Transcript OODM
Chapter 11 11 Object-Oriented Databases Database Systems: Design, Implementation, and Management 4th Edition Peter Rob & Carlos Coronel Object Schemas: The Graphical Representation of Objects 11 Figure 11.14 Shared Representation For All Objects Of the Class Person State Of A Person Object Instance 11 Figure 11.15 Defining Three Abstract Data Types 11 Figure 11.16 Object Representation For Instances Of The Class Person With ADTs 11 Figure 11.17 Object Schemas: The Graphical Representation of Objects 11 The object space or object schema is the equivalent of a database schema or a relational schema at a given time. Figure 11.18 11 Figure 11.19 Referential Sharing Of Objects Object Schemas: The Graphical Representation of Objects Class-Subclass Relationships 11 Figure 11.20 Class Hierarchy Employee Object Representation 11 Figure 11.21 Object Schemas: The Graphical Representation of Objects Interobject Relationships: Attribute-Class Link 11 A attribute-class or interobject relationship is created when an object’s attribute references another object of the same or different class. Relationship Representation: Representing 1:M Relationships Representing M:N Relationships Representing M:N Relationships with an Intersection Class Class Hierarchy For The EDLP Retail Corporation 11 Figure 11.22 Object Schemas: The Graphical Representation of Objects Representing 1:M Relationships 11 Related classes are enclosed in boxes to make relationships more noticeable. The double line on the box’s right side indicates that the relationship is mandatory. Connectivity is indicated by labeling each box. Representing The 1:M Relationship 11 Figure 11.23 Representing The 1:1 And 1:M Relationships 11 Figure 11.24 Employee-Dependent Relationship 11 Figure 11.25 Object Schemas: The Graphical Representation of Objects Representing M:N Relationships 11 Figure 11.26 Object Schemas: The Graphical Representation of Objects Representing M:N Relationships with an Intersection Class 11 Figure 11.27 Representing the M:N Relationship With Associated Attributes Representing The M:N Relationship With Intersection Class 11 Figure 11.28 11 Figure 11.29 Object Space Representation Object Schemas: The Graphical Representation of Objects Late and Early Binding: Use and Importance 11 With late binding the data type of an attribute is not known until execution time or run-time. Late binding allows two different object instances of the same class to contain values of different data types for the same attribute. Early binding allows the database to check the data type for each of the attribute’s values at compilation or definition time. Inventory Table With Predetermined (Base) Data Types 11 Figure 11.30 Inventory Class With Early Binding 11 Figure 11.31 OODM Inventory Class With Late Binding 11 Figure 11.32 Object Schemas: The Graphical Representation of Objects Support for Versioning 11 Versioning is an OODM feature that allows us to track the history of change in the state of an object. It is a very powerful modeling feature, especially in a CAD environment. OODM and Previous Data Models Object, Entity, and Tuple 11 An OODM object has additional characteristics such as behavior, inheritance, and encapsulation. Such characteristics make OO modeling much more natural than E-R and relational modeling. An Invoice Representation 11 Figure 11.33 OODM and Previous Data Models Class, Entity Set, and Table 11 Class is a more powerful concept that allows not only the description of the data structure but also the description of the behavior. A class allows both the concept and the implementation of abstract data types. Encapsulation and Inheritance An object belonging to a class inherits all the properties of its superclasses. Encapsulation hides the data representation and the method’s implementation from other objects and the user. OODM and Previous Data Models Object ID 11 Object ID is not supported in either the E-R model or the relational model. The hierarchical and the CODASYL models support some form of ID. Relationships Relationships in an OODM can be of two types: interclass references or class hierarchy inheritance. E-R and relational models use a value-based relationship approach. OODM and Previous Data Models Access 11 E-R and relational models use an ad hoc, setoriented query language. OODM is suited to support both navigational and set-oriented access.