(C) 2000, The University of Michigan 1 Database Application Design Handout #2 January 14, 2000

(C) 2000, The University of Michigan 2 Course information Instructor: Dragomir R. Radev Office: 305A, WH, Phone: Office hours: TBD and Friday 1-2 Course page: Meeting time: Fridays, 2:30 - 5:30 PM, 311 WH

(C) 2000, The University of Michigan 3 Introduction to database development (cont’d)

(C) 2000, The University of Michigan 4 Metadata System tables Overhead data (indexes) Application metadata

(C) 2000, The University of Michigan 5 Components of a DBMS Design tools subsystem: design and creation of databases and applications; creations of tables, forms, queries, and reports; interfaces to programming languages Run-time subsystem: e.g., for linking forms to backend DBMS engine: translates requests into commands; transaction management; backup and recovery; locking

(C) 2000, The University of Michigan 6 Creating the database Database schemas Tables: –CAPTAIN (CaptainName, Phone, Street, City, State, Zip) –ITEM (Quantity, Description, DateOut, DateIn) –Uniqueness?

(C) 2000, The University of Michigan 7 Creating the database Relationships: –one captain to many items (1:N) –need to add CAPTAIN_ID to ITEM Domains –sets of values that a column may have

(C) 2000, The University of Michigan 8 Creating the database Business rules (constraints) –In order to check out any equipment, a captain must have a local phone –No captain may have more than 7 balls checked out at any time –Captain must return all equipment within five days after the end of each semester –No captain may check out any equipment if he or she has any overdue

(C) 2000, The University of Michigan 9 Enforcing business rules Depends on system Stored procedures

(C) 2000, The University of Michigan 10 Creating tables Relationships Foreign keys (CAPTAIN_ID) Forms Queries Reports Menus Application programs

(C) 2000, The University of Michigan 11 DB654 database Students Projects

(C) 2000, The University of Michigan 12 Database development process Top-down development: –general to specific –start with the strategic goals of the organization –means by which they will be accomplished –information requirements –necessary systems –BUILD ABSTRACT DATA MODEL

(C) 2000, The University of Michigan 13 Database development process Bottom-up development: –Start from needed reports, forms, queries –analyze existing systems, input & output –BU design: produces systems more quickly than TD design –Other tradeoffs

(C) 2000, The University of Michigan 14 Data modeling Inference process: from users’ statements to the structure and relationships of items to be stored in the database Reports and forms are shadows on the wall Inferencing is more an art than a science Multi-user systems: how to resolve differences; who decides

(C) 2000, The University of Michigan 15 The entity-relationship model

(C) 2000, The University of Michigan 16 E-R model Introduced by Peter Chen in 1976 (“The Entity- Relationship Model - Towards a Unified View of Data”) in ACM TODS, January 1976 Key elements: –entities: something that the user wants to track –entity classes –attributes (or properties); e.g, employee name –identifiers (name, but not salary): unique or not; composite –relationships: by degree

(C) 2000, The University of Michigan 17 Binary relationships 1:1 1:N N:M HAS-A relationships: e.g., a CLUB has STUDENTS STUDENT CLUB N:M STUDENT-CLUB

(C) 2000, The University of Michigan 18 Entity-relationship diagrams Maximum cardinality Minimum cardinality Recursive relationships: examples? DORMITORY STUDENT 1:N DORM-OCCUPANT O

(C) 2000, The University of Michigan 19 ****