Identifying object class in architecture design

• Approaches use a grammatical approach to identify objects and their behaviors. For example, nouns often represent potential objects while verbs indicate potential methods or behaviors.
• Base the identification on tangible things in the application domain
• Look for hierarchies and relationships between components in the architecture. Hierarchies may indicate inheritance relationships between object classes.

Design Model

• Design models show the objects and object classes and relationships between entities
• Structural models
  • Subsystem models show how the design is organized into logically related groups
  • Sequence models show the sequence of object interactions that take place
• State diagrams are used to show how objects respond to different service requests and the state transitions triggered by these requests
  • Useful high-level models of a system or an object runtime behavior
  • Relatively simple and a state model adds unnecessary detail

Examples of design models

• Class Models
• Subsystem
• Sequence models
• State machine models

Unified modeling language

• A standardized specification for analysis and design
• A language, not a model
• Allows for visualized design and architecture
• [[More UML Relationships]]

Class

• The class represents a concept
• Encapsulates state and behavior
  • Has a name and a type, and can be the initial value
  • Each method has a signature: name, parameter, type, return

Access level	Meaning	Explanation
+	Public	The member is visible to all code in the application
-	Private	The member is only visible to code inside the class
#	Protected	The member is visible only to code inside the class and derived classes
-	Package	The member is visible only to code inside the same package

For more info on class protections and I/O read [[CPP_Review]]

Interface

• Specifies a contract
• Any other class that implements the interface must fulfill the contract

Generalization

• Informally called "Inheritance" or "is A" relationship
• Generalization is a directed relationship between a more general class and a more specific class
• Multiple inheritance is allowed in UML
• The children classes inherit the attributes and operations of the parent class and can have additional ones

Association

• Describes the presence of a relationship between classes
• The name of the association and multiplicity may be placed on the line
• The association end name is commonly referred to as role
• The professor is the author of a book; a book is used as a textbook by a professor
• The multiplicity of an association denotes how many objects the instance of a class can legitimately reference
  • every book has at least one author, a professor can write as may books, including none

Multiplicity of Associations

Indication	Meaning
0..1	Zero or one
1	One
0..or *	Zero or more
1..*	One or more
n	Only n (n > 1)
0..n	Zero to n (n > 1)
1..n	One to n (n > 1)

• Captured in source code by means of reference properties
• A class can have an association with itself

Aggregation

• A special type of association denoting a part-whole relationship
• Parts can exist without the whole; when the whole is destroyed the parts aren't
  • The exhaust system "consists of"
  • Muffler "is part of " the exhaust system
  • The tailpipe "is part of " the exhaust system

Dependency

• Represents a "using" relationship
• If a change in the specification in one class affects another (but vice versa) there is a dependency