Introduction to Entity-Relationship Diagrams, Data Flow Diagrams, and UML

1. Introduction to Entity-Relationship Diagrams, Data Flow Diagrams, and UML Todd BacastowPenn State UniversityGeography 583Geospatial System Analysis & Design

2. Data modeling – a technique for organizing and documenting a system’s data. Sometimes called database modeling. Entity relationship diagram (ERD) – a data model utilizing several notations to depict data in terms of the entities and relationships described by that data. Data Modeling

3. Entity – a class of persons, places, objects, events, or concepts about which we need to capture and store data. Named by a singular noun Data Modeling Concepts: Entity • Persons: agency, contractor, customer, department, division, employee, instructor, student, supplier. • Places: sales region, building, room, branch office, campus. • Objects: book, machine, part, product, raw material, software license, software package, tool, vehicle model, vehicle. • Events: application, award, cancellation, class, flight, invoice, order, registration, renewal, requisition, reservation, sale, trip. • Concepts: account, block of time, bond, course, fund, qualification, stock.

4. Attribute – a descriptive property or characteristic of an entity. Synonyms include element, property, and field. Just as a physical student can have attributes, such as hair color, height, etc., data entity has data attributes Compound attribute – an attribute that consists of other attributes. Synonyms in different data modeling languages are numerous: concatenated attribute, composite attribute, and data structure. Data Modeling Concepts: Attributes

5. Key – an attribute, or a group of attributes, that assumes a unique value for each entity instance. It is sometimes called an identifier. Concatenated key - group of attributes that uniquely identifies an instance. Synonyms: composite key, compound key. Candidate key – one of a number of keys that may serve as the primary key. Synonym: candidate identifier. Primary key – a candidate key used to uniquely identify a single entity instance. Alternate key – a candidate key not selected to become the primary key. Synonym: secondary key. Data Modeling Concepts: Identification

6. Relationship – a natural business association that exists between one or more entities. The relationship may represent an event that links the entities or merely a logical affinity that exists between the entities. Data Modeling Concepts: Relationships

7. Cardinality – the minimum and maximum number of occurrences of one entity that may be related to a single occurrence of the other entity. Because all relationships are bidirectional, cardinality must be defined in both directions for every relationship. Data Modeling Concepts: Cardinality bidirectional

8. Degree – the number of entities that participate in the relationship. A relationship between two entities is called a binary relationship. A relationship between three entities is called a 3-ary or ternary relationship. A relationship between different instances of the same entity is called a recursive relationship. Data Modeling Concepts: Degree

9. Logical models remove biases that are the result of the way the system is currently implemented, or the way that any one person thinks the system might be implemented. Logical models reduce the risk of missing business requirements because we are too preoccupied with technical results. Logical models allow us to communicate with end-users in nontechnical or less technical languages. Why Logical System Models

10. Process modeling – a technique used to organize and document a system’s processes. Flow of data through processes Logic Policies Procedures Data flow diagram (DFD) – a process model used to depict the flow of data through a system and the work or processing performed by the system. Synonyms are bubble chart, transformation graph, and process model. The DFD has also become a popular tool for business process redesign. Process Modeling and DFDs

11. Processes on DFDs can operate in parallel (at-the-same-time) Processes on flowcharts execute one at a time DFDs show the flow of data through a system Flowcharts show the flow of control (sequence and transfer of control) Processes on a DFD can have dramatically different timing (daily, weekly, on demand) Processes on flowcharts are part of a single program with consistent timing Differences Between DFDs and Flowcharts

12. What is the UML? • Unified Modeling Language • It is a modeling language, not a process • In 1996, work on the UML was begun by Rational.

13. UML Diagrams • Class Diagrams • Use Case Diagrams • Collaboration Diagrams • Sequence Diagrams • Package Diagrams • Component Diagrams • Deployment Diagrams • Activity Diagrams • State Diagrams

14. Class Diagrams • Are the most fundamental UML Diagram. • Describe the classes in the system, and the static relationships between classes. • Class diagrams are used during Analysis, Design and Development.

15. UML Class Diagram Customer 1 Rental Invoice 1..* Rental Item 1 0..1 1 Checkout Screen DVD Movie VHS Movie Video Game

16. UML Class Diagram Multiplicity Customer Simple Aggregation 1 Class Abstract Class Rental Invoice 1..* Rental Item {abstract} 1 0..1 Composition (Dependency) Simple Association Generalization Checkout Screen DVD Movie VHS Movie Video Game

17. MyClassName +SomePublicAttribute : SomeType -SomePrivateAttribute : SomeType #SomeProtectedAttribute : SomeType +ClassMethodOne() +ClassMethodTwo() Responsibilities -- can optionally be described here. Parts of a Class • Classes can have four parts • Name • Attributes • Operations • Responsibilities • Classes can show visibility and types. • All parts but the Name are optional.

18. ThisOne : MyClassName +SomePublicAttribute : SomeType -SomePrivateAttribute : SomeType #SomeProtectedAttribute : SomeType +ClassMethodOne() +ClassMethodTwo() Object Diagrams • An Object is an instance of a class. • Object names are underlined. • Object diagrams are similar to class diagrams. Many of the same notations are used. • Object diagrams capture instances of classes, and allow the dynamic relationships to be shown.

19. Class and Object Diagrams Class Name Association Name Customer Rental Item Rents +id:integer +id:integer 0..n +name:string +released:date 0..1 Class Diagram Attributes Object Name Joe: Customer Casablanca: Movie +id:1667 +id:22340 +name:Joe Smith +released:1942 Object Diagram

20. Use Cases • Describe interactions between users and computer systems (both called actors) . • Capture user-visible functions. • Achieve discrete measurable goals. • Are typically used during Analysis and Design.

21. Use Case Diagram Use Case Actor Identify Movie Open Account Customer Clerk Return Movie Review In-Store Telephone Account Status Customer Customer

22. Use Case Report • The Use Case Report provides documentation for the Use Case. • A Use Case is not complete without the report. • The elements of the Use Case Report are shown on the right. • Brief description • Precondition • Flow of events • Main flow • Subflows • Alternate flows • Postcondition • Special Requirements • Enclosures • Diagrams • Pictures of the UI

23. Collaboration Diagrams • Collaboration diagrams describe interactions and links • Focus on exchange of messages between objects • Appears during Analysis phase • Enhanced during Design phase

24. Collaboration Diagram - Rent Movie :Rented Items Object 5: add(customer, movies) 1: enter_customer() 8: generateRentalTotal() 3: enter_movies() 2: IsValidCust(CustId) 7: print invoice() :Check-out Manager :Customer :Clerk 4:GetMovieByBarcode() :Inventory Message

25. Sequence Diagrams • Can be “morphed” from Collaboration Diagrams. • Describe interactions between objects arranged in time sequence • Focus on objects and classes involved in the scenario and the sequence of messages exchanged • Associated with use cases • Used heavily during Analysis phase and are enhanced and refined during Design phase

26. Sequence Diagram - Rent Movie :CheckoutMgr Cust:Customer :Inventory :RentedItems :Employee 1: find customer() 2: search (string) Object 3: enter movie() 4: search (string) Activation Message 5: rent (movie) 6: add(Cust, item) Lifeline 7: printInvoice() 8: generateRentalTotal()

27. Package Diagram Class Package

28. Component Diagram Component Interface Dependency Note

29. Deployment Diagram Node Communication Association

30. Activity Diagram Start State Identify Caller Action State Obtain Name & Address Decision Open Account? Current Customer? [no] [no] [yes] [yes] End State Create Account

31. Swimlanes and Fork/Join Points Customer Manager Walking Clerk Identify Movie Fork Point Place Order Place Order Fill Order Pay Collect Money Pickup Movie Deliver Movie Join Point

32. State Diagram Guard Event Transition Action Activity State

33. UML Diagram Usage

34. Conclusion • UML is a robust notation that can express information gathered throughout a project’s lifecycle. • Adopting standard use of UML can improve communication between clients and developers. • UML can be used as an effective data modeling tool as well as an object modeling tool.