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You need to estimate the size of your tables, indexes, and other database objects at this stage so you can allocate the proper space for them. You can follow some basic rules of thumb or use some fairly elaborate sizing algorithms to size your database. You also have to choose the type of storage. Although most systems today are based on hard disks, you have several choices to make with regard to disk configuration and other issues, all of which could have a significant impact on the database s performance down the road. 3 discusses details of disk configuration and related issues.

Before you actually implement your new system, you need to make sure you have a security policy in place. There are several possible layers and levels of security, and you should ultimately ensure that the system is indeed secure at all these levels. Normally, you need to worry about security at the system and network levels, and you will usually entrust the system and network administrators with this type of security. You also need to ensure security at the database level, which includes locking up passwords and so forth. Finally, in consultation with the application designers, you also have to come up with the right application security scheme. This involves controlling the privileges and roles of the users of the database. 12 discusses user management and database security in detail.

Receiver +Run() +Stop()

During this final implementation stage, you establish exact timings for the actual switch to the new business system. You may be replacing an older system, or you may be implementing a brand-new business system. In either case, you need a checklist of the detailed steps to be undertaken to ensure a smooth transition to the new system. This checklist should also include fallback options if things don t go quite as planned. 16 discusses recovery techniques that help you restore an older database in case you need to scrap the new one for some reason. You can also run ad hoc queries at this stage to fine-tune your system and find out where any bottlenecks lie.

This chapter has provided you with an introduction to the art of database design and normalization, and this information will help you when you are designing and implementing a database from scratch. However, what do you do when you walk into a company to manage its databases and you have no idea of the underlying physical data model or entity-relationship diagrams Not to worry; you can use any of the data-modeling tools discussed earlier in the chapter to reverse-engineer the underlying database model. The process of generating a logical model from an actual physical database is called reverse engineering. By using the reverse-engineering feature in a database design tool, you can quickly generate the physical model or the entity-relationship model of your database. Reverse-engineering a database can help you understand the underlying model. It can also serve to provide documentation that may be missing in situations where the DBA or the lead developer has left and nobody can find the entity-relationship diagram. Reverse-engineering diagrams can be crucial in tracking the foreign key relationships in the data model. Developers can also make good use of entity-relationship diagrams when making improvements to the application.

Connection -HostAddress -IsIdle -LastActivity +Connect() +Disconnect()

This chapter has dealt with the relational database model, where all the data is stored in the form of tables. Relational databases have been accepted as the superior model for storing most kinds of simple data, such as ordinary accounting data. For modeling complex data relationships, however, the object database management system (ODBMS) has been put forward as being more appropriate. ODBMSs are still not at the point where they can seriously compete with traditional relational databases. The relational model and the object model can be seen as two different extremes in data modeling, and a newer extension of the relational model has come forth to bridge the gap between the two. This new model is the object-relational database management system, and Oracle has adopted this ORDBMS model since the Oracle8 version of its server software. Oracle defines the 11g version of its database server as an ORDBMS. The following sections compare and contrast the three database management system categories: relational, object, and object-relational.