1 2015-10-03 Component-based Approach and Dependable Systems Concerning Predictability of Component-based Systems: Classification of Quality Attributes.
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Component-based Approach and Dependable Systems
Concerning Predictability of Component-basedSystems: Classification of Quality Attributes
Ivica Crnkovic Mälardalen University, Sweden
Department of Computer Science and Engineeringwww.idt.mdh.se/~icc, ivica.crnkovic@mdh.se
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Mälardalen University (MdH)Mälardalen University, Vasteras (Västerås)
Department of Computer Science and electronics (IDE)
Real-Time Systems Design Lab Computer Architecture Lab
Computer Science Lab Software Engineering Lab Intelligent sensors Lab
Medical Equipment
Prof. in Software Engineering http://www.idt.mdh.se/~icc ivica.crnkovic@mdh.se
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Sources of information
Ivica Crnkovic and Magnus Larsson:
Building Reliable Component-Based Software Systems
Artech House Publishers, 2002, ISBN 1-58053-327-2
http://www.idt.mdh.se/cbse-book/
Ivica Crnkovic, Magnus Larsson Otto PreissConcerning Predictability in Dependable Component-Based Systems: Classification of Quality Attributes, Architecting Dependable Systems III,, p pp. 257 – 278, Springer, LNCS 3549, Editor(s): R. de Lemos et al. (Eds.):, 2005
ISO/IEC, “Software engineering - Product quality - Part1: Quality model”, ISO/IEC, International, Standard 9126-1:2001(E).
Ralf H. Reussner, Heinz W. Schmidt, Iman H. Poernomo, Reliability prediction for component-based software architectures The Journal of Systems and Software 66 (2003) 241–252
Claes Wohlin, Per Runeson: Certification of Software ComponentsIEEE Trans. Software Eng. 20(6): 494-499 (1994)
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Outline
• Introduction– Why CBD
• Parti I– Properties (Quality attributes)
• Part II– Composability vs. predictability of Quality
Attributes– Classification of Quality attributes
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What is Component-based approach?
• Building systems from (existing) software components– Providing support for the development of systems as assemblies
of components
– Supporting the development of components as reusable units
– Facilitating the maintenance and evolution of systems by customizing and replacing their components
– Separation of building components from building systems
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Why component-based approach?
• Primary a concern of business and life-cycle factors– Costs, Time-to-market– Flexibility– Understandability, maintainability– Reuse of already existing software
• Higher abstraction level for functional properties• To less degree a concern of non-functional properties
– The requirements that must be fulfilled also with this approach– Sometimes more difficult to achieve– Might be a reason that component-based approach is less (or
not) feasible
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The main question
• CBD has shown to be successful in many domains (desktop, distributed web-based applications...)
• What are the benefits and what are the drawbacks of CBD for particular domains?– Benefits /drawbacks for dependable (embedded) systems?
• What are the primary concerns and requirements of particular domains?– Can CBD contribute in providing solutions that meet these
requirements/concerns?• Yes• No• Make it more difficult
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Part I
Components and system properties
What are properties?
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Properties• Attribute/property
– “a construct whereby objects and individuals can be distinguished”
– “a quality or trait belonging to an individual or thing” • A required attribute/property is expressed as a need or
desire on an entity by some stakeholder. • An exhibited attribute/property is an attribute/property
ascribed to an entity as a result of evaluating (for example measurement of) the entity.
• The need for properties is motivated by their explanatory roles they have to fill. They describe phenomena of interest – There are no “absolute” properties
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Some example of properties• Reusability, Configurability, Distributeability, Availability, Confidentiality,
Integrity, Maintainability, Reliability, Safety, Security, Affordability, Accessibility, Administrability, Understandability, Generality, Operability, Simplicity, Mobility, Nomadicity, Hardware independence Software, independence, Accuracy, Footprint, Responsiveness, Scalability, Schedulability, Timeliness, CPU utilization, Latency, Transaction, Throughput, Concurrency, Efficiency, Flexibility, Changeability, Evolvability, Extensibility, Modifiability, Tailorability, Upgradeability, Expandability, Consistency, Adaptability, Composability, Interoperability, Openness, Heterogenity, Integrability, Audibility, Completeness, , Conciseness, Correctness, Testability, Traceability, Coherence, Analyzability, Modularity, ….
Kazman, R., L. Bass, G. Abowd, M. Webb, “SAAM: A method for analyzing properties of software architectures,” Proceedings of the 16th International Conference on Software Engineering, 1994.
Kazman et al, Toward Deriving Software Architectures from Quality Attributes, Technical Report CMU/SEI-94-TR-10, 1994.
McCall J., Richards P., Walters G., Factors in Software Quality, Vols I,II,III', US Rome Air Development Center Reports, 1977.Bosch, J., P. Molin, “Software Architecture Design: Evaluation and Transformation,” Proceedings of the IEEE Conference and Workshop on Engineering of Computer-Based Systems, 1999.
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Classification of properties
• Different classification– Run-time properties – Life cycle properties– Run time
• Reliability, safety, performance, robustness
– Life cycle• Maintainability, portability, reusability,…
• CBSE– Component properties– System properties
• Emerging properties
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Quality model in ISO 9126-I
Examplehaving source code reviews” (a Software development process quality) influences the source code in that “the number of not initialized variables” (an internal quality attribute of a software product) is minimized. This positively influences the reliability, of the system (an external quality attribute of a software product).
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General Concepts of the ISO/IEC 9126-1
Existing Components
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ISO/IEC 9126-1 quality attributes
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Other views – example: Dependability
1. Ability of a system to deliver service that can justifiably be trusted2. Ability of a system to avoid failures that are more frequent or more
severe than is acceptable to user(s)
Related to 1. Trustworthiness (assurance that a system will perform as expected)2. Survivability (capability to fulfill its mission in a timely manner)
Dependability
Safety-critical systems
Mission-critical systems
Business-critical systems
Avizienis, A.; Laprie, J.-C.; Randell, B.; Landwehr, C., “Basic concepts and taxonomy ofdependable and secure computing”, IEEE Trans. Dependable Sec. Comput., Vol. 1, Issue1, 2004
Other systems – embedded systems - Desktop systems
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Dependability
Availability Reliability Safety Confidentiality Integrity Maintainability
Readinessfor usage
Continuity of services
Absence ofcatastrophic consequences
Absence ofunauthorized disclosure ofinformation
Absence of impropersystemalternations
Ability toUndergorepairs andevolutions
Attributes of Dependability
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Dependability
Attributes
Threats
Means
AvailabilityReliabilitySafetyConfidentialityIntegrityMaintainability
Fault PreventionFault ToleranceFault RemovalFault Forecasting
FaultsErrorsFailures
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Part II
Composition Predictability of properties
What do we know about properties compositions?
What do we need to know to predict system properties from component properties?
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Main concern: Composability and predictability of extra-functional properties
• Classification in respect to:– to ability to predict system properties from
component properties• (ability to verify the predictability)
Ivica Crnkovic, Magnus Larsson, Otto PreissConcerning Predictability in Dependable Component-basedSystems: Classification of Quality AttributesArchitecting Dependable Systems II, Springer LNCS 2005
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Some definitions first…
Assembly – a set of components
System
System Usage
System context
Component
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Component development (COTS type)Known: Architectural Framework, component modelUnknown: system architecture, products, usage,..
Product lineKnown: domain, architectural framework, application skeleton,Variation (integration) pointsUnknown: Final products
Open systemsKnown: similar to PLA,but integrators are not necessary known
Final product ready to use(usage not necessary known)
Final product in use
What can we predict (or guarantee) about the system properties In each stage of development?
Different levels of knowledge about future component-based systems
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Classification1. Directly composable properties. A property of an assembly
which is a function of, and only of the same property of the components involved.
2. Architecture-related properties. A property of an assembly which is a function of the same property of the components and of the software architecture.
3. Derived (emerging) properties. A property of an assembly which depends on several different properties of the components.
4. Usage-depended properties. A property of an assembly which is determined by its usage profile.
5. System context properties. A property which is determined by other properties and by the state of the system environment.
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1. Definition: A directly composable property of an assembly is a function of, and only of the same property of the components.
• Consequence: to derive (predict) an assembly property it is not necessary to know anything about the system(s)
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Example
• “Physical characteristics”– Static memory
– (the “function” can be much more complicated)– (the functions are determined by different factors,
such as technologies)
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Example (cont)
• Dynamic memory – components with parameterized configurations/deployment paramentars
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2. Definition: An architecture-related property of an assembly is a function of the same property of the components and of the software architecture.
• Consequence: System/assembly architecture must be known
– Ok when building systems of particular class• (product-line architectures)
rearchitectu software
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Clients
Client tier Web server tier Business logic tier Data tier
Web server
Businesscomponents
Data accesscomponents Data
Variabilitypoints
tionimplementaparticularaforfactorsalproportion,,
componentsofnumber;clientsofnumber
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Example - distributed systems
Yan L., Gorton I., Liu A., and Chen S., "Evaluating the scalability of enterprise javabeans technology", In Proceedings of 9th Asia-Pacific Software Engineer-ing Conference, IEEE, 2002.
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3.Definition: A derived property of an assembly is a property that depends on several different properties of the components.
– Consequence: we must know different properties and their relations (might be quite complex)
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Inputports
Outputports
end-to-end deadline is a function of different component properties, such as worst case execution time (WCET) and execution period.
Example
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4. Definition: A Usage-dependent property of an assembly is a property which is determined by its usage profile.
Consequence: It is not enough to know which system will be built. It must be known how the system will be used
profileusagecomponent'
profileusageassembly
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Example Reliability
• the probability that a system will perform its intended function during a specified period of time under stated conditions.
• Mean time between failure• How to calculate reliability for Software System?
– Start from from a usage profile– Identify probability of the execution of components– Find out (measure) reliability of components– Calculate reliability of the system
Ralf H. Reussner, Heinz W. Schmidt, Iman H. Poernomo, Reliability prediction for component-based software architectures
The Journal of Systems and Software 66 (2003) 241–252
Claes Wohlin, Per Runeson: Certification of Software ComponentsIEEE Trans. Software Eng. 20(6): 494-499 (1994)
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Uk
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Uk-min Uk-max
Ul -min Ul -max
Pl
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Can we predict reliability using existing usage profiles?Reuse problem:
mapping system usage profile to component usage profileWhen the known (measured) properties values can be reused?
),(),(),( maxmin kkllkkkl UAPUAPUAPUU
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5. Definition: A System Environment Context property is a property which is determined by other properties and by context of the system environment.
– Consequence: It is not sufficient to know the systems and their usage, it is necessary to know particular systems and the context in which they are being performed
profile usageComponent ´
System
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profile; usage System
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Example
• safety property – related to the potential catastrophe– the same property may have different
degrees of safety even for the same usage profile.
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Summary - Classification1. (DIR) - Directly composable properties. A property of an assembly which is a function of, and only of the
same property of the components involved.
2. (ART) - Architecture-related properties. A property of an assembly which is a function of the same property of the components and of the software architecture.
3. (EMG) - Derived (emerging) properties. A property of an assembly which depends on several different properties of the components.
4. (USG) - Usage-depended properties. A property of an assembly which is determined by its usage profile.
5. (SYS) - System context properties. A property which is determined by other properties and by the state of the system environment.
DIR – component context
DIR – Architecture (assembly) context
EMG – Architecture and other components context
USG – Use context
Sys – System (including external environemnt) context
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Composition Combination of Different Types of Properties
• Classification should be– Complete– Orthogonal
• The shown classification is an idealization
– Some properties will be of combination of different types
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Experiment
• Questionnaire– A set of defined properties– Grouped in different “sets of concerns”
• Following ISO 9126 standard and Dependability classification
• Assignment:– Classify the proposed properties
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Questionnaire – instructions
For each property (Quality attribute) in the table ask the following questions:
a. (Directly composable attributes) Is it possible to analyze this assembly quality attribute given the same quality attribute of the components involved?
b. (Architecture Related attributes) Is it possible to analyze this assembly quality attribute given the assembly software architecture and the same quality attribute of the components involved?
c. (Derived attributes) Is it possible to analyze this assembly quality attribute from several different component attributes of the components involved?
d. (Usage-dependent attributes) Is it necessary to know the usage profile of the assembly to analyze this quality attribute?
e. (System environment context dependent attributes) Is it necessary to have system environment information to analyze this quality attribute?
Answer each question with:0 = No, 1 = yes, 2 = yes, significantly
There is also a question where you can indicate the confidence in your answers for each attribute. (scale 1 to 5)
Please fill in answers on all attributes and indicate with the confidence of your selection1= little confidence 5=high confidence
Questionnaire
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Survey -Distribution of attribute classification
16%
44%
13%
12%
15%
a) Directly composable
b) Architecture-related
c) Derived
d) Usage-dependent
e) System environmentcontext
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Level of agreement of the participants for the classification
57%
95%
66%74%
56%
0%
20%
40%
60%
80%
100%
Le
vel
of
ag
ree
me
nt
a) Directly composable
b) Architecture-related
c) Derived
d) Usage-dependent
e) System environmentcontext
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Conclusion
• “Return of investment” for component-based approach depends also on predictability and assurance of quality attributes
• Composability of different quality attributes is different• The ability of predicting system properties from
component properties vary – from pure component properties to properties of systems exhibited differently in different context
• This limits the prediction ability of CB system’s behaviour
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