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
Information processing drives the growth of computers, as it has from the earliest days of commercial computers. In fact, automation of data processing tasks predates computers.
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
There are several implicit relationships among the various entity types. In fact, whenever an attribute of one entity type refers to another entity type, some relationship exists. For example, the attribute Manager of DEPARTMENT refers to an employee who manages the department; the attribute
The natural join operation operates on two relations and produces a relation as the result.
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.
The database administrator (DBA) is the central authority for managing a database system. The DBA’s responsibilities include granting privileges to users who need to use the system and classifying users and data in accordance with the policy of the organization
A database schema, along with primary key and foreign key dependencies, can be depicted by schema diagrams.
The UML methodology is being used extensively in software design and has many types of diagrams for various software design purposes. We only briefly present the basics of UML class diagrams here, and compare them with ER diagrams
Several types of locks are used in concurrency control. To introduce locking concepts gradually, first we discuss binary locks, which are simple, but are also too restrictive for database concurrency control purposes, and so are not used in practice. Then shared/exclusive locks - also known as read/...
In our examples up to this point, we have operated at the logical-model level. That is, we have assumed that the relations in the collection we are given are the actual relations stored in the database.
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.
Recovery from transaction failures usually means that the database is restored to the most recent consistent state just before the time of failure. To do this, the system must keep information about the changes that were applied to data items by the various transactions.
A relational database consists of a collection of tables, each of which is assigned a unique name.
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 ...
Object databases is the power they give the designer to specify both the structure of complex objects and the operations that can be applied to these objects
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 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 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 SQL operations union, intersect, and except operate on relations.
A database system is a collection of interrelated data and a set of programs that allow users to access and modify these data. A major purpose of a database system is to provide users with an abstract view of the data. That is, the system hides certain details of how the data are stored and maint...
A query language is a language in which a user requests information from the database.