Architecture Tradeoff Analysis Method Software Engineering Institute Carnegie Mellon University Presented by: Senthil ayyasamy CS 590l- winter 2003

Road Map I.Introduction – Software Evaluation II.Case Study – Web content Delivery Secret behind Akamai technologies III.ATAM ( Paper Summary) Terminologies Steps IV.Applying ATAM to the case study V.Going beyond the paper VI. what I have done last summer?

I. Software Evaluation Software Architecture Analysis and Evaluation Need for Analysis AIAM AIAM Rough Plan

Software Architecture - Bridge for Requirements & Code - Choices + tradeoffs View. {Elements, Forms, Rationale}. Logical, Physical, Process and Development View Requirements Code Architecture

Analysis and Evaluation How can we use software architectures to evaluate a Quality Attribute Quality attributes Tussle in Software space Architectural Trade-off and Analysis

Why analysis ? Risk mitigation for a particular systems What does the quality of attributes imply? How to you determine these desired QA Knowing whether the architecture is suitable without even building them Real time systems

AIAM Assumes –that attribute-specific analyses are interdependent –that each quality attribute has connections with other quality attributes through specific architectural elements Architectural element: a component, a property of a component, or a property of the relationship between components that affects some quality attributes

ATAM Rough Plan Collect Scenarios Collect Requirements, Constraints, Environment Describe Architectural Views Realize Scenarios Attribute Specific Analyses Identify Sensitivities Identify Tradeoffs Phase I: Scenario and Requirements Gathering Phase II: Architectural Views and Scenario Realization Phase III: Model Building and Analyses Phase IV: Tradeoffs

II. Case Study – Web content Delivery Akamai Technologies – Content Delivery – Host Web Service Possible Architectural Models –Client – Server –Client – Server – Server –Client – Intelligent Cache – Server –Client – Redirection Proxies – Server

QA for Content Delivery Performance Reliability Cost

III. Summary of [KKC99] Evaluation Scenarios: Use/growth/exploratory QA: stimulus, architectural parameters, responses. elicitation/screening questions sensitivity/trade off point ABAS – problem description, stimuli/response, arch style, analysis Quality analysis heuristics

ATAM Steps Scenario elicitation Architecture elicitation Mapping of Scenarios onto the architecture representations Analysis

Collect Scenarios Elicit system usage scenarios from stakeholders Purpose: –to operationalize both functional and quality requirements –facilitate communication –develop a common vision of the important activities the system should support

Collect Requirements, Constraints, and Environment Identify attribute-based requirements, constraints, and environment Run-time qualities Non run-time qualities

Describe Architectural Views Generate candidate architectures Can do this by matching the architectural styles to the quality attributes of the system Realize the scenarios by verifying the architectures against the scenarios

Identify Sensitivities Involves varying elements of the architecture to identify if values from the attribute analyses change If a significant change is identified, then the modeled values are considered “sensitivity points”

Identify Tradeoffs Focuses on the interaction of attribute- specific analyses Finding tradeoff points: –multiple attributes may be sensitive to a single architectural element –the architectural element is considered a tradeoff point

IV. Applying ATAM to the case study In a client-server architecture, each of the following is sensitive to the # of servers –Performance –Availability –Security

Iterations When analyses show that the system’s predicted behavior comes adequately close to its requirements, the designers can proceed to a more detailed level of design When analyses reveal a problem, we can develop a plan for changing the architecture and repeating the steps Steps do not have to be linear

Tradeoffs Attribute 1Attribute 2 Architecture 1Architecture 2 Attribute-specific architecture analysis Attribute-specific architecture analysis Change in software architecture Effect of change on attribute

Tradeoffs Attribute Set 1 Attribute Set 2 Architecture 1Architecture 2 Attribute-specific architecture analyses Attribute-specific architecture analyses Change in software architecture Effect of change on attributes

Attribute Analysis Several analysis techniques already exist for performing: –reliability and risk analysis –safety analysis –performance analysis –security analysis

V. Beyond the Paper Identification of analysis methods Applicability of methods across several architectural styles Specification of quality attributes in order to facilitate measurement Examples!

VI So, How is my work related ? Validation of software systems FSMs Markov Analysis Abstract State Machines –Open source from Microsoft Research –Compatible with all platforms Will have something exciting soon