1. Entity-Relationship Design
Information Level Design
8/25/98 and 8/337/98

2. TOP DOWN DATA ANALYSIS
Computer systems are extremely complicated and cannot be developed without careful planning. The most common MIS is the Systems Development Life Cycle. This approach is to build a model of the information system based on the objectives and goals it must meet. This is called top down modeling.

3. Babysitter Service
The AITP Service Club wants to run a babysitting service. Customers call to request a sitter and the Club Coordinator assigns an employee to sit for the customer from a list of employees available for the particular day requested.

4. Entity-Relationship Model
A logical representation of the data of an organization or business area in graphical form

5. Enterprise E-R Diagram
Employee
Customer
Job

6. Data Flow Diagram Context Diagram Request Customer Confirm- ation
Babysitter Information
System
Availability
Assignment
Employee

7. Data Flow Diagram Level 1
Request
Assignment
Availability
Confirm-
ation 1.
Assign
Employee
Avail
Times 2.
Record
Avail-
ability
New
Current
Avail
Times
Job
Assign
D1 | Customer
D2 | Employee
D3 | Jobs

8. Communications Model
A representation of the location at which data is stored and processed and the communications links that connect them.

9. Entity Relationship Models
A good E-R model has
One table for every entity in the business system
Correctly drawn relationships indicating 1-1 or 1-m cardinalities
Optionality indicators to support needed referential integrity

10. ENTITY:
A person, place, object, event, or concept about which the organization wishes to maintain data.
Must need to store data
Must have at least two attributes
Must have at least two records

11. ENTITY TYPES
classes of people, objects or concepts about which we wish to store data.
become tables in a new computer system.
Instances are rows
Attributes are columns

12. ATTRIBUTE: A description or property of a given entity type.
Must depend on the entity key alone
Must contain information that we explicitly need
Must have the same data type for all entity occurrences

13. RELATIONSHIP: .
A connection between entity instances in different entity classes
Must specify what row connects with what row in associated tables
Must not describe processing

14. LOGICAL AND PHYSICAL COMPONENTS

15. Narrative Description
The conceptual modeling process starts with a narrative description of the process. This is a direct, active depiction of what the system should do. This is the basis of the initial data and process models.

16. Discovering Entities
Entities are normally described by NOUNS and ADJECTIVES
Entities do not change anything.
Entity occurrences are records, entity types are files.
Reports are derived output and not entities.

17. Discovering Entities
Entities with only one attribute are usually modeled as attributes of another entity.
Entities that have only one record are usually modeled as a set of parameters and not as files.
Include only files (entity types) that are needed by a system. Extra entities require maintenance and space that can add considerably to the cost of a system.

18. Converting a text description into an E-R model:
1. Review the conceptual description of the business area for nouns that describe the system.
2. Each entity type should have more than one potential instance.
3. Each entity type should have more than one attribute.
4. Each entity type should be relevant..

19. Relationships
A relationship is a connection between records in one table and those in another.
Instructor assigned to class (section)
Student enrolled in class (section)

20. RELATIONSHIP.
Does not describe processing or change any data. Relationship names should be passive (ordered by).
CARDINALITY Refers to the number of records that a relationship connects to a given child record in a relationship.
PARTICIPATION (Optionality) Refers to whether a record must exist in one table before a related one is inserted into another.

21. Diagrams: 1:m Relationships
InstructorID
Section
CourseSection
Instructor
InstructorID

22. Diagrams: m:n Relationships
CourseSection
StudentID
Section
Student-Section
CourseSection
Student
StudentID

23. Optionality (Referential Integrity)
Records in a table that have a relationship with another table may be restricted by optionality requirements.
Relationship Optional
Relationship Mandatory (referential integrity enforced)

24. Optionality
Optional (0 allowed)
Mandatory (1 or more required) 1

25. Optionality
A constraint should be mandatory only if the relationship must be known whenever a record is first entered. Most relationships are optional.

26. Maintaining Integrity
If a parent record is deleted then an optionality relationships can be maintained in several ways
Cascade delete
Cascade update
Cascade null

27. Data