Oracle Tips  by Burleson Consulting

High Performance Data Warehousing

Database Architectures For The 1990s Encapsulation

Encapsulation means that each object within the system has a well-defined interface with distinct borders. In plain English, encapsulation refers to the "localized” variables that may be used within an object behavior and cannot be referenced outside of that behavior. This closely parallels the concept of information hiding. Encapsulation also ensures that all updates to the database are performed by using (or by way of) the behaviors associated with the database objects.

Code and data can be enclosed together into a black box, and these "boxes" may then function independently of all other objects within the system. (Figure 1.13) From a programming perspective, an object is an encapsulated routine of data and behaviors. Objects may contain public variables, which are used to handle the interfaces to the object, and private variables, which are known only to the object. Once created, an object is treated as a variable of its own type. For example, an object of class car is created as a routine with a datatype called car and is treated as a compound variable by the program.

Figure 1.13 An example of encapsulation.

Encapsulation is used in non-database object-oriented applications to ensure that all operations are performed through the programmer-defined interface, and that data will never be modified outside of the application shell. But, what about ad hoc queries and updates? It appears that any declarative database language, such as SQL, that allows external retrieval and update does not follow the dictates of encapsulation and is, therefore, inconsistent with object-oriented database management.

For example, a relational database could be defined to have a behavior called add_line_item which serves to check inventory levels for an item and add an item to an order only if sufficient stock is available. This behavior ensures that orders are not entered for out-of-stock items. However, with a language such as SQL, the object-oriented behavior could be bypassed, and line_item records could be added without any regard for inventory levels.

Because encapsulation and SQL are clearly incompatible, the only conclusion that can be reached is that encapsulation may be violated in Oracle8 by using ad hoc tools such as SQL*Plus.

If you like Oracle tuning, you may enjoy the book Oracle Tuning: The Definitive Reference , with over 900 pages of BC's favorite tuning tips & scripts.  You can buy it directly from the publisher and save 30%, and get instant access to the code depot of Oracle tuning scripts.