ITM 5400 Chapter 5 - Data and Process Modeling Flashcards
What is a data flow diagram (DFD)?
Shows how data flows through a system. Does not show logic or processing steps.
- Logic model
- Does not show how transformations are done
- Prevents any restrictions on how the processes are implemented
Two basic schools of DFD are?
Gane and Sarson
Yourdon
What are the four basic symbols in DFD?
Process
Data Store
Entity
Data Flow
What is the minimum number of inputs for a Process Symbol?
There must be at least 1 input and at least 1 output
What are three incorrect data flows?
Spontaneous generation - process has no input
Black Hole - no output flows
Gray hole - has input and output but it is obvious that in input itself is insufficient
What is a data store in DFD?
Represents data the system stores
Does not show detailed content of a data store
** Data store must be connected to a process witha data flow.
What is an entity symbol?
Shows how the system interfaces to the world
DFD shows only external entities
DFD Entities are called terminators
*** Each entity must be connected to the process by a data flow
What is a context diagram?
A high level view of a system
- Defines boundaries of a system
- Shows all external entities that interact with a system
T/F A DFD should fit on 2 pages.
False it should fit on one page
T/F A DFD should use the same name for an item whenever it is used
True. Student should be named student any time it is used
What are the three steps in developing a set of DFDs?
- Draw the Context Diagram
- Draw the Level 0 DFD
- Decompose Level 0 DFD into lower level DFDs until processes are decomposed to lowest level
What is a data dictionary
Central storehouse of information about a systems data
- Describes contents of each data flow
- Describes contents of each data store
- ID the data elements or data items within a system
What is used to build the data dictionary of a system?
A CASE tool
What is the lowest piece of data called?
Data Element - eg. customer name
Data elements are grouped into records based called
Data structures based on some common attribute, ig customer record contains customer name, phone number, address etc
What contains individual records which use all the same data structures?
Data store - customer data store contains one record for each customer
What information should be collected for each data element?
- Data element name
- Alias
- Data type
- Length of field
- Default value - value if nothing is entered
- Acceptable values
- Source
- Security - who can add or delete or view element
- Responsible users
- Description or comments
What should be collected for each data flow?
Name Description Alias Origin Destination Record - what data structure is used Volume and Freqencies
What items should be collected for each data store?
Name
Description
Alias
Volume and freq
What should be collected for each process?
Name
Descri[tion
Process number
Process description
What should be collected for each record
Name
Definition
Alias
Attributes
What does a process description describe?
The processing steps and business logic in each functional primative
Processes are generally describe as using what 3 things?
English
Decision tables
Decision trees
What are processes broken down into?
Related steps called modules
What is used to break processes down info a series of logic structures?
Modular design
- each structure has single entry and exit point
- control structures are sequence, selection and iteration (loop)
COntrol structures have three types
Structured - steps completed in order
Selection - based on results of a test
Iteration - executed until a condition is met
A decision table is a logical structure that shows every combination of conditions and outcomes.
True
- Used to insure all possible situations have been considered
- Number of rules double each time a condition is added
- `Very effective in describing complex conditions
What is a graphical representation of conditions, actions and rules found in decision table
Decision tree
What is 4 model approach
Develops models to describe the current system before developing models of a new system
What are the 4 models in the 4 model approach
Physical model of current system
Physical model of new system
Logical model of current system
Logical model of new system
What are the 3 main tools used for data process modeling?
DFD
Data Dictionary
Process Description
