An Engineering Approach towards Action Refinement

In the abstract modelling of distributed systems we may need methods to replace abstract behaviours by more concrete behaviours which are closer to implementation mechanisms. Furthermore, we may want these methods to preserve the correctness of such a replacement. This paper introduces an approach towards action refinement in which an abstract action is replaced by a concrete activity. This approach is based on a careful consideration of the `action' and `causality relation' architectural concepts, which enable an abstract action to be replaced by many alternative concrete activities in a general way. This approach is based on the application of abstraction rules to determine whether a concrete activity conforms to an abstract action, considering the context in which the concrete activity and the abstract action are embedde

Control Plane Compression

We develop an algorithm capable of compressing large networks into a smaller ones with similar control plane behavior: For every stable routing solution in the large, original network, there exists a corresponding solution in the compressed network, and vice versa. Our compression algorithm preserves a wide variety of network properties including reachability, loop freedom, and path length. Consequently, operators may speed up network analysis, based on simulation, emulation, or verification, by analyzing only the compressed network. Our approach is based on a new theory of control plane equivalence. We implement these ideas in a tool called Bonsai and apply it to real and synthetic networks. Bonsai can shrink real networks by over a factor of 5 and speed up analysis by several orders of magnitude.Comment: Extended version of the paper appearing in ACM SIGCOMM 201

Attribute abstraction, feature-dimensionality, and the scaling of product similarities

This paper examines the attributes that consumers use when making product similarity judgments and their effect on similarity scaling. Previous research suggests that concrete brands are judged using dichotomous features while more abstract product categories are judged using continuous dimensions. This, in turn, suggests that the appropriateness of spatial scaling increases relative to tree scaling as one moves from brands to product categories. The results of two studies support an increase in the fit of spaces relative to trees from brands to categories. However, the abstractness of the judgments appears to be driving the effect, not the use of features or dimensions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30067/1/0000437.pd

The Nature and Methodological Implications of the Cognitive Representation of Products

A general relationship is proposed wherein more abstract attributes are likely to resemble continuous dimensions while more concrete attributes are likely to resemble dichotomous features. While some methodologies assume dimensional representations, others assume feature-based representations. This suggests that dimensional methods may better capture abstract product representations while feature-based methods may better capture concrete representations. The results of two studies that support both the general relationship and its methodological implications are reported

Mixed Tree and Spatial Representation of Dissimilarity Judgments

Whereas previous research has shown that either tree or spatial representations of dissimilarity judgments may be appropriate, focussing on the comparative fit at the aggregate level, we investigate whether there is heterogeneity among subjects in the extent to which their dissimilarity judgments are better represented by ultrametric tree or spatial multidimensional scaling models. We develop a mixture model for the analysis of dissimilarity data, that is formulated in a stochastic context, and entails a representation and a measurement model component. The latter involves distributional assumptions on the measurement error, and enables estimation by maximum likelihood. The representation component allows dissimilarity judgments to be represented either by a tree structure or by a spatial configuration, or a mixture of both. In order to investigate the appropriateness of tree versus spatial representations, the model is applied to twenty empirical data sets. We compare the fit of our model with that of aggregate tree and spatial models, as well as with mixtures of pure trees and mixtures of pure spaces, respectively. We formulate some empirical generalizations on the relative importance of tree versus spatial structures in representing dissimilarity judgments at the individual level.Multidimensional scaling;tree models;mixture models;dissimilarity judgments

Adaptive Multidimensional Scaling: The Spatial Representation of Brand Consideration and Dissimilarity Judgments

We propose Adaptive Multidimensional Scaling (AMDS) for simultaneously deriving a brand map and market segments using consumer data on cognitive decision sets and brand dissimilarities.In AMDS, the judgment task is adapted to the individual respondent: dissimilarity judgments are collected only for those brands within a consumers' awareness set.Thus, respondent fatigue and subjects' unfamiliarity with any subset of the brands are circumvented; thereby improving the validity of the dissimilarity data obtained, as well as the multidimensional spatial structure derived.Estimation of the AMDS model results in a spatial map in which the brands and derived segments of consumers are jointly represented as points.The closer a brand is positioned to a segment's ideal brand, the higher the probability that the brand is considered and chosen.An assumption underlying this model representation is that brands within a consumers' consideration set are relatively similar.In an experiment with 200 subjects and 4 product categories, this assumption is validated.We illustrate adaptive multidimensional scaling on commercial data for 20 midsize car brands evaluated by 212 members of a consumer panel.Potential applications of the method and future research opportunities are discussed.scaling;brands;market segmentation

Architectural notes: a framework for distributed systems development

This thesis develops a framework of methods and techniques for distributed systems development. This framework consists of two related domains in which design concepts for distributed systems are defined: the entity domain and the behaviour domain. In the entity domain we consider structures of functional entities and their interconnection, while in the behaviour domain we consider behaviour definition and structuring. An interaction in which we abstract from the particular responsibilities of the participating functional entities is considered as an action. Behaviours consist of actions, interactions and their relationships. Relationships between actions and interactions are defined in terms of causality relations. In each causality relation the conditions and constraints for an action or interaction to occur are defined. Two important behaviour structuring techniques have been identified from the possible ways causality relations can be distributed: causality-oriented behaviour composition and constraint-oriented behaviour composition. Causality-oriented behaviour composition consists of placing some conditions of an action and the action itself in different sub-behaviours. Constraint-oriented behaviour composition consists of placing parts of the conditions and constraints of an action in different sub-behaviours, such that this action is shared by these sub-behaviours. This thesis identifies milestones in the design process of distributed systems, as well as the design steps to move from one milestone to another. These design steps are characterized using the concepts of the entity and the behaviour domain. We identified two crucial design operations of the behaviour domain that support these design steps: behaviour refinement and action refinement. Behaviour refinement consists of introducing (internal) structure in the causality relations of reference actions of an abstract behaviour, but preserving their causality and exclusion relationships and their attribute values. Action refinement consists of replacing abstract actions by activities, such that the completion of these activities correspond to the occurrence of the abstract actions. One important characteristic of action refinement is the possibility of distributing attribute values of the abstract actions over actions of the activities that replace them in the concrete behaviours. The area of research, scope and objectives of this thesis are discussed in Chapter 1. The concept of design culture and its elements is introduced in this chapter in order to provide an overview of the important aspects of the design process. Entity domain, behaviour domain, and design milestones are introduced and discussed in Chapter 2. This chapter also discusses the global objectives of design steps, and the abstraction obtained by considering interactions between cooperating functional entities as actions of the interaction system between these entities. Action, action attributes, causality and exclusion are discussed in Chapter 3. This chapter shows how a behaviour can be defined in terms of the causality relations of its actions in a monolithic form. Causality-oriented behaviour composition is discussed in Chapter 4. Entries and exits of a behaviour are the mechanisms that make it possible to assign parts of a condition of an action and the action itself to different sub-behaviours. Constraint-oriented behaviour composition is discussed in Chapter 5. Decomposition possibilities of monolithic behaviours are systematically studied in this chapter. Behaviour refinement is discussed in Chapter 6. This chapter defines a method to obtain an abstraction of a concrete behaviour. This method can be used to check whether the concrete behaviour corresponds to a certain abstract behaviour. Action refinement is discussed in Chapter 7. This chapter identifies some activity forms, and define the rules for considering these activities as implementations of an abstract action. These rules are used in a method to derive an abstraction of a concrete behaviour in which the abstract actions are implemented as activities. This method can be used to check whether the concrete behaviour corresponds to a certain abstract behaviour. Chapter 8 discusses a design example that is meant to illustrate the use of our design concepts. The example is an interaction server, which is a component that supports the interaction between multiple functional entities. Chapter 9 draws some conclusions and revisits the design milestones of Chapter 2, showing alternatives for the design trajectory which have been created with the use of actions and interactions in a single framework

Comparison Study and Review on Object-Oriented Metrics

The best elucidations to software development problems are regularly touted as object-oriented processes. The popularity of object-oriented design metrics is essential in software engineering for measuring the software complexity, estimating size, quality and project efforts. There are various approaches through which we can find the software cost estimation and predicates on various kinds of deliverable items. Object-oriented metrics assures to reduce cost and the maintenance effort by serving as early predictors to estimate software faults. Such an early quantification augments the quality of the final software. This paper reviews object-oriented metrics. A comparison table is maintained via which we can analyze the difference between all the object-oriented metrics effectively