Podcast
Questions and Answers
What guideline should be followed to create a data flow diagram?
What guideline should be followed to create a data flow diagram?
- Avoiding isolating candidate processes for representation
- Creating multiple bubbles for the same data
- Maintaining information flow continuity from level to level (correct)
- Ensuring arrows and bubbles are not labeled
What is the purpose of listing all sensors 'read' by the software when developing a control flow diagram?
What is the purpose of listing all sensors 'read' by the software when developing a control flow diagram?
- To hide important information
- To increase the complexity of the diagram
- To identify potential candidate events (correct)
- To reduce the number of states in the system
What is a very common error in specifying control?
What is a very common error in specifying control?
- Possible omissions (correct)
- Focusing on candidate processes
- Reviewing all control items as possible inputs/outputs
- Listing all possible data conditions
How are system states described in a control specification?
How are system states described in a control specification?
What should be done when refining a data flow diagram at the next level?
What should be done when refining a data flow diagram at the next level?
Why is it essential to describe the behavior of a system in a control specification?
Why is it essential to describe the behavior of a system in a control specification?
What is a crucial aspect of creating a control flow diagram?
What is a crucial aspect of creating a control flow diagram?
What does 'nound-verb parse' applied to the processing narrative help identify?
What does 'nound-verb parse' applied to the processing narrative help identify?
What should be focused on to avoid common errors in specifying control?
What should be focused on to avoid common errors in specifying control?
What must be maintained from one level of a data flow diagram to another?
What must be maintained from one level of a data flow diagram to another?
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Study Notes
Data Flow Diagram (DFD)
- A level 2 DFD refines the Monitor Sensor Process level 1 DFD for Safe Home
- The Control Specification represents the behavior of the system in two ways:
- Programm Design Language (PDL) for designing and documenting methods and procedures in software
- Process Specification for describing all flow model processes at the final level of refinement
Data Dictionary
- A centralized repository of information about data, including:
- Meaning
- Relationships to other data
- Origin
- Usage
- Format
- Organized listing of all data elements pertinent to the system with precise definitions
- Contains the following information:
- Name: primary name of data or control item, data store, or external entity
- Alias: other names used for the first entry
- Where-used/How-used: listing of processes that use the data or control item and how it is used
- Content description: notation for representing content
- Supplementary information: other information about data types, preset values, restrictions, or limitations
Behavioral Modeling
- Operational principle for all requirements analysis methods
- State Transition Diagram represents the behavior of a system by depicting its states and the events that cause the system to change state
Entity Relationship Diagram
- Approach to create an ERD:
- List "things" that the application or business process addresses
- Define connections between data objects and external entities
- Create object relationships with cardinality and modality
- Iterate steps until all object relationships are defined
- Define attributes of each entity
- Formalize and review ERD
- Repeat steps until data modeling is complete
Creating a Data Flow Diagram
- Approach to create a DFD:
- Depict the software/system as a single bubble
- Identify primary input and output
- Refine by isolating candidate processes, data objects, and stores
- Label all arrows and bubbles with meaningful names
- Maintain information flow continuity from level to level
- Refine one bubble at a time
Establishing Connections and Cardinality/Modality
- Approach to establish connections and cardinality/modality:
- List all sensors that are "read" by the software
- List all interrupt conditions
- List all "switches" that are actuated by an operator
- List all data conditions
- Review all "control items" as possible CSPEC inputs/outputs
- Describe the behavior of a system by identifying its states, and define transitions between states
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