1. Intro to Software System Modeling

2. Model vs Design Model Design may be used in the SRS
used by the software designers
may be useful as an overview for the programmers
may be used for validation with the customer
Design
what the programmers are told to build

3. What info is modeled? Relationships between Data Process Flow
Data Transformation
Control Flow within the source code
Format of the Database
Timing constraints (real-time systems)
User Interface Flow
etc…

4. Major Modeling and Design Diagrams
UML
Data Flow Diagrams
State Transition Diagrams
Structure Charts
Entity Relationship Diagrams
Use Cases

5. Data Flow Diagrams Illustrate how processes transform data
Very good for modeling a system at a high level, e.g. for the SRS
Poor at conveying design of software, except a few cases such as distributed systems
process
external
entity
data flow
data file

6. DFD Syntax Rules
a model is composed of a series of diagrams that present more and more detail
the top-level diagram is the "context" level and contains only one process (our software)
data cannot just appear or disappear, i.e. inputs and outputs must match between levels
process numbers indicate both family and level of detail
all data flows are defined in a Data Dictionary

7. DFD Example Display Panel display Control data Keypad commands Alarm
Alarm
System
alarm
type
Alarm
sensor
status
Sensors
number tones
and recorded msgs
Phone
Line

8. DFD Example commands Configure config config data System request2
Configure
System
config
data
config
request 1
User
Interface
config info
config
data
on,off 4
Activate/
Deactivate
passwd
on/off msg 5
Generate
Display
display
data 3
Check
Password
valid id msg
sensor data
alarm
type 6
Sensor
Monitor
sensor
status
number tones
and recorded msgs

9. State Transition Diagrams
Illustrates events and their effects on the system's state or status
Good for
design of user interfaces
real-time and event-based systems
system
state
transition

10. STD Example checking off valid passwd password start activate invalid
de-activate
working
idle
valid
passwd
problem
valid
passwd
alerting
via
alarm
alerting
via
phone
not acknowledged
invalid
passwd

11. Petri Nets - similar to STDs

12. Structure Charts Illustrates Control Flow
Very good for conveying the design of source code
Very inappropriate for modeling a system in a SRS
module

13. SC Syntax Rules one single tree for entire system
tree has one node at the top
nodes are individual code units / modules
nodes call nodes below them
nodes are called left to right
leaf nodes are usually utility modules
may show data flow
may show conditionals and loops

14. SC Example main get_cmd check_sensors Is this correct? turn_off
change_
phone_num
activate_
alarm
send_
phone_msg
check_passwd

15. SC Example main get_cmd check_sensors turn_off change_ phone activate_
alarm
send_
phone_msg
check_passwd

16. Entity Relationship Diagrams
Illustrates connections between data objects
Excellent for design of a database
Good for modeling or specifying what data a system should handle
Cardinality = max number of objects that can participate in the relationship
Modality = is the relationship required

17. ER Example security sensor system monitors enables/disables tests
programs
is programmed by

18. Use Cases Illustrates activities performed by the user.
Excellent for modeling a system
helps identify data, processes, features
Not directly a design spec, but shows programmers the context of their code.
system
components
an action done
by an actor
actor

19. Example Use Case Alarm System smoke detector access sensor
status via internet
motion
detector
configure the
sensor ranges
home
owner
turn on and off
Other Use Cases:
other homeowner activities
security guard
burglar

20. Use Cases for System Modeling

21. Example Modeling Problem
System Req : every employee has a home office
Does "home office" mean they have a spare bedroom at home with a computer, or that everyone is assigned to a regional main office?
employee
home office
employee
home office

22. Example Modeling Problem
Any user can delete a regular file, but deleting a reserved file must require a password confirmation.
Unclear : can any user delete a "reserved file"?
How do we show that Requirement in the SRS?
How do we show that in the Design?

23. Summary Good for Modeling: Good for Design: Use Cases DFDs ERs
what the user wants to do
DFDs
process / how the data is transformed
ERs
structure and nature of the data
Good for Design:
Structure Charts