Introduction to ODL

ODL (Object Definition Language) is a standardized language for specifying the structure of databases in object-oriented terms. It is an extension of IDL (Interface Description Language), a component of CORBA (Common Object Request Broker Architecture). The latter is a

Attributes in ODL

The simplest type of property is the attribute. These properties explain some feature of an object by connecting a value of a fixed type with that object. For instance, person objects might each have an attribute name whose kind is string and whose value is the name of that

Relationships in ODL / Inverse Relationships

While we can learn much about an object by examining its attributes, often a critical fact about an object is the way it connects to other objects in the same or another class.

Multiplicity of Relationships

Like the binary relationships of the E/R model, a pair of inverse relationships in ODL can be classified as either many-many, many-one in either direction, or one-one. The type declarations for the pair of relationships tells us which.

Methods in ODL

The third kind of feature of ODL classes is the method. As in other object-oriented languages, a method is a piece of executable code that may be applied to the objects of the class.

Types in ODL

ODL gives the database designer a type system similar to that found in C or other usual programming languages. A type system is built from a basis of types that are described by themselves and certain recursive rules whereby complicated types are built from simpler types. In

Subclasses in ODL / Multiple Inheritance in ODL

Let us remember the discussion of subclasses in the E/R model from "Subclasses in the E/R Model". There is a similar capability in ODL to declare one class C to be a subclass of another class D. We follow the name C in its declaration with the keyword extends and the name D.

Declaring Keys in ODL

ODL is different from the other models studied so far in that the declaration and use of keys is optional. That is, in the E/R model, entity sets require keys to distinguish members of the entity set from one another. In the relational model, where relations are sets, all attributes

Nonatomic Attributes in Classes

Unluckily, even when a class properties are all attributes we may have some trouble converting the class to a relation. The reason is that attributes in ODL can have complicated types such as structures, sets, bags, or lists. On the other hand, a basic principle of the relational

Representing Set-Valued Attributes

Record structures are not the most complicated kind of attribute that can appear in ODL class definitions. Values can also be made using type constructors Set, Bag, List, Array, and Dictionary from Types in ODL. Each presents its own problems when migrating to the relational

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