1. IMS 4212: Data Modeling—Business Rules 1 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Business Rules—Topics Intro to Business Rules Business Policies Legal Restrictions Allowable Attribute Values Domain Rules Existential Integrity Referential Integrity Complex Policies and Triggers

2. IMS 4212: Data Modeling—Business Rules 2 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Intro to Business Rules Business Rules are a broad collection of statements that constrain what the organization can do or how it acts Because many organizational activities are reflected in data stored in the database the rules must also be reflected in the database and/or its use There are many categories of business rules –Different expressions in the data modeling process –Different implementation techniques Dependent on DBMS capabilities Developer and organizational preferences

3. IMS 4212: Data Modeling—Business Rules 3 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Business Policies Examples –Only managers can authorize a price discount –If customers return a product without a receipt they can only receive the lowest price charged for the product in the last year –All hours worked beyond 40 in the same calendar week will be paid at time-and-a-half –The manager’s key must be inserted in the register to cancel a sale –Credit purchases may not be made by customers with a positive credit balance over 60 days old who have not made a payment in 60 days

4. IMS 4212: Data Modeling—Business Rules 4 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Business Policies (cont.) Documenting Business Policies –If policy pertains to only one table list policy in simple English with table design –If policy involves multiple tables list policies in their own documentation section –May consolidate all policies (single- or multi-table in the same area) –This list of policies can be quite large Document where in the system the rule is enforced –Maintaining the rules when they change (frequently) can be troublesome without documentation

5. IMS 4212: Data Modeling—Business Rules 5 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Ensure that Data Makes Sense Examples –A student’s graduation date cannot be before their birth date or enrollment date –A zip code must match the specified city/state combination –A student’s degree objective cannot be “MD” if they are an undergraduate student Document with attribute (or table) definition with English statements Enforce with rules (single table checks) or triggers (multi table checks)

6. IMS 4212: Data Modeling—Business Rules 6 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Legal Restrictions Examples –Employees under 18 must finish work by 10:00 PM Sunday through Thursday and may not work more than 20 hours per week or six hours per day Sunday through Thursday except in the summer –Alcohol may not be sold to anyone under 21 and tobacco may not be sold to anyone under 18 –Sales tax must be collected unless the purchaser has a tax exempt ID number or the products are being shipped out of state

7. IMS 4212: Data Modeling—Business Rules 7 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Legal Restrictions (cont.) Documenting Legal Restrictions –Same as business policies Enforcing Legal Restrictions –Same as business policies

8. IMS 4212: Data Modeling—Business Rules 8 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Enforcing Business Rules Business rules that pertain to data values can be enforced when attempts are made to change data –Insert, Update, or Delete data If the data change violates a rule the database will automatically reject the change Changes rejected by the database raise errors in the using application Design philosophy is to protect the data at the DB level Identify the correct technique for enforcing each rule Can you think of business rules that are not reflected in data?

9. IMS 4212: Data Modeling—Business Rules 9 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Enforcing Business Rules (Other Options) Enforce in application logic –Logic must be replicated in all using applications –Makes maintenance more difficult Enforce in employee training, policies, and procedures Layered approach –Protect in the DB –Use application and training protection to minimize database rejections Protect applications—must use error handling in applications to trap database rejections

10. IMS 4212: Data Modeling—Business Rules 10 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Hierarchy of Business Rules Attribute Data Types: Incompatible data is rejected Domain rules for individual attributes –Ranges, Null or not Null, allowable values –Uniqueness of a non-PK column’s values Exestential Integrity (Uniqueness and existence of PK) Referential integrity (PK-FK requirements) Complex business rules: –May require calculations to enforce –Often require checks of multiple tables (other than PK- FK referential integrity checks) or multiple records –Enforced with separate objects called “Triggers”

11. IMS 4212: Data Modeling—Business Rules 11 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Attribute Data Types Attempting to insert certain data types in a field will lead to rejection –$1,456.25 cannot go into a smallmoney field because of the non-numeric characters (dollar sign and comma) –Dates must be in an acceptable format to go into a datetime field Excessively long strings will be truncated and entered Compatible values can be accepted –SmallMoney value will go into a Money column –Varchar(10) value will go into Char(15) column

12. IMS 4212: Data Modeling—Business Rules 12 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Allowable Attribute Values These are the domain rules for attributes –Price must be greater than zero –Social security numbers must be specified as exactly nine numeric digits with no other characters allowed –Employee first and last names may not be left blank Document these as statements with the table design Enforcing Attribute Values –Most enforceable by attribute type specifications –Constraints can be declared for domain values (Will cover for SQL Server in the lab later)

13. IMS 4212: Data Modeling—Business Rules 13 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Existential Integrity Duplicate records are not allowed PK must be unique Empty PKs are not allowed Documentation is inherent in declaration of PK fields Enforcement –DBMS will automatically enforce uniqueness and existence of field(s) declared to be PKs –May enforce uniqueness on alternate keys by creating unique index on the key attribute(s)

14. IMS 4212: Data Modeling—Business Rules 14 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Referential Integrity Referential integrity refers to the possibility of having “orphaned” child records Is it possible to have a product record without a matching category record or supplier record? Many (but not all) business situations require that there be a matching parent record for every child record in a Parent-Child relationship –Occasionally an orphaned child can be allowed

15. IMS 4212: Data Modeling—Business Rules 15 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Referential Integrity (cont.) Documenting Referential Integrity –Cardinality to the parent entity documents referential integrity indicates that related parent is required indicates that related parent is not required

16. IMS 4212: Data Modeling—Business Rules 16 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Referential Integrity (cont.) Enforcing Referential Integrity –Enforced in DBMS through properties of the relationship, depending on DBMS capabilities –Cascade delete deletes all related child records when the parent record is deleted –Cascade update updates FK in related child records when parent PK is changed –Nullify changes FK to Null when parent is deleted –No effect (do not enforce) leaves original FK value in place when parent is deleted or changed OR allows insertion of unrelated FK in child

17. IMS 4212: Data Modeling—Business Rules 17 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Referential Integrity (cont.) Enforcing Referential Integrity (cont.) –Take care when selecting cascade delete or nullify rules –Deleting an obsolete product will delete all records of receipts or sales of the product Destroys all accounting information pertaining to these transactions Destroys customer purchase information –Consider archiving obsolete data along with all related child data –Can also mark records as being inactive and write queries to ignore them

18. IMS 4212: Data Modeling—Business Rules 18 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Complex Policies and Triggers An important class of business rules requires checks outside the value of interest, record of interest, or even the current table for detection of a policy violation –Students may only enroll in ISM 4212 if They have completed ISM 3005; or They have completed ISM 3253; or They have an approved petition to do so –Employees may not work more than 40 hours in one calendar week without approval of their division manager

19. IMS 4212: Data Modeling—Business Rules 19 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Complex Policies and Triggers (cont.) Enforcing Business Policies –Policies are enforced with “Triggers” Procedural code that is run automatically when certain events take place against the DB Trigger returns a success or failure code or may be written to prohibit the attempted action –Inserting an EmployeeShift record may cause the violation of different underage employee work rules Check rules (we’ll see how for SQL Server later) whenever an Insert is attempted against the table Same for Update of an EmployeeShift record

20. IMS 4212: Data Modeling—Business Rules 20 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Complex Policies and Triggers (cont.) Triggers contain procedural code similar to that in stored procedures Can perform whatever queries are needed to gather the information needed to evaluate the policy criteria –Query previous work shifts completed in the week –Query scheduler’s managerial status Can make a determination as to whether the policy has been violated Reject the action if the policy is violated

21. IMS 4212: Data Modeling—Business Rules 21 Dr. Lawrence West, Management Dept., University of Central Florida lwest@bus.ucf.edu Complex Policies and Triggers (cont.) Rules can only be broken when records are inserted, updated, or deleted The same insert, update, or delete action can affect many rules All potentially violated rules must be checked –Checks can take place in the Database Enforcement applies to all use Faster execution –Checks can also take place in the procedural code that uses the DB Enforcement restricted to just that application