Software Modelling, UML Class Diagram, Data Storage and Databases Flashcards
When are class diagrams used
They are used when developing an OO system model to show the classes in a system and the association between these classes.
What are class models and class diagrams?
A class model is a representation of classes in a problem or software solution. Class diagrams are graphical forms of class models
What is an Object, Class, Attribute, Operation and Association
Object - An entity that holds data and exhibits behaviour
Class - An abstraction of a set of objects with common operations and attributes
Attribute - A data item held by an object or class
Operation - An object or class behaviour
Association - A connection between classes representing a relation on the sets of instances of the connected classes.
What are the types of class models?
Analysis or Conceptual so important entities or concepts in the problem, their attributes, important relationships.
Design, so classes in a software system, attributes, operations, associations, but no implementation details.
Implementation, so classes in a software system with implementation details
What are the UML class symbols?
Class names, attributes, operations and other
What are the different symbols for feature visibility?
+ means public attribute or function meaning it is visible to all classes
- means private attribute or function so it is visible only in the class
means protected attribute or function which means it is visible in the class that it appears and all the sub classes that have that symbol.
~ means package, so it is visible anywhere in the package containing the class in which it appears.
What are Association Lines?
They are connection between classes representing a relation on the sets of instances of the connected classes.
Association Lines are labelled or unlabelled, Readable in two directions and Direction arrows.
They may also have role names.
What is Association Multiplicity, what does it do and what does * mean?
The multiplicity at target class end of an association is the number of instance of the target class that can be associated with a single instance of the source class.
Basically states how many instances of the associated class can be connected to this class and object.
A * means indefinite (unknown)
What are the class diagram rules?
Class symbols must have a name compartment.
Compartments must be in order.
Attributes and operations must be listed one per line.
Attribute and operation specification must be syntactically correct.
What are Class diagram Heuristics?
Name classes, attributes, and roles with noun phrases.
Name operations and associations with verb phrases.
Capitalize class names only
Centre class and compartment names but left justify other compartment contents
Only use binary associations
Prefer association names to rolenames.
Place association names, rolenames and multiplicities on opposite sides of the line.
What is conceptual modelling and what is it’s process ?
A conceptual model is a static model of the important entities in a problem, their responsibilities or attributes, the important relationships among them, and perhaps their behaviours.
Conceptual models are about real world entities in the problem domain and not about software and they help in the understanding of the problem and design of the solution
The Process:
Identify classes
Add attributes
Add associations
Add multiplicities
What are the steps of creating a concept uml model.
- Identifying Real World Objects, so identifying the main components of the system and some params of each component.
- Adding Attributes, this step is about studying the specs and add attributes to our components, so only including the types, multiplicities and initial values specified in the problem, don’t add irrelevant object identifiers, don’t add implementation attributes and add operations sparingly.
- Add associations, the third step is about adding association via brainstorming so studying the spec looking for verbs and propositions describing relationships between model entities.
Look for relationships such as:
Physical or organisational proximity
Control, coordination and influence
Creation, Destruction or modification
Communication
Ownership
- Add multiplicities, so take pairs of associated entities in turn this includes making one class the target, the other the source and determining how many instances of the target class can be related to a single instance of the source class.
It also includes reversing the target and source and determine the other multiplicity, consulting the specification and add only multiplicities important in the problem.
What is a Generalization?
A generalization is the UML relation that holds between one model element and another when the child is a special type of the parent, this is represented by a hollow triangle and lines this triangle attaches to the parent and lines to the children.
Generalization is used to represent UML diagrams to model inheritance.
Difference between Generalization vs Association
Generalization is a relation between classes whereas associations represent relations between objects. Generalisation is not a kind of association.
What is Inheritance?
Inheritance refers to a class inheriting the identical functionality to another class. This is usually the relationship between the parent and child class.
What is Bi-Directional and Uni-directional Association
Bi directional association is shown by a solid line between two classes. This means that both classes are aware of each other and their relationship, unless you qualify the association as some other type.
In Uni-directional association, two classes are related but only one of them knows that the relationship exists. It is drawn with as a solid line with an arrowhead. (not the closed one)
What are packages?
Packages enable modelers to organise the model’s classifiers into namespaces like folders in a filing system.
What is aggregation and composition?
Aggregation relationship is where one class is part of another class. In the aggregation relationship the child class instance can outlive its parent class.
The composition aggregation relationship is just another form of aggregation but the child class lifecycle is dependent on the parent class lifecycle.
