Kĩ thuật lập trình - Chapter 8: Dispelling the myth of component evaluation

Chapter 8Dispelling the Myth of Component Evaluation Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationOverviewIntroductionMulti-criteria evaluation Exploding the myth of component evaluation Multi-attribute evaluation and beyond Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationIntroductionComponents:Independently deployed software implementations.Assemblies:Aggregations of components that provide integrated behavior. Selection: Choosing one component over another involves selection.Evaluation: Formalized process of quantifying human judgment by assigning value to choices.Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationEvaluationIfThe quality of software components determines of the quality of the composed system,ThenCBSE must provide techniques to reliably and repeatedly select high quality components.And it follows from this that Component evaluation is a distinguished CBSE activity, with distinguished workflows and techniques.Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationEvaluation Attributes selectvendorcomponenthealthfunctionusabilityreputationcomposed attributebasic attributequalitative dependencyPage Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationEvaluation Attributes selectvendorcomponenthealthusabilityfunctionalityreputationjudgmentusability indexjudgment#menu itemsnon-repeatable judgmentessential judgmentPage Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationGenus: Preference Structure-based Evaluation A preference structure. This is the model of the decision.A preference structure emerges when we express preference relations in terms of attributes.An aggregation technique. This is the tool that generates interpretations of the model.Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationPreference Relation P(x, y), strict preference:States that x is strictly preferred to y.I(x, y), indifference:States that neither x nor y is preferred.R(x, y), incomparability:States that x and y are incomparable.For example, we might define a preference relation: S(x, y) = P(x, y) È I(x, y)Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationSpecies: Multi-attribute Utility Evaluation The species can be seen through its formulaic expression, in which each evaluation attribute gk Î G is defined as the triple: Ux = S wk · uk(gk(x)) Ux denotes the overall utility of component x, uk denotes a transform function that maps the scale of attribute measure gk to a universal utility scale ukwk denotes the substitution rate for gk Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationMulti-attribute UtilityThe preference structure most frequently associated with multi-attribute utility is: S(x, y, g) = P(x, y, g) È I(x, y, g)P(x, y, g) « Ux > UyI(x, y, g) « Ux = Uy Which states that x is preferred to y if it has a higher utility, and x and y are indifferent if they have the same utility. Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationSimple Utility Transform Functions Usually usability indexutility1000u(usability)# menu itemsutility1000u(functionality)Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationExploding the Myth of Component EvaluationAn Assembly:Reflects the convenience in representing the composition of commercial components as systems, subsystems, sub-subsystems, and so forth. The scope of a system, or its relative position in a hierarchy of systems is not material to what follows, we will use the term ‘assembly’ in place of ‘system’. That is, commercial components are assembled into assemblies.Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationAssemblies and ComponentsAssemblies, once they exist, and commercial components will exhibit a variety of properties: functionality, reliability, usability, and so forth. The properties of an assembly are determined, in some way, by the properties of the components themselves Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationAssembly PropertiesC1C2P1P2APAPA = D(P1, P2)Assembly Properties Determined by Component Properties Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationSatisfaction of Normative Abstract Interface C1P1PE1APAPA = D(PE1, PE2)satisfiesPage Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationAccommodating VarianceC1P1PE1APAPA = D(PE1- P1, PE2 - P2)P1 Í PE1satPage Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationThe Inevitability of Hidden PropertiesC1P1PE1APAPA = D(PH1 , PH2 , PE1- P1, PE2 - P2)P1 Í PE1satPH1PE1 Ç PH1 = Æ Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component EvaluationFragment of Design Search Space Page Building Reliable Component-based Systems Chapter 8 - Dispelling the Myth of Component Evaluation