Lecture Chapter 6: The traditional approach to requirements

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Lecture "Chapter 6: The traditional approach to requirements" provides students with the knowledge: Data flow diagrams, DFD fragment from the RMO case, context diagrams, DFD fragments, event-Partitioned system model, DFD fagments for course,... Invite you to consult.

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Nội dung Text: Lecture Chapter 6: The traditional approach to requirements

6 6 Learning Objectives Chapter 6:  Explain how the traditional approach and the The Traditional Approach object-oriented approach differ when an event occurs to Requirements  List the components of a traditional system and Systems Analysis and Design in a Changing the symbols representing them on a data flow World, 3rd Edition diagram  Describe how data flow diagrams can show the system at various levels of abstraction Systems Analysis and Design in a Changing World, 3rd Edition 2 6 6 Learning Objectives (continued) Overview  Develop data flow diagrams, data element  What the system does what an event occurs: definitions, data store definitions, and process activities and interactions descriptions  Traditional structured approach to representing activities and interactions  Develop tables to show the distribution of  Diagrams and other models of the traditional processing and data access across system approach locations  RMO customer support system example shows  Read and interpret Information Engineering how each model is related models that can be incorporated within traditional  How traditional and IE approaches and models structured analysis can be used together to describe system Systems Analysis and Design in a Changing World, 3rd Edition 3 Systems Analysis and Design in a Changing World, 3rd Edition 4 6 6 Traditional and Object-Oriented Views of Requirements Models for the Traditional Activities and OO Approaches Systems Analysis and Design in a Changing World, 3rd Edition 5 Systems Analysis and Design in a Changing World, 3rd Edition 6
6 6 Data Flow Diagrams Data Flow Diagram Symbols  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 Systems Analysis and Design in a Changing World, 3rd Edition 7 Systems Analysis and Design in a Changing World, 3rd Edition 8 6 6 DFD Fragment from the RMO Case DFD Integrates Event Table and ERD Systems Analysis and Design in a Changing World, 3rd Edition 9 Systems Analysis and Design in a Changing World, 3rd Edition 10 6 6 DFD and Levels of Abstraction Layers of DFD Abstraction  Data flow diagrams (DFDs) are decomposed into additional diagrams to provide multiple levels of detail  Higher level diagrams provide general views of system  Lower level diagrams provide detailed views of system  Differing views are called levels of abstraction Systems Analysis and Design in a Changing World, 3rd Edition 11 Systems Analysis and Design in a Changing World, 3rd Edition 12
6 6 Context Diagrams DFD Fragments  DFD that summarizes all processing activity  Created for each event in the event table  Represents system response to one event within  Highest level (most abstract) view of system a single process symbol  Shows system boundaries  Self contained model  Focuses attention on single part of system  System scope is represented by a single process, external agents, and all data flows into and out of  Shows only data stores required to respond to the system events Systems Analysis and Design in a Changing World, 3rd Edition 13 Systems Analysis and Design in a Changing World, 3rd Edition 14 6 6 DFD Fragments for Course Event-Partitioned System Model Registration System  DFD to model system requirements using single process for each event in system or subsystem  Decomposition of the context level diagram  Sometimes called diagram 0  Used primarily as a presentation tool  Decomposed into more detailed DFD fragments Systems Analysis and Design in a Changing World, 3rd Edition 15 Systems Analysis and Design in a Changing World, 3rd Edition 16 6 6 Context Diagram for RMO Combining DFD Fragments Customer Support System Systems Analysis and Design in a Changing World, 3rd Edition 17 Systems Analysis and Design in a Changing World, 3rd Edition 18
6 6 Context Diagram for RMO RMO Subsystems and Events Order-Entry Subsystem Systems Analysis and Design in a Changing World, 3rd Edition 19 Systems Analysis and Design in a Changing World, 3rd Edition 20 6 6 DFD Fragments for RMO Decomposing DFD Fragments Order-Entry System  Sometimes DFD fragments need to be explored in more detail  Broken into subprocesses with additional detail  DFD numbering scheme:  Does not equate to subprocess execution sequence  It is just a way for analyst to divide up work Systems Analysis and Design in a Changing World, 3rd Edition 21 Systems Analysis and Design in a Changing World, 3rd Edition 22 6 6 Physical and Logical DFDs Detailed Diagram for Create New Order  Logical model  Assumes implementation in perfect technology  Does not tell how system is implemented  Physical model  Describes assumptions about implementation technology  Developed in last stages of analysis or in early design Systems Analysis and Design in a Changing World, 3rd Edition 23 Systems Analysis and Design in a Changing World, 3rd Edition 24
6 6 Physical DFD for scheduling courses Evaluating DFD Quality  Readable  Internally consistent  Accurately represents system requirements  Reduces information overload: Rule of 7 +/- 2  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 DFD  Minimizes required number of interfaces Systems Analysis and Design in a Changing World, 3rd Edition 25 Systems Analysis and Design in a Changing World, 3rd Edition 26 6 6 Data Flow Consistency Problems Consistency Rules  Differences in data flow content between a  All data that flows into a process must: process and its process decomposition  Flow out of the process or  Be used to generate data that flow out of the  Data outflows without corresponding inflows process  All data that flows out of a process must:  Data inflows without corresponding outflows  Have flowed into the process or  Have been generated from data that flowed into  Results in unbalanced DFDs the process Systems Analysis and Design in a Changing World, 3rd Edition 27 Systems Analysis and Design in a Changing World, 3rd Edition 28 6 6 Process with Impossible Data Output: Unnecessary Data Input: Black Hole Miracle Systems Analysis and Design in a Changing World, 3rd Edition 29 Systems Analysis and Design in a Changing World, 3rd Edition 30
6 6 Process with Unnecessary Data Input Process with Impossible Data Output Systems Analysis and Design in a Changing World, 3rd Edition 31 Systems Analysis and Design in a Changing World, 3rd Edition 32 6 6 Documentation of DFD Components Structured English  Lowest level processes need to be described in  Method of writing process specifications detail  Combines structured programming techniques  Data flow contents need to be described with narrative English  Data stores need to be described in terms of data  Well suited to lengthy sequential processes or elements simple control logic (single loop or if-then-else)  Each data element needs to be described  Ill-suited for complex decision logic or few (or no) sequential processing steps  Various options for process definition exist Systems Analysis and Design in a Changing World, 3rd Edition 33 Systems Analysis and Design in a Changing World, 3rd Edition 34 6 6 Process 2.1 and Structured Structured English Example English Process Description Systems Analysis and Design in a Changing World, 3rd Edition 35 Systems Analysis and Design in a Changing World, 3rd Edition 36
6 6 Decision Tree for Calculating Decision Tables and Decision Trees Shipping Charges  Can summarize complex decision logic better than structured English  Incorporates logic into the table or tree structure to make descriptions more readable Systems Analysis and Design in a Changing World, 3rd Edition 37 Systems Analysis and Design in a Changing World, 3rd Edition 38 6 6 Data Flow Definitions Data Element Definitions  Textual description of data flow’s content and  Data type description internal structure  e.g. string, integer, floating point, Boolean  Often coincide with attributes of data entities included in ERD  Sometimes very specific  Length of element  Maximum and minimum values  Data dictionary – repository for definitions of data flows, data stores, and data elements Systems Analysis and Design in a Changing World, 3rd Edition 39 Systems Analysis and Design in a Changing World, 3rd Edition 40 6 6 Components of a Traditional Analysis Model Information Engineering Models  Focuses on strategic planning, enterprise size, and data requirements of new system  Shares features with structured system development methodology  Developed by James Martin in early 1980’s  Thought to be more rigorous and complete than the structured approach Systems Analysis and Design in a Changing World, 3rd Edition 41 Systems Analysis and Design in a Changing World, 3rd Edition 42
6 6 Information Engineering System Process Decomposition and Dependency Development Life Cycle Phases Models  IE process models show three information types  Decomposition of processes into other processes  Dependency relationships among processes  Internal processing logic  Process decomposition diagram – represents hierarchical relationship among processes at different levels of abstraction  Process dependency model – describes ordering of processes and interaction with stored entities Systems Analysis and Design in a Changing World, 3rd Edition 43 Systems Analysis and Design in a Changing World, 3rd Edition 44 6 6 Process Dependency Diagram Process Dependency Diagram with Data Flows Systems Analysis and Design in a Changing World, 3rd Edition 45 Systems Analysis and Design in a Changing World, 3rd Edition 46 6 6 Locations and Communication Gathering Location Information Through Networks  Logical information needed during analysis  Identify locations where work is to be performed  Number of user locations  Draw location diagram  Processing and data access requirements at  List functions performed by users at each location various locations  Build activity-location matrix  Volume and timing of processing and data access  Rows are system activities from event table requests  Columns are physical locations  Needed to make initial design decisions such as:  Build Activity-data (CRUD) matrix  Distribution of computer systems, application software, database components, network capacity  CRUD – create, read, update, and delete Systems Analysis and Design in a Changing World, 3rd Edition 47 Systems Analysis and Design in a Changing World, 3rd Edition 48
6 6 RMO Location Diagram RMO Activity-Location Matrix Systems Analysis and Design in a Changing World, 3rd Edition 49 Systems Analysis and Design in a Changing World, 3rd Edition 50 6 6 Summary Summary (continued)  Data flow diagrams (DFDs) used in combination  Each process, data flow, and data store requires with event table and entity-relationship diagram detailed definition (ERD) to model system requirements  Analyst may define processes as structured  DFDs model system as set of processes, data English process specification, decision table, flows, external agents, and data stores decision tree, or process decomposition DFD  DFDs easy to read - graphically represent key  Process decomposition DFDs used when internal features of system using small set of symbols process complexity is great  Many types of DFDs: context diagrams, DFD fragments, subsystem DFDs, event-partitioned  Data flows defined by component data elements DFDs, and process decomposition DFDs and their internal structure Systems Analysis and Design in a Changing World, 3rd Edition 51 Systems Analysis and Design in a Changing World, 3rd Edition 52 6 Summary (continued)  Models from IE may supplement DFDs  Process decomposition diagram (how processes on multiple DFD levels are related)  Process dependency diagram (emphasizes interaction with stored entities)  Location diagram (geographic where system used)  Activity-location matrix (which processes are implemented at which locations)  Activity-data (or CRUD) matrix (where data used) Systems Analysis and Design in a Changing World, 3rd Edition 53