The database server provides reliable access to a database for client application programs. A client is an application program that a user runs to request information from a database that the database server manages.
When a client application connects to the database server and requests information, the database server locates the requested data within its databases and sends back the results. Depending on the type of request that the client application issues, the database server can return selected rows from tables within the databases that it manages, add or delete rows, or update particular columns within selected rows.
Client applications use Structured Query Language (SQL) to send requests for data to the database server. Client applications can use the data that the database server returns in a variety of ways, including simple displays on computer screens or complicated reports. Client programs include the DB-Access utility and programs that you write with an IBM Informix application programming interface (API) such as IBM Informix ESQL/C, IBM Informix ODBC Driver, C++, or Java.
The database server performs additional activities such as coordinating concurrent requests from multiple clients and enforcing physical and logical consistency on the data to provide reliable access to the database.
The database server administrator starts the database server processes. After the database server is initialized, database server processes run continuously during the period that users access data. For more information on starting the database server, refer to Initializing the Database Server.
Two broad classes of applications operate on data that is stored in a relational database:
OLTP applications are often used to capture new data or update existing data. These operations usually involve quick, indexed access to a small number of rows. An order-entry system is a typical example of an OLTP application. OLTP applications are usually multiuser applications with acceptable response times measured in fractions of a second.
OLTP applications have the following characteristics:
DSS applications are often used to report on or consolidate data that has been captured through OLTP operations over time. These applications provide information that is often used for accounting, strategic planning, and decision-making. Data within the database is usually queried but not updated during DSS operations. Typical DSS applications include payroll, inventory, and financial reports.
A recent approach to DSS consolidates enterprise wide data in a separately designed environment, commonly called a data warehouse. A data warehouse stores business data for a company in a single, integrated relational database that provides a historical perspective on information for DSS applications.
Another approach to DSS operations, called a data mart, draws selected data from OLTP operations or a data warehouse to answer specific types of questions or to support a specific department or initiative within an organization.
Decision-support applications have the following characteristics:
A client application communicates with the database server through the connection features that the database server provides.
At the source-code level, a client application connects to the database server through an SQL statement. Beyond that, the client use of connection facilities is transparent to the application. Library functions that are automatically included when a client program is compiled enable the client to connect to the database server.
As the database administrator, you specify the database server or coserver names and types of connections that can be made. The connectivity information is in the sqlhosts file.
To connect to the database server, the client specifies a database server name, which is a logical name assigned by the database administrator. The DBA associates this name with physical characteristics stored in sqlhosts, such as the host name, connection type and port number.
For a description of these connection features, refer to Client/Server Communications.
Home | [ Top of Page | Previous Page | Next Page | Contents | Index ]