The types of transparencies the NOS middleware is expected to provide are:-
Local/Remote access transparency
Distributed time transparency
Failure transparency and
File servers are useful for sharing files across a network. With a file server, the client passes requests for file records over nerwork to file server.
TP lite, based on stored procedures.
TP heavy, based on the TP monitors.
Base services - It is a part of the standard OS.
Extended services - These are add-on modular software components that are layered on top of base service.
With an object server, the Client/Server application is written as a set of communicating objects. Client object communicate with server objects using an Object Request Broker (ORB). The client invokes a method on a remote object. The ORB locates an instance of that object server class, invokes the requested method and returns the results to the client object. Server objects must provide support for concurrency and sharing. The ORB brings it all together.
An object is define ba a distrinct set up attribute that represent a network resources. For example User1 ,user2, group1 group2 etc.
It includes the communication stacks, distributed directories, authentication services, network time, RPC, Queuing services along with the network OS extensions such as the distributed file and print services.
Transparency of location
Message based exchanges
Encapsulation of services
Client/Server computing is the ultimate "Open platform". It gives the freedom to mix-and-match components of almost any level. Clients and servers are loosely coupled systems that interact through a message-passing mechanism.
SQL is a powerful set-oriented language which was developed by IBM research for the databases that adhere to the relational model. It consists of a short list of powerful, yet highly flexible, commands that can be used to manipulate information collected in tables. Through SQL, we can manipulate and control sets of records at a time.
It treats all processors as equal. Any processor can do the work of any other processor. Applications are divided into threads that can run concurrently on any available processor. Any processor in the pool can run the OS kernel and execute user-written threads.