Chapter 3: Relational Databases 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,publisherId,copyright,imageFile,price) AUTHORISBN(isbn,authorId) AUTHORS(authorId,firstName,lastName)

And a last one:

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