UML - Relationships Insight into Extending the Model

Types of Relationship UML Relationships Association unidirectional Bidirectiohal Dependency Generalization Realization Specialization Inheritance Aggregation ByValue ByReference

Association: unidirectional Bidirectiohal Attribute Visibility

Dependency: Non Attribute Level Visibility

Generalization - Specialization Relationship What is a Correct Subtype? 1.> 100% Rule (definition conformance) 100 % of the supertype’s definition should be applicable to the subtype. The subtype must conform to 100% of the supertype’s attribute and association. 2. > Is-a Rule (set membership conformance) All the members of a subtype must be members of their supertype set I.e subtype is a supertype.

Generalization - Specialization Relationship Motivations to Partition a Type into Subtypes: 1> Create a subtype has additional attributes of interest. 2> The subtype has additional associations of interest. 3> The subtype concept is operated upon, handled, reacted to or manipulated differently than the supertype or other subtypes, in ways that are of interest. 4> The subtype concept represents an animate thing ( for example, animal, robot) that behaves differently than the supertype or other subtypes, in ways that are of interest.

Generalization - Specialization Relationship Motivations to Partition a Type into supertype: Create a supertype in a generalization relationship to subtypes when: > The potential subtypes represent variations on a similar concept > All subtypes have the same attribute which can be factored out and expressed in the supertype. >All subtypes have the same association which can be factored out and related to the supertype .

AGGREGATION: Consider showing aggregation when: > The Lifetime of the part is bound within the lifetime of the composite there is a create-delete dependency of the part on the whole. > There is an obvious whole-part physical or logical assembly. > Some properties of the composite propagate to the parts, such as its location. > Operations applied to the composite propagate to the parts, such as destruction, movement, recording.

Benefit of Showing Aggregation: NOTE: Identifying and illustrating aggregation is not profoundly important; it is quite feasible to exclude it from a conceptual model. Include aggregation because it has the following benefits: It clarifies the domain constraints regarding the eligible existence of the part independent of the whole. In aggregation-by val, the part may not exist outside of the lifetime of the whole. During the code phase, this has an impact on the create-delete dependencies between the whole and part software classes. It assists in the identification of a creator ( the composite) using the GRASP Creator patterns. Operations - such as copy or delete - applied to the whole should often propagate to the parts. Identifying a whole in relation to a part supports encapsulation. The GRASP Don’t Talk to Strangers pattern is used to hide the parts within the whole.

NOTE: Identifying and illustrating aggregation is not profoundly important; it is quite feasible to exclude it from a conceptual model.

Include aggregation because it has the following benefits:

It clarifies the domain constraints regarding the eligible existence of the part independent of the whole. In aggregation-by val, the part may not exist outside of the lifetime of the whole.

During the code phase, this has an impact on the create-delete dependencies between the whole and part software classes.

It assists in the identification of a creator ( the composite) using the GRASP Creator patterns.

Operations - such as copy or delete - applied to the whole should often propagate to the parts.

Identifying a whole in relation to a part supports encapsulation. The GRASP Don’t Talk to Strangers pattern is used to hide the parts within the whole.

Aggregation in the Point-of-sale application

Realization: Interface is realized in the class.

An associative Type/Class:

Qualified Associations: A qualifier may be used in an association; it distinguishes the set of objects at the far end of the association based upon the qualifier value. An association with a qualifier is a qualified association .