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1989 | Buch

Kapitel lesen Erstes Kapitel lesen

The Structure of the Relational Database Model

verfasst von: Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht

Verlag: Springer Berlin Heidelberg

Buchreihe : Monographs in Theoretical Computer Science. An EATCS Series

Enthalten in: Professional Book Archive

Inhaltsverzeichnis
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SUCHEN

Über dieses Buch

This book presents an overview of the most fundamental aspects of the theory that underlies the Relational Database Model. As such it is self-contained though experience with formal models and abstract data manipulating on the one hand and with the practical use of a relational system on the other hand can help the reader. Such experience will offer the reader a better understanding of and a motivation for the different concepts, theories and results mentioned in the book. We have focussed on the most basic concepts and aspects of the relational model, without trying to give a complete overview of the state of the art of database theory. Recently a lot of books on databases in general and on the relational model in particular have been published. Most of them describe the use of database systems. 'Some clarify how information has to be structured and organized before it can be used to build applications. Others help the user in writing down his applications or in finding tricky ways to optimize the running time or the necessary space. Another category of books treat more fundamental and more general aspects such as the description of the relational model, independent of any implementation, the decomposition in normal forms or the global design of distributed databases. Few, however, are the books that describe in a formal way some of the subjects mentioned above.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Relational Database Model
Abstract
A database system is a collection of programs that run on a computer and that help the user to get information, to update information, to protect information, in general to manage information.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 2. Query Systems
Abstract
In this chapter we discuss three different systems for expressing a question or a query: the relational algebra, the tuple calculus and SQL.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 3. Constraints
Abstract
As we saw in Chapter 1, we need to specify constraints in the description of a database in order to ensure that the instances we might obtain are meaningful. We distinguished relation constraints, database constraints, dynamic relation constraints and dynamic database constraints. In this chapter, we restrict ourselves to “static” relation constraints. Database constraints will not be discussed in detail; however we do urge the reader to convince himself that there exist database constraints which cannot be expressed by constraints on the relations contained in the database (see Exercise 1.8). Dynamic constraints will be discussed in Chapter 8. Section 3.1 is devoted to some general terminology concerning constraints. In Sections 3.2 till 3.6, we discuss some important types of relation constraints.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 4. Vertical Decompositions
Abstract
In Example 3.11 and Theorem 3.7 we saw that the presence of fds can give rise to lossless decompositions of a given relation scheme. We summarize the main advantages of decomposing a relation scheme:
  • smaller relations are easier to understand;
  • independent information should not be stored in one relation;
  • it is often possible to eliminate redundancy;
  • in distributed databases different components can be located in different sites.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 5. Horizontal Decompositions
Abstract
The vertical decomposition, explained in Chapter 4, is a useful tool for reducing redundancy in the database and for improving the speed of query evaluation and updating. However, in the real world the constraints on which the decomposition relies may not be easy to find, and exceptions may appear after a database system is in use for some period of time.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 6. Incomplete Information
Abstract
In the previous chapters we have usually assumed that tuples are complete, i. e. that a tuple of a relation instance has, for each attribute of the relation scheme, a value of the domain of that attribute. In a “real” database however it is sometimes necessary to insert a new tuple into an instance, although the value of that tuple for some attributes is (still) unknown. In Example 1.10 we said that if a stay is not yet finished, the LEAV-DATE-value of a tuple is unknown. The definition of a relation instance (Definition 1.4) however does not allow the use of unknown unless this is a “normal” element of the domain of the attribute LEAV-DATE.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 7. The Nested Relational Database Model
Abstract
Up to this point, we have been dealing with the standard relational model introduced by Codd. Probably, one of the most fundamental assumptions made in this model is that data is represented in the form of flat tables; this is the so called first normal form assumption. In many practical circumstances, however, data is not represented as flat tables but rather in the form of hierarchically organized tables. For example consider the table shown in Figure 7.1. A row in that table represents a person, the set of his or her natural children and for each child, the set of his or her toys. In the relational model this table would be represented as shown in Figure 7.2. The argument made by many people is that the hierarchically organized table is a more natural representation of this data. So there is a need to represent and manipulate such data.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Chapter 8. Updates
Abstract
In this chapter we describe some problems and some important results about updates in a database. Most databases are very dynamic in the sense that regularly their contents or their instances change. These updates are described by the user in some language. It is not the aim of this chapter to describe such a language. Nor is it the aim to give a complete overview over the expressive power of such a language. We will discuss a very elegant and easy formalism that can only express a rather small class of updates. This formalism mainly includes transactions, which are sequences of insertions, deletions and modifications.
Jan Paredaens, Paul De Bra, Marc Gyssens, Dirk Van Gucht
Backmatter
Metadaten
Titel
The Structure of the Relational Database Model
verfasst von
Jan Paredaens
Paul De Bra
Marc Gyssens
Dirk Van Gucht
Copyright-Jahr
1989
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-642-69956-6
Print ISBN
978-3-642-69958-0
DOI
https://doi.org/10.1007/978-3-642-69956-6