Object-Oriented Modeling: Static Models

Object-Oriented Modeling: Static Models Grady Booch, James Rumbaugh, and Ivar Jacobson, The Unified Modeling Language User Guide, 2nd edition, Addison Wesley, 2005.

Object-Oriented Modeling • Object-orientation as a base for modeling • 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. • Often easy to understand and maintain • Directly related to reality • I.e., no "semantic gap" or “impendence mismatch”

Key Object-Oriented Ideas • Identity • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Persistence

Key Object-Oriented Ideas • Identity • Data are organized into discrete entities called objects. • Objects have behavior and state. • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Persistence

Key Object-Oriented Ideas • Identity • Abstraction • OO design uses different abstractions to capture different parts of the system. • Classification • Encapsulation • Inheritance • Polymorphism • Persistence

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

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

Key Object-Oriented Ideas • Identity • Abstraction • Classification • Encapsulation • Inheritance • Different OO objects can reuse common behaviors through inheritance. • Polymorphism • Persistence

Key Object-Oriented Ideas • Identity • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Objects inherit types from parent classes as well as behavior • Persistence

Key Object-Oriented Ideas • Identity • Abstraction • Classification • Encapsulation • Inheritance • Polymorphism • Persistence • Objects have lifetime. • Attributes of an object may change over its lifetime.

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.

OO Analysis Objective • To develop precise, concise, understandable, and correct models of the problem context.

Object Modeling • Involves systems analysis and design based on three different views of the system: • Object Models • Dynamic Models • Functional Models

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

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

2. Develop a Dynamic Model • Prepare scenarios of typical interaction sequences • Identify events between objects and prepare an event trace • Build a state machine diagram, sequence diagram, or communication diagram • Match events between objects to verify consistency

3. Construct a Functional Model • Identify input and output values • Build use case scenarios • Build data flow diagrams (DFD) showing functional dependencies • Describe functions • Identify constraints • Specify optimization criteria

Three Orthogonal Models • Object model (class diagram) • specifies static structure of objects and their relationships • specifies what objects a system contains • Dynamic model (state machine 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)

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.

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.

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.

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.

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

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.

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.

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, . . .

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

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

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)

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.

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.

UML Class Diagram ---Notation for Classes Class Name These may be abstract or at the source code level Class Name Attributes Operations

Attributes and Operations Car Level of detail varies with level of abstraction: start with high abstraction speed wheel

Attributes and Operations Car Car speed wheel speed: Integer wheel: Wheel[*] Refine with Types

Attributes and Operations Car Car speed wheel speed: Integer wheel: Wheel[*] Car Refine with Types Visibility Defaults Multiplicities Properties +speed: Integer = 0 +wheel: Wheel[0..4] {unique} 35

Attributes and Operations Visibility is: “+” for public, “-” for private, # for protected, ~ for package Default is attribute=value Types correspond to the types from an implementation language Multiplicity is 3, 2..4, 0..*, etc. Car Refine with Types Visibility Defaults Multiplicities Properties +speed: Integer = 0 +direction: Tuple {readOnly} Property string is {} with one or more of readOnly, ordered, unique, etc. 36

Notation for Objects • Rectangular box with one or two compartments The top compartment shows the name of the object and its class. The bottom compartment contains a list of the fields and their values.

Interfaces and Abstract Classes

Enumeration Class • Special kind of class defining a fixed set of distinct values 39

Class Relationships Association Aggregation Composition Generalization Realization Dependency • Class relationships of different types and strengths

Q: Strength of Relationship? Stronger Weaker Association Aggregation Composition Generalization Realization Dependency 41

Association • General binary relationships between classes • Commonly represented as direct or indirect references between classes Student Course

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. enroll Course Student

Association (Cont.) • An arrow may be attached to the end of path to indicate that navigation is supported in that direction • If omitted? enroll Course Student

Student 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, … 1 0..* Faculty advisee advisor

Example has enrolled 1 6..* Student Course 1..* advisee 0..* teach 1 1 Faculty advisor

Component Aggregate Aggregation • Special form of association representing has-a or part-whole relationship. • Distinguishes the whole (aggregate class) from its parts (component class). • No relationship in the lifetime of the aggregate and the components (can exist separately).

Component Composition 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).

University Example 1 1..* 1 0..* 1..* 1 Department College Student 1 1 member-of chair-of 1..* 1 Faculty

Class2 Class1 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. <<use>>

Object-Oriented Modeling: Static Models