing World, 3rd Edition 10 DFD Integrates Event Table and ERD [...]... flows into and out of the system 13 6 DFD Fragments x Created for each event in the event table x Represents system response to one event within a single process symbol x Self contained model x Focuses attention on single part of system x Shows only data stores required to respond to events 14 DFD Fragments for Course Registration System 6 15 6 Event-Partitioned System Model x DFD to model system requirements. .. flowed into the process or q Have been generated from data that flowed into the process 28 6 Unnecessary Data Input: Black Hole 29 Process with Impossible Data Output: Miracle 6 30 6 Process with Unnecessary Data Input 31 6 Process with Impossible Data Output 32 6 Documentation of DFD Components x Lowest level processes need to be described in detail x Data flow contents need to be described x Data stores... subsystem x Decomposition of the context level diagram x Sometimes called diagram 0 x Used primarily as a presentation tool x Decomposed into more detailed DFD fragments 16 6 Combining DFD Fragments 17 Context Diagram for RMO Customer Support System 6 18 6 RMO Subsystems and Events 19 Context Diagram for RMO Order-Entry Subsystem 6 20 DFD Fragments for RMO Order-Entry System 6 21 6 Decomposing DFD Fragments... interfaces 26 6 Data Flow Consistency Problems x Differences in data flow content between a process and its process decomposition x Data outflows without corresponding inflows x Data inflows without corresponding outflows x Results in unbalanced DFDs 27 6 Consistency Rules x All data that flows into a process must: q q x Flow out of the process or Be used to generate data that flow out of the process... early design 23 6 Detailed Diagram for Create New Order 24 6 Physical DFD for scheduling courses 25 6 Evaluating DFD Quality x Readable x Internally consistent x Accurately represents system requirements x Reduces information overload: Rule of 7 +/- 2 q q x Single DFD should have not more than 7 +/-2 processes No more than 7 +/- 2 data flows should enter or leave a process or data store on a single... described x Data stores need to be described in terms of data elements x Each data element needs to be described x Various options for process definition exist 33 6 Structured English x Method of writing process specifications x Combines structured programming techniques with narrative English x Well suited to lengthy sequential processes or simple control logic (single loop or if-then-else) x Ill-suited.. .6 DFD and Levels of Abstraction x Data flow diagrams (DFDs) are decomposed into additional diagrams to provide multiple levels of detail x Higher level diagrams provide general views of system x Lower level diagrams provide detailed views of system x Differing views are called levels of abstraction 11 6 Layers of DFD Abstraction 12 6 Context Diagrams x DFD that summarizes... Fragments for RMO Order-Entry System 6 21 6 Decomposing DFD Fragments x Sometimes DFD fragments need to be explored in more detail x Broken into subprocesses with additional detail x DFD numbering scheme: q Does not equate to subprocess execution sequence q It is just a way for analyst to divide up work 22 6 Physical and Logical DFDs x Logical model q q x Assumes implementation in perfect technology Does... sequential processes or simple control logic (single loop or if-then-else) x Ill-suited for complex decision logic or few (or no) sequential processing steps 34 6 Structured English Example 35 Process 2.1 and Structured English Process Description 6 36 . Objectives ◆ Explain how the traditional approach and the object-oriented approach differ when an event occurs ◆ List the components of a traditional system and the symbols representing them on a data. structured approach to representing activities and interactions ◆ Diagrams and other models of the traditional approach ◆ RMO customer support system example shows how each model is related ◆ How traditional. 6 Chapter 6: The Traditional Approach to Requirements Systems Analysis and Design in a Changing World, 3 rd Edition 6 Systems Analysis and Design in a