1. MIS 385/MBA 664 Systems Implementation with DBMS/ Database Management
Dave Salisbury
( )
(web site)

2. Modeling reality
A database must mirror the real world if it is to answer questions about the real world
Data Modeling is a design technique for capturing reality
STUDENT
Social_Security_No
Name
Major

3. Business rules
Statements that define or constrain some aspect of the business
Assert business structure
Control/influence business behavior
Expressed in terms familiar to end users
Automated through DBMS software

4. A good business rule is:
Declarative – what, not how
Precise – clear, agreed-upon meaning
Atomic – one statement
Consistent – internally and externally
Expressible – structured, natural language
Distinct – non-redundant
Business-oriented – understood by business people

5. The conceptual model (ER diagram)
Delta & Pine Land Company
11/25/97
The conceptual model (ER diagram)
Representation of structure and constraints of database independent of software
Mainstream approach to conceptual modeling is ERD
ease of use
CASE support
entities and relationships are “natural”
No standard notation
Building blocks are entities, attributes, relationships, and identifiers

6. Delta & Pine Land Company
11/25/97
E-R model constructs
Entity instance - person, place, object, event, concept (often corresponds to a row in a table)
Entity Type – collection of entities (often corresponds to a table)
Attribute - property or characteristic of an entity type (often corresponds to a field in a table)
Relationship instance – link between entities (corresponds to primary key-foreign key equivalencies in related tables)
Relationship type – category of relationship…link between entity types 2

7. Elements of an E-R diagram
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11/25/97
Elements of an E-R diagram
ASSOCIATIVE
ENTITY
ENTITY
WEAK
ENTITY
ATTRIBUTE
MULTIVALUED
ATTRIBUTE
DERIVED
ATTRIBUTE
RELATIONSHIP
INDENTIFYING
RELATIONSHIP

8. What should an entity be?
Should be:
An object that will have many instances in the database
An object that will be composed of multiple attributes
An object that we are trying to model
Should NOT be:
A user of the database system
An output of the database system (e.g. a report)

9. Attributes A discrete data element
Describes an entity (i.e., is a characteristic)
Meaningful (for the system being modeled)
Attributes are the items of interest to the organization -- the things being stored
Customer_Number
12345
Last_Name
Salisbury
First_Name
Dave
Address
2425 Jasper Road
City
Xenia
State OH
Zip
45385
Phone

10. Delta & Pine Land Company
11/25/97
Identifiers (keys)
Identifier (Key) - An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type
Simple Key versus Composite Key
Candidate Key – an attribute that could be a key…satisfies the requirements for being a key 6

11. Characteristics of Identifiers
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Characteristics of Identifiers
Will not change in value
Will not be null
No intelligent identifiers (e.g. containing locations or people that might change)
Substitute new, simple keys for long, composite keys 7

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Composite Attributes
An attribute broken into component parts 12

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Simple key attribute
The key is underlined 14

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Composite Key
The key is composed
of two subparts 15

15. Multi-valued & derived attributes
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11/25/97
Multi-valued & derived attributes
Derived
from date employed and current date
What’s wrong with this?
Multivalued:
an employee can have
more than one skill 13

16. Both multivalued & composite attribute
Delta & Pine Land Company
11/25/97
Both multivalued & composite attribute
This is an example of time-stamping 37

17. More on relationships Relationship Types vs. Relationship Instances
The relationship type is modeled as the diamond and lines between entity types…the instance is between specific entity instances
Relationships can have attributes
These describe features pertaining to the association between the entities in the relationship
Two entities can have more than one type of relationship between them (multiple relationships)
Associative Entity = combination of relationship and entity
More on this later

18. Delta & Pine Land Company
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Relationship degree
Binary – two different entity types
Unary – related to same entity type
Ternary – three different entity types

19. Cardinality Constraints
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Cardinality Constraints
Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.
Minimum Cardinality
If zero, then optional
If one or more, then mandatory
Maximum Cardinality
The maximum number 29

20. Relationship cardinality notation
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Relationship cardinality notation
Mandatory one
Mandatory many
Optional one
Optional many

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Unary 22

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Binary 23

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Ternary 24

24. Delta & Pine Land Company
11/25/97
Ternary relationship w/ attributes (Relationships can have attributes of their own) 24

25. Hierarchical Relationships
Occur frequently
Model as multiple 1:M relationships
Firm
Division
Dept

26. Strong vs. weak entities & identifying relationships
Strong entities
exist independently of other types of entities
has its own unique identifier
represented with single-line rectangle
Weak entity
dependent on a strong entity…cannot exist on its own
Does not have a unique identifier
represented with double-line rectangle
Identifying relationship
links strong entities to weak entities
represented with double line diamond

27. Strong & weak entities Weak entity Strong entity
Identifying relationship

28. Associative entities It’s an entity – it has attributes
AND it’s a relationship – it links entities together
When should a relationship with attributes instead be an associative entity?
All relationships for the associative entity should be many
The associative entity could have meaning independent of the other entities
The associative entity preferably has a unique identifier, and should also have other attributes
The associative may be participating in other relationships other than the entities of the associated relationship
Ternary relationships should be converted to associative entities (p )

29. Maximum & minimum cardinalities
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11/25/97
Maximum & minimum cardinalities
Only maximum showing
Mandatory minimums showing 1

30. Delta & Pine Land Company
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Optional cardinality 34

31. Relationship type; entity & relationship instances
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11/25/97
Relationship type
Relationship type; entity & relationship instances 17

32. Binary relationship with an attribute
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Binary relationship with an attribute
Here, the date completed attribute pertains specifically to the employee’s completion of a course…it is an attribute of the relationship 20

33. Unary with an attribute
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11/25/97
Unary with an attribute
Representing a bill-of -materials structure 25

34. Delta & Pine Land Company
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Multiple relationships (entities can be related to one another in more than one way)
Employees and departments 40

35. Professors & courses (fixed upon constraint)
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Professors & courses (fixed upon constraint)
Here,max cardinality constraint is 4 41

36. Multivalued attribute vs. relationship

37. Delta & Pine Land Company
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Associative entity
Associative entity involves a rectangle with a diamond inside. Note that the many-to-many cardinality symbols face toward the associative entity and not toward the other entities 21

38. Delta & Pine Land Company
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Associative Entity
This is the Bill of Materials laid out a different way. It could just be a relationship with attributes…it’s a judgment call 27

39. Ternary as Associative Entity
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Ternary as Associative Entity 36

40. Sample E-R Diagram (Similar to figure 3-1 with different notation)
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Sample E-R Diagram (Similar to figure 3-1 with different notation) 3

41. Pine Valley Furniture

42. Notation used in earlier edition of our textbook – what’s different?
Delta & Pine Land Company
11/25/97
Notation used in earlier edition of our textbook – what’s different?

43. Delta & Pine Land Company
11/25/97
Different notation
CUSTOMER
* Customer ID
Customer name
ORDER
* Order ID
Order Date

44. Third style of notation
Delta & Pine Land Company
11/25/97
Third style of notation
Customer ID
Customer name
CUSTOMER 1
SUBMITS M
Order ID
Order date
ORDER

45. Oracle notation CUSTOMER ORDER #Customer_ID #Order_ID *Customer Name
*Order Date

46. Access Notation