1. Implementation of the Relational Model
There is no substitute for the comfort supplied by the utterly taken-for-granted relationship. Iris Murdoch

2. Class Outline
What are the features of a relational database management system (RDBMS)?
What is entity integrity and referential integrity?
To what extent are entity and referential integrity supported by MS Access 97?
What are the eight algebraic functions supported by a fully relational DBMS? Give examples of each.

3. Relational Database Management Systems
Relational database architecture
Codd, E.F. (1970). A relational model for large shared data banks. CACM, 13(6),
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)
relational algebra and relational calculus are logically equivaluent (any query that can be solved in one language can be solved in the other) - relational calculus is more difficult so we’ll concentrate on the algebra

4. 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.

5. 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 (e.g., MS Access) 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
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 Langauge) or forms of the application

6. 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++

7. 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

8. 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
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.
foreign key
primary key

9. Entity Integrity Elements of a primary key:
It must uniquely identify each record n 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
concatenated primary key

10. 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

11. Referential Integrity in Access ’97
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 Null value in the foreign key is allowed, specifying that the records are unrelated.
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.

12. Referential Integrity Options in Access ’97
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.

13. Relationship Integrity is a way of minimizing data errors
MS Access 97 On-line Help

14. Requirements of a RDBMS
2. Supports many of the relational algebraic functions - a collection of operations on relations, resulting in relations
Set theory operators:
union
intersect
difference
product
Specific relational operators:
select
project
divide
join

15. Algebraic function: 1. Union
Combination of data without repeating common rows; must have equivalent columns as to number and domains (“union compatible”).
Provide information on all employees regardless of their position:
Union - Who are all the employees? For newsletter, do not send Anne more than one.
Intersection - Who is an Employee AND a Salesperson?
note that Anne appears only once even though she’s in both tables

16. Algebraic function: 2. Intersection
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:
Union - Who are all the employees? For newsletter, do not send Anne more than one.
Intersection - Who is an Employee AND a Salesperson?

17. Algebraic Function: 3. Difference
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:
Difference: Who is ONLY a salesperson - not a manager?
Product: Lists all possible combinations of rows from both tables - not directly used this way but used while trying to accomplish something else

18. Algebraic Function: 4. Product
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.
Difference: Who is ONLY a salesperson - not a manager?
Product: Lists all possible combinations of rows from both tables - not directly used this way but used while trying to accomplish something else

19. Algebraic Function: 5. Select
Creation of a relation by identifying only rows that satisfy specific conditions
Provide information on employees who are based in Tokyo:
Select: Used a LOT - restricts rows based on a criteria; can combine criteria - ie. whose office is Tokyo and has a salary of at least 2000? (Only Goro Azuma);
who is NOT in Brussels? (works somewhere other than in Brussels)
Provide information on employees whose salary is at least $2000

20. Algebraic Function: 6. Project
Creates a relation by deleting columns from an existing relation
Select: Used a LOT - restricts rows based on a criteria; can combine criteria - ie. whose office is Tokyo and has a salary of at least 2000? (Only Goro Azuma);
who is NOT in Brussels? (works somewhere other than in Brussels)
Provide a list of employee names (not all information):
Can “nest” (combine) operators (e.g., select, project)
Provide names of employees whose office is in Tokyo:

21. Algebraic Function: 7. Divide
Creating a new relation by selecting the rows in one relation that match every row in another relation
Difference: Who is ONLY a salesperson - not a manager?
Product: Lists all possible combinations of rows from both tables - not directly used this way but used while trying to accomplish something else
Who has sold every product?

22. 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
Difference: Who is ONLY a salesperson - not a manager?
Product: Lists all possible combinations of rows from both tables - not directly used this way but used while trying to accomplish something else
Provide all products and all suppliers, joining where possible