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Hi600 u05_inst_slides

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Hi600 u05_inst_slides

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Hi600 u05_inst_slides

  1. 1. HI-600: Analysis and Design of Health Information Systems Analysis: Part III Process Modeling: Data Flow Diagrams
  2. 2. Process Modeling • A process model can be used to further clarify the requirements definition and use cases. • A process model is a graphical way of representing how a business system should operate. • A process model can be used to document the as-is system or the to-be system, whether computerized or not.
  3. 3. Process Modeling • Data flow diagramming is a process modeling technique that diagrams the business processes and the data that pass among them. • Logical process models describe processes without suggesting how they are conducted. • Physical process models provide information that is needed to build the system.
  4. 4. Data Flow Diagrams (DFDs)
  5. 5. Elements of Data Flow Diagrams • Process – A process is an activity or a function performed for some specific business reason. • Data Flow – A data flow is a single piece of data, or a logical collection of several pieces of information. • Data Store – A data store is a collection of data that is stored in some way. • External Entity – An external entity is a person, organization, organization unit, or system that is external to the system, but interacts with it.
  6. 6. Using DFDs to Define Business Processes
  7. 7. Process Descriptions • The purpose of the process descriptions is to explain what the process does and provide additional information that the DFD does not provide. • Three techniques are commonly used to describe more complex processing logic: • Structured English • Decision trees • Decision tables
  8. 8. Data Flow Diagram Creation Steps 1. Build the context diagram. 2. Create DFD fragments for each use case. 3. Organize the DFD fragments into level 0 diagram. 4. Develop level 1 DFDs based on the steps with each use case. In some cases, these level 1 DFDs are further decomposed into level 2 DFDs, level 3 DFDs, and so son. 5. Validate the set of DFDs to make sure that they are complete and correct.
  9. 9. Step 1: Creating the Context Diagram
  10. 10. Step 2: Creating DFD Fragments
  11. 11. Step 3: Creating the Level 0 Diagram
  12. 12. Step 4: Creating Level 1 Data Flow Diagrams (and Below)
  13. 13. Step 5: Validating the DFD • There two fundamental types of errors in DFDs: • Syntax errors – can be thought of as grammatical errors that violate the rules of the DFD language. • Semantics errors – can be thought of as misunderstandings by the analyst in collecting, analyzing, and reporting information about the system.
  14. 14. Common Syntax Errors Law of conservation of data • Data at rest stays at rest until moved by a process • Processes cannot consume or create data
  15. 15. How to Check for Semantic Errors • To ensure that the model is an appropriate representation by asking the users to validate the model in a walk-through • To ensure consistent decomposition • To ensure that the terminology is consistent throughout the model
  16. 16. SUMMARY • Data Flow Diagram Syntax – four symbols are used on data flow diagrams (processes, data flows, data stores, and external entities). • Creating Data Flow Diagrams • The DFDs are created from use cases. • Every set of DFDs starts with a context diagram. • DFDs segments are created for each use case, and are then organized into a level 0 DFD. • Level 1 DFDs are developed on the basis of the steps within each use case. • The set of DFDs are validated to make sure that they are complete and correct and contain no syntax or semantics errors.

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