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