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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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Online Chapter B Systems Analysis and Design in a Changing World, 6th Edition
The Traditional Approach to Requirements Online Chapter B Systems Analysis and Design in a Changing World 6th Ed Satzinger, Jackson & Burd
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
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
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
Traditional vs. OO Approach Systems Analysis and Design in a Changing World, 6th Edition
Requirements Models for Traditional vs. OO Approach Systems Analysis and Design in a Changing World, 6th Edition
Data Flow Diagram Symbols Systems Analysis and Design in a Changing World, 6th Edition
DFD for process Look up item availability Systems Analysis and Design in a Changing World, 6th Edition
DFD DecomposesTo show different levels of abstractionContext DiagramDiagram 0Diagram 1 Systems Analysis and Design in a Changing World, 6th Edition
DFD FragmentsOne for each use case Systems Analysis and Design in a Changing World, 6th Edition
Combine DFD FragmentsTo Create Diagram 0 Systems Analysis and Design in a Changing World, 6th Edition
RMO Data Flow DiagramsContext Diagram Systems Analysis and Design in a Changing World, 6th Edition
RMO Subsystems and Use Cases Systems Analysis and Design in a Changing World, 6th Edition
Context Diagram for RMO Order Entry Subsystem Systems Analysis and Design in a Changing World, 6th Edition
DFD Fragments for RMO Order Entry Subsystem Systems Analysis and Design in a Changing World, 6th Edition
Diagram 0 for RMO Order Entry Subsystem Systems Analysis and Design in a Changing World, 6th Edition
Decomposing Process 2 from DFD Fragment 2 Systems Analysis and Design in a Changing World, 6th Edition
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
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
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
Structured English Example Systems Analysis and Design in a Changing World, 6th Edition
RMO Process 2.1 Structured English Systems Analysis and Design in a Changing World, 6th Edition
Structured English to determine delivery charges Systems Analysis and Design in a Changing World, 6th Edition
Decision Tablecalculating shipping charges Systems Analysis and Design in a Changing World, 6th Edition
Decision Treecalculating shipping charges Systems Analysis and Design in a Changing World, 6th Edition
Decision Table with multiple action rows Systems Analysis and Design in a Changing World, 6th Edition
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
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
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
Data Element Definitions Systems Analysis and Design in a Changing World, 6th Edition
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
RMO Location Diagram Systems Analysis and Design in a Changing World, 6th Edition
RMO Activity-Location Matrix Systems Analysis and Design in a Changing World, 6th Edition
RMO Activity-Data Matrix Systems Analysis and Design in a Changing World, 6th Edition
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
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