EEL6883 Fall14 Pres1 Balasubramanian Karthik

8/10/2019 EEL6883 Fall14 Pres1 Balasubramanian Karthik

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SYSTEMATIC ELABORATION OFSCALIBILITY REQUIREMENTS THROUGH

GOAL-OBSTACLE ANALYSIS

Leticia Dubo

and David

IEEE


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EXAMPLES OF SCALABILITY

Scenario 1Web search Engine

Scenario 2Air traffic control system

Indicators of scalabilityPerformance, Reliability, Availability, Dependabilit


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ISSUES DURING ELABORATION

Specifying scalability requirements that are precise and testable

Identify and manage scalability-related risks early in the development pro

Dealing with unknowns, uncertainties

Ensure scalability requirements are neither too strong nor too weak

Adequate tradeoffs between scalability and other qualities


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SCALABILITY OBSTACLE

Systematically identifying and resolving potential variations in domain quanthat will cause goal to fail


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GOAL-ORIENTED REQUIREMENTS ENGINEERIN

KAOS Approach - Knowledge Acquisition in Automated Specification or KeObjectives Satisfied

Comprises of modeling language and a constructive elaboration techniques

Approach

Goa


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TERMS AND DEFINITIONS

Goal - statement of intent that a system should satisfy through the cooperaagents.

Agents - active system components, such as humans, hardware devices and components

System refers to the composition of the software under development and

environment.

Goals range from high-level business objectives involving multiple agents tograined technical properties involving fewer agents

Domain Properties and Domain HypothesesDescriptive states about appldomain


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AND/OR REFINEMENT STRUCTURE

Goals are organized in AND/OR refinement structures

AND-refinement

Relates a goal to a set of subgoals

Satisfying all subgoals is a sufficient condition for satisfying the goal

OR-refinement

Relates a goal to a set of alternative AND-refinements

Each AND-refinement represents an alternative way to satisfy the parent g


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KAOS APPROACH

Goal elaboration

o Define initial set of high level goals & objects they refer to

o Define initial set of agents and actions they are capable of

Iteratively do the following:

o Refine goals using AND/OR decompositiono Identify obstacles to goals, and goal conflicts

o Operationalize goals into constraints

o Refine & formalize definitions of objects & actions


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GOAL-OBSTACLE ANALYSIS

Goal obstacle analysis consists of identifying, assessing and resolving obsta

Identifying as many obstacles as possible

Assessing the relative importance of the identified obstacles in terms of thei

Resolving more critical obstacles by modifying existing goals, requirements

assumptions Identify-Assess-Resolve loop is repeated until all obstacles are consideredacceptable.


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UNDERSTANDING SCALABILITYScalability

assumptionsobstacle an


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SCALABILITY REQUIREMENTS

Elements required to define scalability

quality goals of the system,

characteristics of application domain and

acceptable levels of quality goal satisfaction

Requires translation to KAOS Framework


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TRANSLATION TO KAOS FRAMEWORK

Quality goals correspond to goals whose specification includes domain-depobjective functions

Scaling assumptionvariation of characteristics in application domain

Scalability goalsquality goals constrained by scaling assumptions


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SCALING ASSUMPTIONS

Domain assumption specifying how certain characteristics in the application are expected to vary over time

Specification of scaling assumptions

One or more domain quantities whose expected variations are defined in thassumption

The periods of time and classes of system instances over which the assumptiodefined

The range of values each quantity is expected to assume for each system cover each period of time


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EXAMPLE

Assumption - Expected Batch Size Evolution

Category - Scaling Assumption

Definition - From 2011 to 2015,daily batches are expected to contain up tofollowing number of transactions for different bank categories

BANK 2011 UNTIL 2013 UNTIL 2015

Small 10,000 15,000 20,000

Medium 1 million 1.2 million 1.8 million

Large 50 million 55 million 60 million

Merger 80 million 85 million 95 million


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Our definition of scaling assumption covers the case where variations of doquantities refer to a single period of time and a unique class of system instan

Alternative simpler scaling assumption

Assumption - Expected Batch Size Evolution

Category- Scaling Assumption

DefinitionOver the next five years, daily batches of transactions for all bare expected to vary between 10,000 and 95 million transactions


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SUBGOALS FOR GOALS

Subgoal by using the scaling assumption

Goal Achieve [Batch Processed Overnight Under Expected Batch Size Evolu

Category Performance goal, scalability goal

Definition At the end of each day, the batch of transactions submitted by thshould be processed in less than 8 hours, provided that the batch size does noexceed the bounds stated in the scaling assumption Expected Batch Size Evol

Scaling assumptioncould be descriptive or prescriptive


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SCALABILITY GOALS

A scalability goal is a goal whose definition and required levels of goalsatisfaction (as specified by its objective functions) make explicit reference to more scaling assumptions.

The goal Achieve [Batch Processed Overnight Under Expected Batch Size Eis a scalability goal.

Reason - its definition refers to the scaling assumption Expected Batch SizeEvolution.

Comparison of scaling assumptions for air traffic control system and online s

Scalability goals with fixed objectives and varying objectives


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SCALABILITY OBSTACLE ANALYSIS

PROCEDURE

Identifying scalability obstacles that may obstruct the satisfaction of goals,requirements and expectations elaborated so far.

assessing the likelihood and criticality of those obstacles

Resolving obstacles by modifying existing goals


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IDENTIFYING SCALABILITY OBSTACLES

For each goal identify

What defines the goal load.

Agent resources involved in its satisfaction

An obstacle of the form Goal Load exceeds Agent Capacity


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ASSESSING SCALABILITY OBSTACLES

Using a qualitative risk analysis matrix

Likelihood of scalability obstacle estimated

Scale ranges from Very unlikely to almost certain

Criticality estimated from Insignificant to catastrophic


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RESOLVING SCALABILITY OBSTACLES

Obstacle resolution process comprises two activities

Generation of alternative resolutions

Selection of resolutions among generated alternatives


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SCALABILITY OBSTACLE RESOLUTION TACTICS

Goal substitutionfinding alternative goals

Agent substitutionchanging the responsibility assignment

Obstacle preventionIntroduce new goals and assumptions

Obstacle reduction Introduce new goal to reduce obstacles likelihood

Goal restorationIntroduce new goal to restore satisfaction of obstructed

Obstacle mitigationIntroduce new goal to mitigate consequences of an o

Do-NothingLeave the obstacle unresolved


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CONCLUSION

STRENGTHS

By extending KAOS, we facilitate precise specification of testable scalabilitrequirements

Scalability obstacle analysis method provides new obstacle resolution tactic

Elaboration covers achieving scalability as well as goal-resolving technique

WEAKNESS

Statistics from real-time projects not mentioned

No real-time values and experiments included in the elaboration for achievscalability


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QUESTIONS ?

EEL6883 Fall14 Pres1 Balasubramanian Karthik

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