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SVU (Subject) / Teilklausur 1 (Lesson)

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• What is a DS? Name some examples. System comprising hardware and software components on networked computers which communicate and coordinate their actions by messages. WWW Wikipedia Financial Trading System MMOs (WoW, Eve)
• What are the key implications of distribution? Concurrency No global clock Local failure
• What are technological trends regarding Distributed Systems? Pervasive networking Mobile Computing Distributed Multimedia Systems Cloud Computing
• What are the challenges of DS? Heterogeneity: Very different systems and software working together Open distributed systems: Extensibility, standards Security Scalability: Cost of extending service shoudl be linear Failure handling Concurrency Network Transparency
• What is the WWW? Network of networks Growing, open system for publishing and searching/consuming documents and services
• What are elements of the WWW? HTML Web Servers Web Browsers URLs HTTP
• What is HTTP? Hyper Text Transfer Protocol Sends variety of data: MIME types Request reply protocol
• What can be used for dynamic content? AJAX Javascript CGI
• Regarding WWW: What can be used to support programmers? Webservices with APIs
• What are DS models used for? For describing, designing and understanding distributed systems.
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• What types of models are there? Physical: Hardware Architecture: Computation and communication Fundamental: Provisions?? (e.g. interaction, failure, security)
• Regarding the physical model: What is IoT? Most devices are networkedLow-cost and low-energyUsed everywhere: Households, media, transportation, etc
• Regarding architectural models: What are communication entities from a systems perspective? Processes, threads and sensors
• Regarding architectural models: What are communication entities from a programming perspective? Objects, components, web services
• What are the four communication paradigms? Interprocess communication Remote procedure calls Remote method invocation (integrated with OO, but similar to RPC) Remote invocation (e.g. HTTP request)
• What does indirect communication mean? Uncoupling of space and time Group communication
• What is the difference between client-server and peer-to-peer? Peer to peer is more scalable and doesn't use servers Client-server is centralized
• Describe the placement problem Where to set up processes and objects in a distributed system? Depends on: communication patterns, requirements, costs
• Describe publish-subscribe systems Many publishers and recipients. Uses middleware to efficiently manage listsExamples: Twitter, RSS
• Regarding architectural models: What are layers? They aggregate components in layers and layers use services of lower layers: VERTICAL
• Regarding architectural models: What are tiers? Organize functionality within a given layer into appropriate entities Complementary to layering
• What are the layers in an DS? Hardware OS Middleware Application/Service
• How can two-tier and three-tier architectures be distinguished? Two-tier architectures split application logic between client and server Three tier architectures are client-user/view, server application logic and then server data(base).
• What is a thin client? Doesn't contain any application logic. e.g. VNC or X Server over a network
• What is the goal of fundamental models? To generalize and understand systems: Aim at formalizationAnd to achieve reliability and performance
• What types of fundamental models are there? Interaction Failure Security
• What are interaction models? They handle the message delay and the timing of events The main models are: Synchronous Asynchrounous
• What is the problem about synchronous interaction models? Boundaries have to be defined and not exceeded: Max process execution time Max message transmission time Max local clock drift
• What failures does a fundamental model have to handle? Omission failures: Crashes, network failures, etc Arbitrary failures: Data corruption, etc Timing failures: Time-out Masking failures: Tries to heal a component's failure
• What does a security model classify? Provides security through encryption, authentication, etc

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