Introduction
The first release of relational database. It is designed to provide a dependable relational database solution for small- to medium-sized businesses without placing extra demands on the business's human and machine resources.
A client/server database system is where the application programs, known as clients, must run as processes separate from the programs that maintain and store the data, called servers.
INFORMIX-SE is a complete relational database management system, also known as RDBMS, that comes with not only the previous mentioned server, but also its own front-end client—DBaccess.
Performance
Because INFORMIX-SE's server deals with the client and the server as separate entities, it is able to provide better performance. Because the client applications are responsible for creating, processing, and displaying the data, the server can concentrate on storing and retrieving the data faster and more safely.
Data Protection
To make sure that the data is safe and sound after such an event, SE uses transaction logging, auditing, and backups. Every activity performed by the SE server is considered a transaction, whether it's a query, an insertion, or a deletion. As SE performs the activity, it also writes what it did in a log file. When a failure occurs, SE uses an auditing process to compare what is in the log file to what is actually in the database. If they don't match, the audit process applies the activities from the log against the database.
For data to maintain its integrity and consistency, SE uses integrity constraints, data locking, and process isolation levels.
Integrity Constraints
Entity Integrity
Entity integrity includes any constraints placed on a specific entity's data range. For example, a data item called discount can have a constraint of 0 to 50. This implies that any percentage between 0 and 50 is permitted for the entry stored in the discount field in the database. A client application that tries to store 75 percent is rejected by the SE server.
Referential Integrity
Referential integrity prevents client applications from breaking any predetermined rules when dealing with a data item that has a relationship with other data items.
Data Locking
SE uses data locking to stop a client from changing a data item while another client is working with the same item. Locking does not prevent other clients from querying data that is currently being updated; it only restricts concurrent updates on the same data.
The three levels of data locking are:
- Table row
- Entire table
- Database
Isolation Levels
When client applications are querying the database, another client process can change the data being accessed. To prevent data change during a read, SE has built-in process isolation levels. A process isolation level is the stage at which a data update can or cannot occur while a select (or read) query is being performed. The standard level is the basic SELECT statement.
The next level is the SELECT FOR UPDATE statement. This statement locks the data at the current locking level, preventing other clients from changing the data until the original client completes its query. A SELECT FOR UPDATE query fails if the data is already locked by another client.
The next restriction is placed at the table level. Privileges at this level let specific users access data that others may not have permission to see.
Uses
The most common use of INFORMIX-SE is the standard business-related database. With Informix's development tools, these businesses can create elaborate front-end programs to customize the storage and retrieval of their companies' important information.
Limitations
The largest of SE's limitations is that it is not an online transaction processing (OLTP), client/server-type of system. An OLTP system has multiple users connected to a database system at the same time, accessing the database constantly during the day. Each access is considered a transaction, a specific task that is performed on the database, such as a query, an insert, or a delete.
Availability is another limitation of SE. A transaction log is maintained by SE, recording all changes made to the database. This log is cleared and restarted fresh after you make a backup on the database. If a crash occurs and some recent data is lost, you must restore the last backup and then apply the last transaction log.
System Architecture
INFORMIX-SE relies heavily on the UNIX operating system to provide a backbone architecture. UNIX has its own set of programs that provide interprocess communications (IPCs) and file system operations.
