Basic Networking

Task preemption

Task priority

Semaphores

Interprocess communications (IPC)

Local/Remote Interprocess communication

Threads

Intertask protection

Multiuser

High performance file system

Efficient memory management and

Dynamically linked Run-time extensions.

SQL is an interactive query language for ad hoc database queries.

SQL is a database programming language.

SQL is a data definition and data administration language.

SQL is the language of networked database servers

SQL helps protect the data in a multi-user networked environment.

Because of these multifacted roles it plays, physicists might call SQL as "The grand unified theory of database".

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.

Service

Shared resources

Asymmetrical protocols

Transparency of location

Mix-and-match

Message based exchanges

Encapsulation of services

Scalability

Integrity

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.

RPC hides the intricacies of the network by using the ordinary procedure call mechanism familiar to every programmer. A client process calls a function on a remote server and suspends itself until it gets back the results. Parameters are passed like in any ordinary procedure. The RPC, like an ordinary procedure, is synchronous. The process that issues the call waits until it gets the results.

Under the covers, the RPC run-time software collects values for the parameters, forms a message, and sends it to the remote server. The server receives the request, unpack the parameters, calls the procedures, and sends the reply back to the client. It is a telephone-like metaphor.

Resource Manager

Transaction Manager and

Application Program.

Process-per-client Architecture. (Example: Oracle 6, Informix )

Multithreaded Architecture. (Example: Sybase, SQL server)

Hybrid Architecture (Example: Oracle 7)

Non-GUI clients - Two types are:-

Non-GUI clients that do not need multi-tasking

(Example: Automatic Teller Machines (ATM), Cell phone)

Non-GUI clients that need multi-tasking

(Example: ROBOTs)

GUI clients

OOUI clients

Non-GUI Client: These are applications, generate server requests with a minimal amount of human interaction.

GUI Clients: These are applications, where occasional requests to the server result from a human interacting with a GUI

(Example: Windows 3.x, NT 3.5)

OOUI clients : These are applications, which are highly-iconic, object-oriented user interface that provides seamless access to information in very visual formats.

(Example: MAC OS, Windows 95, NT 4.0)

MOM allows general purpose messages to be exchanged in a Client/Server system using message queues. Applications communicate over networks by simply putting messages in the queues and getting messages from queues. It typically provides a very simple high level APIs to its services.

MOM's messaging and queuing allow clients and servers to communicate across a network without being linked by a private, dedicated, logical connection. The clients and server can run at different times. It is a post-office like metaphor.

Middleware is a distributed software needed to support interaction between clients and servers. In short, it is the software that is in the middle of the Client/Server systems and it acts as a bridge between the clients and servers. It starts with the API set on the client side that is used to invoke a service and it covers the transmission of the request over the network and the resulting response.

It neither includes the software that provides the actual service - that is in the servers domain nor the user interface or the application login - that's in clients domain.

It waits for client-initiated requests. Executes many requests at the same time. Takes care of VIP clients first. Initiates and runs background task activity. Keeps running. Grown bigger and faster.

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.

It is needed to accomplish a particular Client/Server type of services which includes:-

Database specific middleware

OLTP specific middleware

Groupware specific middleware

Object specific middleware

Internet specific middleware and

System management specific middleware.

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.

It imposes hierarchy and a division of labor among processors. Only one designated processor, the master, controls (in a tightly coupled arrangement) slave processors dedicated to specific functions.

In the transaction server, the client component usually includes GUI and the server components usually consists of SQL transactions against a database. These applications are called OLTP (Online Transaction Processing) OLTP Applications typically,

Receive a fixed set of inputs from remote clients. Perform multiple pre-compiled SQL comments against a local database. Commit the work and Return a fixed set of results.

In 3-tier Client/Server systems, the application logic (or process) lives in the middle tier and it is separated from the data and the user interface. In theory, the 3-tier Client/Server systems are more scalable, robust and flexible.

Example: TP monitor, Web.

In 2-tier Client/Server systems, the application logic is either buried inside the user interface on the client or within the database on the server.

Example: File servers and Database servers with stored procedures.

If the number of incoming clients requests exceeds the number of processes in a server class, the TP Monitor may dynamically start new ones and this is called Load balancing.