September 2013 Archive

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

From ODL Designs to Relational Designs

As the E/R model is meant to be converted into a model such as the relational model when we put into operation the design as an actual database, ODL was initially meant to be used as the specification language for real, object-oriented DBMS's. Nevertheless ODL, like all object-

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

Representing Other Type Constructors

Above and beyond record structures and sets, an ODL class definition could use Bag, List, Array, or Dictionary to construct values. To represent a bag (multiset), in which a single object can be a member of the bag n times, we cannot simply introduce into a relation n the

Representing ODL Relationships

Generally, an ODL class definition will include relationships to other ODL classes. As in the E/R model, we can create for each relationship a new relation that connects the keys of the two related classes. However, in ODL, relationships come in inverse pairs, and we must create

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