Structured Design and Modeling CS 123/CS 231

Design Models Revisited zUML: Modeling Language for OO Systems zFor the Procedural (Structured) Paradigm ÕData and processes are separately considered ÕData Model: Entity-Relationship Diagram ÕProcess Model: Data-Flow Diagram zSome modeling techniques apply to both paradigms Õe.g., use case diagram and state diagrams

ERDs zEntity-Relationship Diagrams zUsed to produce a data model for an enterprise zDatabase Design

Entities and Attributes zEntity Õthing, person, place Õexamples: Book, Sales Invoice, Student, Customer, Employee, Department, Airport zAttribute Õfeature of an entity Õexamples: Name, Address, Age, QCA, Title, Author, Amount, City

Relationships zRelationship Õan association between (at least) two entities Õexamples: student borrows a book zCardinality ÕOne-to-one, one-to-many, many-to-many zIntersection Data Õattribute resulting from relationship Õexample: date-borrowed

The Notation zRectangles - Entities zEllipses - Attributes zDiamonds - Relationships zLinks zLabels

Example: The University Setting zDescription ÕStudents enroll in classes. Each class is a section of a particular course. zEntities ÕStudent, Section, Course

Student id number name address year qca

StudentenrollsSection Coursehas MM M 1 grade index room sched cat num title desc

Example 2: Library zStudent borrows book Õmany to many relationship between students and books Õsee first diagram zFurther analysis reveals there could be several copies of a book Õstudent borrows copy, book has copy Õsee second diagram

StudentborrowsBook MM

StudentborrowsCopy Bookhas MM M 1 Exercise: Complete Diagram by filling in attributes

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

From ERD to Tables zCreate a table for each entity Õattributes associated to entity are columns of the table (a primary key should exist per table) zFor each 1:M relationship Õadd 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

ERD to Tables, continued zFor each 1:1 relationship Õadd primary key of one table plus intersection data to the other table zFor each M:M relationship Õcreate a new table Õattributes are the primary keys of the participants plus intersection data

University Setting Example zStudent Õid number, name, address, year, qca zSection Õindex, room, sched, cat num zCourse Õcat num, title, desc zEnroll Õid number, index, grade

DFDs zData Flow Diagrams zModels Operations (Processes) zAlso used in analysis and design

Processes zAn operation or function in a system Õexample: Borrow Book zInvolves Õdata flow (input and results) Õdata sources and sinks Example: student and book-copy info are data that flow into the process; results stored in borrow table

Notation zCircle (Bubble) - Process zArrows - Data Flows zRectangles - Sources and Sinks zLabels

1 Borrow Book Student Copy Borrow id num, copy numborrow confirmation

DFD Levels zA process may involve sub-processes Õprovides detail about the process zDFD levels emerge zProcess hierarchy also depicted using a structure chart

1.1 Check Student Status id numborrower status copy numcopy status 1.2 Check Book Copy Status Student Copy

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

About DFDs zData flows should “balance” between levels zNumber label format X.X.X provides level information zContext Diagram ÕLevel 0 (or system-level) DFD zNotational Variations

Summary zModeling techniques and notation Õneeded in analysis and design Õmodels data and processes of a system zOther techniques and notation Õstate diagrams, structure charts, flowcharts, document flow diagrams, more... zStructured vs OO Paradigm Õsome techniques specific to the paradigm