Software Engineering Client / Server

Structure system C / S

In the structure of C / S computer that is located on the other computers called servers and computer-komoputer level below is called client. Client request (request) a service provided by the server. In fact there is some type of structure the implementation of the C / S:

1. File server: the client requested a specific record from the file, and the server sends this record to record, via the client network
2. Database server: the client send a SQL (structured Query Language) to the server via the network. Server processes, gain information, and then send to client hasi
3. Transaction server: Client send a request to request a remote procedure on the server. Remote procedure in the form of a set of SQL statements (or can be also a function). Transaction occurs when the request is done by remote procedure and the results are sent back to the client.
4. Groupware server: the server provides various applications that enable communication between the client (and users who use) with the use of text, image, bulletin boards, video, and other way

Figure 1 provides an illustration of client and server are connected in a network and some services provided by a server based implementation structure of the type of C / S at the top.

System software components on the C / S
Software system for C / S has some component / subsystem which each have different roles and cooperate with one another. Sub-sub-system can be allocated on the client or diserver, or distributed in both. Components / Sub-system are:

1. User interaction subsystem: the subsystem consisting of all functions associated with the user interface. Subsystem that serves as a data presentation to the user.
2. Application subsystem: subsystem implementing this requirement have been defined according to the context domain. For example, business applications generate reports based on numerical input, calculations and database information. Groupware application provides bulletin boards, email or calendar. Software applications can be divided so that some components in the client and the other on the server. Application subsystem is also often called the business logic.
3. Database management subsystem: this subsystem is to manipulate and manage data required by the application. Data manipulation means such as records tell, or process a complex SQL transactions.
4. Middleware: software consists of the elements on the client and the server such as:

• elements of the network operating systems
• database software that supports specific applications
• object-request broker (ORB) standards
• groupware technologies
• communication management
• other features that facilitate the client-server connection

Distribution of software components
After the components are clear, then how to distribute these components. How the distribution of component models below:

1. Fat client: user interaction / presentation, and application on the client, while the server provides the data management. This model is used on the file server and database server.
2. Thin Client: only user interaction / presentation of the client, while the server provides the application / service and data management. This model applies to transaction and groupware server.

Fat or Thin term is based on how much business logic in the client, the less, for example, only for user interaction, then the Thin. Instead more and more business logic on the client, then the Fat. For example, our browser does not do anything except display the information or act as any user interaction. Another approach in allocating or distributing software component C / S is with 5 different types of configuration:

1. distributed presentation: a database and application / business logic diserver allocated, usually Mainframe. The server also includes logic to prepare the information on the screen using a specific software. On the client software is used to change the characters to the public for display on the screen. Information sent from the server to the presentation in the GUI in the PC.
2. remote presentation: in the database and application server, data that is sent by a server used by the client to prepare a presentation on the screen.
3. distributed logic: a focus on the user client presentation, data entry process. Focus on the management server to process database queries from the client, update the file server, client control, and other business applications.
4. Remote data management: an application on the server to create new sources of data with formatting data extract results from elsewhere. Applications placed on the client used to use the new data is formatted by the new server. Included in the DSS that this.
5. distributed databases: the data that form the database in some server and client. Therefore the client must support the data management software components, software components and application GUI components.

Make a link between the sub-sub-system software C / S
There are several mechanisms used to create a link on the sub-subsystem. This mechanism to be part of the network and operating system. The mechanism is transparent to end-user on the client side. The mechanism used is:

1. pipes commands -> used in the UNIX operating system, allows the transmission between the different engine operating system.
2. Remote Procedure Call (RPC) -> process can run one or the other modules that are in a different machine
3. C / S SQL interaction -> used to pass SQL requests and related data from one component (usually the client) to the other components (usually in the DBMS server). This mechanism is limited to applications RDBMS (Relational Database Management System).

For the implementation of object-oriented in the sub-sub-system software C / S using the Object Request Broker.

ORB is middleware that allows an object that is in the client to send a messsage to the method of ter-encapsulated by an object on the server.
That is, ORB and forward the message to handle all communication and coordination needed to find the object referred to by the earlier message, call methodnya, through which data is appropriate to the object and send the results back to the data object that message earlier.
Standards commonly used to implement the ORB: CORBA, COM, and JavaBeans. CORBA is a simple structure as in Figure 2. Time CORBA system implemented in C / S, object and object class and object in the client and the server is defined using the interface description language (IDL).