Decomposing Processes and DFDs Overview
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Questions and Answers

What does a context diagram represent?

  • A detailed breakdown of system processes
  • An overview of the business process with external data flows (correct)
  • A list of data stores used in the system
  • The interactions between internal and external entities

    • Which of the following statements is true about the context diagram?

  • It is the lowest level of detail in DFDs.
  • It includes data stores for clarity.
  • It represents a single process and its external data flows. (correct)
  • It is labeled with decimal numbers for each process.

    • What process level follows the context diagram in a DFD?

  • Level 0
  • Level 2
  • Level 3
  • Level 1 (correct)

    • How are processes numbered in a DFD?

    <p>With decimal places corresponding to their level of detail</p> Signup and view all the answers

    What is the term used for breaking down a DFD into levels?

    <p>Decomposition</p> Signup and view all the answers

    Which of the following levels in a DFD indicates the greatest detail?

    <p>Level 3</p> Signup and view all the answers

    What is not included in a context diagram?

    <p>Data stores</p> Signup and view all the answers

    What is the primary purpose of using Data Flow Diagrams (DFDs) in business processes?

    <p>To illustrate how data flows within a system</p> Signup and view all the answers

    Why is it important to use different numbering for DFD processes at multiple levels?

    <p>To avoid confusion about the current level</p> Signup and view all the answers

    Which statement best describes a Logical DFD?

    <p>It highlights how data flows within the system process</p> Signup and view all the answers

    Which symbol is used to represent a data store in a Data Flow Diagram?

    <p>Two parallel lines</p> Signup and view all the answers

    What distinguishes a Physical DFD from a Logical DFD?

    <p>Physical DFD focuses on data flow implementation; Logical DFD focuses on data flow processes</p> Signup and view all the answers

    Which notation system for DFDs uses different symbols for each element?

    <p>Gane &amp; Sarson</p> Signup and view all the answers

    How does decomposing a process into DFDs help in managing complexity?

    <p>It provides a detailed view of individual data interactions</p> Signup and view all the answers

    Which element in a DFD is represented by a circle or a rectangle with rounded corners?

    <p>Process</p> Signup and view all the answers

    What is indicated by the data flow represented as an arrow in a DFD?

    <p>The direction of data movement</p> Signup and view all the answers

    What is the main purpose of a context diagram in a business process?

    <p>To represent the entire system in context with its environment</p> Signup and view all the answers

    Which rule states that inputs to a process must be different from outputs?

    <p>Rule #2</p> Signup and view all the answers

    What happens if data were to move directly from a source to a data store?

    <p>It violates Rule #4</p> Signup and view all the answers

    What does it mean when a process is classified as a 'black hole'?

    <p>The process has only outputs</p> Signup and view all the answers

    Which level diagram can a process model be decomposed into?

    <p>Level 1 diagram</p> Signup and view all the answers

    What is a necessary condition for level 0 and level 1 DFDs?

    <p>They should be balanced</p> Signup and view all the answers

    What is true about the naming of objects in a DFD?

    <p>Each object must have a unique name</p> Signup and view all the answers

    What occurs when data moves directly from one data store to another without processing?

    <p>This violates Rule #6</p> Signup and view all the answers

    What does cardinality define in a data model?

    <p>The relationship ratio between related entities</p> Signup and view all the answers

    Which option correctly describes a 1:N relationship?

    <p>One instructor can teach multiple courses</p> Signup and view all the answers

    What is the primary key in a physical data model?

    <p>A unique identifier for each instance in an entity</p> Signup and view all the answers

    What does Rule #10 state about data flow in Data Flow Diagrams (DFDs)?

    <p>A data flow should not flow in only one direction between symbols.</p> Signup and view all the answers

    Which of the following best defines modality in a data model?

    <p>The necessity of an instance’s existence in relation to another</p> Signup and view all the answers

    What is meant by a 'fork' in the context of data flow within DFDs?

    <p>The same data going from a common location to two or more processes.</p> Signup and view all the answers

    What does a foreign key accomplish in a database?

    <p>Links tables by referencing a primary key from another table</p> Signup and view all the answers

    Which step is NOT part of creating an Entity Relationship Diagram (ERD)?

    <p>Assign random identifiers to entities</p> Signup and view all the answers

    According to DFD rules, what does an arrow into a process represent?

    <p>Input to the process.</p> Signup and view all the answers

    What do entities represent in a data model?

    <p>Real-world objects or concepts</p> Signup and view all the answers

    Which rule specifies the output characteristics of a data flow?

    <p>Rule #14 indicates that a data flow updates a data store.</p> Signup and view all the answers

    How are process models and data models interrelated?

    <p>Process models contain data components related to data models</p> Signup and view all the answers

    What does Rule #19 state about how processes should be labeled in DFDs?

    <p>Processes should be labeled with a verb phrase.</p> Signup and view all the answers

    Which of these statements is incorrect about data flow in relation to its rules?

    <p>A data flow can go directly back to the same process it leaves.</p> Signup and view all the answers

    What does Rule #18 specify regarding data stores in DFDs?

    <p>They are labeled with noun phrases.</p> Signup and view all the answers

    Which statement regarding a Data Flow Diagram (DFD) is false?

    <p>DFDs can also represent control flows between processes.</p> Signup and view all the answers

    Study Notes

    Decomposing Processes and Data Flow Diagrams (DFDs)

    • Data Flow Diagrams (DFDs) visually represent data movement in a system, aiding in managing process complexity.
    • Consistency in DFD notation is essential for clearly identifying processes and their relationships.
    • Two primary types of DFDs:
      • Logical DFD: Concentrates on system processes and data flow.
      • Physical DFD: Shows data flow implementation, including processing locations.

    Elements of DFDs

    • Entity (Source/Sink): External source interacting with the system, represented by a square.
    • Process: An action performed on data, depicted with a circle or rounded rectangle.
    • Data Store: Collection of stored data, shown with two parallel lines or an open-ended rectangle.
    • Data Flow: Movement of data between elements, indicated by an arrow.

    DFD Notations

    • Gane & Sarson: Utilizes unique symbols for different DFD elements.
    • Yourdon & DeMarco: Employs a standardized set of symbols.

    Context Diagram and Decomposition

    • The context diagram (level 0) provides a high-level overview of the entire process without data stores.
    • Level "1" DFDs detail specific processes, decomposing them further for clarity.
    • Up to 6 or 7 levels may exist depending on system complexity, emphasizing decomposition.

    Numbering Levels and Balancing

    • Level numbering follows a decimal system; for example, Level 1 processes are labeled 1.0, 1.1, etc.
    • Balancing: Information in DFDs must be accurately represented across levels; ensuring inputs and outputs match is critical.

    DFD Rules

    • Rule #1: Maintain balanced DFD levels; conservation of inputs/outputs is vital.
    • Additional rules define behaviors of data flow and processing restrictions:
      • Inputs and outputs must differ.
      • Processes cannot consist solely of outputs or inputs (termed "miracle" and "black hole").
      • Data flow must be labeled correctly, and a source cannot send data directly to another source.

    Entity-Relationship Diagram (ERD)

    • ERDs illustrate business system data creation, storage, and utilization.
    • Cardinality: Indicates instance ratios between entities (e.g., 1:1, 1:N, M:N).
    • Primary Key: Uniquely identifies entity instances.
    • Foreign Key: Establishes links between tables.
    • Modality: Suggests whether child instances can exist without parent instances.

    Relationships in ERDs

    • Entities represent real-life objects (e.g., student, department) and are linked through relationships like "enrolls" or "teaches".
    • Adding attributes to entities enhances data specifications (e.g., student name, product price).

    Balancing ERDs with DFDs

    • Process models and data models are interrelated; the process model incorporates two data components—data and data store—bridging DFD and ERD understanding.

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    Description

    This quiz covers the essential elements and notation of Data Flow Diagrams (DFDs), including the distinction between logical and physical DFDs. It emphasizes the importance of consistency in DFD notation for effective system analysis and visualization of data movement. Test your understanding of how DFDs represent processes and data flow within a system.

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