Database Memorandum

The major purpose of a database is to provide an information system (in its broadest sense) that utilizes it with the information the system needs according to its own requirements. A certain broad set of requirements refines this general goal. Certain general functional requirements need to be met in conjunction with a database. They describe what is needed to be defined in a database that supports any specific application. The database type needs to be based on data models that are sufficiently rich to describe all the application's aspects needed to be supported by that database. Data definition languages exist to describe needed databases within the models. Data definition languages are typically data model specific.

Operational requirements are needed to be met by a database in order to effectively support an application when operational. Though it typically may be expected that operational requirements be automatically met by a DBMS, in fact it is not so for most of them: To be met substantial work of design and tuning is needed by database administrators. It is typically done through special database user interfaces and tools, and thus may be viewed as secondary functional requirements (but not less important than the primary).

If you are using UNIX or Linux platforms, Oracle and IBM tend to battle for the mid-range database market on UNIX and Linux platforms. Oracle database management tracks its computer data storage with the help of information stored in the SYSTEM table-space. The SYSTEM table-space contains the data dictionary and often by default indexes and clusters. A data dictionary consists of a special collection of tables that contains information about all user-objects in the database. The Oracle RDBMS also supports "locally managed" table-spaces, which can store space management information in bitmaps in their own headers rather than in the SYSTEM table-space (as happens with the default "dictionary-managed" table-spaces). Oracle later introduced the SYSAUX table-space that contains some of the tables formerly in the SYSTEM table-space.

If Oracle is not for you, another DBMS software is IBM's DB2. DB2 is a relational model database server developed by IBM. It primarily runs on Unix (namely AIX), Linux, IBM i (formerly OS/400), z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions. Alongside DB2 is another RDBMS: Informix, which was acquired by IBM in 2001.

DB2 can be administered from either the command-line or a GUI. The command-line interface requires more knowledge of the product but can be more easily scripted and automated. The GUI is a multi-platform Java client that contains a variety of wizards suitable for novice users. DB2 supports both SQL and XQuery. DB2 has native implementation of XML data storage, where XML data is stored as XML (not as relational data or CLOB data) for faster access using XQuery.

IBM