10 Questions
What guideline should be followed to create a data flow diagram?
Maintaining information flow continuity from level to level
What is the purpose of listing all sensors 'read' by the software when developing a control flow diagram?
To identify potential candidate events
What is a very common error in specifying control?
Possible omissions
How are system states described in a control specification?
By identifying transitions between states
What should be done when refining a data flow diagram at the next level?
Carefully noting primary inputs and outputs again
Why is it essential to describe the behavior of a system in a control specification?
To identify how each state is reached and defined transitions between states
What is a crucial aspect of creating a control flow diagram?
Listing all possible switches that are actuated by an operator
What does 'nound-verb parse' applied to the processing narrative help identify?
Control specification inputs/outputs
What should be focused on to avoid common errors in specifying control?
Possible omissions
What must be maintained from one level of a data flow diagram to another?
Information flow continuity
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
This quiz covers the refinement of the Monitor Sensor process in the Level 1 DFD for a Safe Home system, along with the Control Specification, Program Design Language (PDL), Process Specification, and Data Dictionary in software development.
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