ch8-2 - Chapter 8 Object-Oriented Databases Need for...

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1 ©Silberschatz, Korth and Sudarshan 8.1 Database System Concepts Chapter 8: Object Chapter 8: Object -Oriented Databases Oriented Databases ! Need for Complex Data Types ! The Object-Oriented Data Model ! Object-Oriented Languages ! Persistent Programming Languages ! Persistent C++ Systems ©Silberschatz, Korth and Sudarshan 8.2 Database System Concepts Need for Complex Data Types Need for Complex Data Types ! Traditional database applications in data processing had conceptually simple data types ! Relatively few data types, first normal form holds ! Complex data types have grown more important in recent years ! E.g. Addresses can be viewed as a " Single string, or " Separate attributes for each part, or " Composite attributes (which are not in first normal form) ! E.g. it is often convenient to store multivalued attributes as-is, without creating a separate relation to store the values in first normal form ! Applications ! computer-aided design, computer-aided software engineering ! multimedia and image databases, and document/hypertext databases.
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2 ©Silberschatz, Korth and Sudarshan 8.3 Database System Concepts Object Object -Oriented Data Model Oriented Data Model ! Loosely speaking, an object corresponds to an entity in the E- R model. ! The object-oriented paradigm is based on encapsulating code and data related to an object into single unit. ! The object-oriented data model is a logical data model (like the E-R model). ! Adaptation of the object-oriented programming paradigm (e.g., Smalltalk, C++) to database systems. ©Silberschatz, Korth and Sudarshan 8.4 Database System Concepts Object Structure Object Structure ! An object has associated with it: ! A set of variables that contain the data for the object. The value of each variable is itself an object. ! A set of messages to which the object responds; each message may have zero, one, or more parameters. ! A set of methods , each of which is a body of code to implement a message; a method returns a value as the response to the message ! The physical representation of data is visible only to the implementor of the object ! Messages and responses provide the only external interface to an object. ! The term message does not necessarily imply physical message passing. Messages can be implemented as procedure invocations .
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3 ©Silberschatz, Korth and Sudarshan 8.5 Database System Concepts Messages and Methods Messages and Methods ! Methods are programs written in general-purpose language with the following features ! only variables in the object itself may be referenced directly ! data in other objects are referenced only by sending messages . ! Methods can be read-only or update methods ! Read-only methods do not change the value of the object ! Strictly speaking, every attribute of an entity must be represented by a variable and two methods, one to read and the other to update the attribute ! e.g., the attribute address is represented by a variable address and two messages get-address and set-address
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ch8-2 - Chapter 8 Object-Oriented Databases Need for...

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