csci 578 software architectures
DESCRIPTION
CSCI 578 Software Architectures. Exam #2 Review. Materials you are responsible for. Chapters 9-17 in the text book Also Chapter 8 on Architectural Analysis since we didn’t cover this in the first exam - PowerPoint PPT PresentationTRANSCRIPT
CSCI 578Software Architectures
Exam #2 Review
Materials you are responsible for
• Chapters 9-17 in the text book– Also Chapter 8 on Architectural Analysis since
we didn’t cover this in the first exam
• All lecture material from Implementation Architectures through People, Roles and Teams (Week 15)
• Homework #3 and Course Project• Dan Crichton’s lecture, T. S. Mohan’s lecture
Exam
• Closed book, closed note
• Format– Write in answers– No multiple choice
Material Review
• Implementing Architectures– Mapping problem of design decisions to
implementation artifacts (code, executables, etc.)– Common Element Mapping
• Understand how components, connectors, interfaces, configurations are reified in the actual system implementation
– One way versus Round-trip Mapping– Architectural Implementation Frameworks
• a piece of software that acts as a bridge between a particular architectural style and a set of implementation technologies
Material Review
• Architectural implementation framework examples– stdio, java.io, iostream => pipe and filter
• Evaluating architectural implementation frameworks– Platform support, fidelity, matching assumptions, efficiency,
size, cost, ease of use, reliability, robustness, availability of source code, portability, long-term maintainability and support
• Middleware– Represents the implementation-level reification of software
connectors
• New Frameworks– Avoid constructing these unless you have to!
Material Review
• Implementation Techniques– Detailed description of pipe and filter Lunar
Lander
Material Review
• Applied Architectures– 8 limitations (“fallacies”) of distributed computing
(Deutsch & Gosling)• The network is reliable• Latency is zero• Bandwidth is infinite• The network is secure• Topology doesn’t change• There is one administrator• Transport cost is zero• The network is homogeneous
Material Review
• Applied Architectures– REST/WWW
• Architectural principles– Resources, resources include metadata + bits, context free
communication (stateless), small set of well defined methods, representation metadata for caching, presence of intermediaries to distributed computation/workload
– Akami• Caching of content and localized delivery architecture
– Google MapReduce/GFS• Distribution of computation/parallelization and data over
a commodity cluster of machines
Material Review
• Applied Architectures– Grid Protocol Architecture (Globus)– P2P Architectures
• Napster, Gnutella• Skype• Bittorrent
• Overall takeaways– A great architecture is the ticket to runaway success– A great architecture reflects deep understanding of the problem
domain– A great architecture probably combines aspects of several simpler
architectures– Develop a new architectural style with great care and caution.
Most likely you don’t need a new style.
Material Review
• Designing for Non-Functional Properties (NFPs)– A software system’s non-functional property (NFP) is a
constraint on the manner in which the system implements and delivers its functionality
• Example NFPs– Efficiency– Complexity– Scalability– Heterogeneity– Adaptability– Dependability
Material Review
• Ascertain the role of software architecture in ensuring various NFPs– At the level of major architectural building blocks
• Components• Connectors• Configurations
– As embodied in architectural style-level design guidelines
• Efficiency, Complexity, Scalability, Heterogeneity, Adaptability, Dependability
Material Review
• Security and Trust– “The protection afforded to an automated information system in
order to attain the applicable objectives of preserving the integrity, availability and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications).”
• National Institute of Standards and Technology
• Design Principles– Least Privilege: give each component only the privileges it
requires– Fail-safe Defaults: deny access if explicit permission is absent– Economy of Mechanism: adopt simple security mechanisms– Complete Mediation: ensure every access is permitted– Design: do not rely on secrecy for security
Material Review
• Security and Trust• Design Principles
– Separation of Privilege: introduce multiple parties to avoid exploitation of privileges
– Least Common Mechanism: limit critical resource sharing to only a few mechanisms
– Psychological Acceptability: make security mechanisms usable
– Defense in Depth: have multiple layers of countermeasures
Material Review
• Decentralized– No centralized authority to coordinate and control
entities– Independent peers, with possibly conflicting goals,
interact with each other and make local autonomous decisions
– Presence of malicious peers in open decentralized applications
– Need for measures to protect peers against malicious attacks
Material Review
• Some Threats of Decentralization– Impersonation: Mallory says she is Bob to Alice– Fraudulent Actions: Mallory doesn’t complete
transactions– Misrepresenting Trust: Mallory tells everyone Bob
is evil– Collusion: Mallory and Eve tell everyone Bob is
evil– Addition of Unknowns: Alice has never met Bob
Marvin(malicious)
Carol
Bob
Alice
Mallory(malicious)
DecentralizedAuctioning
Decentralized Auctioning
• Open decentralized application
• Independent buyers/sellers
• Potentially malicious participants
• Need to counter threats
BobAlice
Mallory(malicious)
“I am Bob”
Bob is reliable and everyonehas a good opinion about Bob
Impersonation
Alice “buyer”
Alice paysfor the items
Marvin “seller”(malicious)
Marvin doesnot ship the items
Fraudulent Actions
BobAlice
Mallory(malicious)
“Bob is unreliable”
Bob is reliable and everyonehas a good opinion about Bob
Misrepresentation
BobAlice
Mallory(malicious)
“Bob is unreliable”
Bob is reliable and everyonehas a good opinion about Bob
Marvin(malicious)
Collusion
Carol(new entrant in the system)
Bob Alice
Bob has no informationabout Carol; he is not sure
whether to interact with Carol
Carol is new and does notknow Alice; she is not sure
whether to interact with Alice
Addition of Unknowns
Material Review• PACE Architecture
Co
mm
un
icat
ion
Lay
erIn
form
atio
nL
ayer
Tru
stL
ayer
Communication Manager
ExternalInformation
InternalInformation
Key Manager
Signature Manager
Trust Manager
Application Trust Rules
HTTP Sender Custom Protocols Multicast Manager
Multicast Handler
Credential
Manager
A P P L I C A T I O N
Material Review
• Deployment and Mobility– Deployment is the process of placement of a
system’s software components on its hardware hosts
– Changing the deployment of a component during runtime is called migration or redeployment
– Migration or redeployment is a type of software system mobility
– Mobility entails a superset of deployment issues
Material Review
• 4 Major Deployment Activities– Planning– Modeling– Analysis– Implementation
Material Review
• Deployment Implementation– Release– Install– Activate– Deactivate– Update– Adapt– Reconfigure– De-install or remove– De-release or retire
Material Review
• Code Mobility Paradigms– Remote evaluation
• Re-deploy needed component at runtime from a source host to a destination host
• Install component on the destination host
– Code-on-demand• Same as remote evaluation, but roles of target and
destination hosts are reversed
– Mobile agent• Migration of a stateful software component that needs
some remote resources to complete its task
Material Review
• Definition. Reference architecture is the set of principal design decisions that are simultaneously applicable to multiple related systems, typically within an application domain, with explicitly defined points of variation.
• Reference architectures are still architectures (since they are also sets of principal design decisions)– Distinguished by the presence of explicit points of variation
(explicitly “unmade” decisions)
Material Review
• DSSA Definition (Hayes-Roth)• Definition: A domain-specific software
architecture (DSSA) comprises:– a reference architecture, which describes a general
computational framework for a significant domain of applications;
– a component library, which contains reusable chunks of domain expertise; and
– an application configuration method for selecting and configuring components within the architecture to meet particular application requirements. (“variation points”)
Material Review
• DSSE and Product Line Architectures– Product Lines
• A set of related products that have substantial commonality
Material Review
• People, Roles and Teams– Architect desired skills
• Software development expertise• Domain expertise• Communicator• Strategist• Consultant• Leader• Technologist• Cost estimator• Cheerleader• Politician• Salesperson
Material Review
• Pitfalls of the architecture team– Imbalance of skills
• Lack of software development experience• Lack of domain expertise
– Lack of authority• Team acts as committee
– Life in ivory tower– Confusing tools/techniques/methodologies with
architectures– Procrastination