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Abstraction Mechanisms

Abstraction Mechanisms. Abstraction: A problem solving tool that allows one to think of a problem at a higher level without worrying about the details. Abstraction refers to organizing information based on three abstraction mechanisms: classification, generalization , and aggregation . .

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Abstraction Mechanisms

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  1. Abstraction Mechanisms • Abstraction: A problem solving tool that allows one to think of a problem at a higher level without worrying about the details. • Abstraction refers to organizing information based on three abstraction mechanisms: classification, generalization, and aggregation.

  2. ABSTRACTION MECHANISMS(Continued) • Classification forms new objects by suppressing the details of individual instances and emphasizing properties of the whole. New object types (classes) are formed by collecting instances. Classification= set theoretic operation 'membership' ==> describes the 'instance-of' relationship

  3. ABSTRACTION MECHANISMS(Continued) EX: Classification would allow one to collect the instances '{Jane, Bob, Sue}' into a new higher-order type called 'secretary.'

  4. ABSTRACTION MECHANISMS(Continued) • Generalization merges existing types to form new types. Individual differences between subtypes are ignored and common traits are emphasized. Generalization= set theoretic operation 'union' ==> describes the 'is-a‘ relationship

  5. ABSTRACTION MECHANISMS(Continued) EX: Existing employee types 'secretary', and 'teacher' can be generalized to form the new type 'employee'.

  6. ABSTRACTION MECHANISMS(Continued) Generalization implies that every instance of the subtype is an instance of the type. Every instance of 'teacher' is also an instance of 'employee'

  7. ABSTRACTION MECHANISMS(Continued) • Aggregation forms an object as a relationship among other objects. It suppresses the details of the components and emphasizes the details of the relationship as a whole. Aggregation = set theoretic operation 'cartesian product' ==> describes the 'is-part-of‘ relationship

  8. ABSTRACTION MECHANISMS(Continued) EX: Consider object types 'stove','refrigerator', 'sink', 'cabinet'. A 'kitchen' object can be abstracted from the given objects. The individual objects (e.g., 'stove') are components of the aggregate ('kitchen').

  9. ABSTRACTION MECHANISMS(Continued) • Classification, generalization, and aggregation are the basic ways we have of structuring information. When they are repeatedly applied to objects, hierarchies of new objects are formed.

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