Transcript class - Courses
Object-Oriented Modeling: Static Models
Grady Booch, James Rumbaugh, and Ivar Jacobson,
The Unified Modeling Language User Guide
, 2 nd edition, Addison Wesley, 2005.
Object-Oriented Modeling
• Using object-orientation as a base, model the system as a number of objects that interact. • Our surroundings consist of objects, such as people, trees, cars, towns and houses which are in some way related to each other. • A model which is designed using an O-O technology is often easy to understand, as it can be directly related to reality. No "semantic gap" 2
Key Object-Oriented Ideas
• Identity • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Persistence 3
Key Object-Oriented Ideas
• Identity – Data are organized into discrete entities called objects.
– Objects have behavior and state.
• Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Persistence 4
Key Object-Oriented Ideas
• Identity • Abstraction – OO design uses different abstractions to capture different parts of the system.
• Classification • Encapsulation • Inheritance • Polymorphism • Persistence 5
Key Object-Oriented Ideas
• Identity • Abstraction • Classification – Objects are grouped together by commonalities.
– Groups of objects become the basis of classes.
• Encapsulation • Inheritance • Polymorphism • Persistence 6
Key Object-Oriented Ideas
• Identity • Abstraction • Classification • Encapsulation – Classes encapsulate behavior and data. – Encapsulated aspects of classes hide details from other classes.
• Inheritance • Polymorphism • Persistence 7
Key Object-Oriented Ideas
• Identity • Abstraction • Classification • Encapsulation • Inheritance – Different OO objects can reuse common behaviors through inheritance.
• Polymorphism • Persistence 8
Key Object-Oriented Ideas
• Identity • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism – Objects inherit types from parent classes as well as behavior • Persistence 9
Key Object-Oriented Ideas
• Identity • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Persistence – Objects have lifetime. – Attributes of an object may change over its lifetime.
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Advantages of O-O Approach
• Shifting of development effort into analysis. – Some development effort is moved to the analysis phase. • Emphasis on data before function. • Seamless development process. – Models developed during analysis are used for design and implementation. The work is progressively refined rather than converting from one representation to another.
• Iterative rather than sequential. – Each iteration adds or clarifies features rather than modifies work that has already been done .
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OO Analysis Objective
• To develop precise, concise, understandable, and correct models of the problem context.
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Object Modeling
• Involves systems analysis and design based on three different views of the system: – Object Models – Dynamic Models – Functional Models 13
Activities and Products of OOA
0. State the requirements 1. Build an Object Model 2. Develop a Dynamic Model 3. Construct a Functional Model 4. Verify, iterate, and refine the three models 14
1. Build an Object Model
• Identify objects and classes • Identify associations between objects • Identify attributes of objects and associations • Organize and simplify object classes using inheritance • Verify that access paths exist for likely queries 15
2. Develop a Dynamic Model
• Prepare scenarios of typical interaction sequences • Identify Events between objects and prepare an event trace • Build a state diagram, sequence diagram, or communication diagram • Match events between objects to verify consistency 16
3. Construct a Functional Model
• Identify Input and Output Values • Build Use Case scenarios • Build Data Flow Diagrams showing functional dependencies • Describe Functions • Identify Constraints • Specify Optimization Criteria 17
Three Orthogonal Models
• Object model (class diagram) – specifies static structure of objects and their relationships – specifies
what
objects a system contains • Dynamic model (state diagrams) – specifies aspects of a system that change over time (
when
objects change) • Functional model (data flow diagrams) – specifies data value transformations in a system (
how
objects change) 18
Object Model --- Objects
• An Object is – A real world entity – Related to the problem domain – With crisply defined boundaries – Encapsulated along with its attributes and behaviors – Whose behavior and attributes must be understood in order to understand the problem.
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Examples
• Objects usually correspond to nouns in a "natural" language.
• Objects may represent physical entities (such as companies, people, lumber, I/O devices, etc.), concepts (such as "business process", "data analysis", etc.), and everything in between.
• Examples of objects include:
IBM, Juan Mendoza, a 2’ 2x4, the ZIP drive, the interview protocol,
and
zero crossing analysis
.
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Classes
• A
class
is a "template" describing a set of objects with – similar properties (attributes), – common behavior (operations), – common relationships to other objects, and – common semantics. 21
Instances
An instance of a class is an object • created at runtime • based on a class (template). • Sometimes class and object are used to mean the same thing (by mistake).
• An instance is used to refer to exactly one thing.
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Terminology
• Class: – A category – A type – A set • Instance (of a class) – Something in the category, is of the type, or an element of the set – Object 23
How to Recognize Objects
• Tangible things – These are the easier to find. They correspond to physical things: airplane, vehicle, book • Roles played by persons or organizations – Example: patient, employee, client, etc.
• Incidents – Used to represent an occurrence or event: something which happens at a specific time. Example: flight, accident, performance, etc.
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More objects
• Interactions – A "transaction" or "contract", and relate to two or more other objects in the model. – Examples are: Purchase (related to buyer, seller, and thing purchased). Marriage (related to man and woman) • Specifications – A standard or a definition. For example: a refrigerator model, the specification of what it means to be a certain model can be an object .
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Attributes
Abstraction of a single characteristic possessed by all the instances of a class. – May corresponds to an adjective or possessive phrase in a natural language. – It is any property, quality, characteristic that can be assigned to an object.
– E.g., color, size, name, . . .
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Good Attributes
complete: includes all the information pertaining an object factorized. Each attribute captures one separated aspect of the objects' abstraction mutually independent. The attributes take on their values independently of one another 27
How to Recognize Attributes
• Descriptive attributes. – Provide facts intrinsic to each instance of an object.
– E.g., length, width • Naming attributes. – Provide facts about the arbitrary labels and names carried by each instance of an object.
– E.g., user-name, part-number • Referential attributes. – Capture the facts that tie an instance of one object to an instance of another object.
– E.g., is-controlled-by, is-driven-by 28
Operations and Methods
• • Behavior of objects is realized via
operations
.
– A function or transformation that may be applied • to objects in a class. • by objects in a class – All objects in a class share the same operations.
Method:
the implementation of an operation. • Operations usually correspond to verbs in a natural language (
print, open, transform, mail
) 29
Recognizing Operations
• Manipulate data – add, delete, format, select, access. • Perform a calculation – The calculation is performed according to the value of the attributes of the object student.
• Monitor the object to verify the occurrence of an event that is controlling the object. – Think about monitoring an object needs to do to respond to an external change. Verify the time continually to activate a process at exactly 12:00 Hrs.
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In Class
• Pairs (2 minutes): create a class list with attributes and operations:
A student may take up to five courses in a semester. Each course may have as many as 30 students in each section. Each course has one section per semester. A class room can hold at most one course at a time .
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UML Class Diagram -- Notation for Classes
Class Name Class Name Attributes Operations These may be abstract or at the source code level 32
Car speed direction
Attributes and Operations
Level of detail varies with level of abstraction: start with high abstraction
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Car speed direction
Attributes and Operations
Car speed: Integer direction: Tuple
Refine with Types
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Car speed direction
Attributes and Operations
Car speed: Integer direction: Tuple
Refine with Types Visibility Defaults Properties
Car +speed: Integer = 0 +direction: Tuple {readOnly}
Attributes and Operations
Types correspond to the types from an implementation language
Refine with Types Visibility Defaults Properties
Visibility is “+” for public, “-” for private, # for protected, ~ for package Default is attribute=value Property string is {} Car with one or more of
readOnly, ordered, sequence
+speed: Integer = 0 +direction: Tuple {readOnly}
Notation for Objects
• Rectangular box with one or two compartments objectName: Classname field 1 = value 1 …… field n = value n p1:Point x = 10 y = 20 The top compartment shows the name of the object and its class. The bottom compartment contains a list of the fields and their values.
p2:Point x = 20 y = 30 37
Interfaces and Abstract Classes
<
Class Relationships
Association Aggregation Composition Generalization Realization Dependency 39
Association
• General binary relationships between classes • Commonly represented as direct or indirect references between classes Student Course 40
Association (Cont.)
• May have an optional label consisting of a name and a direction drawn as a solid arrowhead with no tail. • The direction arrow indicates the direction of association with respect to the name.
Student enroll Course 41
Association (Cont.)
• An arrow may be attached to the end of path to indicate that
navigation
is supported in that direction • If omitted?
enroll Student Course 42
Association (Cont.)
• May have an optional
role name
and an optional
multiplicity specification.
• The multiplicity specifies an integer interval, e.g., –
l..u
closed (inclusive) range of integers – i singleton range – 0..* entire nonnegative integer, i.e., 0, 1, 2, … Student 0..* advisee 1 advisor Faculty 43
Example
Student advisee 0..* 6..* has enrolled 1 1 advisor Course 1..* teach 1 Faculty 44
Aggregation
• Special form of association representing
has-a part-whole
relationship. or • Distinguishes the whole (aggregate class) from its parts (component class). • No relationship in the lifetime of the aggregate and the components (can exist separately).
Aggregate Component 45
Composition
• Stronger form of aggregation • Implies exclusive ownership of the component class by the aggregate class • The lifetime of the components is entirely included in the lifetime of the aggregate (a component can not exist without its aggregate).
Composition Component 46
Example
University 1 1..* College 1 1..* Department 1 0..* Student chair-of 1 1 member-of 1 Faculty 1..* 47
Dependency
• Relationship between the entities such that the proper operation of one entity depends on the presence of the other entity, and changes in one entity would affect the other entity.
• The common form of dependency is the
use
relation among classes.
<
Complex Associations
• Associations may be:
binary, ternary, or higher order
. • Binary associations involve two classes. This is the most common. • Higher order associations are more complicated to draw, implement, and think about than binary associations.
Ternary
associations involve 3 objects: – It is an atomic unit – The division of a ternary association into binary associations may loose information – The associations are represented by a diamond 49
Class diagram Project
Example
Language Programmer Instance diagram p1: Project C: Language Joe: Programmer p2: Project Java: Language 50
Notation: Association Class
Person 0..* 0..2
employer Company Employment period: DateRange Association class Employment keeps information about the association that is not part of either object. Person could have two jobs. Employment is a 1-person/1 company relation.
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Alternate Diagram
Person 1 0..* 0..2
Employer Company 1 0..2
Employment period: DateRange 0..* 52
Recursive Associations
0..* Node 0..* node1 node2 node3 node4 node5 node7 node6 node8 53
In Class: Draw the Class Diagram
There are four classes: Program, Block, CompoundStatement, and SimpleStatement <
program
> ::= program <
name
> : <
block
> .
<
block
> ::= <
statement
>* <
statement
> ::= <
simple statement
> | <
compound
> <
compound
> ::= <
block
> 54
Generalization and Specialization
Customer Every attribute of Customer is also an attribute of its subclasses.
Corporate Customer Private Customer 55
In Class: Draw the Diagram
• A figure is either a group or a polygon.
• A group contains any number of figures.
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