Implementation of the

Relational Model

There is no substitute for the comfort supplied by the utterlytaken-for-granted relationship. Iris Murdoch

Class Outline

What are the required features of a DBMS? What are the features of a relational database

management system (RDBMS)? What is entity integrity and referential integrity? To what extent are entity integrity and referential

integrity supported by MS Access? What are the eight algebraic functions supported

by a fully relational DBMS? Give examples of each.

Functions of a DBMS Data storage and integrity management - creates complex

structures to store data, forms, etc. and enforces data relationships Management of data dictionary - updates as database structure is

modified Data transformation - presents data as user requests Backup and Recovery - ensures data safety in case of damage Multi-user access and Security - allows concurrent use of

database; disallows access to components as determined by the user Database Access Languages - supports non-procedural (user

specifies what must be done, not how) query language Application Programming Interfaces - supports procedural

languages (e.g., MS Access uses Visual Basic) for programmers Communication Interfaces - modern DBMSs provide access to the

database using internet browsers (e.g., Netscape)

Relational Database Management Systems

Relational database architecture Codd, E.F. (1970). A relational model for large shared data

banks. CACM, 13(6), 377-87. based on relational algebra and calculus first relational prototype - early 1970s - IBM’s System R

Relational databases required considerable computing resources (memory, processing speed) not feasible until mid- 1980s when price-performance ratio

dropped low end (Access, Paradox, dBase, FoxPro, Clipper, R:Base) high end (DB2, Oracle, Sybase, MS SQL Server, Informix,

INGRES commercial)

The Relational Model

...consists of relations, which are made up of attributes.

A relation is a set of columns (attributes) with values for each attribute such that: Each column (attribute) value must be a single value only. All values for a given column (attribute) must be of the same

type. Each column (attribute) name must be unique. The order of columns is insignificant. No two rows (tuples) in a relation can be identical. The order of the rows (tuples) is insignificant.

Steps to Relational Implementation

1. Define the database structure to the DBMS for server and mainframe databases, use Data Definition

Language (DDL) in a text file that describes columns of tables, defines indexes, constraints and security restrictions

many PC databases provide a graphical interface to define the database tables

in both cases, the Database Definition Subsystem of the DBMS creates the indexes and metadata

2. Allocation of Media Space usually unnecessary for PC databases, but performance issues

must be considered for server/mainframe dbs

3. Creating the Database Data import pre-existing data or enter data either through DML

(Data Manipulation Language) or forms of the application

Relational Data Manipulation Four strategies for relational data manipulation:

relational algebra - difficult to use because it is procedural - users must specify not only what they want but how to get it

relational calculus - difficult to learn due to theoretical nature, not used in commercial database processing

transform-oriented languages - non-procedural languages (e.g., SQUARE, SQL, SEQUEL)

graphical interface to Data Manipulation Language (DML) query-by-example and query-by-form (behind each is a

corresponding SQL query) - supported by many PC RDBMS (Lotus’ Approach, MS Access,Wall Data’s Cyberprise DBApp)

application program interface - written in programming languages such as COBOL, Pascal, Perl, C++

Relational DBMS Defined Logical database model (rather than physical) that represents all data as if

they are stored in separate two-dimensional but related tables

Each table consists of single-value data elements describing a common theme among which is one (or more) elements that uniquely describe each record in the table (i.e. no two rows are identical)

Tables are related as long as two tables share a common data element

Information in these tables can be combined on an as-needed basis (flexibility) to get answers to queries and generate complex reports

Product ID Product Description Price Supplier ID801 Shur-Lock U-Lock 75.00 3802 SpeedRite Cyclecomputer 60.00 3803 SteelHead Microshell Helmet 40.00 804 SureStop 133-MB Brakes 25.00 1805 Diablo ATM Mountain Bike 1,200.00 2806 Ultravision Helmet Mount Mirrors 7.45 3

Supplier ID Supplier Name1 Bikes-R-Us2 Small moter suppliers3 All Bikes Allways

Requirements of a RDBMS

1. Enforces Integrity rules(a) Entity Integrity - every row must have a unique identifier (primary key) which cannot include null entries

(b) Referential Integrity - foreign key must have either a null entry or an entry that matches the primary key value in a table to which it is related

Product ID Product Description Price Supplier ID801 Shur-Lock U-Lock 75.00 3802 SpeedRite Cyclecomputer 60.00 3803 SteelHead Microshell Helmet 40.00 804 SureStop 133-MB Brakes 25.00 1805 Diablo ATM Mountain Bike 1,200.00 2806 Ultravision Helmet Mount Mirrors 7.45 3

Supplier ID Supplier Name1 Bikes-R-Us2 Small moter suppliers3 All Bikes Allways

primary keyforeign key

Parent Table - Table on the one side of a one-to-many relationship.

Child Table - Table on the many side of a one-to-many relationship.

Entity Integrity Elements of a primary key:

It must uniquely identify each record in the table It must contain unique values It cannot be null It cannot be a multi-part field It should contain the minimum number of fields necessary to define uniqueness It is not optional whole or in part It must directly identify the value of each field in the table Its value can only be modified in rare or extreme cases

EmpID FName LName1 Jane Smith2 Bob Brown3 Lin Chow

EmpID Date Prior approval? Reason1 12-Sep-99 yes holiday3 14-Oct-99 no illness2 14-Oct-99 yes illness1 23-Nov-99 no awlconcatenated primary key

Referential Integrity

Referential integrity is a mechanism that enforces the ties between data in separate tables and prevents them from being broken

Referential integrity minimizes the undesirable likelihood of the existence of a record in the child table for which there is no corresponding record in the parent table - referred to as an orphan (or dangling) record

Prior to setting referential integrity, ensure that the field used to tie two tables together (the link field) must be a

primary key field in the parent table and a foreign key in the child table the link fields have an identical data type the two tables are in the same database container

Referential Integrity in MS Access

A value cannot be entered in the foreign key field of the related table if that

value doesn't exist in the primary key of the parent table.

A record cannot be deleted from a parent table if matching records exist in a related table.

A primary key value in the parent table cannot be changed, if that record has related records.

Determined by MS Access on the basis of primary key settings.

Referential Integrity Options in MS Access

Cascade Update

Special override of the referential integrity mechanism in order to be able to edit the primary key in the one table; MS Access will automatically make the same change to the foreign key in the child table so the relationship is maintained.

Cascade Delete

Special override of the referential integrity mechanism to facilitate deleting records in the parent table even when there are related records in the child table. All related records in the child table will automatically be deleted so that there will be no orphan records.

Do not use these options unless you realize the full implications of making the selection.

Relationship Integrityis a way of minimizing data errors

MS Access On-line Help

Requirements of a RDBMS

2. Supports many of the relational algebraic functions - a collection of operations on relations, resulting in relations

Specific relational operators: select project divide join

Set theory operators: union intersect difference product

Algebraic function: 1. Union

Salesperson

Employee ID Name Office27 Rodney JonesToronto44 Goro Azuma Tokyo35 Francine MoireBrussels37 Anne Abel Tokyo

Manager

Employee ID Name Office12 Brigit SanchezToronto99 Mary Chen Brussels37 Anne Abel Tokyo

Combination of data without repeating common rows; must have equivalent columns as to number and domains (“union compatible”).

Employee ID Name Office27 Rodney Jones Toronto44 Goro Azuma Tokyo35 Francine Moire Brussels37 Anne Abel Tokyo12 Brigit Sanchez Toronto99 Mary Chen Brussels

Provide information on all employees regardless of their position:

note that Anne appears only once even though she’s in both tables

Algebraic function: 2. Intersection

Employee ID Name Office37 Anne Abel Tokyo

Salesperson

Employee ID Name Office27 Rodney Jones Toronto44 Goro Azuma Tokyo35 Francine Moire Brussels37 Anne Abel Tokyo

Manager

Employee ID Name Office12 Brigit Sanchez Toronto99 Mary Chen Brussels37 Anne Abel Tokyo

Identification of rows that are common to two relations; must have equivalent columns as to number and domains.

Provide information on employees who have both a salesperson and manager role:

Algebraic Function: 3. Difference

Employee ID Name Office27 Rodney Jones Toronto44 Goro Azuma Tokyo35 Francine Moire Brussels

Salesperson

Employee ID Name Office27 Rodney Jones Toronto44 Goro Azuma Tokyo35 Francine Moire Brussels37 Anne Abel Tokyo

Manager

Employee ID Name Office12 Brigit Sanchez Toronto99 Mary Chen Brussels37 Anne Abel Tokyo

Identification of rows that are in one relation and not in another; must have equivalent columns as to number and domains.

Provide information on employees who have a salesperson role but do not have a managerial role:

Algebraic Function: 4. Product

SEmployee ID SName SOffice MEmployee ID MName MOffice27 Rodney Jones Toronto 12 Brigit Sanchez Toronto27 Rodney Jones Toronto 99 Mary Chen Brussels27 Rodney Jones Toronto 37 Anne Abel Tokyo44 Goro Azuma Tokyo 12 Brigit Sanchez Toronto44 Goro Azuma Tokyo 99 Mary Chen Brussels44 Goro Azuma Tokyo 37 Anne Abel Tokyo35 Francine Moire Brussels 12 Brigit Sanchez Toronto35 Francine Moire Brussels 99 Mary Chen Brussels35 Francine Moire Brussels 37 Anne Abel Tokyo37 Anne Abel Tokyo 12 Brigit Sanchez Toronto37 Anne Abel Tokyo 99 Mary Chen Brussels37 Anne Abel Tokyo 37 Anne Abel Tokyo

Salesperson

SEmployee ID SName SOffice27 Rodney Jones Toronto44 Goro Azuma Tokyo35 Francine Moire Brussels37 Anne Abel Tokyo

Manager

MEmployee ID Mname MOffice12 Brigit Sanchez Toronto99 Mary Chen Brussels37 Anne Abel Tokyo

Adjoining (concatenating) each row in the first relation to each row in the second relation; must have different column names

No obvious query; conceptually important because it is used as a building block (Cartesian product) for the join operator.

Algebraic Function: 5. Select

Salesperson

Employee ID Name Office Salary27 Rodney Jones Toronto 300044 Goro Azuma Tokyo 200035 Francine Moire Brussels 250037 Anne Abel Tokyo 1500

Provide information on employees whose salary is at least $2000

Employee ID Name Office Salary44 Goro Azuma Tokyo 200037 Anne Abel Tokyo 2500

Employee ID Name Office Salary27 Rodney Jones Toronto 300044 Goro Azuma Tokyo 200035 Francine Moire Brussels 2500

Creation of a relation by identifying only rows that satisfy specific conditions

Provide information on employees who are based in Tokyo:

Algebraic Function: 6. Project

NameRodney JonesGoro AzumaFrancine MoireAnne Abel

Creates a relation by deleting columns from an existing relation

Provide a list of employee names (not all information):

Salesperson

Employee ID Name Office27 Rodney Jones Toronto44 Goro Azuma Tokyo35 Francine Moire Brussels37 Anne Abel Tokyo

Provide names of employees whose office is in Tokyo:

NameGoro AzumaAnne Abel

Can “nest” (combine) operators (e.g., select, project)

Algebraic Function: 7. Divide

Sales

Employee ID Product IDRodney Jones 801Francine Moire 803Anne Abel 802Anne Abel 801Rodney Jones 802Anne Abel 803

Product

Product ID801802803

Creating a new relation by selecting the rows in one relation that match every row in another relation

Who has sold every product?

NameAnne Abel

Algebraic Function: 8. Join

Connection of data across relations: natural join (rows are joined when common columns have equal values); outer join (all rows from both tables even if there is no matching column value) and theta join (not covered)

Provide the Supplier Name for each product

Product

Product ID Product Description Price Supplier ID801 Shur-Lock U-Lock 75.00 3802 SpeedRite Cyclecomputer 60.00 3803 SteelHead Microshell Helmet 40.00 804 SureStop 133-MB Brakes 25.00 1805 Diablo ATM Mountain Bike 1,200.00 2806 Ultravision Helmet Mount Mirrors 7.45 3

Supplier

Supplier ID Supplier Name1 Bikes-R-Us2 Small moter suppliers3 All Bikes Allways4 Bikes for Fun

Provide all products and all suppliers, joining where possible

Product ID Product Description Price Supplier ID Supplier Name801 Shur-Lock U-Lock 75.00 3 All Bikes Allways802 SpeedRite Cyclecomputer 60.00 3 All Bikes Allways803 SteelHead Microshell Helmet 40.00 804 SureStop 133-MB Brakes 25.00 1 Bikes-R-Us805 Diablo ATM Mountain Bike1,200.00 2 Small moter suppliers806 Ultravision Helmet Mount Mirrors7.45 3 All Bikes Allways

4 Bikes for Fun

Product ID Product Description Price Supplier ID Supplier Name801 Shur-Lock U-Lock 75.00 3 All Bikes Allways802 SpeedRite Cyclecomputer 60.00 3 All Bikes Allways804 SureStop 133-MB Brakes 25.00 1 Bikes-R-Us805 Diablo ATM Mountain Bike 1,200.00 2 Small moter suppliers806 Ultravision Helmet Mount Mirrors 7.45 3 All Bikes Allways