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Traditional Approach to Requirements - Systems Analysis and Design in a Changing World

This chapter explores the traditional approach to representing requirements in systems analysis and design. It covers topics such as data flow diagrams, documentation of DFD components, and communication through networks.

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Traditional Approach to Requirements - Systems Analysis and Design in a Changing World

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  1. Online Chapter B Systems Analysis and Design in a Changing World, 6th Edition

  2. The Traditional Approach to Requirements Online Chapter B Systems Analysis and Design in a Changing World 6th Ed Satzinger, Jackson & Burd

  3. Online Chapter B Outline • Traditional and Object-Oriented Views of Activities and Use Cases • Data Flow Diagrams • Documentation of DFD Components • Locations and Communication through Networks Systems Analysis and Design in a Changing World, 6th Edition

  4. Learning Objectives • Explain how the traditional approach and the object-oriented approach differ when modeling the details of a use case • 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 • 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 Systems Analysis and Design in a Changing World, 6th Edition

  5. Overview • Chapters 3, 4, and 5 described two key concepts associated with modeling functional requirements in the newer (OO) approaches to information systems development: the use cases and the domain classes involved in users’ work • This chapter describes an older and more traditional approach to representing requirements • Entity-relationship diagrams represent things in the user’s work domain • Data flow diagrams (DFDs) and associated concepts model system processes instead of use case diagrams and system sequence diagrams Systems Analysis and Design in a Changing World, 6th Edition

  6. Traditional vs. OO Approach Systems Analysis and Design in a Changing World, 6th Edition

  7. Requirements Models for Traditional vs. OO Approach Systems Analysis and Design in a Changing World, 6th Edition

  8. Data Flow Diagram Symbols Systems Analysis and Design in a Changing World, 6th Edition

  9. DFD for process Look up item availability Systems Analysis and Design in a Changing World, 6th Edition

  10. DFD DecomposesTo show different levels of abstractionContext DiagramDiagram 0Diagram 1 Systems Analysis and Design in a Changing World, 6th Edition

  11. DFD FragmentsOne for each use case Systems Analysis and Design in a Changing World, 6th Edition

  12. Combine DFD FragmentsTo Create Diagram 0 Systems Analysis and Design in a Changing World, 6th Edition

  13. RMO Data Flow DiagramsContext Diagram Systems Analysis and Design in a Changing World, 6th Edition

  14. RMO Subsystems and Use Cases Systems Analysis and Design in a Changing World, 6th Edition

  15. Context Diagram for RMO Order Entry Subsystem Systems Analysis and Design in a Changing World, 6th Edition

  16. DFD Fragments for RMO Order Entry Subsystem Systems Analysis and Design in a Changing World, 6th Edition

  17. Diagram 0 for RMO Order Entry Subsystem Systems Analysis and Design in a Changing World, 6th Edition

  18. Decomposing Process 2 from DFD Fragment 2 Systems Analysis and Design in a Changing World, 6th Edition

  19. Evaluating DFD Quality • Minimize complexity • Information overload– difficulty in understanding that occurs when a reader receives too much information at one time • Rule of 7 ± 2 (Miller’s number)– the rule of model design that limits the number of model components or connections among components to no more than nine • Minimization of interfaces– a principle of model design that seeks simplicity by limiting the number of connections among model components Systems Analysis and Design in a Changing World, 6th Edition

  20. Evaluating DFD Quality • Ensuring Data Flow Consistency • Three Common Errors • Differences in data flow content between a process and its process decomposition • Data outflows without corresponding data inflows • Data inflows without corresponding outflows • Balancing – equivalence of data content between data flows entering and leaving a process and data flows entering and leaving a process decomposition DFD • Black hole– a process or data store with a data input that is never used to produce a data output • Miracle – a process or data store with a data element that is created out of nothing Systems Analysis and Design in a Changing World, 6th Edition

  21. Process Descriptions • Structured English– a method of writing process specifications that combines structured programming techniques with narrative English • Decision table– a tabular representation of processing logic containing decision variables, decision variable values, and actions or formulas • Decision tree– a graphical description of process logic that uses lines organized like branches of a tree Systems Analysis and Design in a Changing World, 6th Edition

  22. Structured English Example Systems Analysis and Design in a Changing World, 6th Edition

  23. RMO Process 2.1 Structured English Systems Analysis and Design in a Changing World, 6th Edition

  24. Structured English to determine delivery charges Systems Analysis and Design in a Changing World, 6th Edition

  25. Decision Tablecalculating shipping charges Systems Analysis and Design in a Changing World, 6th Edition

  26. Decision Treecalculating shipping charges Systems Analysis and Design in a Changing World, 6th Edition

  27. Decision Table with multiple action rows Systems Analysis and Design in a Changing World, 6th Edition

  28. Data Flow Definitions • Data flow definition– a textual description of a data flow’s content and internal structure • Can be simple list of data elements that make up the data flow. For new order: • Can use an algebraic notation to indicate elements and structure Systems Analysis and Design in a Changing World, 6th Edition

  29. Data Flow Definitions • RMO products and items report defined using algebraic notation. Note nested repeating groups like typical control break report. Systems Analysis and Design in a Changing World, 6th Edition

  30. Data Dictionary and Other Definitions • Data dictionary– a repository for definitions of data flows, data elements, and data stores • A data store on the DFD represents a data entity on the ERD, no separate definition is typically needed • Data element definitions • Describe a data type, such as string, integer, floating point, or Boolean • Each element should also be defined to indicate specifically what it represents and how it is validated • Use the person from Mars concept—would someone from Mars know what element means? Systems Analysis and Design in a Changing World, 6th Edition

  31. Data Element Definitions Systems Analysis and Design in a Changing World, 6th Edition

  32. Locations and Communication Through Networks • Location diagram– a diagram or map that identifies all the processing locations of a system • Activity-location matrix– a table that describes the relationship between processes and the locations in which they are performed • Activity-data matrix– a table that describes storeddata entities, the locations from which they are accessed, and the nature of the accesses • CRUD – acronym for create, read, update, and delete Systems Analysis and Design in a Changing World, 6th Edition

  33. RMO Location Diagram Systems Analysis and Design in a Changing World, 6th Edition

  34. RMO Activity-Location Matrix Systems Analysis and Design in a Changing World, 6th Edition

  35. RMO Activity-Data Matrix Systems Analysis and Design in a Changing World, 6th Edition

  36. Summary • Data flow diagrams (DFDs) are used in combination with the use cases and entity-relationship diagram (ERD) to model system requirements • DFDs model a system as a set of processes, data flows, external agents, and data stores • Many types of DFDs are developed, including context diagrams, DFD fragments, subsystem DFDs, diagram 0, and process decomposition DFDs • Each process, data flow, and data store requires a detailed definition Systems Analysis and Design in a Changing World, 6th Edition

  37. Summary (continued) • Analysts may define processes in a number of ways, including a structured English process specification, a decision table, a decision tree, or a process decomposition DFD • Data flows are defined in terms of their component data elements and their internal structure. • Data elements may be further defined in terms of their type and allowable content • Data stores correspond to entities on the ERD and thus require no additional definition • The location diagram, activity-location matrix, and activity-data matrix describe important information about system locations Systems Analysis and Design in a Changing World, 6th Edition

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