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Embedded Systems Software: Modeling and Programming--The Object-oriented Paradigm
andThe Unified Modeling Language (UML)
2
"problems" of software development (review):
**conceptual integrity
**incremental build, progressive refinement
**large projects "differ" from small ones
programming paradigms (1950’s-present): attempts to deal effectively with these problems, make software easier to develop and to maintain
Problems of software development
3
1950's:unstructured, no information hiding--”spaghetti” code, GOTO, flowcharts--machine code--assembly lang. --FORTRAN, LISP (Algol; COBOL)
1970s,1980s: structured, top-down design (“3 basic control structures, no GOTO”), modularity--Pascal, C, PL/I, Ada
1990’s: encapsulation, information-hiding, reuse, hardware/software codesign (from simulation languages developed much earlier, e.g., Modula, simula)--C++, Java
2000’s: info hiding; web languages; environments encapsulating multiple languages, styles--.NET, C#, Python, Perl, MATLAB, Mathematica, Labview, …
A Brief History: Computer Hardware, Computer Languages, Design Techniques
Early machines—large, central (Eniac)
Supercomputers, “Minicomputers”, PCs, multiuser machines, PICs
Beowulf clusters, Spread of the Internet
“Ubiquitous computing”, laptops,.Personal communication devices, multicore processors, GPUs
wpclipart.com
chilton-computing.org.uk
techxav.com
http://en.wikipedia.org/wiki/PIC_microcontroller#History
cse.mtu.edu
visual.merriam-webster.com
http://t0.gstatic.com/images?q=tbn:ANd9GcS3J9yAV0YibC4keB8M_6hc0xh3sZYbbGKZUK-pHLzx7Lkek74w
http://www.amd.com/us-en/assets/content_type/Additional/43494A_QuadCore_Opt_Die_BLK_HRes.jpg textually.org
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Important basic OO concepts:
class: encapsulates data structure (object) and associated methods (functions) these may be declared public / private / protected
appropriate uses:
public: pass info to object or request info about object(use "messages") (can be used by anyone)
private: modify object (can be used in class or by “friends”)
protected: for descendants (in class or by derived class and “friends”)
OO class
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traditional: record (struct): functions to use or modify this record can be anywhere in the program
OO: class concept supports encapsulation, information hiding
Record/class
DATA
DATA
DATA
DATA
DATA
DATA
DATA
Procedural Prog.
OO Prog.
6
Useful OO techniques:
Inheritance:ex: in a program modeling an ecosystem, we might have the relationships:
wolf is carnivore; sheep is herbivore; grass is plant carnivore is animal; herbivore is animalanimal is organism; plant is organism
here the base class “organism” holds data fields which apply to all organisms, e.g., amount of water needed to survive two derived classes, plant and animal, hold information specific to each of these types of organisms, e.g., kind of soil preferred by plantthe animal class also has two derived classes, wolf and sheep
Inheritance allows the collection of common attributes and methods in "base" class and inclusion of more specific attributes and methods in derived classes
Inheritance
A. B.Ex: Object data
structures:
A. Base class
B. Derived class
X
Y
Z
X
Y
Z
W
7
Polymorphism:
base class can define a “virtual” function; appropriate versions of this function can be instantiated in each derived class (e.g., "draw" in the base class of graphical objects can have its own specific meaning for rectangles, lines, ellipses)
Overloading:
ex: cin >> num1;>> is overloaded "shift”
ex: “+” can be overloaded to allow the addition of two vectors
ex: a function name can be overloaded to apply to more than one situation; e.g., a constructor can be defined one way if initial values are given and a different way if initial values are not given
Polymorphism and overloading
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Templates:
example:
template <class T> T method1 (T x) …..
can be specialized: int method1 (int x)
float method1 (float y)
usertype method1 (usertype a)
templates promote reuse
Templates
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Separate compilation:
Typically, an object-oriented program can be broken into three sets of components:
definitions and prototypes (text files, “header files”)
implementations (compiled--source code need not be available to user)
application program--uses the classes defined in header files and supported by the implementation files
This strategy promotes reuse and information hiding
Separate compilation
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Note: no paradigm is misuse-proof
Misuse of object-oriented paradigm
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Design: “top-down”; Test: “bottom-up” : “Design for testability”
determine specifications: use cases system tests
determine classes and connections (static behavior): ER or class diagrams; CRC cards module (“black box”) tests
model dynamic behavior:interaction (object message) diagrams activity diagramsstate diagramssequence diagrams
[ individual class functions “white box” or “glass box” tests]
Using OO & (a subset of) UML in a project: design; design for testability
dynamic module interactions / “boundary” behavior
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UML: a language for specifying and designing an OO project
UML: stands for "unified modeling language”
unifies methods of Booch, Rumbaugh (OMT or Object Modeling Technique), and Jacobson (OOSE or Object-Oriented Software Engineering)
mainly a modeling language, not a complete development method
Early versions -- second half of the 90's
Not all methods we will use are officially part of the UML description
13
USE CASES: a part of the ”Unified Modeling Language" (UML) which we will use for requirements analysis and specification
each identifies a way the system will be used and the "actors" (people or devices) that will use it (an interaction between the user and the system)
each use case should capture some user-visible function and achieve some discrete goal for the user
an actual user can have many actor roles in these use cases
an instance of a use case is usually called a "scenario”
Use case will typically have graphical & verbal forms
Use cases
14
Example: cellular network place and receive calls use case (based on Booch, Rumbaugh, and Jacobson, The Unified Modeling Language User Guide)
Place call
Receive call
Use scheduler
Receive additional
call
Place conference
call
Cellular network
User
Use Case (Example) Key: Use Case Actor “Extends” “Uses”
Validate user
Example use case
System boundary
Text description
--Use case name (cellular network place and receive calls)
--Participating actors (cellular network and human user)
--Flow of events (network or user accesses network to use its functionality)
--Entry condition(s) (user accesses network using device or password) --Exit condition(s) (call completed lost or network busy)
--Quality requirements (speed, service quality)
Text description—gives important details
Use case diagram—summarizes, provides system overview
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use case
Text description:
Use case name
Participating actors
Flow of events
Entry condition(s)
Exit condition(s)
Quality requirements
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Use case—detailed example (Pressman)
Example: “SAFEHOME” system (Pressman)
Use case: InitiateMonitoring
(Pressman text categories:•Primary actor (1)
•Goal in context (2)
•Preconditions (3)
•Trigger (4)
•Scenario (5)
•Exceptions (6)
•Priority (system development) (7)
•When available (8)
•Frequency of use (9)
•Channel to actor (10)
•Secondary actors (11)
•Channels to secondary actors (12)
•Open issues (13) )
Arms/disarms system
Accesses system via internet
Responds to alarm event
Encounters an error condition
Reconfigures sensors
and related system features
Homeowner
System administrator
Sensors
Pressman, p. 163, Figure 7.3
17
Use case—detailed example (Pressman)
Example: “SAFEHOME” system (Pressman)
Use case name: InitiateMonitoring
Participating actors: homeowner, technicians, sensors
Flow of events (homeowner):--Homeowner wants to set the system when the homeowner leaves house or remains in house--Homeowner observes control panel--Homeowner enters password--Homeowner selects “stay” or “away”--Homeowner observes that read alarm light has come on, indicating the system is armed
18
Use detailed example (Pressman)--continued
Entry condition(s)
Homeowner decides to set control panel
Exit condition(s)
Control panel is not ready; homeowner must check all sensors and reset them if necessary
Control panel indicates incorrect password (one beep)—homeowner enters correct password
Password not recognized—must contact monitoring and response subsystem to reprogram password
Stay selected: control panel beeps twice and lights stay light; perimeter sensors are activated
Away selected: control panel beeps three times and lights away light; all sensors are activated
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Use case—detailed example (Pressman)
Quality requirements:
Control panel may display additional text messages
time the homeowner has to enter the password from the time the first key is pressed
Ability to activate the system without the use of a password or with an abbreviated password
Ability to deactivate the system before it actually activates
20
Use case additions—simplifications of use case descriptions
A. Include: one use case includes another in its flow of events (cases A and B both include case C)
B. Extend: extend one use case to include additional behavior (cases D and E are extensions of case F)
A
B
C<<include>>
<<include>>
FE
D
<<extend>>
<<extend>>
21
Use case additions
C. Inheritance: one use case specializes the more general behavior of another G and H specialize behavior of J)
H
J
authenticate
Authenticate with card
Authenticate with password
G
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Use case continued
Examples: what would be a use case for: vending machine traffic light
Use case nameParticipating actorsFlow of eventsEntry conditionExit conditionQuality requirements
23
Note:
Use cases can form a basis for system acceptance tests
For each use case:• Develop one or more system tests to confirm that the use case requirements will be satisfied• Add explicit test values as soon as possible during design phase• These tests are now specifically tied to the use case and will be used as the top level acceptance tests
Do not forget use cases / tests for performance and usability requirements (these may be qualitative as well as quantitative)
System Tests
24
Analysis model (UML version):
--functional model (use cases and scenarios)
--analysis object model (static: class and object diagrams)
--dynamic model (state and sequence diagrams)
As system is analyzed, specifications are refined and made more explicit; if necessary, requirements are also updated
25
Example: an activity diagram for analyzing a system you are building:
26
Arms/disarms system
Accesses system via internet
Responds to alarm event
Encounters an error condition
Reconfigures sensors
and related system features
Homeowner
System administrator
Sensors
Pressman, p. 163, Figure 7.3
“Review”: use case: Graphical description:
Text description: Use case name
Participating actors
Flow of events
Entry condition(s)
Exit condition(s)
Quality requirements
27
“Review”: Use case writing guide:
--each use case should be traceable to requirements
--name should be a verb phrase to indicate user goal
--actor names should be noun phrases
--system boundary needs to be clearly defined
--use active voice in describing flow of events, to make clear who does what
--make sure the flow of events describes a complete user transaction
---if there is a dependence among steps, this needs to be made clear
--describe exceptions separately
--DO NOT describe the user interface to the system, only functions
--DO NOT make the use case too long—use extends, includes instead
--as you develop use cases, develop associated tests
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Class and object diagrams:Identify Objects from Use Case Specifications:USE ENDUSER’s TERMS AS MUCH AS POSSIBLE
Entity objects: “things”, for example:--nouns (customer, hospital, infection)--real-world entities (resource, dispatcher)--real-world activities to be tracked (evacuation_plan)--data sources or sinks (printer)
Boundary objects: system interfaces, for example:--controls (report(emergencybutton)--forms (savings_deposit_form)--messages (notify_of_error)
Control objects: usually one per use case--coordinate boundary and entity objects in the use case
Use the identified objects in a sequence diagram to carry out the use case
29
Common classes
Other common types of classes which the developer can look for include:
•tangible things, e.g., Mailbox, Document
•system interfaces and devices, e.g., DisplayWindow, Input Reader
•agents, e.g., Paginator, which computes document page breaks, or InputReader
•events and transactions, e.g., MouseEvent,CustomerArrival
•users and roles, e.g., Administrator, User
•systems, e.g., mailsystem (overall), InitializationSystem (initializes)
•containers, e.g., Mailbox, Invoice, Event
•foundation classes, e.g., String, Date, Vector, etc.
30
Sequence Diagram
Sequence Diagram:
a sequence diagram also models dynamic behavior
typically a sequence diagram shows how objects act together to implement a single use case
messages passed between the objects are also shown
sequence diagrams help to show the overall flow of control in the part of the program being modeled
they can also be used to show:concurrent processesasynchronous behavior
31
Sequence Diagram--Syntax
Objects in the sequence diagram are shown as boxes at the top
below each object is a dashed vertical line--the object’s “lifeline”
an arrow between two lifelines represents each message
arrows are labeled with message names and can also include information on arguments and control information
two types of control:condition, e.g., [is greaterthan zero]iteration, e.g., *[for all array items]
“return” arrows can also be included
32
Sequence Diagram Example
33
ER diagrams
Useful object relationships
These diagrams represent the relationships between the classes in the system. These represent a static view of the system.
There are three basic types of relationship:
•inheritance ("is-a")
•aggregation ("has-a”)
•association ("uses")
These are commonly diagrammed as follows:
34
ER diagram: is-a
is-a: draw an arrow from the derived to the base class:
manager employee
35
ER diagram--has-a
has-a: draw a line with a diamond on the end at the "container" class. Cardinalities may also be shown (1:1, 1:n, 1:0…m; 1:*, i.e., any number > 0, 1:1…*, i.e., any number > 1):
car tire1 4tire & car can exist independently—shared aggregation
person arm1 2arm is part of the person– composition aggregation
36
ER diagram--uses
uses or association: there are many ways to represent this relationship, e.g.,
car gasstationcompany
employee
employs
works for
*
1
*
n
1
*
37
CRC cards
CRC cards: class--responsibilities--collaborators cards
"responsibilities" = operators, methods
"collaborators" = related classes (for a particular operator or method)
Make one actual card for each discovered class, with responsibilities and collaborators on the front, data fields on the back. CRC cards are not really part of UML, but are often used in conjunction with it.
38
CRC card--example
Example (based on Horstmann, Practical Object-Oriented Development in C++ and Java):
front back
Class Mailbox
Operations Relationships(Responsibilities) (Collaborators)
get current message Message, Messagequeue
play greeting -----------
Queue of new messagesQueue of kept messagesGreetingExtension numberPasscode
Class Mailbox
39
State Diagram
State Diagram:
another way of adding detail to the design--models dynamic behavior
describes all the possible states a particular object can be in and how that object's state changes as a result of events that affect that object
usually drawn for a single class to show behavior of a single object
used to clarify dynamic behavior within the system, as needed
40
State Diagram--Properties
A state diagram contains a "start" point, states, and transitions from one state to another.
Each state is labeled by its name and by the activities which occur when in that state.
Transitions can have three optional labels: Event [Guard] / Action.
A transition is triggered by an Event.
If there is no Event, then the transition is triggered as soon as the state activities are completed.
A Guard can be true or false. If the Guard is false, the transition is not taken.
An Action is completed during the transition.
41
State Diagram--Example
Example: this state diagram example for an "order" in an order-processing system is from Fowler and Scott, UML Distilled (Addison-Wesley, 1997):
Checking
check item
Dispatching
initiate delivery
Waiting Delivered
start/get first item
[not all items checked]/get next item
[all items checked && all items available]
[all items checked && some items not instock]
item received[some items not in stock]
item received[all items in stock]
delivered
42
Example—bank simulation (Horstmann)
Teller 1
Teller 2
Teller 3
Teller 4
Customer 1Customer 3 Customer 2
Horstmann, Mastering Object-Oriented Design in C++, Wiley, 1995
43
Example—bank simulation (Horstmann), cont.
An initial solution (Horstmann, p. 388):
Event
Departure
Arrival
Customer Bank
EventQueue
Application
Bank Statistics
44
Example—bank simulation (Horstmann), cont.
An improved solution (Horstmann, p. 391):
Event
Departure
Arrival
Customer Bank
EventQueue
Simulation
Bank Statistics
45
Comparison
What simplifications
have been made?
Why?
Event
Departure
Arrival
Customer Bank
EventQueue
Application
Bank Statistics
Event
Departure
Arrival
Customer Bank
EventQueue
Simulation
Bank Statistics
46
Example:
How would we use the tools described so far to design a “smart” vending machine? How would we develop test cases at each stage?
Use cases?
Class diagram?
Sequence diagram?
Classes / CRC cards?
47
Software modeling for embedded systems: static and dynamic behavior
48
Important concepts in embedded systems:
--concurrency: the system can handle multiple active independent or cooperating objects at the same time
--thread [of control]—models sequential execution of a set of instructions; embedded system may have several concurrent threads operating simultaneously
--persistence—how long does a software object last?
Examples:
Temporary variable
Global variable
Software module
49
table_05_00
Recall: “UML” syntax can vary among implementations;
Previously we looked at one implementation, here we consider examples from the text
50
fig_05_00
UML: Use case diagram (graphical)
51
fig_05_01
UML Use case diagram--example
52
fig_05_02
UML: Use case diagram (text); note exceptions
53
UML—static modeling
54fig_05_03
UML: Class diagram (“CRC card”)
Class name
data
Methods (responsibilitiesandcollaborators)
(+ collaborators)
55
fig_05_04
UML: class relationships: inheritance
56
fig_05_05
UML: “interface”—similar to inheritance but different
public appearance
Hidden operation
57
fig_05_06
UML: containment of one class within another
Type 1: aggregation—statistical analysis has a number of algorithm “parts”
58
fig_05_07
UML: containment of one class within another
Type 2: composition—here the intervals are meaningless outside the schedule (~ “local variables”)
59
UML—dynamic modeling
60
fig_05_08
UML: interaction diagram—call and return
61
fig_05_09
UML: interaction diagram—create and destroy
62
fig_05_10
UML: interaction diagram—send (no response expected)
63
fig_05_11
UML: sequence diagram:sequence of actions; carries out a use case
64
fig_05_12
UML sequence diagram--example
65
fig_05_13
UML: concurrent behavior. Example: fork and join
66
fig_05_14
UML: concurrent behavior. Example: branch and merge
67
fig_05_15
UML activity diagram—captures all actions and control flows within a task
68
fig_05_16
UML state machine models--4 types of events:
UML state chart is a directed graph
69
fig_05_18
UML state chart: types of transitions
initial state
final state
70
fig_05_19
UML state chart: actions and guard conditionsIf guard condition is false, transition does not happen
71
fig_05_20
UML: can decompose state into sequential substates
72
fig_05_21
UML: can define a “history” state (e.g., for an interrupt)—system will probably eventually return to this state
73
fig_05_22
UML: can have concurrent substates
74
UML is a tool for a structured design methodology
It helps manage the design and development process
We can also look at modifying / refining the PROCESS itself
"hardware / software life cycle": easier specify requirements (cheaper) (levels:1. functional to fix 2. performance mistakes (time/space) 3. implementation 4. use 5. maintenance)
analyze requirements design implement harder to fix test mistakes maintain
CMM : capability maturity model--defines level of the development process itself
1. Initial: ad hoc
2. Repeatable: basic project management processes in place
3. Defined: documented process integrated into an organization-wide software process
4. Managed: detailed measures are collected
5. Optimizing--desired level: Continuous process improvement from quantitative feedback
75
UML is a tool for a structured design methodology
It helps manage the design and development process
We can also look at modifying / refining the PROCESS itself
"hardware / software life cycle": easier specify requirements (cheaper) (levels:1. functional to fix 2. performance mistakes (time/space) 3. implementation 4. use 5. maintenance)
analyze requirements design implement harder to fix test mistakes maintain
CMM : capability maturity model--defines level of the development process itself
1. Initial: ad hoc
2. Repeatable: basic project management processes in place
3. Defined: documented process integrated into an organization-wide software process
4. Managed: detailed measures are collected
5. Optimizing--desired level: Continuous process improvement from quantitative feedback
76
fig_05_23
Alternative methodology: control flow and data flow diagrams(Note: in a processor we usually have a data path and a control path)
77
fig_05_24
Control and data flow diagrams: tasks (with hierarchy levels)
78
fig_05_25
Control and data flow diagrams: Data sources and sinks
79
fig_05_26
Control and data flow diagrams: Data stores
80
fig_05_27
Control and data flow diagrams: Example
81
fig_05_28
Control and data flow diagrams: Hierarchical view of an input / output task