Tuples

Reasoning About Multivalued Dependencies

There are a many rules about MVD's that are similar to the rules we learned for FD's in "Rules About Functional Dependencies". For instance, MVD's obey

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.

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 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

The Object-Relational Model

The relational model and the object-oriented model typified by ODL are two important points in a spectrum of options that could underlie a DBMS. For an extended period, the relational model was dominant in the commercial DBMS world. Object-oriented DBMS's made limited

Nested Relations

Relations extended by point (1) of The Object-Relational Model are sometimes called "nested relations''. In the nested-relational model, we allow attributes of relations to have a type that is not atomic: particularly, a type can be a relation schema. Thus, there is a convenient,

Information Integration Via Semistructured Data

Unlike the other models we have discussed, data in the semistructured model is self-describing; the schema is attached to the data itself. That is, each node (except the root) has an arc or arcs entering it, and the labels on these arcs tell what role the node

Relational Algebra

This section begins a study of database programming, that is, how the user can ask queries of the database and can change the contents of the database. Our focus is on the relational model, and especially on a notation for describing queries about the content of relations called

An Algebra of Relational Operations

In order to start our study of operations on relations, we shall learn about a special algebra, called relational algebra that comprises some simple but powerful ways to construct new relations from given relations. When the given relations are stored data, then the constructed

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