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
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