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.
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.
An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are table-oriented. Object-relational databases are a hybrid of both approaches.
The basic structure of an SQL query consists of three clauses: select, from, and where.
it is sometimes necessary to represent a single superclass/subclass relationship with more than one superclass, where the superclasses represent different entity types. In this case, the subclass will represent a collection of objects that is a subset of the UNION of distinct entity types.
A database system provides a data-definition language to specify the database schema and a data-manipulation language to express database queries and updates.
Databases are widely used in enterprises, banking and finance, universities, airlines, telecommunication, etc.
If some cardinality ratio or dependency cannot be determined from the requirements, the users must be questioned further to determine these structural constraints
Select clause uses.
This chapter discusses techniques for securing databases against a variety of threats. It also presents schemes of providing access privileges to authorized users.
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 database-management system (DBMS) is a collection of interrelated data and a set of programs to access those data.
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 ...
The similarities and differences between conceptual modeling and knowledge representation, and introduces some of the alternative terminology and a few additional concepts.The goal of KR techniques is to develop concepts for accurately modeling some domain of knowledge by creating an ontology that d...
The SQL operations union, intersect, and except operate on relations.
we defined the degree of a relationship type as the number of participating entity types and called a relationship type of degree two binary and a relationship type of degree three ternary
In this section we discuss the concepts of concurrent execution of transactions and recovery from transaction failures
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.