Database

Review of Object-Oriented Concepts

Before introducing object-oriented database models, let us review the main object-oriented concepts themselves. Object-oriented programming has been extensively regarded as a tool for better program organization and, finally, more reliable software implementation.

The Type System

An object-oriented programming language offers the user a rich collection of types. Starting with atomic types, such as integers, real numbers, booleans, and character strings, one may construct new types by using type constructors. Usually, the type constructors let us

Extents

When an ODL class is part of the database being described, we need to differentiate the class definition itself from the set of objects of that class that exist at a given time. The difference is the same as that between a relation schema and a relation instance, even though both can

Semistructured Data Representation

A database of semistructured data is a collection of nodes. Each node is either a leaf or interior. Leaf nodes have associated data; the type of this data can be any atomic type, such as numbers and strings. Interior nodes have one or more arcs out. Each arc has a label, which shows

Relational Operations on Bags

While a set of tuples (i.e., a relation) is a simple, natural model of data as it might appear in a database, commercial database systems rarely, if ever, are based entirely on sets. In some situations, relations as they appear in database systems are allowed to have duplicate

Deletion / Updates

A deletion statement consists of: 1. The keywords DELETE FROM, 2. The name of a relation, say R, 3. The keyword WHERE, and 4. A condition. That is, the form of a deletion is DELETE FROM R WHERE ; The effect of executing this statement is that every tuple satisfying the condition (4) will be deleted from relation R.

Defining a Relation Schema in SQL

Now we shall begin a discussion of data definition, the portions of SQL that involve explaining the structure of information in the database. On the contrary, the aspects of SQL discussed previously - queries and modifications - are often called data manipulation.

Simple Table Declarations

The simplest form of declaration of a relation schema comprises the keywords CREATE TABLE followed by the name of the relation and a parenthesized list of the attribute names and their types.

Introduction to Selection of Indexes

Selection of indexes requires a trade-off by the database designer, and in fact, this choice is one of the principal factors that influence whether a database design is acceptable. Two important factors to examine are:

View Definitions

Relations that are defined with a CREATE TABLE statement in fact exist in the database. That is an SQL system stores tables in some physical organization. They are persistent, in the sense that they can be expected to exist indefinitely and not to change unless they are clearly told to

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