The typical method of enforcing discretionary access control in a database system is based on the granting and revoking of privileges. Let us consider privileges in the context of a relational DBMS.
A database usually contains groups of entities that are similar. For example, a company employing hundreds of employees may want to store similar information concerning each of the employees. These employee entities share the same attributes, but each entity has its own value(s) for each attribut
The main Idea for the Sampling Algorithm is to select a small sample , one that fits in main memory of the database of transaction
A database system is partitioned into modules that deal with each of the responsibilities of the overall system. The functional components of a database system can be broadly divided into the storage manager and the query processor components.
The architecture of a database system is greatly influenced by the underlying computer system on which the database system runs. Database systems can be centralized, or client-server, where one server machine executes work on behalf of multiple client machines.
We introduced the natural join operation. SQL provides other forms of the join operation, including the ability to specify an explicit join predicate, and the ability to include in the result tuples that are excluded by natural join. We shall discuss these forms of join in this section.
A database system provides a data-definition language to specify the database schema and a data-manipulation language to express database queries and updates.
The basic structure of an SQL query consists of three clauses: select, from, and where.
A primary goal of a database system is to retrieve information from and store new information into the database. People who work with a database can be categorized as database users or database administrators.
The rapid advancement of the use of information technology (IT) in industry, government, and academia raises challenging questions and problems regarding the protection and use of personal information. Questions of who has what rights to information about individuals for which purposes become more i...
Self-describing nature of a database system Insulation between programs and data, and data abstraction Support of multiple views of the data Sharing of data and multiuser transaction processing
In this section we discuss the concepts of concurrent execution of transactions and recovery from transaction failures.
Researchers have developed several data-models to deal with these application domains, including object-based data models and semi-structured data models.
The basic notation for specialization/generalization is to connect the subclasses by vertical lines to a horizontal line, which has a triangle connecting the horizontal line through another vertical line to the superclass. A blank triangle indicates a specialization/generalization with the disjoint ...
Conceptual modeling is a very important phase in designing a successful database application. Generally, the term database application refers to a particular database and the associated programs that implement the database queries and updates.
The specialization relationship may also be referred to as a superclass-subclass relationship. Higher- and lower-level entity sets also may be designated by the terms superclass and subclass, respectively. The person entity set is the superclass of the employee and student subclasses.