Structured Design and Modeling

1. Structured Designand Modeling CS 123/CS 231

2. Design Models Revisited • UML: Modeling Language for OO Systems • For the Procedural (Structured) Paradigm • Data and processes are separately considered • Data Model: Entity-Relationship Diagram • Process Model: Data-Flow Diagram • Some modeling techniques apply to both paradigms • e.g., use case diagram and state diagrams

3. ERDs • Entity-Relationship Diagrams • Used to produce a datamodel for an enterprise • Database Design

4. Entities and Attributes • Entity • thing, person, place • examples: Book, Sales Invoice, Student, Customer, Employee, Department, Airport • Attribute • feature of an entity • examples: Name, Address, Age, QCA, Title, Author, Amount, City

5. Relationships • Relationship • an association between (at least) two entities • examples: student borrows a book • Cardinality • One-to-one, one-to-many, many-to-many • Intersection Data • attribute resulting from relationship • example: date-borrowed

6. The Notation • Rectangles - Entities • Ellipses - Attributes • Diamonds - Relationships • Links • Labels

7. Example: The University Setting • Description • Students enroll in classes. Each class is a section of a particular course. • Entities • Student, Section, Course

8. address name year id number qca Student

9. room index sched M M Student enrolls Section M grade 1 Course has cat num desc title

10. Example 2: Library • Student borrows book • many to many relationship between students and books • see first diagram • Further analysis reveals there could be several copies of a book • student borrows copy, book has copy • see second diagram

11. M M Student borrows Book

12. M M Student borrows Copy M 1 Book has Exercise: Complete Diagram by filling in attributes

13. ERDs and the Software Life Cycle • Used at the design phase of the software life cycle for database systems, although it is often used as early as the analysis phase • In design, it precedes table definition

14. From ERD to Tables • Create a table for each entity • attributes associated to entity are columns of the table (a primary key should exist per table) • For each 1:M relationship • add the primary key of the “1” participant as an attribute of the “M” participant (foreign key); intersection data is also added to the “M” participant

15. ERD to Tables, continued • For each 1:1 relationship • add primary key of one table plus intersection data to the other table • For each M:M relationship • create a new table • attributes are the primary keys of the participants plus intersection data

16. University Setting Example • Student • id number, name, address, year, qca • Section • index, room, sched, cat num • Course • cat num, title, desc • Enroll • id number, index, grade

17. DFDs • Data Flow Diagrams • Models Operations (Processes) • Also used in analysis and design

18. Processes • An operation or function in a system • example: Borrow Book • Involves • data flow (input and results) • data sources and sinks Example: student and book-copy info are data that flow into the process; results stored in borrow table

19. Notation • Circle (Bubble) - Process • Arrows - Data Flows • Rectangles - Sources and Sinks • Labels

20. 1 Borrow Book id num, copy num borrow confirmation Student Borrow Copy

21. DFD Levels • A process may involve sub-processes • provides detail about the process • DFD levels emerge • Process hierarchy also depicted using a structure chart

22. 1.1 Check Student Status id num borrower status Student 1.2 Check Book Copy Status copy num copy status Copy

23. borrower status, copy status 1.3 Record Borrow borrow confirmation id num, copy num Borrow Copy

24. About DFDs • Data flows should “balance” between levels • Number label format X.X.X provides level information • Context Diagram • Level 0 (or system-level) DFD • Notational Variations

25. Summary • Modeling techniques and notation • needed in analysis and design • models data and processes of a system • Other techniques and notation • state diagrams, structure charts, flowcharts, document flow diagrams, more... • Structured vs OO Paradigm • some techniques specific to the paradigm