ECSE 6770- Software Engineering
- 1 -HO 4
© HY 2012
Lecture 4
System ModelingIn SE, we have an array of notations and diagrams for modeling in each of the three views mentioned in lecture 1.
Structure ModelingEntity Relationship Diagrams, Formal Structural Models (e.g. Z, Object Z or VDM), Class Diagrams,…
Transformational ModelingTransformational Relations(Functional Specification), Activity Diagrams , Data Flow Diagrams (with specification), Flow Charts, …
Causal (Dynamic) ModelingSequence Diagrams, Collaboration Diagrams, State-charts (State Transition Diagrams), Petri-nets, Entity Life Histories,…
ECSE 6770- Software Engineering
- 2 -HO 4
© HY 2012
Lecture 4
Structure modeling is modeling of things and their situational relationships. A photograph is a good structure model. It shows things that were there when the picture was taken and how they were situated with respect to one another.
We can similarly compose diagrams or other models of a problem situation in which we depict all the relevant things and relationships.
There are many ways to do this. We shall discuss the three most popular and prevalent of these. Namely:
Entity Relationship Modeling which is used mainly for database design
Formal Schemas and Formal Object Schemas (using Z and Object Z)
Class Diagrams (using UML) used mainly as part of object oriented modeling
Structure Modeling
ECSE 6770- Software Engineering
- 3 -HO 4
© HY 2012
Lecture 4
Entity Relationship (ER) Modeling:
This is an informal (or semi-formal) approach to structure modeling in which a situation is studied so that static and persistent elements in it are identified, along with their static relationships. A collection of like elements is called an entity. A mapping of elements of one entity onto another entity (or itself) is called a relationship.
Entities are defined in terms of a name and a set of attributes. Relationships are defined in terms of a verb phrase (e.g. works-for) that establishes the nature of the mapping between the entities.
The results of ER modeling are almost always shown using diagrams. There are many different conventions. In the absence of an industry standard, we use a popular one here of my preference.
Structure Modeling
ECSE 6770- Software Engineering
- 4 -HO 4
© HY 2012
Lecture 4
Example:Employee
Name:
SSN:
Salary:
Department
Name:
Location:
Budget:
Works-Form 1
This means that there are many elements belonging to the set Employee (i.e. many persons employed) each is mapped into (has a relationship with) only one element belonging to the entity Department (a specific department). The relationship is that this particular employee works for one specific department. For each employee we keep his or her name, social security number and current salary. For each department we keep the name of the department, its location and its budget.
You will learn (or may have already learned) a lot more about this modeling approach in your database course.
Structure Modeling
ECSE 6770- Software Engineering
- 5 -HO 4
© HY 2012
Lecture 4
Formal Object Schemas: Object Z
Stack[T]max:N
items: seq T
#items max
INITitems = ‹ ›
Push( items)
#items < maxitems’ = ‹item?›⁀items
item?:T
Structure Modeling
ECSE 6770- Software Engineering
- 6 -HO 4
© HY 2012
Lecture 4
Pop( items)
item! ‹ ›items = ‹item!›⁀items’
item!:T
top( items)
item! ‹ ›items’ = items
item!:T
Structure Modeling
ECSE 6770- Software Engineering
- 7 -HO 4
© HY 2012
Lecture 4
There are many different approaches to causal modeling. Whilst they all attempt to do the same thing, they are not all of the same level of capability, formality, ease of use or learnability. In this course we cover a number of popular approaches to causal modeling, including:
Entity Life Histories
The UML suite of dynamic modeling facilities, which include
Petri-nets
Sequence diagrams
Collaboration diagrams
State diagrams
Causal Modeling
ECSE 6770- Software Engineering
- 8 -HO 4
© HY 2012
Lecture 4
Entity Life Histories
These are diagrams that depict the various states of a class or type of object from inception to demise. Usually used in relation to persistent database “entities”, they can become overwhelmed if the states are too numerous or the object can possess concurrent states. They also do not necessarily depict the events that lead to state transitions.
EMP
CREATE INIT UPDATE REPORT RETIRE ARCHIVE* *
Causal Modeling
ECSE 6770- Software Engineering
- 9 -HO 4
© HY 2012
Lecture 4
Petri nets:
Petri nets are a formal graphical approach to causal modeling. They improve on the capabilities of state diagrams by allowing for proper description of some major issues in concurrency such as synchronization, deadlocks and conflicts.
Petri nets are composed of two types of nodes and one type of arc. The two types of node are called places and transitions. The arc is called an event. A fourth artifact called a token, when located inside a place, marks it as enabled.
Causal Modeling
ECSE 6770- Software Engineering
- 10 -HO 4
© HY 2012
Lecture 4
A token ( ) inside a place indicates that the place has satisfied all pre-conditions for causing an event to occur. Such a place is called “enabled”
p1
p2 p3
p4
p5
t1
t2
t3
A Petri net composed of five places P={p1,p2,p3,p4,p5} and three transitions T={t1,t2,t3}
A transition takes place only when all places leading to it are enabled. Such a transition is called an enabled transition.
Causal Modeling
ECSE 6770- Software Engineering
- 11 -HO 4
© HY 2012
Lecture 4
The system stops here.
A transition takes place to p2. But t2 is not enabled as p3 is not enabled.
p5
p1
p2 p3
p4
t1
t2
t3
P1 is enabled, thus enabling t1
Causal Modeling
ECSE 6770- Software Engineering
- 12 -HO 4
© HY 2012
Lecture 4
p5
p1
p2 p3
p4
t1
t2
t3
Causal Modeling
ECSE 6770- Software Engineering
- 13 -HO 4
© HY 2012
Lecture 4
p5
p1
p2 p3
p4
t1
t2
t3
p’1
p’2p’3
p’4
t’1
t’2
t’3
Conflict
?
Causal Modeling
ECSE 6770- Software Engineering
- 14 -HO 4
© HY 2012
Lecture 4
p5
p1
p2 p3
p4
t1
t2
t3
Deadlock
?
Causal Modeling
ECSE 6770- Software Engineering
- 15 -HO 4
© HY 2012
Lecture 4
Transformation modeling is the third modeling view. It answers the question “how”.
Depending on level of granularity there are many techniques. Including:
Abstraction Level:
Dataflow Diagrams
Activity Diagrams
Low Level:
Pseudo-code
Flowcharts
etc.
Not part of UML
Transformational Modeling
ECSE 6770- Software Engineering
- 16 -HO 4
© HY 2012
Lecture 4
Flow charts
Flow charts depict the flow of control. They show how operations are performed and decisions made by depicting how the control in the program is exchanged from the beginning to the end of all paths of interest.
Flow charts show how the program works.
Flow charts are composed of a number of node types and one type of arc. The node types are:
Start/End node Transformation node Decision node Link node Special processing nodes Logic nodes
Transformational Modeling
ECSE 6770- Software Engineering
- 17 -HO 4
© HY 2012
Lecture 4
Flow charts can be high level or low level
High level flow charts depict the flow of control at a high level of granularity, such as the organization or the entire system. Low level ones usually depict the flow of control in a specific program unit.
The difference between a high level and low level flow chart is that in a low level flow chart all transformational nodes contain transformations that can not be usefully broken down to simpler flowcharts themselves. By this we mean doing so would produce transformation at a lower level of granularity than that of the target programming language.
Transformational Modeling
ECSE 6770- Software Engineering
- 18 -HO 4
© HY 2012
Lecture 4
Flow chart nodes:
Start/End nodes: These mark the beginning and end of a flow within a flowchart
Transformation nodes: These show a logical step taken
Terminator
Transformation Alternate transformation
Manual transformation
Transformational Modeling
ECSE 6770- Software Engineering
- 19 -HO 4
© HY 2012
Lecture 4
Decision nodes: These show alternate conditions or paths the flow may take
Link nodes: These connect various parts of the diagram (e.g. continue on next page)
Logic nodes: These are logical operators such as AND, OR and NOT
Condition
AND OR NOT
On page connector
Off page connector
Transformational Modeling
ECSE 6770- Software Engineering
- 20 -HO 4
© HY 2012
Lecture 4
Special processing nodes: These are nodes that depict specific large scale processing or machine interaction. Useful in the early days when flowcharting was amongst the only modeling methods available, they are now largely disused.
Manual input
Disk Other mag. storage
Stored data Punched tape Punched card
Seq. Access device
Console or display
Extract Merge Sort Collate Internal storage
Delay
Transformational Modeling
ECSE 6770- Software Engineering
- 21 -HO 4
© HY 2012
Lecture 4
Start
End
Read N
N>0
T
F
Read A,B
A=A+B N=N-1
N=0F
T
Write A
Transformational Modeling
ECSE 6770- Software Engineering
- 22 -HO 4
© HY 2012
Lecture 4
Data Flow DiagramsData flow diagrams depict the flow of data. They show how data received as input is changed to outputs by the various operations performed.
Data flow diagrams show how the data changes.
Basic data flow diagrams are composed of a number of node types and one type of arch. The node types are:
External Entities (Sources and Sinks) Processing node
Data-stores Link nodes
Transformational Modeling
ECSE 6770- Software Engineering
- 23 -HO 4
© HY 2012
Lecture 4
External entities (sources and Sinks): These are entities outside the scope of our focus that provide the inputs from the outside or receive the outputs generated. They are labeled by a noun or an object or class name.
Process nodes: These depict the processing that is done to the inputs into that process to form the output. Usually these nodes are labeled by a verb phrase representing the nature of the processing to be done and a number sequence depicting the process and its level
Customer
Book seatBook seat
1.4.71.4.7
Transformational Modeling
ECSE 6770- Software Engineering
- 24 -HO 4
© HY 2012
Lecture 4
Data-stores: These are buffers where interim outputs generated are stored for future usage. Data-stores are usually named.Link nodes: They connect the various parts of the diagrams to yield a less cluttered result. They are usually numbered or carry a symbol.
Primary Buffer
The only arc is called a dataflow and it depicts the flow of data (as input into or output from) an external entity or process. They are usually named.
client address
22
Transformational Modeling
ECSE 6770- Software Engineering
- 25 -HO 4
© HY 2012
Lecture 4
Example DFD
1.2.1
Validate Sell
1.2.2
Prepare SX Transaction
1.2.3
Register Transaction
Account
Invalid Req. Advice
Transaction A
dvice
Sell Validation
Trans. Confirmation
Sell Details
Account Update
Sell Advice
No. of Stock owned
Account Sell
Market Stock Price
Sell Stock; Level 3
Transformational Modeling
ECSE 6770- Software Engineering
- 26 -HO 4
© HY 2012
Lecture 4
Data Flow diagrams may depict a situation at multiple levels of granularity. By that we mean a process in a data flow diagram may be decomposed into an entire new dataflow diagram at a lower level, and so on. At each lower level, there will be more detail of the model visible. Conversely, one can say that a higher level process can be described in terms of a dataflow diagram composed of simpler, lower level processes, data flows and data-stores. However this decomposition process must stop at some stage. At that stage we shall still have a dataflow diagram that only depicts the transformation of inputs to outputs of various processes. It however does not say HOW each leaf level process should achieve this. This may be obvious but is not defined.
Transformational Modeling
ECSE 6770- Software Engineering
- 27 -HO 4
© HY 2012
Lecture 4
Dataflow diagrams are more so a mechanism for abstraction than a transformational modeling technique. They must be accompanied by a complementary mechanism that defines the leaf level transformations. Something like a flowchart of each leaf process, a pseudo-code, mathematical equation, truth table or formal definition is needed.
Important Note:
Transformational Modeling
ECSE 6770- Software Engineering
- 28 -HO 4
© HY 2012
Lecture 4
Pseudo-code:begin
Read r,a;
Declare x,y;
if { (a) L.T. 0
a=(-1)*a; };
Set x to r*sin(a);
Set y to r*cos(a);
Write x;
Write y;
end
Convert to Cartesian
1.5.6r
a
x
y
Transformational Modeling
ECSE 6770- Software Engineering
- 29 -HO 4
© HY 2012
Lecture 4
Mathematical expression:
)cos(
)sin(
ary
arx
Convert to Cartesian
1.5.6r
a
x
y
Desc. For 1.5.6
Transformational Modeling
ECSE 6770- Software Engineering
- 30 -HO 4
© HY 2012
Lecture 4
Activity diagrams depict the processing aspects of the system. They are similar to flowcharts except:
ACTIVITY DIAGRAMS
Activity charts allow synchronization
They are similar to dataflow diagrams except:
Transition between activities is via conditions not data. Activity charts allow synchronization
Transformational Modeling
ECSE 6770- Software Engineering
- 31 -HO 4
© HY 2012
Lecture 4
Order ProcessingFinance
Receive
Order
Receive
Supply
Select Outstanding order item
Assign Goods to
OrderAssign Item to Order
Reorder
Item Add Remainder
to Stock
Check Line Item
Cancel Order
Check order
Authorize payment
[failed][succeeded]
Dispatch Order [Stock assigned to all line items and payment
authorized]
*[for each line item on order]
* [for each chosen order item]
[in stock]
[all outstanding order items filled]
[notify supply]
[out of stock]
Stock Manager
Transformational Modeling
ECSE 6770- Software Engineering
- 32 -HO 4
© HY 2012
Lecture 4
Structure Transformation Causality
Objects
Classes
Relationships
Inputs
Outputs
Transformations
Events
States
Sequences
ENCAPSULATION
ECSE 6770- Software Engineering
- 33 -HO 4
© HY 2012
Lecture 4
UML has a an array of notations and diagrams for modeling in each of these three views.
Structure Modeling
Class notation, object notation, Associations, Links, Class diagrams, object diagrams,…
Transformational ModelingActors, Transformational relations, Use Case diagrams, Context Diagrams, Activity diagrams ,Transformational definitions, …
ECSE 6770- Software Engineering
- 34 -HO 4
© HY 2012
Lecture 4
Causal (Dynamic) Modeling
Events, Activities, Actions, Transitions, States, Sequence diagrams, Collaboration diagrams, Statechart diagrams, etc.…
In the next session we shall start with structural modeling and introduce some important elements of the UML
notation set.
ECSE 6770- Software Engineering
- 35 -HO 4
© HY 2012
Lecture 4
Structural Modeling: Answers the question WHAT?
We need to concentrate on static relationships between objects (SNAPSHOT). So, we need to depict:
Objects Classes
Links
Associations
Class Diagram
ECSE 6770- Software Engineering
- 36 -HO 4
© HY 2012
Lecture 4
CLASSES
The implementation of a type
A generator for instances
A class is depicted as a solid-outlined rectangle with compartments:
• Must have a name compartment
• May have other compartments (up to 3 more)
ECSE 6770- Software Engineering
- 37 -HO 4
© HY 2012
Lecture 4
The other compartments may contain:
Compartment 2: Attributes
Compartment 3: Operations
Compartment 4: Others (Business rules, exceptions, etc.)
Name Compartment
Attributes Compartment
Operations Compartment
Other Compartment
Widget
color: Color
position:Coord=(0,0)
move(from:Coord,to:Coord=(50,50))
get_color( ):Color
draw( )
draw_all( )
color /= “white”
ECSE 6770- Software Engineering
- 38 -HO 4
© HY 2012
Lecture 4
Class name and the class name compartment:
• The name compartment must be present
• The name compartment contains the name of the class. Class names are centered, begin with a capital letter and are in boldface. Abstract class names are italicized.
ECSE 6770- Software Engineering
- 39 -HO 4
© HY 2012
Lecture 4
Attributes and the attribute compartment:
• May be omitted when drawing high level diagrams
• Are denoted as left justified plain lowercase text strings
• The name may be followed by a colon ( : ) followed by the type of the attribute
• Optionally we can set the initial value of the attribute. To do so, the type name is followed by ( = ) and then the value
ECSE 6770- Software Engineering
- 40 -HO 4
© HY 2012
Lecture 4
• May contain a visibility tag. A visibility tag could be:
• + Public
• # Protected
• - Private
ECSE 6770- Software Engineering
- 41 -HO 4
© HY 2012
Lecture 4
Operations and the operations compartment:
• May be omitted when drawing high level diagrams
• Are denoted as left justified plain lowercase text strings. Abstract operations are italicized
• May have parentheses containing a comma separated list of the parameters of the method that implements the operation.
• Optionally the parameter list may have indicators. These are:
ECSE 6770- Software Engineering
- 42 -HO 4
© HY 2012
Lecture 4
in Parameter is only passed in to the operation
out Parameter is only passed out (returned)
inout Both (Default is “in”)
• May have a return list containing one or a comma separated list of more than one formal parameters following a colon after the parameter list.
• Multiple return parameters, if there, must have a name and a type separated by a colon.
ECSE 6770- Software Engineering
- 43 -HO 4
© HY 2012
Lecture 4
• An operation may have a class scope. Class operations are underlined.
• May contain a visibility tag. A visibility tag could be:
• + Public
• # Protected
• - Private
ECSE 6770- Software Engineering
- 44 -HO 4
© HY 2012
Lecture 4
Attribute
- color:Color=red
Operation:
# credit_rating(in candidate:Customer=current, in agency: Agent=dandb) : rating : Integer, reason : Text
Usually we do not bother with this level of detail unless we aim to generate code automatically
ECSE 6770- Software Engineering
- 45 -HO 4
© HY 2012
Lecture 4
TEMPLATES AND GENERIC CLASSES
PAIRT1,T2
first:T1
second:T2
set_first(in T1)
set_second(in T2)
out( ): STRING
Pair <Integer, Integer>
Pair<<bind>> (Integer,Integer)
OR
ECSE 6770- Software Engineering
- 46 -HO 4
© HY 2012
Lecture 4
OBJECTS
An element of a type set. An instance of a class.
An object is depicted as a solid-outline rectangle with up to 3 compartments:
• The top compartment is the name compartment.
• May have other compartments (up to 2 more)
ECSE 6770- Software Engineering
- 47 -HO 4
© HY 2012
Lecture 4
The other compartments may contain:
Compartment 2: Attribute values
Compartment 3: Other
Name Compartment
Attributes Compartment
Other Compartment
doowak: Widget
color=Red
position=(10,45)
ECSE 6770- Software Engineering
- 48 -HO 4
© HY 2012
Lecture 4
Object name and the name compartment:
• The name compartment must be present
• The name compartment contains the name of the object; if a name exists. The name structure, if there, must be underlined. If the name is not there, or for “un-named” objects, the colon must remain.
• The name may be followed by a colon ( : ) followed by a comma separated list of class to which the object belongs.
ECSE 6770- Software Engineering
- 49 -HO 4
© HY 2012
Lecture 4
:Widget
color=Red
position=(10,45)
An un-known or un-named object:
An object, any object
ECSE 6770- Software Engineering
- 50 -HO 4
© HY 2012
Lecture 4
Attribute values and the attribute values compartment:
• It is optional and may not be present.
• If present, it contains the names of the relevant attributes of the class of which this object is an instance and the values relating to that attribute.
• Only attribute names and values of interest should be shown.
ECSE 6770- Software Engineering
- 51 -HO 4
© HY 2012
Lecture 4
RELATIONSHIPS
There are three basic types of relationship between classes. These are:
• Inheritance
• Aggregation
• Association
ECSE 6770- Software Engineering
- 52 -HO 4
© HY 2012
Lecture 4
INHERITANCE
Parent
Child 2Child 1
Discriminator
…...
ECSE 6770- Software Engineering
- 53 -HO 4
© HY 2012
Lecture 4
Person
FemaleMale
gender
Example:
ECSE 6770- Software Engineering
- 54 -HO 4
© HY 2012
Lecture 4
AGGREGATION
Two types in UML:
• Weak aggregation
• Composition
Brain Person
Department Professor
Composition
Weak aggregation
ECSE 6770- Software Engineering
- 55 -HO 4
© HY 2012
Lecture 4
ASSOCIATIONS
Association shows a named relationship between instances of a class and other instances of itself or between instances of two or more other classes.
Class A Class BRole A:Class
Role B:Class
Name of Association
Multiplicity Multiplicity
ECSE 6770- Software Engineering
- 56 -HO 4
© HY 2012
Lecture 4
Each association has two roles, each role is a direction on the association. These roles can be explicitly named on the association with a label. If not explicitly labeled, then the role name is the same as the target class and may be omitted.
Order Personcustomer
Is placed by
ECSE 6770- Software Engineering
- 57 -HO 4
© HY 2012
Lecture 4
A B
A B
A B
A B
1
1..*
0..1
*
An A is always associated with exactly one B
An A is always associated with one or more B
An A is always associated with zero or one B
An A is always associated with zero or more B
A Bn
An A is always associated with exactly n B
n..m An A is always associated with n to m BWhere n is any integer number greater than 1
Where n,m are integer numbers and m>nA B
ECSE 6770- Software Engineering
- 58 -HO 4
© HY 2012
Lecture 4
An association may have direction. When it does, the direction is shown with an arrow.
A B
In the above diagram, A, is called the source and B is the target.
A bi-directional arrow indicates navigability in both directions.
A B
ECSE 6770- Software Engineering
- 59 -HO 4
© HY 2012
Lecture 4
An association with a “many” side may be ordered. Ordering is shown as a label on the target class.
Screen Window*{ordered}
Visible on
ECSE 6770- Software Engineering
- 60 -HO 4
© HY 2012
Lecture 4
An association may be higher than binary.
A Ternary Association
NameClass A Class B
Class C
ECSE 6770- Software Engineering
- 61 -HO 4
© HY 2012
Lecture 4
reservation
Person Flight
Seat
Example:
ECSE 6770- Software Engineering
- 62 -HO 4
© HY 2012
Lecture 4
Association Attributes
PersonAccesses
File* *
permissionAssociation Attribute
ECSE 6770- Software Engineering
- 63 -HO 4
© HY 2012
Lecture 4
Employeesales rep
0..1 *
Corporate Customer Personal Customer
Product
contactName
creditRating
remind()
bill(Real)
creditCard#
Customer
name
address
rating():Integer
1
{if Order.customer.rating = 5
then Order.isPrepaid := True}
*line item
Order
1*
dateReceived: Date
isPrepaid:Boolean
number:String
price:Moneydispatch()
close(Real)
quantity:Integer
price:Money
isFilled: Boolean
creditRating() >=4
Courtesy: Martin Fowler, with some changes by Houman Younessi
Order Line