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Information Systems System Analysis 421 Class Seven

Information Systems System Analysis 421 Class Seven. Structuring System Requirements: Process Modeling. Learning Objectives. Understand the logical modeling of processes through studying data flow diagrams How to draw data flow diagrams using rules and guidelines

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Information Systems System Analysis 421 Class Seven

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  1. Information Systems System Analysis 421Class Seven Structuring System Requirements: Process Modeling

  2. Learning Objectives • Understand the logical modeling of processes through studying data flow diagrams • How to draw data flow diagrams using rules and guidelines • How to decompose data flow diagrams into lower-level diagrams • Balancing of data flow diagrams 8.2

  3. Learning Objectives • Explain the differences among four types of DFDs: current physical, current logical, new physical and new logical • Discuss the use of data flow diagrams as analysis tools • Compare and contrast data flow diagrams with Oracle’s process modeling tool and with functional hierarchy diagrams • Discuss process modeling for Internet applications 8.3

  4. Data Modeling Entity Relationship Data Flow Diagram Prototypes

  5. System Modeling • One way to structure unstructured problems is to draw a model • A model is a representation of reality - picture worth a thousand words • Built to understand the existing system as a way to document business requirements • Data modeling is a technique for defining business requirements • Data is viewed as a resource to be shared by as many processes as possible, data must be organized in a way that is flexible and adaptable to unanticipated business requirements

  6. System Modeling • Physical model shows not only what a system does but how the system is physically and technically implemented - depicts technical design • Logical models depict business requirements illustrates the essence of the system • Move biases that are the results of the way the current system is implemented • Reduce the risk of missing requirements • Allow us to communicate with end users • Help analysts and users understand business terminology and rules

  7. Process Modeling • The simplest process model of a system is based on inputs, outputs, and the system itself – Viewed a process. • The process symbol defines the boundary of the system. • The system is inside the boundary; the environment is outside that boundary. • The system exchanges inputs and outputs with its environment. • Process is work performed on, or in response to, incoming data flows or conditions.

  8. Process Modeling • Graphically represent the processes that capture, manipulate, store and distribute data between a system and its environment and among system components • Data flow diagrams (DFD) • Graphically illustrate movement of data between external entities and the processes and data stores within a system • Modeling a system’s process • Utilize information gathered during requirements determination • Structure of the data is also modeled in addition to the processes 8.8

  9. Process Modeling • Deliverables and Outcomes • Set of coherent, interrelated data flow diagrams • Context data flow diagram (DFD) • Scope of system • DFDs of current system • Enables analysts to understand current system • DFDs of new logical system • Technology independent • Show data flows, structure and functional requirements of new system • Project dictionary and CASE repository 8.9

  10. Data Flow Diagrams • Data modeling is done during the project definition stage and refined in physical design • Similar to ERD Data model - DFD also helps the analyst identify business vocabulary and uncover business requirements • Can be used on current system to understand requirements • Can be fit on several sheets of paper • The level of data flow diagram can be compared to a highway and street maps that you might use - National => State => City

  11. Data Flow Diagrams Tool that depicts the flow of data through a system and the work or processing performed by that system Graphical tool used to describe and analyze the movement of data through a system manual or automated Central tool in which other components are developed A data flow diagram (DFD) is a tool that depicts the flow of data through a system and the work or processing performed by that system. Synonyms include bubble chart, transformation graph, and process model

  12. DFD Symbols

  13. DFD Symbols new order Verify Credit 3.2 3.2 Verify Credit Customer Master File Customer • Named vector or arrow • Called a data flow • Portrays a data path • Bubble • Called a process • Portrays transformation of data • Narrow open rectangle • Called a data store • Portrays a file or data base • Box • Called a source or sink • Portrays an internal or external agent • Used to define a system’s boundaries

  14. DFD Symbols 2.0 Update Goods Sold • Data flow - data move in a specific direction • Processes - people, procedures or device that transforms data - work to be done • Source or destination - external source or destination of data which may be people, program, organization or other entities - The squares represent external agents – the boundary of the system. • Data Store - where data is house Customer Good Sold File

  15. DFD Symbols 1 Accepted Orders Orders Customer Verify Credit 2 Ship Order Data Flow Credit History External Entity Process Customer File Data Store

  16. DFD Symbols

  17. Data Flow • A data flow is data in motion. • The flow of data between a system and its environment, or between two processes inside a system an relationship between a system and its environment, or between two processes is communication. • A data flow represents an input of data to a process, or the output of data (or information) from a process. A data flow is also used to represent the creation, deletion, or update of data in a file or database (called a data store on the DFD). • A data flow is depicted as a solid-line with arrow.

  18. Data Flow

  19. Data Flow • No data flow should ever go completely unnamed. • Data flow names should describe the data flow without describing how the flow is or could be implemented. • All data flows must begin or end at a process, because data flows are the inputs and outputs of a process. • Naming Convention - Should be descriptive nouns and noun phrases that are singular, as opposed to plural. • Should be unique. • Use adjectives and adverbs to help to describe how processing has changed a data flow.

  20. Data Flow

  21. Data Flow Packet Concept • Data is seen as a package of information

  22. Data Store • Data Store • Depicts data at rest • May represent data in • File folder • Computer-based file • Notebook • The name of the store as well as the number are recorded in between lines 8.22

  23. Data Stores • Most information systems capture data for later use. • The data is kept in a data store. • A data store is an ``inventory’’ of data. Synonyms include file and database (although those terms are too implementation-oriented for essential process modeling). • A data store is represented by the open-end box. • If data flows are data in motion, think of data stores as data at rest. • Data stores should describe ``things’’ about which the business wants to store data. • It is permissible to duplicate data stores on a DFD to avoid crossing data flow lines.

  24. Data Stores • Data cannot be moved from one data store to another data stored it must be moved by a process • Data cannot be moved from an outside source to a data store it must be moved by a process • Data Stores should have noun phrase labels • Data Stores can be labeled • Data flow to a data store means new/update • Data flow from a data store means retrieve A Good Sold File

  25. DFD Rules - Data Stores Good Sold File Inventory Students Customer Inventory 3.0 Produce Mgmt Reports Manager What’s valid ! Good Sold File Management Reports

  26. DFD Rules - Data Stores Good Sold File Inventory 3.0 Creates Reports Students Customer Inventory 3.0 Produce Mgmt Reports Manager What’s valid ! Sold data Sold data Student Data Inventory Data Good Sold File Management Reports

  27. Process 1.0 Process Customer Food Order • Process names should be descriptive. • Processes should have a single Action Verb and a Singular Object. • Process numbers strictly used for identification • All Processes are connected to something. • All Processes have both Inputs and Outputs. • No Process has only outputs or only inputs. • Processes may connect to anything: other processes, data stores or entities. • Each Process has a unique name and number. • A Process number is used only once in a diagram set.

  28. Process • Black Holes and Miracles 1 1 Process 1 Process 1 Entity Entity y x x y Data Store Data Store

  29. Process Example 1.0 1.0 Process Customer Food Order Process Customer Food Order 1.0 1.0 Process Customer Food Order Process Customer Food Order Which ones are correct and incorrect?

  30. External Entities • Source/Sink • Depicts the origin and/or destination of the data • Sometimes referred to as an external entity • Drawn as a square symbol • Name states what the external agent is • Because they are external, many characteristics are not of interest to us 8.30

  31. External Entities • All information systems respond to events and conditions in the environment. • The environment of an information system includes external entities that form the boundary of the system, and define places where the system interfaces with its environment. • A external entity defines an a person, organization unit, other system, or other organization that lies outside of the scope of the project, but which interacts with the system being studied. • External agents provide the net inputs into a system, and receive net outputs from a system. • Common synonyms include external agents

  32. External Entities • The term external means “external to the system being analyzed or designed.” • An external agent is represented by a square on the data flow diagram. • External agents on a logical data flow diagram may include people, business units, other internal systems with which your system must interact, and external organizations. • External agents should be named with descriptive, singular nouns. • As a general rule, external agents should be located on the perimeters of the page, consistent with their definition as a system boundary.

  33. Data Flow Diagramming Definitions • Context Diagram • A data flow diagram (DFD) of the scope of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the entities and the system • Level-O Diagram • A data flow diagram (DFD) that represents a system’s major processes, data flows and data stores at a high level of detail 8.33

  34. Fast Food Restaurant • Context diagram an overview of an organization system that shows • the system boundaries • sources that interact with the system • major information flow between the entities

  35. Fast Food Restaurant • The Context Diagram • The context diagram contains one and only one process. • External entities are drawn around the perimeter. • Data flows define the interactions of your system with the boundaries and with the external data stores. • Refer as Level Zero • Let’s draw a context diagram • What does a restaurant do - think McDonalds or Hoosier • What are the boundaries • Who does it interact with

  36. Developing DFDs: An Example • Hoosier Burger’s automated food ordering system • Context Diagram (Figure 8-4) contains no data stores • Next step is to expand the context diagram to show the breakdown of processes (Figure 8-5) 8.36

  37. Figure 8-4Context diagram of Hoosier Burger’s food ordering system 8.37

  38. Figure 8-5Level-0 DFD of Hoosier Burger’s food ordering system 8.38

  39. Source/Sink Data cannot move directly from a source to a sink A source/sink has a noun phrase label Data Flow A data flow has only one direction of flow between symbols A fork means that exactly the same data goes from a common location to two or more processes, data stores or sources/sinks Data Flow Diagramming Rules 8.39

  40. Data Flow Diagramming Rules • Data Flow (Continued) • A join means that exactly the same data comes from any two or more different processes, data stores or sources/sinks to a common location • A data flow cannot go directly back to the same process it leaves • A data flow to a data store means update • A data flow from a data store means retrieve or use • A data flow has a noun phrase label 8.40

  41. Data Flow Example Incorrect Correct

  42. DFD Rules -- Data Flow Incorrect Correct

  43. What are the rules violations? 2 2.1 Process Green Process Blue Data Store 1 Dataflow 2 Entity A Dataflow 5 Dataflow 3 Dataflow 6 Dataflow 7 Dataflow 1 Dataflow 4 Entity B Dataflow 2 Dataflow 8 That’s All

  44. Decomposition of DFDs • Functional decomposition • Act of going from one single system to many component processes • Repetitive procedure • Lowest level is called a primitive DFD • Level-N Diagrams • A DFD that is the result of n nested decompositions of a series of subprocesses from a process on a level-0 diagram 8.46

  45. Relationship Among DFD levels

  46. Shows all the processes that comprise the overall system Shows how information moves from and to each process Adds data stores Level 0 Diagram

  47. Shows all the processes that comprise a single process on the level 0 diagram Shows how information moves from and to each of these processes Shows in more detail the content of higher level process Level 1 diagrams may not be needed for all level 0 processes Level 1 Diagrams

  48. Shows all processes that comprise a single process on the level 1 diagram Shows how information moves from and to each of these processes Level 2 diagrams may not be needed for all level 1 processes Correctly numbering each process helps the user understand where the process fits into the overall system The Data Flow Diagram (DFD) is an essential tool for creating formal descriptions of business processes and data flows. Use cases record the input, transformation, and output of business processes. Eliciting scenario descriptions and modeling business processes are critically important skills for the systems analyst to master. Level 2 Diagrams

  49. Balancing DFDs • When decomposing a DFD, you must conserve inputs to and outputs from a process at the next level of decomposition • This is called balancing • Example: Hoosier Burgers • In Figure 8-4, notice that there is one input to the system, the customer order • Three outputs: • Customer receipt • Food order • Management reports 8.51

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