Basic Class Diagrams Classifier Generalizable Element is Root

Basic Class Diagrams Classifier Generalizable Element is. Root Model Element Namespace name visibility is. Specification CS/SWE 421 Introduction to Software Engineering Dan Fleck (Slides adapted from Dr. Stephen Clyde with permission) Coming up: Class Syntax Constraint Body

UML class diagrams n Show the classes of a system – Their interrelationships Classifier • Inheritance Generalizable Element • Aggregation is. Root • Association – Attributes – Operations Model Element name visibility is. Specification Namespace Constraint Body

Class Syntax n A box divided into compartments – Name – Attributes – Operations – Responsibilities (rarely seen) – Used-defined compartments (rarely seen) Coming up: Class Names Student major: String gpa: Real standing: String add(Class Section) drop(Class Section) -- The set of students known to the registration system -- An exception occurs if gpa falls below 2. 0

Class Names n n n The name should be a noun or noun phrase The name should be singular and description of each object in the class The name should be meaningful from a problem-domain perspective – “Student” is better than “Student Data” or “Srecord” or any other implementation driven name Coming up: Exercise – Class Identification

Exercise – Class Identification n Identify meaningful classes in the Elevator System n http: //www. web-feats. com/classes/dj/lessons/uml/elevator. htm n Answers (possible): – Elevator controller – Door – Button • Elevator • Floor Coming up: Attributes

Attributes n n n Attributes represent characteristics or properties of classes They are place holders or slots that hold values The values they hold are other objects (or primitive types) Coming up: Attributes from an Analysis Perspective

Attribute Syntax [visibility] name [multiplicity] [: type] [=initial-value] [{property-string}] visibility: public “+”, protected “#”, or private “-” name: capitalize first letter of each word that makes up the name, except for the first multiplicity: number, range, or sequence of number or ranges. type: built-in type or any user-defined class initial-value: any constant and user-defined object property-string: e. g, changeable, add. Only, frozen Coming up: Operations

Attributes from an Analysis Perspective n n An attribute relates an object to some other object It has the same semantics as an association joe: Student name: String = “Joe Jones” joe: Student Coming up: Attribute Syntax name 1 Is basically the same as. . . Joe Jones : String

Operation Syntax [visibility] name [(parameter-list)] [: returntype] [{property-string}] visibility: “+”, “#”, “-” name: verb or verb phase, capitalize first letter of every word, except first parameter-list: coma separated list of parameters return-type: primitive type or user-defined type property-string: is. Query, sequential, guarded, concurrent Coming up: Type of Relationships in Class Diagrams

Operations Student major: String GPA: Real standing: String takes> name: String capacity: Integer add(Student) drop(Student) check. Prerequisites(Students) <has add(Class Section) drop(Class Section) Class Section Course Coming up: Operation Syntax Prerequisite

Type of Relationships in Class Diagrams A consolidated snippet of the UML Meta-model Relation Generalization Association Binary Association Coming up: Associations Aggregation Dependency N-ary Association

Associations n An association is a structural relationship that specifies that objects of class may be connected to objects of another class n Associations typically represent “long-lived” relationships – e. g. In a library system a Person always has a name (association), but may infrequently have a book (dependency) Coming up: Associations

Associations n n n Connect two classes Have an optional label Have multiplicities Are directional Have optional roles

Association Names n Associations may be named (or labeled) – The names should communicate the meaning of the links – The names are typically verb phases – The name should include an arrow indicating the direction in which the name should be read – The direction on the name does NOT change navigability! Coming up: Navigation

Associations Semester rin g> Student is registered for> tak is he ld du es> <works for Instructor Department Coming up: Association Names teaches> Class Section is sponsors> in st an ce of > Course

Navigation n The navigation of associations can be – uni-directional – bi-directional – unspecified n Navigation is specified by the arrow, not the label <works for Instructor Department Coming up: Navigation teaches> Class Section is sponsors> in st an ce of > Course

Navigation n n The navigation of association without an arrowhead is assumed to be undefined Navigation has less value when modeling from a conceptual perspective – Why? n Navigation is more important during specification and implementation perspectives – Why? Coming up: Generalization

Generalization n n Generalization is another kind of relationship in UML In a Java implementation what is this? Person Coming up: Exercise – Simple Associations Student Graduate Student

Exercise – Simple Associations n From an analysis perspective: – Identify meaningful associations and generalization/specializations among classes in the Elevator System Coming up: Class Diagrams

Class Diagrams n Class Diagrams describe – the types of objects in a system – their properties (attributes and operations) – relationships between objects n They can also include – Grouping concepts like packages – Constraints – Various kinds of annotations Coming up: Multiplicity Constraints

Multiplicity Constraints n A multiplicity constraint can be – a single number – a “*”, meaning an arbitrarily large number or simply “many” – a range, denoted by “min. . max” – a sequence of single numbers and ranges 1. . 2, 7, 10 -20 This is also called the cardinality constraint Coming up: Dependencies

Multiplicity Constraints is registered for> Student 1. . * rin tak <works for 1 Department Coming up: Questions teaches> 1. . 3 1 0. . 6 sponsors> is 0. . 8 he ld du es> 1. . * 1 g> 0. . * Instructor Semester 1. . * Class Section is 1. . * in st an ce of > Course

Questions n From the previous diagram – How many classes can a student take? – Do you have to be registered in any classes to be a student? – Do I need to teach this class to be an Instructor? Do I need to teach ANY classes? – Can a class have no students? Is that valid? Coming up: Multiplicity Constraints

Dependencies A consolidated snippet of the UML Meta-model Relation Generalization Association Binary Association Aggregation Coming up: Dependency Relationship Dependency N-ary Association

Dependency Relationship n It says that one modeling component “uses” another. n If the later changes then, the former may have to change as well Coming up: Dependencies

Dependencies n Syntax: – a dashed link – arrowhead point to a component on which there is a dependency n n n Dependencies can be defined among: classes, notes, packages, and other types of components Can dependencies go both ways? Any problems with having lots of dependencies? Coming up: Aggregations (is part of)

Aggregations (is part of) A consolidated snippet of the UML Meta-model Relation Generalization Association Binary Association Coming up: Aggregation Dependency N-ary Association

Aggregation n n Aggregation: is a special kind of association that means “part of” Aggregations should focus on single type of composition (physical, organization, etc. ) Crust 1 1 Sauce Serving 1 1 Cheese Serving Topping Serving * Pizza 1. . 3 1 1 0. . 9 1 4. . * Coming up: Composition (very similar to aggregation) Slice 1 Order

Composition (very similar to aggregation) n Think of composition as a stronger form of aggregation. Composition means something is a part of the whole, but cannot survive on it’s own. Room Coming up: Lets look at Bookstore. Example 4. jpg Building

Lets look at Bookstore. Example 4. jpg n n n Does John Mc. Cain (who has 7 houses) have a problem using this system? If Barack Obama decides to create a Federal sales tax, how would we change the system? Why is there a display method in Item, Book, Music. CD and Software? An Item. Order is part of how many Orders? Can you explain how a search works using this diagram? Coming up: Class Exercise

Class Exercise n Lets create the We. Grow class diagram Coming up: Safety System Example

Safety System Example n A safety software system for housing areas: – – – n enables its owner to configure it during installation, controls through its sensors the environmental areas against fire and burglary and interacts with the owner through the keypad of the system control panel. During installation, the system programming and configuration is carried out by using the numerical and functional keys of the control panel. Each sensor in the system is identified by a number and a type (fire or burglary). The system stores two passwords (each of them is up to six digits) used for the system activation/deactivation and a telephone number used for emergency calls when an alarm event arises. The system polls the fire sensors for M seconds, then disables them for other N seconds. After that, the system resumes the same cycle. The Ready indicator is lighting when the sensors are polled and is turned off when the sensors are disabled. When a sensor indicates an event, the system launches an alarm signal. After K seconds, the system calls the security forces office and provides it with information about the event nature and location. In order to log in, the owner enters the password and presses Enter. If any of the six digits is wrong the password is ignored by the system and the sensors’ state doesn’t change. The owner cancel the password with the Clear key. If a sensor is activated, the system is armed and the Armed indicator on the control panel is turn on. In the case of the sensor deactivation, the Armed indicator is turn off. Moreover, the system logs all events. Each logged event is characterized by its type and the date and time of its occurrence. The event list can be delivered by pressing the MEM key. Example specification from: http: //www. emis. de/journals/ASUO/mathematics/pdf 3/bogdan. ps Coming up: Questions

Questions n What’s the difference between an attribute and an association with another class? For example, should “grade” be an attribute or a link to another class called “Grade”? n When during the software engineering life cycle should you build classes diagrams? Coming up: More Questions

More Questions n How do you know when a class diagram is complete? n How can you manage change control on all the class diagrams for project? n What do you do with class diagrams after a system has been built and delivered? Coming up: What’s important

What’s important n n Understanding the 3 main parts of the class box Generalization/Specialization Associations and multiplicity constraints Aggregation (and composition) understand how to use them, but don’t worry about the differences between them – too subtle Coming up: Bonus Slide!