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Transcript
Information Systems Chapter 3: Relational Databases • A relational database is: – A set of related tables that is created and managed by a database management system (DBMS) – Tables are linked using common data fields – Integrity rules are part of the database and are enforced by the DBMS • A relational DBMS (RDBMS) should provide the following facilities: – Query interface – Transactions processing – Concurrent access – Security Example • Another description: – PUBLISHERS(publisherId,publisherName) – TITLES(isbn,title,editionNumber,description,publis herId,copyright,imageFile,price) – AUTHORISBN(isbn,authorId) – AUTHORS(authorId,firstName,lastName) • And a last one: isbn 0130923613 0130622214 0130341517 0130649341 0130895601 0130308978 0130293636 0130895636 0130895512 Fig. 22.10 title editionNumber Python How to Program 1 C# How to Program 1 Java How to Program 4 The Complete Java Training 4 Course Advanced Java 2 Platform 1 How to Program Internet and World Wide 2 Web How to Program Visual Basic .NET How to 2 Program The Complete C++ Training 3 Course The Complete e-Business & 1 e-Commerce Programming Training Course publisherID price 1 1 1 2 copyright 2002 2002 2002 2002 1 2002 $69.95 1 2002 $69.95 1 2002 $69.95 2 2001 $109.95 2 2001 $109.95 Portion of the data from the Titles table of Books.mdb. $69.95 $69.95 $69.95 $109.95 authorID firstName lastName 1 Harvey Deitel 2 Paul Deitel 3 Tem Nieto 4 Kate Steinbuhler 5 Sean Santry 6 Ted Lin 7 Praveen Sadhu 8 David McPhie 9 Cheryl Yaeger 10 Marina Zlatkina 11 Ben Wiedermann 12 Jonathan Liperi Fig. 22.4 Data from the Authors table of Books.mdb. Primary Definitions • Table, a set of columns that contain data. In the old days, a table was called a file. • Row, a set of columns from a table reflecting a record. • Index, an object that allows for fast retrieval of table rows. Every primary key and foreign key should have an index for retrieval speed. • Primary key, often designated pk, is 1 or more columns in a table that makes a record unique. • Foreign key, often designated fk, is a common column common between 2 tables that define the relationship between those 2 tables. • Foreign keys are either mandatory or optional. Mandatory forces a child to have a parent by creating a not null column at the child. Optional allows a child to exist without a parent, allowing a nullable column at the child table (not a common circumstance). • Entity Relationship Diagram – or ER is a pictorial representation of the application schema (see the next chapter). • Constraints – are rules residing in the database’s data dictionary governing relationships and dictating the ways records are manipulated, what is a legal move vs. what is an illegal move. These are of the utmost importance for a secure and consistent set of data. • Data Manipulation Language or DML, sql statements that insert, update or delete database in a database. • Data Definition Language or DDL, sql used to create and modify database objects used in an application schema. Relational Design • The design of the application schema will determine the usability and query ability of the application. • Done incorrectly, the application and users will suffer until someone else is forced to rewrite it. • Main chalenge: How to efficiently design a “good” relational database • see next chapters