9. What is a Thin client?
Thin client: Windows-based UI on user machines and application execution on remote computers. Examples of X-11 systems.
10. What are proxy patterns?
Proxy patterns are software design patterns. Proxies, in their most common form, are classes that function as interfaces for something else. Proxies can interact with anything: network connections, large objects in memory, files, or other resources that are expensive or impossible to duplicate. In short, proxy is a wrapper object or agent called by the client to access real serving objects behind the scenes.
11. Explain the pattern of reflection?
Reflection architectural patterns provide a mechanism for dynamically changing the structure and behavior of software systems. It supports modification of fundamental aspects such as type structure and function call mechanism. In this pattern, the application is divided into two parts:
· The meta level provides information about selected system properties and creates self-aware software. Changes to the information stored at the meta level affect the following basic level behavior.
· Basic levels including application logic. The implementation is built above the meta level.
Also Known as: Open Implementation, Meta-Level Architecture
Example:
Consider a C ++ application that needs to write objects to disk and read them again. Because perseverance is not a default C ++ feature, we must determine how to save and read each type in the application. A solution involves specifying metaobjects that provide run-time type information. For example, to store an object, we must know its internal structure and also the layout of all members of the data. With this information available, we can repeatedly repeat each given object structure to break it down into default order types. The persistence component 'knows' how to save this. If we change the run-time type information, we also modify the store method's behavior.
12. Mention three basic models of distributed systems!
· Physical Model:
o Three Generations of DS: Beginning, Scale of the Internet, Contemporary
· Architectural Model
o Software Layer
o System Architecture
o Client Server
§ Clients and Single Servers, Multiple Servers, Proxy Servers with Cache, Peer Models
§ The Sever-Client Alternative Model is driven by:
§ Cellular codes, cellular agents, network computers, thin clients, cellular devices, and spontaneous networks
§ Design / Requirement Challenges
· Fundamental Model - formal description
o Models of interaction, failure and security.
13. Give a description of the interaction model!
· Computing occurs in the process;
· The process of interacting with sending messages, produces:
o Communication (information flow)
o Coordination (synchronization and ordering of activities) between processes.
· Two significant factors that influence the process of interacting in a distributed system are:
o Communication performance is often a limiting characteristic.
o It is impossible to maintain a global idea of time.
14. Give a description of the failure model!
In DS, both communication processes and channels may fail, they can deviate from what is considered correct or desirable behavior. Type of failure:
· Negligence failure
· Arbitrary failure
· Time Management Failure
Failure failure refers to cases where the communication process or channel fails to take the requested action
Arbitrary failure is the most difficult to deal with, where all kinds of errors can occur. Data is damaged, unexpected response Time failure is related to synchronous messages, where [floating hours are bound, not messages, process execution time] exceeds the specified limit
15. Give a description of the security model!
DS security can be achieved by securing the processes and channels used in their interactions and by protecting the objects they encapsulate against unauthorized access.
Two components: safe channel and safe process
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